Papers for Thursday, Oct 06 2022

In over a thousand known cataclysmic variables (CVs), where a white dwarf is accreting from a hydrogen-rich star, only a dozen have orbital periods below 75 minutes. One way to achieve these short periods requires the donor star to have undergone substantial nuclear evolution prior to interacting with the white dwarf, and it is expected that these objects will transition to helium accretion. These transitional CVs have been proposed as progenitors of helium CVs. However, no known transitional CV is expected to reach an orbital period short enough to account for most of the helium CV population, leaving the role of this evolutionary pathway unclear. Here we report observations of ZTF J1813+4251, a 51-minute orbital period, fully eclipsing binary system consisting of a star with a temperature comparable to that of the Sun but a density 100 times greater due to its helium-rich composition, accreting onto a white dwarf. Phase-resolved spectra, multi-band light curves and the broadband spectral energy distribution allow us to obtain precise and robust constraints on the masses, radii and temperatures of both components. Evolutionary modeling shows that ZTF J1813+4251 is destined to become a helium CV binary, reaching an orbital period under 20 minutes, rendering ZTF J1813+4251 a previously missing link between helium CV binaries and hydrogen-rich CVs.

Ark 564 is an extreme high-Eddington Narrow-line Seyfert 1 galaxy, known for being one of the brightest, most rapidly variable soft X-ray AGN, and for having one of the lowest temperature coronae. Here we present a 410-ks NuSTAR observation and two 115-ks XMM-Newton observations of this unique source, which reveal a very strong, relativistically broadened iron line. We compute the Fourier-resolved time lags by first using Gaussian processes to interpolate the NuSTAR gaps, implementing the first employment of multi-task learning for application in AGN timing. By fitting simultaneously the time lags and the flux spectra with the relativistic reverberation model RELTRANS, we constrain the mass at $2.3^{+2.6}_{-1.3} \times 10^6M_\odot$, although additional components are required to describe the prominent soft excess in this source. These results motivate future combinations of machine learning, Fourier-resolved timing, and the development of reverberation models.

High redshift quasars ($z>5$) that also shine brightly at radio wavelengths are unique signposts of supermassive black hole activity in the early universe. However, bright radio sources at $z\ge5$ are extremely rare and therefore we have started a campaign to search for new high-$z$ quasars by combining an optical dropout selection driven by the $g$, $r$, and $z$ bands from the Dark Energy Spectroscopic Instrument (DESI) Legacy Imaging Surveys with low-frequency radio observations from the LOFAR Two-metre Sky Survey (LoTSS). Currently, LoTSS covers a large fraction of the northern sky (5720 deg$^2$) to such a depth (median noise level of 83 $\mu$Jy beam$^{-1}$) that about 30% of the general quasar population is detected $-$ which is a factor of 5-10 more than previous large sky radio surveys such as NVSS and FIRST, respectively. In this paper, we present the discovery of 20 new quasars (and the independent confirmation of 4) between $4.9\leq z\leq 6.6$. Out of the 24 quasars, 21 satisfy the traditional radio-loudness criterion of $R=f_{5\text{GHz}}/f_{4400A} > 10$, with the full sample spanning $R\sim$6-1000, thereby more than doubling the sample of known radio-loud quasars at $z \ge 5$. Our radio detection requirement strongly decreases the contamination of stellar sources and allows one to select these quasars in a broad redshift range. Despite selecting our quasar candidates using fewer and less conservative colour restrictions, both the optical and near-infrared colours, Ly$\alpha$ emission line properties, and dust reddening, $E(B-V)$, measurements of our quasar sample do not deviate from the known radio-quiet quasar population, suggesting similar optical quasar properties of the radio-loud and radio-quiet quasar population at high-$z$. Our campaign demonstrates the potential for discovering new high-$z$ quasar populations through next generation radio continuum surveys.

The amount and complexity of data delivered by modern galaxy surveys has been steadily increasing over the past years. Extracting coherent scientific information from these large and multi-modal data sets remains an open issue and data driven approaches such as deep learning have rapidly emerged as a potentially powerful solution to some long lasting challenges. This enthusiasm is reflected in an unprecedented exponential growth of publications using neural networks. Half a decade after the first published work in astronomy mentioning deep learning, we believe it is timely to review what has been the real impact of this new technology in the field and its potential to solve key challenges raised by the size and complexity of the new datasets. In this review we first aim at summarizing the main applications of deep learning for galaxy surveys that have emerged so far. We then extract the major achievements and lessons learned and highlight key open questions and limitations. Overall, state-of-the art deep learning methods are rapidly adopted by the astronomical community, reflecting a democratization of these methods. We show that the majority of works using deep learning up to date are oriented to computer vision tasks. This is also the domain of application where deep learning has brought the most important breakthroughs so far. We report that the applications are becoming more diverse and deep learning is used for estimating galaxy properties, identifying outliers or constraining the cosmological model. Most of these works remain at the exploratory level. Some common challenges will most likely need to be addressed before moving to the next phase of deployment of deep learning in the processing of future surveys; e.g. uncertainty quantification, interpretability, data labeling and domain shift issues from training with simulations, which constitutes a common practice in astronomy.

The Moon is traditionally thought to have coalesced from the debris ejected by a giant impact onto the early Earth. However, such models struggle to explain the similar isotopic compositions of Earth and lunar rocks at the same time as the system's angular momentum, and the details of potential impact scenarios are hotly debated. Above a high resolution threshold for simulations, we find that giant impacts can immediately place a satellite with similar mass and iron content to the Moon into orbit far outside the Earth's Roche limit. Even satellites that initially pass within the Roche limit can reliably and predictably survive, by being partially stripped then torqued onto wider, stable orbits. Furthermore, the outer layers of these directly formed satellites are molten over cooler interiors and are composed of around 60% proto-Earth material. This could alleviate the tension between the Moon's Earth-like isotopic composition and the different signature expected for the impactor. Immediate formation opens up new options for the Moon's early orbit and evolution, including the possibility of a highly tilted orbit to explain the lunar inclination, and offers a simpler, single-stage scenario for the origin of the Moon.

We model the stellar abundances and ages of two disrupted dwarf galaxies in the Milky Way stellar halo: Gaia-Sausage Enceladus (GSE) and Wukong/LMS-1. Using a statistically robust likelihood function, we fit one-zone models of galactic chemical evolution with exponential infall histories to both systems, deriving e-folding timescales of $\tau_\text{in} = 1.01 \pm 0.13$ Gyr for GSE and $\tau_\text{in} = 3.08^{+3.19}_{-1.16}$ Gyr for Wukong/LMS-1. GSE formed stars for $\tau_\text{tot} = 5.40^{+0.32}_{-0.31}$ Gyr, sustaining star formation for $\sim$$1.5 - 2$ Gyr after its first infall into the Milky Way $\sim$10 Gyr ago. Our fit suggests that star formation lasted for $\tau_\text{tot} = 3.36^{+0.55}_{-0.47}$ Gyr in Wukong/LMS-1, though our sample does not contain any age measurements. The differences in evolutionary parameters between the two are qualitatively consistent with trends with stellar mass $M_\star$ predicted by simulations and semi-analytic models of galaxy formation. Our fitting method is based only on poisson sampling from an evolutionary track and requires no binning of the data. We demonstrate its accuracy by testing against mock data, showing that it accurately recovers the input model across a broad range of sample sizes ($20 \leq N \leq 2000$) and measurement uncertainties ($0.01 \leq \sigma_\text{[$\alpha$/Fe]}, \sigma_\text{[Fe/H]} \leq 0.5$; $0.02 \leq \sigma_{\log_{10}(\text{age})} \leq 1$). Our inferred values of the outflow mass-loading factor reasonably match $\eta \propto M_\star^{-1/3}$ as predicted by galactic wind models. Due to the generic nature of our derivation, this likelihood function should be applicable to one-zone models of any parametrization and easily extensible to other astrophysical models which predict tracks in some observed space.

Milky Way (MW) satellites exhibit a diverse range of internal kinematics, reflecting in turn a diverse set of subhalo density profiles. These profiles include large cores and dense cusps, which any successful dark matter model must explain simultaneously. A plausible driver of such diversity is self-interactions between dark matter particles (SIDM) if the cross section passes the threshold for the gravothermal collapse phase at the characteristic velocities of the MW satellites. In this case, some of the satellites are expected to be hosted by subhalos that are still in the classical SIDM core phase, while those in the collapse phase would have cuspy inner profiles, with a SIDM-driven intermediate mass black hole (IMBH) in the centre as a consequence of the runaway collapse. We develop an analytical framework that takes into account the cosmological assembly of halos and is calibrated to previous simulations; we then predict the timescales and mass scales ($M_{\rm BH}$) for the formation of IMBHs in velocity-dependent SIDM (vdSIDM) models as a function of the present-day halo mass, $M_0$. Finally, we estimate the region in the parameter space of the effective cross section and $M_0$ for a subclass of vdSIDM models that result in a diverse MW satellite population, as well as their corresponding fraction of SIDM-collapsed halos and those halos' inferred IMBH masses. We predict the latter to be in the range $0.1-1000~ {\rm M_\odot}$ with a $M_{\rm BH}-M_0$ relation that has a similar slope, but lower normalization, than the extrapolated empirical relation of super-massive black holes found in massive galaxies.

The scaling of the specific Type Ia supernova (SN Ia) rate with host galaxy stellar mass $\dot{N}_\text{Ia} / M_\star \sim M_\star^{-0.3}$ as measured in ASAS-SN and DES strongly suggests that the number of SNe Ia produced by a stellar population depends inversely on its metallicity. We estimate the strength of the required metallicity dependence by combining the average star formation histories (SFHs) of galaxies as a function of their stellar mass with the mass-metallicity relation (MZR) for galaxies and common parametrizations for the SN Ia delay-time distribution. The differences in SFHs can account for only $\sim$30% of the increase in the specific SN Ia rate between stellar masses of $M_\star = 10^{10}$ and $10^{7.2} M_\odot$. We find that an additional metallicity dependence of approximately $\sim$Z$^{-0.5}$ is required to explain the observed scaling. This scaling matches the metallicity dependence of the close binary fraction observed in APOGEE, suggesting that the enhanced SN Ia rate in low-mass galaxies can be explained by a combination of their more extended SFHs and a higher binary fraction due to their lower metallicities. Due to the shape of the MZR, only galaxies below $M_\star \approx 3\times10^9 M_\odot$ are significantly affected by the metallicity-dependent SN Ia rates. The $\dot{N}_\text{Ia} / M_\star \sim M_\star^{-0.3}$ scaling becomes shallower with increasing redshift, dropping by factor of $\sim$2 at $10^{7.2} M_\odot$ between $z = 0$ and $1$ with our $\sim$$Z^{-0.5}$ scaling. With metallicity-independent rates, this decrease is a factor of $\sim$3. We discuss the implications of metallicity-dependent SN Ia rates for one-zone models of galactic chemical evolution.

Luminous fast blue optical transients (LFBOTs) such as AT2018cow form a rare class of engine-powered explosions of uncertain origin. A hallmark feature of these events is radio/millimeter synchrotron emission powered by the interaction of fast (v > 0.1 c) ejecta and dense circumstellar material (CSM) extending to large radii > 1e16 cm surrounding the progenitor. Assuming this CSM to be an outflow from the progenitor, we show that dust grains up to ~1 micron in size can form in the outflow in the years before the explosion. This dusty CSM would attenuate the transient's ultraviolet (UV) emission prior to peak light, before being destroyed by the rising luminosity, reddening the pre-maximum colors (consistent with the pre-maximum red-to-blue color evolution of the LFBOT candidate MUSSES2020J). Re-radiation by the dust before being destroyed generates an near-infrared (NIR) "echo" of luminosity ~1e41-1e42 erg/s lasting weeks, which is detectable over the transient's rapidly fading blue continuum. We show that this dust echo is compatible with the previously unexplained NIR excess observed in AT2018cow. The gradual decay of the early NIR light curve can result from CSM which is concentrated in wide-angle outflow or torus, consistent with the highly aspherical geometry of AT2018cow's ejecta. Pre-maximum optical/UV and NIR follow-up of LFBOTs provide an new probe of their CSM environments and place additional constraints on their progenitors.

We measure abundances of 12 elements (Na, Mg, Si, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni) in a sample of 86 metal-poor ($-2 \lesssim \text{[Fe/H]} \lesssim -1$) subgiant stars in the solar neighborhood. Abundances are derived from high-resolution spectra taken with the Potsdam Echelle Polarimetric and Spectroscopic Instrument on the Large Binocular Telescope, modeled using iSpec and MOOG. By carefully quantifying the impact of photon-noise ($< 0.05$ dex for all elements) we robustly measure the intrinsic scatter of abundance ratios. At fixed [Fe/H] the RMS intrinsic scatter in [X/Fe] ranges from 0.04 dex (Cr) to 0.16 dex (Na), with a median of 0.08 dex. Scatter in [X/Mg] is similar, and accounting for [$\alpha$/Fe] only reduces the overall scatter moderately. We consider several possible origins of the intrinsic scatter with particular attention to fluctuations in the relative enrichment by core-collapse supernovae (CCSN) and Type Ia supernovae (SNIa) and stochastic sampling of the CCSN progenitor mass distribution. The stochastic sampling scenario provides a good quantitative explanation of our data if the effective number of CCSN contributing to the enrichment of a typical sample star is $N \sim 50$. At the median metallicity of our sample, this interpretation implies that the CCSN ejecta are mixed over a gas mass $\sim 10^5 M_{\odot}$ before forming stars. The scatter of elemental abundance ratios is a powerful diagnostic test for simulations of star formation, feedback, and gas mixing in the early phases of the Galaxy.

There are few observed high-mass X-ray binaries (HMXBs) that harbor massive black holes, and none are likely to result in a binary black hole (BBH) that merges within a Hubble time; however, we know that massive merging BBHs exist from gravitational-wave observations. We investigate the role that X-ray and gravitational-wave observational selection effects play in determining the properties of their respective detected binary populations. We confirm that, as a result of selection effects, observable HMXBs and observable BBHs form at different redshifts and metallicities, with observable HMXBs forming at much lower redshifts and higher metallicities than observable BBHs. We also find disparities in the mass distributions of these populations, with observable merging BBH progenitors pulling to higher component masses relative to the full observable HMXB population. Fewer than $3\%$ of observable HMXBs host black holes $> 35M_{\odot}$ in our simulated populations. Furthermore, we find the probability that a detectable HMXB will merge as a BBH system within a Hubble time is $\simeq 0.6\%$. Thus, it is unsurprising that no currently observed HMXB is predicted to form a merging BBH with high probability.

Comparison of echelle spectra to synthetic models has become a computational statistics challenge, with over ten thousand individual spectral lines affecting a typical cool star echelle spectrum. Telluric artifacts, imperfect line lists, inexact continuum placement, and inflexible models frustrate the scientific promise of these information-rich datasets. Here we debut an interpretable machine-learning framework "blas\'e" that addresses these and other challenges. The semi-empirical approach can be viewed as "transfer learning" -- first pre-training models on noise-free precomputed synthetic spectral models, then learning the corrections to line depths and widths from whole-spectrum fitting to an observed spectrum. The auto-differentiable model employs back-propagation, the fundamental algorithm empowering modern Deep Learning and Neural Networks. Here, however, the 40,000+ parameters symbolize physically interpretable line profile properties such as amplitude, width, location, and shape, plus radial velocity and rotational broadening. This hybrid data-/model- driven framework allows joint modeling of stellar and telluric lines simultaneously, a potentially transformative step forwards for mitigating the deleterious telluric contamination in the near-infrared. The blas\'e approach acts as both a deconvolution tool and semi-empirical model. The general purpose scaffolding may be extensible to many scientific applications, including precision radial velocities, Doppler imaging, chemical abundances, and remote sensing. Its sparse-matrix architecture and GPU-acceleration make blas\'e fast. The open-source PyTorch-based code includes tutorials, Application Programming Interface (API) documentation, and more. We show how the tool fits into the existing Python spectroscopy ecosystem, demonstrate a range of astrophysical applications, and discuss limitations and future extensions.

A big question in the field of star and planet formation is the time at which substantial dust grain growth occurs. The observed properties of dust emission across different wavelength ranges have been used as an indication that millimeter-sized grains are already present in the envelopes of young protostars. However, this interpretation is in tension with results from coagulation simulations, which are not able to produce such large grains in these conditions. In this work, we show analytically that the production of millimeter-sized grains in protostellar envelopes is impossible under the standard assumptions about the coagulation process. We discuss several possibilities that may serve to explain the observed dust emission in the absence of in-situ grain growth to millimeter sizes.

A tidal disruption event (TDE) occurs when the gravitational field of a supermassive black hole (SMBH) destroys a star. For TDEs in which the star enters deep within the tidal radius, such that the ratio of the tidal radius to the pericenter distance $\beta$ satisfies $\beta \gg 1$, the star is tidally compressed and heated. It was predicted that the maximum density and temperature attained during deep TDEs scale as $\propto \beta^3$ and $\propto \beta^2$, respectively, and nuclear detonation triggered by $\beta \gtrsim 5$, but these predictions have been debated over the last four decades. We perform Newtonian smoothed-particle hydrodynamics (SPH) simulations of deep TDEs between a Sun-like star and a $10^6 M_\odot$ SMBH for $2 \le \beta \le 10$. We find that neither the maximum density nor temperature follow the $\propto \beta^3$ and $\propto \beta^2$ scalings or, for that matter, any power-law dependence, and that the maximum-achieved density and temperature are reduced by $\sim$ an order of magnitude compared to past predictions. We also perform simulations in the Schwarzschild metric, and find that relativistic effects modestly increase the maximum density (by a factor of $\lesssim 1.5$) and induce a time lag relative to the Newtonian simulations, which is induced by time dilation. We also confirm that the time the star spends at high density and temperature is a very small fraction of its dynamical time. We therefore predict that the amount of nuclear burning achieved by radiative stars during deep TDEs is minimal.

The iconic planetary nebula (PN) NGC 7027 is bright, nearby (D ~ 1 kpc), highly ionized, intricately structured, and well observed. This nebula is hence an ideal case study for understanding PN shaping and evolution processes. Accordingly, we have conducted a comprehensive imaging survey of NGC 7027 comprised of twelve HST Wide Field Camera 3 images in narrow-band and continuum filters spanning the wavelength range 0.243--1.67 microns. The resulting panchromatic image suite reveals the spatial distributions of emission lines covering low-ionization species such as singly ionized Fe, N, and Si, through H recombination lines, to more highly ionized O and Ne. These images, combined with available X-ray and radio data, provide the most extensive view of the structure of NGC 7027 obtained to date. Among other findings, we have traced the ionization structure and dust extinction within the nebula in sub-arcsecond detail; uncovered multipolar structures actively driven by collimated winds that protrude through and beyond the PN's bright inner core; compared the ionization patterns in the WFC3 images to X-ray and radio images of its interior hot gas and to its molecular outflows; pinpointed the loci of thin, shocked interfaces deep inside the nebula; and more precisely characterized the central star. We use these results to describe the recent history of this young and rapidly evolving PN in terms of a series of shaping events. This evolutionary sequence involves both thermal and ram pressures, and is far more complex than predicted by extant models of UV photoionization or winds from a single central progenitor star, thereby highlighting the likely influence of an unseen binary companion.

We explore the potential of our novel triaxial modeling machinery in recovering the viewing angles, the shape and the orbit distribution of galaxies by using a high-resolution $N$-body merger simulation. Our modelling technique includes several recent advancements. (i) Our new triaxial deprojection algorithm SHAPE3D is able to significantly shrink the range of possible orientations of a triaxial galaxy and therefore to constrain its shape relying only on photometric information. It also allows to probe degeneracies, i.e. to recover different deprojections at the same assumed orientation. With this method we can constrain the intrinsic shape of the $N$-body simulation, i.e. the axis ratios $p=b/a$ and $q=c/a$, with $\Delta p$ and $\Delta q$ $\lesssim$ 0.1 using only photometric information. The typical accuracy of the viewing angles reconstruction is 15-20$^\circ$. (ii) Our new triaxial Schwarzschild code SMART exploits the full kinematic information contained in the entire non-parametric line-of-sight velocity distributions (LOSVDs) along with a 5D orbital sampling in phase space. (iii) We use a new generalised information criterion AIC$_p$ to optimise the smoothing and to select the best-fit model, avoiding potential biases in purely $\chi^2$-based approaches. With our deprojected densities, we recover the correct orbital structure and anisotropy parameter $\beta$ with $\Delta \beta$ $\lesssim$ 0.1. These results are valid regardless of the tested orientation of the simulation and suggest that even despite the known intrinsic photometric and kinematic degeneracies the above described advanced methods make it possible to recover the shape and the orbital structure of triaxial bodies with unprecedented accuracy.

The nanoflare model of coronal heating is one of the most successful scenarios to explain, within a single framework, the diverse set of coronal observations available with the present instrument resolutions. The model is based on the idea that the coronal structure is formed by elementary magnetic strands which are tangled and twisted by the displacement of their photospheric footpoints by convective motions. These displacements inject magnetic stress between neighbor strands that promotes current sheet formation, reconnection, plasma heating, and possibly also particle acceleration. Among other features, the model predicts the ubiquitous presence of plasma flows at different temperatures. These flows should, in principle, produce measurable effects on observed spectral lines in the form of Doppler-shifts, line asymmetries and non-thermal broadenings. In this work we use a Two-Dimensional Cellular Automaton Model (2DCAM) developed in previous works, in combination with the Enthalpy Based Thermal Evolution of Loops (EBTEL) model, to analyze the effect of nanoflare heating on a set of known EUV spectral lines. We find that the complex combination of the emission from plasmas at different temperatures, densities and velocities, in simultaneously evolving unresolved strands, produces characteristic properties in the constructed synthetic lines, such as Doppler-shifts and non-thermal velocities up to tens of km s$^{-1}$ for the higher analyzed temperatures. Our results might prove useful to guide future modeling and observations, in particular, regarding the new generation of proposed instruments designed to diagnose plasmas in the 5 to 10 MK temperature range.

We observed the periodic radio transient GLEAM-X J162759.5-523504.3 (GLEAM-X J1627) using the Chandra X-ray Observatory for about 30-ks on January 22-23, 2022, simultaneously with radio observations from MWA, MeerKAT and ATCA. Its radio emission and 18-min periodicity led the source to be tentatively interpreted as an extreme magnetar or a peculiar highly magnetic white dwarf. The source was not detected in the 0.3-8 keV energy range with a 3-sigma upper-limit on the count rate of 3x10^{-4} counts/s. No radio emission was detected during our X-ray observations either. Furthermore, we studied the field around GLEAM-X J1627 using archival ESO and DECam data, as well as recent SALT observations. Many sources are present close to the position of GLEAM-X J1627, but only two within the 2" radio position uncertainty. Depending on the assumed spectral distribution, the upper limits converted to an X-ray luminosity of L_{X}<6.5x10^{29} erg/s for a blackbody with temperature kT=0.3 keV, or L_{X}<9x10^{29} erg/s for a power-law with photon index Gamma = 2 (assuming a 1.3 kpc distance). Furthermore, we performed magneto-thermal simulations for neutron stars considering crust- and core-dominated field configurations. Based on our multi-band limits, we conclude that: i) in the magnetar scenario, the X-ray upper limits suggest that GLEAM-X J1627 should be older than ~1 Myr, unless it has a core-dominated magnetic field or has experienced fast-cooling; ii) in the white dwarf scenario, we can rule out most binary systems, a hot sub-dwarf and a hot magnetic isolated white dwarf (T>10.000 K), while a cold isolated white dwarf is still compatible with our limits.

The detection of a fast radio burst (FRB), FRB 200428, coincident with an X-ray burst (XRB) from the Galactic magnetar soft gamma repeater (SGR) SGR J1935+2154 suggests that magnetars can produce FRBs. Many XRBs have been detected from the source but none were associated with bursty radio emission. Meanwhile, a number of weaker radio bursts have been detected from the source, which could in principle be slow radio bursts (SRBs): FRBs detected at viewing angles outside the FRB jet cone. In this paper, we use these X-ray and radio observations to constrain the geometric and relativistic beaming factors of FRBs under two hypotheses. First, we assume that all FRBs/SRBs should be associated with XRBs like FRB 200428. For beaming to produce the observed scarcity of FRB/SRB-associated XRBs, the FRB must be geometrically narrow, $\theta_j \leq 0.1$ rad. We additionally derive a lower limit of $\theta_j\Gamma > 3$. If the XRB associated with FRB 200428 was unique from the majority, the geometric constraint is loosened to its maximum value, $\pi/2$ rad. Second, we assume a less stringent constraint for FRBs/SRBs by not requiring that they are associated with XRBs. We use the FRB$-$SRB closure relations to identify a total of 4 SRBs and then derive FRB beaming factors, $\theta_j\Gamma \lesssim 3$.

Rotation is typically assumed to induce strictly symmetric rotational splitting into the rotational multiplets of pure p- and g-modes. However, for evolved stars exhibiting mixed modes, avoided crossings between different multiplet components are known to yield asymmetric rotational splitting, particularly for near-degenerate mixed-mode pairs, where notional pure p-modes are fortuitiously in resonance with pure g-modes. These near-degeneracy effects have been described in subgiants, but their consequences for the characterisation of internal rotation in red giants has not previously been investigated in detail, in part owing to theoretical intractability. We employ new developments in the analytic theory of mixed-mode coupling to study these near-resonance phenomena. In the vicinity of the most p-dominated mixed modes, the near-degenerate intrinsic asymmetry from pure rotational splitting increases dramatically over the course of stellar evolution, and depends strongly on the mode mixing fraction $\zeta$. We also find that a linear treatment of rotation remains viable for describing the underlying p- and g-modes, even when it does not for the resulting mixed modes undergoing these avoided crossings. We explore observational consequences for potential measurements of asymmetric mixed-mode splitting, which has been proposed as a magnetic-field diagnostic. Finally, we propose improved measurement techniques for rotational characterisation, exploiting the linearity of rotational effects on the underlying p/g modes, while still accounting for these mixed-mode coupling effects.

Making use of strong correlations between closely separated multiple or double sources and photometric and astrometric metadata in Gaia EDR3, we generate a catalog of candidate double and multiply imaged lensed quasars and AGNs, comprising 3140 systems. It includes two partially overlapping parts, a sample of distant (redshifts mostly greater than 1) sources with perturbed data, and systems resolved into separate components by Gaia at separations less than $2\arcsec$. For the first part, which is roughly one third of the published catalog, we synthesized 0.617 million redshifts by multiple machine learning prediction and classification methods, using independent photometric and astrometric data from Gaia EDR3 and WISE with accurate spectroscopic redshifts from SDSS as a training set. Using these synthetic redshifts, we estimate a rate of 4.9\% of interlopers with spectroscopic redshift below 1 in this part of the catalog. Unresolved candidate double and dual AGNs and quasars are selected as sources with marginally high BP/RP excess factor (phot_bp_rp_excess_factor), which is sensitive to source extent, limiting our search to high-redshift quasars. For the second part of the catalog, additional filters on measured parallax and near-neighbor statistics are applied to diminish the propagation of remaining stellar contaminants. The estimated rate of positives (double or multiple sources) is 98\%, and the estimated rate of dual (physically related quasars) is greater than 54\%. A few dozen serendipitously found objects of interest are discussed in more detail, including known and new lensed images, planetary nebulae and young infrared stars of peculiar morphology, and quasars with catastrophic redshift errors in SDSS.

A recent report by astronomers about Unidentified Aerial Phenomena (UAP) in Ukraine (arXiv:2208.11215) suggests dark phantom objects of size 3-12 meters, moving at speeds of up to 15 km/s at a distance of up to 10-12 km with no optical emission. I show that the friction of such objects with the surrounding air would have generated a bright optical fireball. Reducing their inferred distance by a factor of ten is fully consistent with the size and speed of artillery shells.

Fast radio bursts (FRBs) are millisecond-timescale radio transients, the origins of which are predominantly extragalactic and likely involve highly magnetized compact objects. FRBs undergo multipath propagation, or scattering, from electron density fluctuations on sub-parsec scales in ionized gas along the line-of-sight. Scattering observations have located plasma structures within FRB host galaxies, probed Galactic and extragalactic turbulence, and constrained FRB redshifts. Scattering also inhibits FRB detection and biases the observed FRB population. We report the detection of scattering times from the repeating FRB~20190520B that vary by up to a factor of two or more on minutes to days-long timescales. In one notable case, the scattering time varied from $7.9\pm0.4$ ms to less than 3.1 ms ($95\%$ confidence) over 2.9 minutes at 1.45 GHz. The scattering times appear to be uncorrelated between bursts or with dispersion and rotation measure variations. Scattering variations are attributable to dynamic, inhomogeneous plasma in the circumsource medium, and analogous variations have been observed from the Crab pulsar. Under such circumstances, the frequency dependence of scattering can deviate from the typical power-law used to measure scattering. Similar variations may therefore be detectable from other FRBs, even those with inconspicuous scattering, providing a unique probe of small-scale processes within FRB environments.

We complement the MALATANG sample of dense gas in nearby galaxies with archival observations of $^{12}\rm CO$ and its isotopologues to determine scaling relations between Wide-field Infrared Survey Explorer (WISE) 12 $\mu$m emission and molecular gas tracers at sub-kiloparsec scales. We find that 12 $\mu$m luminosity is more tightly correlated with $^{12}\rm CO$ than it is with $^{13}\rm CO$ or dense gas tracers. Residuals between predicted and observed $^{12}\rm CO$ are only weakly correlated with molecular gas mass surface density ($\Sigma_{\rm mol}$) in regions where $\Sigma_{\rm mol}$ is very low ($\sim 10~{\rm M_{\odot}~pc^{-2}}$). Above this limit, the $^{12}\rm CO$ residuals show no correlations with physical conditions of molecular gas, while $^{13}\rm CO$ residuals depend on the gas optical depth and temperature. By analyzing differences from galaxy to galaxy, we confirm that the $^{12}\rm CO$-12 $\mu$m relation is strong and statistically robust with respect to star forming galaxies and AGN hosts. These results suggest that WISE 12 $\mu$m emission can be used to trace total molecular gas instead of dense molecular gas, likely because polycyclic aromatic hydrocarbons (PAHs, a major contributor to WISE 12 $\mu$m~emission) may be well-mixed with the gas that is traced by $^{12}\rm CO$. We propose that WISE 12 $\mu$m luminosity can be used to estimate molecular gas surface density for statistical analyses of the star formation process in galaxies.

We present deep near-infrared (NIR) imaging of Sh 2-209 (S209), a low-metallicity (${\rm [O/H]} = - 0.5$ dex) HII region in the Galaxy. From the NIR images, combined with astrometric data from Gaia EDR3, we estimate the distance to S209 to be 2.5 kpc. This is close enough to enable us to resolve cluster members clearly ($\simeq$1000 AU separation) down to a mass-detection limit of $\simeq$0.1 $M_\odot$, and we have identified two star-forming clusters in S209, with individual cluster scales $\sim$1 pc. We employ a set of model luminosity functions to derive the underlying initial mass functions (IMFs) and ages for both clusters. The IMFs we obtained for both clusters exhibit slightly flat high-mass slopes ($\Gamma \simeq -1.0$) compared to the Salpeter IMF ($\Gamma = -1.35$), and their break mass of $\simeq$0.1 $M_\odot$ is lower than those generally seen in the solar neighborhood ($\sim$0.3 $M_\odot$). In particular, because the S209 main cluster is a star-forming cluster with a larger number of members ($\sim$1500) than the number ($\sim$100) in regions previously studied in such environments, it is possible for the first time to derive the IMF in a low-metallicity environment with high accuracy over the wide mass range 0.1--20 $M_\odot$.

The erratic spin history of Vela X-1 shows some continuous spin-up/spin-down trend over tens of days. We study the orbital profile and spectral property of Vela X-1 in these spin-up/spin-down intervals, using the spin history monitored by Fermi/GBM and light curve from Swift/BAT and MAXI/GSC. The BAT fluxes in the spin-up intervals are about 1.6 times those of the spin-down intervals for out-of-eclipse orbital phases. The spin-up intervals also show a higher column density than the spin-down intervals, indicating there are more material on the orbital scale for the spin-up intervals. It could be due to the variation of the stellar wind of the optical star (HD 77581) on tens of days. The varying wind could lead to alternating prograde/retrograde accreting flow to the neutron star, which dominates the transfer of the angular momentum to Vela X-1, but not the total observed luminosity.

We present the first observations of spatially resolved oscillation sources obtained with the Siberian Radioheliograph (SRH) at 3-6 GHz. We have found significant flux oscillations with periods of about 3, 5 and 13 minutes emitted from AR12833. The 3-minute periodicity dominates at higher frequencies. It was found that the apparent level of oscillations depends on the active region location on the disc, and scales down towards the limbs. The oscillations were studied in detail during one hour interval on June 19, 2021. We found that sources of 3-min oscillations were located above the umbra and their emission is extraordinary polarized. The 5 and 13-min periods were manifested in emission at lower frequencies, down to 2.8 GHz. Sources with 5-min periodicity were located near the umbra-penumbra boundary and in the pore region. Positions of sources with 13-min oscillations were different at 3.1 GHz and 4.7 GHz. We found consistency between spatial location of the oscillation sources in radio and UV in 171A and 304A. There is significant correlation of signals in two ranges. Time delays between microwave oscillations increase as the frequency decreases, which can be explained by upward propagation of periodic disturbances. The localization of oscillation sources is probably related to magnetic structures with different wave cutoff frequencies at different heights. The obtained results show that SRH can provide the spatial resolved observation of the oscillations in the intensity and polarization channels in 3-6 GHz band.

In our previous work (Paper I), we demonstrated that coagulation instability results in dust concentration against depletion due to the radial drift and accelerates dust growth locally. In this work (Paper II), we perform numerical simulations of coagulation instability taking into account effects of backreaction to gas and collisional fragmentation of dust grains. We find that the slowdown of the dust drift due to backreaction regulates dust concentration in the nonlinear growth phase of coagulation instability. The dust-to-gas surface density ratio increases from $10^{-3}$ up to $\sim10^{-2}$. Each resulting dust ring tends to have mass of $\simeq0.5M_{\oplus}-1.5M_{\oplus}$ in our disk model. In contrast to Paper I, the dust surface density profile shows a local plateau structure at each dust ring. In spite of the regulation at the nonlinear growth, the efficient dust concentration reduces their collision velocity. As a result, dust grains can grow beyond the fragmentation barrier, and the dimensionless stopping time reaches unity as in Paper I. The necessary condition for the efficient dust growth is (1) weak turbulence of $\alpha<1\times10^{-3}$ and (2) a large critical velocity for dust fragmentation ($> 1$ m/s). The efficient dust concentration in outer regions will reduce the inward pebble flux and is expected to decelerate the planet formation via the pebble accretion. We also find that the resulting rings can be unstable to secular gravitational instability (GI). The subsequent secular GI promotes planetesimal formation. We thus expect that a combination of these instabilities is a promising mechanism for dust-ring and planetesimal formation.

Eclipsing binary stars with an oscillating giant component allow accurate stellar parameters to be derived and asteroseismic methods to be tested and calibrated. To this aim, suitable systems need to be firstly identified and secondly measured precisely and accurately. KIC 4054905 is one such system, which has been identified, but with measurements of a relatively low precision and with some confusion regarding its parameters and evolutionary state. Our aim is to provide a detailed and precise characterisation of the system and to test asteroseismic scaling relations. Dynamical and asteroseismic parameters of KIC4054905 were determined from Kepler photometry and multi-epoch high-resolution spectra from FIES at the Nordic Optical Telescope. KIC 4054905 was found to belong to the thick disk and consist of two lower red giant branch (RGB) components with nearly identical masses of 0.95$M_{\odot}$ and an age of $9.9\pm0.6$ Gyr. The most evolved star displays solar-like oscillations, which suggest that the star belongs to the RGB, supported also by the radius, which is significantly smaller than the red clump phase for this mass and metallicity. Masses and radii from corrected asteroseismic scaling relations can be brought into full agreement with the dynamical values if the RGB phase is assumed, but a best scaling method could not be identified. We measured dynamical masses and radii with a precision better than 1.0%. We firmly establish the evolutionary nature of the system to be that of two early RGB stars with an age close to 10 Gyr, unlike previous findings. The metallicity and Galactic velocity suggest that the system belongs to the thick disk of the Milky Way. We investigate the agreement between dynamical and asteroseismic parameters for KIC 4054905. Consistent solutions exist, but the need to analyse more systems continues in order to establish the accuracy of asteroseismic methods.

Blue straggler stars (BSS) are peculiar objects which normally appear as a single broad sequence along the extension of the main sequence. Only four globular clusters (GCs) have been observed to have two distinct and parallel BSS sequences. For the first time for any open cluster (OC), we report double BSS sequences in Berkeley 17. Using the machine-learning based membership algorithm ML-MOC on Gaia EDR3 data, we identify 627 cluster members, including 21 BSS candidates out to 15 arcmin from the cluster center. Both the BSS sequences are almost equally populated and parallel to one another in Gaia as well as in Pan-STARRS colour-magnitude diagram (CMD). We statistically confirm their presence and report that both BSS sequences are highly segregated compared to the reference population out to $\sim$5.5 arcmin and not segregated thereafter. The lower densities of OCs make BSS formation impossible via the collisional channel. Therefore, mass transfer seems to be the only viable channel for forming candidates of both sequences. The gap between the red and blue BSS sequences, on the other hand, is significant and presents a great opportunity to understand the connection between BSS formation and internal as well as external dynamics of the parent clusters.

Universe's matter inhomogeneity gravitationally affects the propagation of gravitational waves (GWs), causing the lensing effect. Particularly, the weak lensing of GWs contains abundance of information about the small scale matter power spectrum and it has been studied within the range of the Born approximation. In this work, we investigate the validity of the Born approximation by accounting for the higher order terms in the gravitational potential $\Phi$. We first develop the formulation of the post-Born approximation, which is made by introducing a new variable. We then derive the expression of the magnitude and the phase of the amplification factor up to third order in $\Phi$ and compute the average and variance beyond the Born approximation. Our results suggest that the post-Born effect is indeed a few orders of magnitude smaller than the leading order contribution within almost all frequency ranges considered in this work except for the high frequency area $f\sim1000$ Hz, where the shot noise is dominant. Intriguingly, the number of necessary GW events for detecting the average, which originates purely from the post-Born effect, could become comparable or even smaller than the number required for detecting the variance, which appears at the level of the Born approximation. This indicates that the average is measurable with the same detection cost as the variance, even though it is only a few percent of the variance. On the other hand, we find that, even though the detection of the post-Born corrections to the variance would be possible in the case of the magnification, extracting the useful information to infer the shape of the matter power spectrum is still challenging even for the future generation GW detectors. This is due to the smallness of the post-Born effect and the difficulty of separating it from both the noise signal and the Born approximation effect.

The accretion of dark matter around the primordial black holes (PBHs) could lead to the formation of surrounding minihalos, whose mass can be several orders of magnitude higher than the central PBH mass. The gravitational microlensing produced by such dressed PBHs could be quite different from that of the bare PBHs, which may greatly affect the constraints on the PBH abundance. In this paper, we study the gravitational microlensing produced by dressed PBHs in details. We find that all the microlensing effects by dressed PBHs have asymptotic behavior depending on the minihalo size, which can be used to predict the microlensing effects by comparing the halo size with the Einstein radius. When the minihalo radius and the Einstein radius are comparable, the effect of the density distribution of halo is significant to the microlensing. Applying the microlensing by dressed PBHs to the data of Optical Gravitational Lensing Experiment and Subaru/HSC Andromeda observations, we obtain the improved constraints on the PBH abundance. It shows that the existence of dark matter minihalos surrounding PBHs can strengthen the constraints on PBH abundance by several orders and can shift the constraints to the well-known mass window where PBHs can constitute all the dark matter.

Establishing the period--Wesenheit relation requires independent and accurate distance measurements of classical Cepheids (DCEPs). The precise distance provided by an associated open cluster independently calibrates the period--Wesenheit relation of DCEPs. 51 DCEPs associated with open clusters are compiled using the constraints of five-dimensional astrometric information. By directly using Gaia DR3 parallax, the period--Wesenheit relation in the Gaia $G$ band is calibrated as $W_G = (-3.06 \pm 0.11) \log P + (-2.96 \pm 0.10)$. Compared with the results derived by directly adopting the DCEP parallaxes or using distance moduli, the Wesenheit magnitudes based on the cluster-averaged parallaxes exhibit a tighter relation with the period. Besides, there is a systematic offset between the observed Wesenheit absolute magnitudes of distant OC-DCEPs and their fitted magnitudes. After considering the parallax zero-point correction, the systematic offset can be reduced, yielding a probably better PW relation of $W_G = (-2.94 \pm 0.12) \log P + (-2.93 \pm 0.11)$.

Families of asteroids generated by the collisional fragmentation of a common parent body have been identified using clustering methods of asteroids in their proper orbital element space. An alternative method has been developed in order to identify collisional families from the correlation between the asteroid fragment sizes and their proper semi-major axis distance from the family centre (V-shape). This method has been shown to be effective in the cases of the very diffuse families that formed billions of years ago. We obtained photometric observations of asteroids in order to construct their rotational light curves; we combine them with the literature light curves and sparse-in-time photometry; we input these data in the light curve inversion methods to determine the shape and the spin pole of the asteroids in order to assess whether an object is prograde or retrograde. The ultimate goal is to assess whether we find an excess of retrograde asteroids on the inward side of the V-shape of a 4 Gyr asteroid family identified via the V-shape method. This excess of retrograde rotators is predicted by the theory of asteroid family evolution. We obtained the spin poles for 55 asteroids claimed to belong to a 4 Gyr collisional family of the inner main belt that consists of low-albedo asteroids. After re-evaluating the albedo and spectroscopic information, we found that nine of these asteroids are interlopers in the 4 Gyr family. Of the 46 remaining asteroids, 31 are found to be retrograde and 15 prograde. We also found that these retrograde rotators have a very low probability (1.29%) of being due to random sampling from an underlying uniform distribution of spin poles. Our results constitute corroborating evidence that the asteroids identified as members of a 4 Gyr collisional family have a common origin, thus strengthening their family membership.

Fast neutrino -flavor conversion (FFC) is a possible game-changing ingredient in core-collapse supernova (CCSN) theory. In this Letter, we examine the impact of FFC on explosive nucleosynthesis by including the effects of FFC in conjunction with asymmetric neutrino emission into nucleosynthetic computations in a parametric way. We find that the ejecta compositions are not appreciably affected by FFC for elements lighter than Co, while the compositions are influenced by FFC for the heavier elements. We also find that the role of FFC varies depending on the asymmetric degree of neutrino emission ($m_{\rm asy}$) and the degree of neutrino-flavor mixing. The impact of FFC is not monotonic to $m_{\rm asy}$; The change in the ejecta composition increases for higher $m_{\rm asy}$ up to $\sim 10\%$ compared with that without FFC, whereas FFC has little effect on the nucleosynthesis in very large asymmetric neutrino emission ($\gtrsim 30 \%$). Our results suggest that FFC facilitates the production of neutron-rich ejecta in most cases, although it makes the ejecta more proton-rich if anti-neutrino conversion is more vigorous than that of neutrino. The key ingredient accounting for this trend is neutrino absorption, whose effects on nucleosynthesis can be quantified by simple diagnostics.

As a basic symmetry of Einstein's theory of special relativity, Lorentz invariance has withstood very strict tests. But there are still motivations for such tests. Firstly, many theories of quantum gravity suggest violations of Lorentz invariance at the Planck energy scale. Secondly, even minute deviations from Lorentz symmetry can accumulate as particle travel across large distances, leading to detectable effects at attainable energies. Thanks to their long baselines and high-energy emission, astrophysical observations provide sensitive tests of Lorentz invariance in the photon sector. In this paper, I briefly introduce astrophysical methods that we adopted to search for Lorentz-violating signatures, including vacuum dispersion and vacuum birefringence.

ELT-HARMONI is the first light visible and near-IR integral field spectrograph (IFS) for the ELT. It covers a large spectral range from 450nm to 2450nm with resolving powers from 3500 to 18000 and spatial sampling from 60mas to 4mas. It can operate in two Adaptive Optics modes - SCAO (including a High Contrast capability) and LTAO - or with NOAO. The project is preparing for Final Design Reviews. The High Contrast Module (HCM) will allow HARMONI to perform direct imaging and spectral analysis of exoplanets up to one million times fainter than their host star. Quasi-static aberrations are a limiting factor and must be calibrated as close as possible to the focal plane masks to reach the specified contrast. A Zernike sensor for Extremely Low-level Differential Aberrations (ZELDA) will be used in real-time and closed-loop operation at 0.1Hz frequency for this purpose. Unlike a Shack-Hartmann, the ZELDA wavefront sensor is sensitive to Island and low-wind effects. The ZELDA sensor has already been tested on VLT-SPHERE and will be used in other instruments. Our objective is to adapt this sensor to the specific case of HARMONI. A ZELDA prototype is being both simulated and experimentally tested at IPAG. Its nanometric precision has first been checked in 2020 in the case of slowly evolving, small wavefront errors, and without dispersion nor turbulence residuals. On this experimental basis, we address the performance of the sensor under realistic operational conditions including residuals, mis-centring, dispersion, sensitivity, etc. Atmospheric refraction residuals were introduced by the use of a prism, and turbulence was introduced by a spatial light modulator which is also used to minimise wavefront residuals in a closed loop in the observing conditions expected with HARMONI.

We present the development of SIR-HUXt, the integration of a sequential importance resampling (SIR) data assimilation scheme with the HUXt solar wind model. SIR-HUXt is designed to assimilate the time-elongation profiles of CME fronts in the low heliosphere, such as those typically extracted from heliospheric imager data returned by the STEREO, Parker Solar Probe, and Solar Orbiter missions. We use Observing System Simulation Experiments to explore the performance of SIR-HUXt for a simple synthetic CME scenario of a fully Earth directed CME flowing through a uniform ambient solar wind, where the CME is initialised with the average observed CME speed and width. These experiments are performed for a range of observer locations, from 20 deg to 90 deg behind Earth, spanning the L5 point where ESA's future Vigil space weather monitor will return heliospheric imager data for operational space weather forecasting. We show that SIR-HUXt performs well at constraining the CME speed, and has some success at constraining the CME longitude. The CME width is largely unconstrained by the SIR-HUXt assimilations, and more experiments are required to determine if this is due to this specific CME scenario, or is a general feature of assimilating time-elongation profiles. Rank-histograms suggest that the SIR-HUXt ensembles are well calibrated, with no clear indications of bias or under/over dispersion. Improved constraints on the initial CME speed lead directly to improvements in the CME transit time to Earth and arrival speed. For an observer in the L5 region, SIR-HUXt returned a 69% reduction in the CME transit time uncertainty, and a 63% reduction in the arrival speed uncertainty. This suggests SIR-HUXt has potential to improve the real-world representivity of HUXt simulations, and therefore has potential to reduce the uncertainty of CME arrival time hindcasts and forecasts.

Observations of interplanetary scintillation (IPS - the scintillation of compact radio sources due to density variations in the solar wind) enable the velocity of the solar wind to be determined, and its bulk density to be estimated, throughout the inner heliosphere. A series of observations using the Low Frequency Array (LOFAR - a radio telescope centred on the Netherlands with stations across Europe) were undertaken using this technique to observe the passage of an ultra-fast CME which launched from the Sun following the X-class flare of 10 September 2017. LOFAR observed the strong radio source 3C147 at an elongation of 82 degrees from the Sun over a period of more than 30 hours and observed a strong increase in speed to 900km/s followed two hours later by a strong increase in the level of scintillation, interpreted as a strong increase in density. Both speed and density remained enhanced for a period of more than seven hours, to beyond the period of observation. Further analysis of these data demonstrates a view of magnetic-field rotation due to the passage of the CME, using advanced IPS techniques only available to a unique instrument such as LOFAR.

Context. The occultation of a radio source by the plasma tail of a comet can be used to probe structure and dynamics in the tail. Such occultations are rare, and the occurrence of scintillation, due to small-scale density variations in the tail, remains somewhat controversial. Aims. A detailed observation taken with the Low-Frequency Array (LOFAR) of a serendipitous occultation of the compact radio source 3C196 by the plasma tail of comet C/2020 F3 (Neowise) is presented. 3C196 tracked almost perpendicularly behind the tail, providing a unique profile cut only a short distance downstream from the cometary nucleus itself. Methods. Interplanetary scintillation (IPS) is observed as the rapid variation of the intensity received of a compact radio source due to density variations in the solar wind. IPS in the signal received from 3C196 was observed for five hours, covering the full transit behind the plasma tail of comet C/2020 F3 (Neowise) on 16 July 2020, and allowing an assessment of the solar wind in which the comet and its tail are embedded. Results. The results reveal a sudden and strong enhancement in scintillation which is unequivocally attributable to the plasma tail. The strongest scintillation is associated with the tail boundaries, weaker scintillation is seen within the tail, and previously-unreported periodic variations in scintillation are noted, possibly associated with individual filaments of plasma. Furthermore, contributions from the solar wind and comet tail are separated to measure a sharp decrease in the velocity of material within the tail, suggesting a steep velocity shear resulting in strong turbulence along the tail boundary

CIZA J1358.9-4750 is a nearby galaxy cluster in the early phase of a major merger. The two-dimensional temperature map using XMM-Newton EPIC-PN observation confirms the existence of a high temperature region, which we call the "hot region", in the "bridge region" connecting the two clusters. The ~ 500 kpc wide region between the southeast and northwest boundaries also has higher pseudo pressure compared to the unshocked regions, suggesting the existence of two shocks. The southern shock front is clearly visible in the X-ray surface brightness image and has already been reported by Kato et al. (2015). The northern one, on the other hand, is newly discovered. To evaluate their Mach number, we constructed a three-dimensional toy merger model with overlapping shocked and unshocked components in line of sight. The unshocked and preshock ICM conditions are estimated based on those outside the interacting bridge region assuming point symmetry. The hot region spectra are modeled with two-temperature thermal components, assuming that the shocked condition follows the Rankin-Hugoniot relation with the preshock condition. As a result, the shocked region is estimated to have a line-of-sight depth of ~ 1 Mpc with a Mach number of ~ 1.3 in the southeast shock and ~ 1.7 in the northwest shock. The age of the shock waves is estimated to be ~ 260 Myr. This three dimensional merger model is consistent with the Sunyaev-Zeldovich signal obtained using the Planck observation within the CMB fluctuations. The total flow of the kinetic energy of the ICM through the southeast shock was estimated to be ~ 2.2 x $10^{42}$ erg/s. Assuming that 10 % of this energy is converted into ICM turbulence, the line-of-sight velocity dispersion is calculated to be ~ 200 km/s, which is basically resolvable via coming high spectral resolution observations.

We search for the reasons behind the spectroscopic diversity of hydrogen-poor superluminous supernovae (SLSNe-I) in the pre-maximum phase. Our analysis is a continuation of the paper of \citet{ktr21}, who disclosed two new subtypes of SLSNe-I characterized by the presence/absence of a W-shaped absorption feature in their pre-maximum spectra between 4000 and 5000 \AA (called Type~W and Type~15bn, respectively). However, the physical cause of this bimodality is still uncertain. Here we present pre-maximum spectral synthesis of 27 SLSNe-I with special attention to the photospheric temperature ($T_{ \rm phot}$) and velocity ($v_{ \rm phot}$) evolution. We find that a $T_{\rm phot}$ limit of 12000~K separates the Type~W and Type~15bn SLSNe-I: Type~W objects tend to show $T_{\rm phot}\geq$12000~K, while Type~15bn ones have $T_{\rm phot} \leq$12000~K. This is consistent with the chemical composition of the studied objects. Another difference between these groups may be found in their ejecta geometry: Type W SLSNe-I may show null-polarization, implying spherical symmetry, while the polarization of Type 15bn objects may increase in time. This suggests a two-component model with a spherical outer carbon-oxygen layer and an asymmetric inner layer containing heavier ions. The two subgroups may have different light curve evolution as well, since 6 Type~W objects show early bumps, unlike Type 15bn SLSNe-I. This feature, however, needs further study, as it is based on only a few objects at present.

Insufficient numerical resolution of grid-based, direct numerical simulations (DNS) hampers the development of instabilitydriven turbulence at small (unresolved) scales. As an alternative to DNS, sub-grid models can potentially reproduce the effects of turbulence at small scales in terms of the resolved scales, and hence can capture physical effects with less computational resources. We present a new sub-grid model, the MHD-instability-induced-turbulence (MInIT) mean-field model. MInIT is a physically motivated model based on the evolution of the turbulent (Maxwell, Reynolds, and Faraday) stress tensors and their relation with the turbulent energy densities of the magneto-rotational (MRI) and parasitic instabilities, modeled with two partial differential evolution equations with stiff source terms. Their solution allows obtaining the turbulent stress tensors through the constant coefficients that link them to the energy densities. The model is assessed using data from MRI in-box DNS and applying a filtering operation to compare the filtered data with that from the model. Using the $L_2$-norm as the metric for the comparison, we find less than one order-of-magnitude difference between the two sets of data. No dependence on filter size or length scale of unresolved scales is found, as opposed to results using the gradient model (which we also use to contrast our model) in which the $L_2$-norm of some of the stresses increases with filter size. We conclude that MInIT can help DNS by properly capturing small-scale turbulent stresses which has potential implications on the dynamics of highly-magnetized rotating compact objects, such as those formed during binary neutron star mergers.

Globular clusters (GCs) are excellent tracers of the formation and early evolution of the Milky Way. The bulge GCs (BGCs) are particularly important because they can reveal vital information about the oldest, in-situ component of the Milky Way. We aim at deriving mean metallicities and radial velocities for 13 GCs that lie towards the bulge and are generally associated with this component. We use near infrared low resolution spectroscopy with the FORS2 instrument on the VLT to measure the wavelengths and equivalent widths of the CaII triplet (CaT) lines for a number of stars per cluster. We derive radial velocities, ascertain membership and apply known calibrations to determine metallicities for cluster members, for a mean of 11 members per cluster. We derive mean cluster RV values to 3 km/s, and mean metallicities to 0.05 dex. Our sample has metallicities lying between -0.21 and -1.64 and is distributed between the traditional metal-rich BGC peak near [Fe/H] aprox. -0.5 and a more metal-poor peak around [Fe/H] aprox. -1.1, which has recently been identified. These latter are candidates for the oldest GCs in the Galaxy, if blue horizontal branches are present, and include BH 261, NGC 6401, NGC 6540, NGC 6642, and Terzan 9. Finally, Terzan 10 is even more metal-poor. However, dynamically, Terzan 10 is likely an intruder from the halo, possibly associated with the Gaia-Enceladus or Kraken accretion events. Terzan 10 is also confirmed as an Oosterhotype II GC based on our results. The lone halo intruder in our sample, Terzan 10, is conspicuous for also having by far the lowest metallicity, and casts doubt on the possibility of any bonafide BGCs at metallicities below about aprox. -1.5.

(Pre-)transitional disks show gaps and cavities that can be related with on-going planet formation. According to theory, young embedded planets can accrete material from the circumplanetary and circumstellar disks, so that they could be detected in accretion tracers, like the H$_{\alpha}$ emission line. In this work, we present spectral angular differential imaging AO-assisted observations of five (pre-)transitional disks obtained with SPHERE/ZIMPOL at the Very Large Telescope (VLT). They were obtained in the H$_{\alpha}$ line and the adjacent continuum. We have combined spectral and angular differential imaging techniques to increase the contrast in the innermost regions close to the star, and search for the signature of young accreting protoplanets. As a result, the reduced images do not show any clear H$_{\alpha}$ point source around any of the targets. We report faint H$_{\alpha}$ emissions around TW Hya and HD163296: while the former is most probably an artifact related with a spike, the nature of the latter remains unclear. The spectral and angular differential images yield contrasts of 6--8 magnitudes at separations of $\sim$ 100 mas from the central stars, except in the case of LkCa15, with values of $\sim$3 mag. We have estimated upper limits to the accretion luminosity of potential protoplanets, obtaining that planetary models provide an average value of $L_{\rm acc} \sim 10^{-4}$ $L_{\odot}$ at 200 mas, which is $\sim$2 orders of magnitude higher than the $L_{\rm acc}$ estimated from the extrapolation of the $L_{H_{\alpha}}$ - $L_{acc}$ stellar relationship. We explain the lack of protoplanet detections as a combination of different factors, like e.g. episodic accretion, extinction from the circumstellar and circumplanetray disks, and/or a majority of low-mass, low-accreting planets.

We analyze the complete chain of effects caused by a solar eruptive event in order to better understand the dynamic evolution of magnetic-field related quantities in interplanetary space, in particular that of magnetic flux and helicity. We study a series of connected events (a confined C4.5 flare, a flare-less filament eruption and a double-peak M-class flare) that originated in NOAA active region (AR) 12891 on 2021 November 1 and November 2. We deduce the magnetic structure of AR 12891 using stereoscopy and nonlinear force-free (NLFF) magnetic field modeling, allowing us to identify a coronal flux rope and to estimate its axial flux and helicity. Additionally, we compute reconnection fluxes based on flare ribbon and coronal dimming signatures from remote sensing imagery. Comparison to corresponding quantities of the associated magnetic cloud (MC), deduced from in-situ measurements from Solar Orbiter and near-Earth spacecraft, allows us to draw conclusions on the evolution of the associated interplanetary coronal mass ejection (ICME). The latter are aided through the application of geometric fitting techniques (graduated cylindrical shell modeling; GCS) and interplanetary propagation models (drag based ensemble modeling; DBEM) to the ICME. NLFF modeling suggests the host AR's magnetic structure in the form of a left-handed (negative-helicity) sheared arcade/flux rope reaching to altitudes of 8-10 Mm above photospheric levels, in close agreement with the corresponding stereoscopic estimate. Revealed from GCS and DBEM modeling, the ejected flux rope propagated in a self-similar expanding manner through interplanetary space. Comparison of magnetic fluxes and helicities processed by magnetic reconnection in the solar source region and the respective budgets of the MC indicate a considerable contribution from the eruptive process, though the pre-eruptive budgets appear of relevance too.

CMB mapmaking relies on a data model to solve for the sky map, and this process is vulnerable to bias if the data model cannot capture the full behavior of the signal. I demonstrate that this bias is not just limited to small-scale effects in high-contrast regions of the sky, but can manifest as $\mathcal{O}(1)$ power loss on large scales in the map under conditions and assumptions realistic for ground-based CMB telescopes. This bias is invisible to simulation-based tests that do not explicitly model them, making it easy to miss. I investigate the common case of sub-pixel errors in more detail and demonstrate that this special case of model error can be eliminated using bilinear pointing matrices. Finally, I provide simple methods for testing for the presence of large-scale model error bias in the general case.

In the gravitational wave event GW170817, there was a $\sim 10$ hours gap before electromagnetic (EM) observations, without detection of the cocoon. The cocoon is heated by a \textit{short} gamma-ray burst (\textit{s}GRB) jet propagating through the ejecta of a Neutron Star (NS) merger, and a part of the cocoon escapes the ejecta with an opening angle of $20^{\circ}$--$30^{\circ}$. Here we model the cocoon and calculate its EM emission. Our 2D hydrodynamic simulations suggest that the density and energy distributions, after entering homologous expansion, are well-fitted with power-law functions, in each of the relativistic and non-relativistic parts of the escaped cocoon. Modeling these features, we calculate the cooling emission analytically. We find that the cocoon outshines the r-process kilonova/macronova at early times (10--10$^{3}$ s), peaking at UV bands. The relativistic velocity of the cocoon's photosphere is measurable with instruments such as Swift and ULTRASAT. We also imply that energetic cocoons, including failed jets, might be detected as X-ray flashes. Our model clarifies the physics and parameter dependence, covering a wide variety of central engines and ejecta of NS mergers and \textit{s}GRBs in the multi-messenger era.

New functionality to process Very Long Baseline Interferometry (VLBI) data has been implemented in the CASA package. This includes two new tasks to handle fringe fitting and VLBI-specific amplitude calibration steps. Existing tasks have been adjusted to handle VLBI visibility data and calibration meta-data properly. With these updates, it is now possible to process VLBI continuum and spectral line observations in CASA. This article describes the development and implementation, and presents an outline for the workflow when calibrating European VLBI Network or Very Long Baseline Array data in CASA. Though the CASA VLBI functionality has already been vetted extensively as part of the Event Horizon Telescope data processing, in this paper we compare results for the same dataset processed in CASA and AIPS. We find identical results for the two packages and conclude that CASA in some cases performs better, though it cannot match AIPS for single-core processing time. The new functionality in CASA allows for easy development of pipelines or Jupyter notebooks, and thus contributes to raising VLBI data processing to present day standards for accessibility, reproducibility, and reusability.

CASA, the Common Astronomy Software Applications, is the primary data processing software for the Atacama Large Millimeter/submillimeter Array (ALMA) and the Karl G. Jansky Very Large Array (VLA), and is frequently used also for other radio telescopes. The CASA software can handle data from single-dish, aperture-synthesis, and Very Long Baseline Interferometery (VLBI) telescopes. One of its core functionalities is to support the calibration and imaging pipelines for ALMA, VLA, VLA Sky Survey (VLASS), and the Nobeyama 45m telescope. This paper presents a high-level overview of the basic structure of the CASA software, as well as procedures for calibrating and imaging astronomical radio data in CASA. CASA is being developed by an international consortium of scientists and software engineers based at the National Radio Astronomical Observatory (NRAO), the European Southern Observatory (ESO), the National Astronomical Observatory of Japan (NAOJ), and the Joint Institute for VLBI European Research Infrastructure Consortium (JIV-ERIC), under the guidance of NRAO.

Fast radio bursts (FRBs) are extremely strong radio flares lasting several micro- to milliseconds and come from unidentified objects at cosmological distances, most of which are only seen once. Based on recently published data in the CHIME/FRB Catalog 1 in the frequency bands 400-800 MHz, we analyze 125 apparently singular FRBs with low dispersion measure (DM) and find that the distribution of their luminosity follows a lognormal form according to statistical tests. In our luminosity measurement, the FRB distance is estimated by using the Macquart relation which was obtained for 8 localized FRBs, and we find it still applicable for 18 sources after adding the latest 10 new localized FRBs. In addition, we test the validity of the luminosity distribution up to the Macquart relation and find that the lognormal form feature decreases as the uncertainty increases. Moreover, we compare the luminosity of these apparent non-repeaters with that of the previously observed 10 repeating FRBs also at low DM, noting that they belong to different lognormal distributions with the mean luminosity of non-repeaters being two times greater than that of repeaters. Therefore, from the two different lognormal distributions, different mechanisms for FRBs can be implied.

We use the kinematic data of the stars in eight dwarf spheroidal galaxies to assess whether $f(R)$ gravity can fit the observed profiles of the line-of-sight velocity dispersion of these systems without resorting to dark matter. Our model assumes that each galaxy is spherically symmetric and has a constant velocity anisotropy parameter $\beta$ and constant mass-to-light ratio consistent with stellar population synthesis models. We solve the spherical Jeans equation that includes the Yukawa-like gravitational potential appearing in the weak field limit of $f(R)$ gravity, and a Plummer density profile for the stellar distribution. The $f(R)$ velocity dispersion profiles depend on two parameters: the scale length $\xi^{-1}$, below which the Yukawa term is negligible, and the boost of the gravitational field $\delta>-1$. $\delta$ and $\xi$ are not universal parameters, but their variation within the same class of objects is expected to be limited. The $f(R)$ velocity dispersion profiles fit the data with a value $\xi^{-1}= 1.2^{+18.6}_{-0.9}$ Mpc for the entire galaxy sample. On the contrary, the values of $\delta$ show a bimodal distribution that picks at $\bar{\delta}=-0.986\pm0.002$ and $\bar{\delta}=-0.92\pm0.01$. These two values disagree at $6\sigma$ and suggest a severe tension for $f(R)$ gravity. It remains to be seen whether an improved model of the dwarf galaxies or additional constraints provided by the proper motions of stars measured by future astrometric space missions can return consistent $\delta$'s for the entire sample and remove this tension.

Observational studies of AGN in the mid-infrared regime are crucial to our understanding of AGN and their role in the evolution of galaxies. Mid-IR-based selection of AGN is complementary to more traditional techniques allowing for a more complete census of AGN activity across cosmic time. Mid-IR observations including time variability and spatially resolved imaging have given us unique insights into the nature of the obscuring structures around AGN. The wealth of fine structure, molecular, and dust features in the mid-IR allow us to simultaneously probe multiple components of the ISM allowing us to explore in detail the impact on the host galaxy by the presence of an AGN -- a crucial step toward understanding galaxy-SMBH co-evolution. This review gives a broad overview of this wide range of studies. It also aims to show the evolution of this field starting with its nascency in the 1960s, through major advances thanks to several generations of space-based and ground-based facilities, as well as the promise of upcoming facilities such as the {\sl James Webb Space Telescope (JWST)}.

The early evolution of the quasar luminosity function (QLF) and black hole mass function (BHMF) encodes key information on the physics determining the radiative and accretion processes of supermassive black holes (BHs) in high-$z$ quasars. Although the QLF shape has been constrained by recent observations, it remains challenging to develop a theoretical model that explains its redshift evolution associated with BH growth self-consistently. In this study, based on a semi-analytical model for the BH formation and growth, we construct the QLF and BHMF of the early BH population that experiences multiple accretion bursts, in each of which a constant Eddington ratio is assigned following a Schechter distribution function. Our best-fit model to reproduce the observed QLF and BHMF at $z\simeq 6$ suggests that several episodes of moderate super-Eddington accretion occur and each of them lasts for $\tau \simeq 20-30$ Myr. The average duty cycle in super-Eddington phases is $\simeq 15\%$ for massive BHs that reach $\gtrsim 10^8~M_\odot$ by $z\simeq 6$, which is nearly twice that of the entire population. We also find that the observed Eddington-ratio distribution function is skewed to a log-normal shape owing to detection limits of quasar surveys. The predicted redshift evolution of the QLF and BHMF suggests a rapid decay of their number and mass density in a cosmic volume toward $z\gtrsim 6$. These results will be unveiled by future deep and wide surveys with the James Webb Space Telescope, Roman Space Telescope, and Euclid.

The aging and gradual brightening of the Sun will challenge Earth's habitability in the next few billion years. If life exists elsewhere in the Universe, the aging of their host star will similarly pose an existential threat. One solution to this threat, which we dub a Lazarus star, is for an advanced civilization to remove (or "star-lift") mass from their host star at a rate which offsets the increase in luminosity, keeping the flux on the habitable planet(s) constant and extending the lifetime of their star. While this idea has existed since 1985 when it was first proposed by Criswell, numerical investigations of star-lifting have been lacking. Here, we use MIST evolutionary tracks to find mass vs. age and $\dot{M}$ vs. age relations with initial mass ranging from $0.15{-}1.3 {\rm M}_{\odot}$. We do this for two different implementations of star-lifting, isoluminosity and isoirradiance, where both hold the incident flux on the habitable planet(s) constant, but the former keeps the orbital radius constant and the latter accounts for a changing orbital radius. We reveal two distinct behaviours for these Lazarus stars. For most stars initially below ${\sim} 0.3 {\rm M}_{\odot}$, we find that their lifetimes can be gradually extended until their mass reaches 0.1${\rm M}_{\odot}$, approaching the hydrogen burning limit - with a lifetime of many trillions of years. In contrast, for more massive stars, their natural evolution causes them to leave the main sequence before reaching the hydrogen burning limit. For example, the Sun has a main-sequence lifetime which can be increased by 10 (6) Gyrs if we started star-lifting for isoluminosity (isoirradiance) today. This requires a mass loss rate of ${\sim}0.02 {\rm M}_{\mathrm{Ceres}}$ per year. We compare star-lifting to other survival strategies and briefly discuss methods for detecting these engineered stars.

We demonstrate the utility of deep learning for modeling the clustering of particles that are aerodynamically coupled to turbulent fluids. Using a Lagrangian particle module within the ATHENA++ hydrodynamics code, we simulate the dynamics of particles in the Epstein drag regime within a periodic domain of isotropic forced hydrodynamic turbulence. This setup is an idealized model relevant to the collisional growth of micron to mmsized dust particles in early stage planet formation. The simulation data is used to train a U-Net deep learning model to predict gridded three-dimensional representations of the particle density and velocity fields, given as input the corresponding fluid fields. The trained model qualitatively captures the filamentary structure of clustered particles in a highly non-linear regime. We assess model fidelity by calculating metrics of the density structure (the radial distribution function) and of the velocity field (the relative velocity and the relative radial velocity between particles). Although trained only on the spatial fields, the model predicts these statistical quantities with errors that are typically < 10%. Our results suggest that, given appropriately expanded training data, deep learning could be used to accelerate calculations of particle clustering and collision outcomes both in protoplanetary disks, and in related two-fluid turbulence problems that arise in other disciplines.

We consider here a proton-synchrotron model to explain the MAGIC observation of GRB 190114C afterglow in the energy band $0.2 - 1$ TeV, while the X-ray spectra are explained by electron-synchrotron emission. Given the uncertainty of the particle acceleration process, we consider several variations of the model, and show that they all match the data very well. We find that the values of the uncertain model parameters are reasonable: explosion energy $\sim 10^{54.5}$ erg, ambient density $\sim 10-100 {\rm cm^{-3}}$, and fraction of electrons/ protons accelerated to a high energy power law of a few per-cents. All these values are directly derived from the observed TeV and X-ray fluxes. They are consistent with both late time data at all bands, from radio to X-rays, and with numerical models of particle acceleration. Our results thus demonstrate the relevance of proton-synchrotron emission to the high energy observations of GRBs during their afterglow phase.

21 cm intensity mapping (IM) has the potential to be a strong and unique probe of cosmology from redshift of order unity to redshift potentially as high as 30. For post-reionization 21 cm observations, the signal is modulated by the thermal and dynamical reaction of gas in the galaxies to the passage of ionization fronts during the Epoch of Reionization. In this work, we investigate the impact of inhomogeneous reionization on the post-reionization 21 cm power spectrum and the induced shifts of cosmological parameters at redshifts $3.5 \lesssim z \lesssim 5.5$. We make use of hydrodynamics simulations that could resolve small-scale baryonic structure evolution to quantify HI abundance fluctuation, while semi-numerical large box 21cmFAST simulations capable of displaying inhomogeneous reionization process are deployed to track the inhomogeneous evolution of reionization bubbles. We find the inhomogeneous reionization effect could impact the HI power spectrum up to tens of percent level and shift cosmological parameters estimation from sub-percent to tens percent in the observation of future post-reionization 21 cm intensity mapping experiments SKA-LOW and PUMA. In particular, the shift is up to 0.033 in the spectral index $n_s$ and 0.025 eV in the sum of the neutrino masses $\sum m_\nu$ depending on the reionization model and the observational parameters. We discuss strategies to mitigate and separate these biases.

We present the results of timing and spectral analysis of the HMXB pulsar, Cen X-3, with the help of observations carried out using the Large Area X-ray Proportional Counter (LAXPC) on board $\textit{AstroSat}$. As part of our analysis, we sampled the source properties during 4 different observation epochs covering two widely different intensity states. We obtain a timing solution and report precise measurements of the spin and orbital parameters corresponding to these observational epochs. The pulse profiles during the two intensity states reveal dramatically varying shapes within a time span of one month. We report the detection of one of the lowest measured frequencies of quasi-periodic oscillations (QPO) at 0.026$\pm$0.001 Hz for Cen X-3 during its low-intensity state. We also find correlated periodic and aperiodic noise components in the power density spectra. We further carried out a phase averaged and a pulse phase resolved spectral study, where we find that the best fit continuum spectrum is well described by an absorbed comptonization model along with a blackbody. Cen X-3 exhibited the presence of the $\sim$28 keV CRSF absorption line and a $\sim$6.6 keV Fe emission line in both the intensity states. Significant variations in the line forming regions and mode of accretion for Cen X-3 within time spans of a month make Cen X-3 a highly dynamic persistent binary.

We present the discovery and analysis of J1316+2614 at z=3.6130, a UV-bright star-forming galaxy ($M_{\rm UV} \simeq -24.7$) with large escape of Lyman continuum (LyC) radiation. J1316+2614 is a young ($\simeq 10$ Myr) star-forming galaxy with $SFR \simeq 500 M_{\odot}$ yr$^{-1}$ and a starburst mass of log($M_{\star}/M_{\odot}) \simeq 9.7$. It shows a very steep UV continuum, $\beta_{\rm UV} \simeq -2.59 \pm 0.05$, consistent with residual dust obscuration, $E(B-V)\simeq 0$. LyC emission is detected with high significance ($\simeq 17 \sigma$) down to $830$\r{A}, for which a very high relative (absolute) LyC escape fraction $f_{\rm esc} \rm (LyC) \simeq 0.92$ ($\simeq 0.87$) is inferred. The contribution of a foreground or AGN contamination to the LyC signal is discussed but is unlikely. J1316$+$2614 is the most powerful ionizing source known among the star-forming galaxy population, both in terms of production ($Q_{\rm H} \approx 10^{56}$ s$^{-1}$) and escape of ionizing photons ($f_{\rm esc} \rm (LyC) \approx 0.9$). Nebular emission in Ly$\alpha$, H$\beta$, and other rest-frame optical lines are detected, but these are weak ($EW_{0} \rm [H\beta] \simeq 35$\r{A}), with their strengths reduced roughly by $\simeq 90\%$. J1316+2614 is the first case known where the effect of large escape of ionizing photons on the strength of nebular lines and continuum emission is clearly observed. Gas inflows are detected in J1316+2614 from the blue-dominated peak Ly$\alpha$ emission (with a blue-to-red peak line ratio $I_{\rm blue}/I_{\rm red} \simeq 3.7$) and redshifted ISM absorption ($\simeq 100$ km s$^{-1}$). Our results suggest that J1316+2614 is undergoing a gas compaction event, possibly representing a short-lived phase in the evolution of massive and compact galaxies, where strong gas inflows have triggered an extreme star formation episode and nearly $100\%$ LyC photons are escaping.

The Atacama Large Millimeter/submillimeter Array (ALMA) is currently revolutionizing observational astrophysics. The aperture synthesis technique provides angular resolution otherwise unachievable with the conventional single-aperture telescope. However, recovering the image from the inherently undersampled data is a challenging task. The CLEAN algorithm has proven successful and reliable and is commonly used in imaging the interferometric observations. It is not, however, free of limitations. Point-source assumption, central to the CLEAN is not optimal for the extended structures of molecular gas recovered by ALMA. Additionally, negative fluxes recovered with CLEAN are not physical. This begs to search for alternatives that would be better suited for specific science cases. We present the recent developments in imaging ALMA data using Bayesian inference techniques, namely the RESOLVE algorithm This algorithm, based on information field theory \cite{Ensslin2013}, has been already successfully applied to image the Very Large Array data. We compare the capability of both CLEAN and RESOLVE to recover known sky signal, convoluted with the simulator of ALMA observation data and we investigate the problem with a set of actual ALMA observations.

The lifetime of protoplanetary disks is a crucial parameter for planet formation research. Observations of disk fractions in star clusters imply median disk lifetimes of 1 -- 3 Myr. This very short disk lifetime calls for planet formation to occur extremely rapidly. We show that young, distant clusters ($\leq$ 5 Myr, $>$ 200 pc) often dominate these types of studies. Such clusters frequently suffer from limiting magnitudes leading to an over-representation of high-mass stars. As high-mass stars disperse their disks earlier, the derived disk lifetimes apply best to high-mass stars rather than low-mass stars. Including only nearby clusters ($<$ 200 pc) minimizes the effect of limiting magnitude. In this case, the median disk lifetime of low-mass stars is with 5 -- 10 Myr, thus much longer than often claimed. The longer timescales provide planets ample time to form. How high-mass stars form planets so much faster than low-mass stars is the next grand challenges.

The magnetic chemically peculiar (mCP) stars of the upper main sequence are perfectly suited to studying the effects of rotation, diffusion, mass-loss, accretion, and pulsation in the presence of an organized stellar magnetic field. Therefore, many important models can only be tested with this star group. In this case study we investigate the possibility of detecting the characteristic 520 nm flux depression of mCP stars using low-resolution BP/RP spectra of the Gaia mission. This would enable us to effectively search for these objects in the ever-increasing database. We employed the tool of Delta a photometry to trace the 520 nm flux depression for 1240 known mCP and 387 normal-type objects including binaries. To this end, we folded the filter curves with the BP/RP spectra and generated the well-established color-color diagram. It is clearly possible to distinguish mCP stars from normal-type objects. The detection rate is almost 95\% for B- and A-type objects. It then drops for cooler-type stars, which is in line with models of the 520 nm flux depression. The BP/RP spectra are clearly qualified to efficiently search for and detect mCP stars.

We analyze the MOA-2020-BLG-208 gravitational microlensing event and present the discovery and characterization of a new planet with an estimated sub-Saturn mass. With a mass ratio $q = 3.17^{+0.28}_{-0.26} \times 10^{-4}$ and a separation $s = 1.3807^{+0.0018}_{-0.0018}$, the planet lies near the peak of the mass-ratio function derived by the MOA collaboration (Suzuki et al. 2016), near the edge of expected sample sensitivity. For these estimates we provide results using two mass law priors: one assuming that all stars have an equal planet-hosting probability, and the other assuming that planets are more likely to orbit around more massive stars. In the first scenario, we estimate that the lens system is likely to be a planet of mass $m_\mathrm{planet} = 46^{+42}_{-24} \; M_\oplus$ and a host star of mass $M_\mathrm{host} = 0.43^{+0.39}_{-0.23} \; M_\odot$, located at a distance $D_L = 7.49^{+0.99}_{-1.13} \; \mathrm{kpc}$. For the second scenario, we estimate $m_\mathrm{planet} = 69^{+37}_{-34} \; M_\oplus$, $M_\mathrm{host} = 0.66^{+0.35}_{-0.32} \; M_\odot$, and $D_L = 7.81^{+0.93}_{-0.93} \; \mathrm{kpc}$. As a cool sub-Saturn-mass planet, this planet adds to a growing collection of evidence for revised planetary formation models and qualifies for inclusion in the extended MOA-II exoplanet microlensing sample.

Merging supermassive black hole binaries is expected as a possible consequence of galaxy mergers, yet the detailed evolution path and underlying mechanisms of these binaries are still subject to large theoretical uncertainties. In this work, we propose to combine the (future) gravitational wave measurements of supermassive black hole binary merger events with the galaxy merger rate distributions from large-scale surveys/cosmological simulations, to infer the delay time of binary mergers, as a function of binary mass. The delay time encodes key information about binary evolution, which can be used to test the predictions of various evolution models. With a mock data set of supermassive black hole binary merger events, we discuss how to infer the distribution of delay time with hierarchical Bayesian inference and test evolution models with the Bayesian model selection method.

Our world is wonderful because of the normal but negligibly small baryonic part (i.e., atoms) although unknown dark matter and dark energy dominate the Universe. A stable atomic nucleus could be simply termed as ``strong matter'' since its nature is dominated by the fundamental strong interaction. Is there any other form of strong matter? Although nuclei are composed of 2-flavoured (i.e., up and down flavours of valence quarks) nucleons, it is conjectured that bulk strong matter could be 3-flavoured (with additional strange quarks) if the baryon number exceeds the critical value, $A_{\rm c}$, in which case quarks could be either free (so-called strange quark matter) or localized (in strangeons, coined by combining ``strange nucleon''). Bulk strong matter could be manifested in the form of compact stars, cosmic rays, and even dark matter. This trinity will be explained in this brief review, that may impact dramatically on today's physics, particularly in the era of multi-messenger astronomy after the discovery of gravitational wave.

The direct capture and accumulation of Galactic dark matter in astrophysical bodies can occur as a result of its scattering with nuclei. In this work we investigate the detailed capture and evaporation of dark matter in terrestrial planets, taking Earth as an example. We focus on the strongly interacting case in which Earth may be opaque to dark matter, referred to as the "optically thick" limit. We investigate light dark matter in particular, addressing important dynamical processes such as the "ping-pong effect" during dark matter capture and the heating of Earth by dark matter annihilation. We do this using Monte-Carlo simulations as well as detailed analytical computations, and obtain improved bounds on dark matter direct detection for both spin-dependent and spin-independent scattering, and also allowing for the interacting species to make up a sub-component of the dark matter density.

We show that a large class of modified gravity theories (MOG) with the Jordan-frame Lagrangian $f(R)$ translate into scalar-field (scalaron) models with hilltop potentials in the Einstein frame. (A rare exception to this rule is provided by the Starobinsky model for which the corresponding scalaron potential is plateau-like for $\phi > 0$.) We find that MOG models featuring two distinct mass scales lead to scalaron potentials that have a flattened hilltop, or tabletop. Inflationary evolution in tabletop models agrees very well with CMB observations. Tabletop potentials therefore provide a new and compelling class of MOG-based inflationary models. By contrast, MOG models with a single mass scale generally correspond to steep hilltop potentials and fail to reproduce the CMB power spectrum. Inflationary evolution in hilltop/tabletop models can proceed in two alternative directions: towards the stable point at small $R$ describing the observable universe, or towards the asymptotic region at large $R$. The MOG models which we examine have several new properties including the fact that gravity can become asymptotically free, with $G_{\rm eff} \to 0$, at infinite or large finite values of the scalar curvature $R$. Interestingly a universe evolving towards the asymptotically free gravity region at large $R$ will either run into a 'Big-Rip' singularity, or inflate eternally.

Strong gravitational lensing of gravitational waves (GWs) occurs when the GWs from a compact binary system travel near a massive object. The mismatch between a lensed signal and unlensed templates determines whether lensing can be identified in a particular GW event. For axisymmetric lens models, the lensed signal is traditionally calculated in terms of model-dependent lens parameters such as the lens mass $M_L$ and source position $y$. We propose that it is useful to parameterize this signal instead in terms of model-independent image parameters: the flux ratio $I$ and time delay $\Delta t_d$ between images. The functional dependence of the lensed signal on these image parameters is far simpler, facilitating data analysis for events with modest signal-to-noise ratios. In the geometrical-optics approximation, constraints on $I$ and $\Delta t_d$ can be inverted to constrain $M_L$ and $y$ for any lens model including the point mass (PM) and singular isothermal sphere (SIS) that we consider. We use our model-independent image parameters to determine the detectability of gravitational lensing in GW signals and find that for GW events with signal-to-noise ratios $\rho$ and total mass $M$, lensing should in principle be identifiable for flux ratios $I \gtrsim 2\rho^{-2}$ and time delays $\Delta t_d \gtrsim M^{-1}$.

We revisit the classic system of a spherically symmetric black hole in general relativity (i.e., a Schwarzschild black hole) surrounded by a geometrically thin accretion disk. Our purpose is to examine whether one can determine three parameters of this system (i.e., black hole mass $M$; distance between the black hole and an observer $r_o$; inclination angle $i$) solely by observing the accretion disk and the black-hole shadow. A point in our analysis is to allow $r_o$ to be finite, which is set to be infinite in most relevant studies. First, it is shown that one can determine the values of $(r_o/M, i)$, where $M/r_o$ is the so-called angular gravitational radius, from the size and shape of shadow. Then, it is shown that if one additionally knows the accretion rate $\dot{M}$ (resp.\ mass $M$) by any independent theoretical or observational approach, one can determine the values of $(M, r_o, i)$ [resp.\ $(\dot{M}, r_o, i)$] without degeneracy, in principle, from the value of flux at any point on the accretion disk.

In 2020, over 60% of launches to low Earth orbit resulted in one or more rocket bodies being abandoned in orbit and eventually returning to Earth in an uncontrolled manner. When they do so, between 20 and 40% of their mass survives the heat of atmospheric reentry. Many of the surviving pieces are heavy enough to pose serious risks to people, on land, at sea, and in airplanes. There is no international consensus on the acceptable level of risk from reentering space objects. This is sometimes a point of contention, such as when a 20 tonne Long March 5B core stage made an uncontrolled reentry in May 2021. Some regulators, including the US, France, and ESA, have implemented a 1 in 10,000 acceptable casualty risk (i.e., statistical threat to human life) threshold from reentering space objects. We argue that this threshold ignores the cumulative effect of the rapidly increasing number of rocket launches. It also fails to address low risk, high consequence outcomes, such as a rocket stage crashing into a high-density city or a large passenger aircraft. In the latter case, even a small piece could cause hundreds of casualties. Compounding this, the threshold is frequently ignored or waived when the costs of adherence are deemed excessive. We analyse the rocket bodies that reentered the atmosphere from 1992 - 2021 and model the associated cumulative casualty expectation. We then extrapolate this trend into the near future (2022 - 2032), modelling the potential risk to the global population from uncontrolled rocket body reentries. We also analyse the population of rocket bodies that are currently in orbit and expected to deorbit soon, and find that the risk distribution is significantly weighted to latitudes close to the equator. This represents a disproportionate burden of casualty risk imposed on the countries of the Global South by major spacefaring countries.

The traditional paradigm for magnetic field lines changing connections ignores magnetic field line chaos and requires an extremely large current density, $j_{max}\propto R_m$, flowing in thin sheets of thickness $1/R_m$, where $R_m$ is the magnetic Reynolds number. The time required for a general natural evolution to take a smooth magnetic field into such a state is rarely considered. Natural evolutions generally cause magnetic field lines to become chaotic. A fast change in field line connections then arises on the timescale defined by the evolution multiplied by a $\ln(R_m)$ factor, and the required maximum current density scales as $\ln(R_m)$. Even when simulations support the new paradigm based on chaos, they have been interpreted as supporting the old. How this could happen is an important example for plasma physics of Kuhn's statements about the acceptance of paradigm change and on Popper's views on the judgment of truth in science.

The kinematics of the three body decay, with a modified energy-momentum relation of the particles due to a violation of Lorentz invariance, is presented in detail in the collinear approximation. The results are applied to the decay of superluminal neutrinos producing an electron-positron or a neutrino-antineutrino pair. Explicit expressions for the energy distributions, required for a study of the cascade of neutrinos produced in the propagation of superluminal neutrinos, are derived.

By considering the quantum Oppenheimer-Snyder model in loop quantum cosmology, a new quantum black hole model whose metric tensor is a suitably deformed Schwarzschild one is derived. The quantum effects imply a lower bound on the mass of the black hole produced by the collapsing dust ball. For the case of larger masses where the event horizon does form, the maximal extension of the spacetime and its properties are investigated. By discussing the opposite scenario to the quantum Oppenheimer-Snyder, a quantum Swiss Cheese model is obtained with a bubble surrounded by the quantum universe. This model is analogous to the black hole cosmology or fecund universes where the big bang is related to a white hole. Thus our models open a new window to the cosmological phenomenology.

Stable scalars can be copiously produced in the Early Universe even if they have no coupling to other fields. We study production of such scalars during and after (high scale) inflation, and obtain strong constraints on their mass scale. Quantum gravity-induced Planck-suppressed operators make an important impact on the abundance of dark relics. Unless the corresponding Wilson coefficients are very small, they normally lead to overproduction of dark states. In the absence of a quantum gravity theory, such effects are uncontrollable, bringing into question predictivity of many non-thermal dark matter models. These considerations may have non-trivial implications for string theory constructions, where scalar fields are abundant.

We show that Einstein's field equations with a negative cosmological constant can admit black hole solutions whose thermodynamics coincides with that of logotropic fluids, recently investigated to heal some cosmological and astrophysical issues. For this purpose, we adopt the Anton-Schmidt equation of state, which represents a generalized version of logotropic fluids. We thus propose a general treatment to obtain an asymptotic anti-de Sitter metric, reproducing the thermodynamic properties of both Anton-Schmidt and logotropic fluids. Hence, we explore how to construct suitable spacetime functions, invoking an event horizon and fulfilling the null, weak, strong and dominant energy conditions. We further relax the strong energy condition to search for possible additional solutions. Finally, we discuss the optical properties related to a specific class of metrics and show how to construct an effective refractive index depending on the spacetime functions and the thermodynamic quantities of the fluid under study. We also explore possible departures with respect to the case without the fluid.