Papers for Friday, Jun 10 2022

The memo describes the methods used to track the long-term gain variations in the NuSTAR detectors. It builds on the analysis presented in Madsen et al. (2015) using the deployable calibration source to measure the gain drift in the NuSTAR CdZnTe detectors. This is intended to be a live document that is periodically updated as new entries are required in the NuSTAR gain CALDB files. This document covers analysis up through early-2022 and the gain v010 CALDB file released in version 20220510.

The outer parts of the Milky Way's disc are significantly out of equilibrium. Using only distances and proper motions of stars from Gaia's Early Data Release 3, in the range |b|<10{\deg}, 130{\deg}<l<230{\deg}, we show that for stars in the disc between around 10 and 14 kpc from the Galactic centre, vertical velocity is strongly dependant on the angular momentum, azimuth, and position above or below the Galactic plane. We further show how this behaviour translates into a bimodality in the velocity distribution of stars in the outer Milky Way disc. We use an N-body model of an impulse-like interaction of the Milky Way disc with a perturber similar to the Sagittarius dwarf to demonstrate that this mechanism can generate a similar disturbance. It has already been shown that this interaction can produce a phase spiral similar to that seen in the Solar neighbourhood. We argue that the details of this substructure in the outer galaxy will be highly sensitive to the timing of the perturbation or the gravitational potential of the Galaxy, and therefore may be key to disentangling the history and structure of the Milky Way.

The $r$-process-enhanced (RPE) stars provide fossil records of the assembly history of the Milky Way and the nucleosynthesis of the heaviest elements. Analysis of observations by the $R$-Process Alliance (RPA) and others have confirmed that hundreds of RPE stars are associated with chemo-dynamically tagged groups, which likely came from accreted dwarf satellite galaxies of the Milky Way (MW). However, we still do not know how RPE stars are formed in the MW. Here, we perform a high-resolution cosmological zoom-in simulation of an MW-like galaxy and demonstrate that RPE stars are primarily formed in gas clumps enhanced in $r$-process elements. For [Fe/H] $\,<-2.5$, most highly RPE ($r$-II; [Eu/Fe] $> +0.7$) stars are formed in low-mass dwarf galaxies that have been enriched in $r$-process elements, while those with higher metallicity are formed in situ, in locally enhanced gas clumps that were not necessarily members of dwarf galaxies. This result suggests that low-mass accreted dwarf galaxies are the main formation site of $r$-II stars with [Fe/H] $\,<-2.5$. We also find that most low-metallicity $r$-II stars exhibit halo-like kinematics. Some $r$-II stars formed in the same halo show low dispersions in [Fe/H] and somewhat larger dispersions of [Eu/Fe], as seen in the observations. The fraction of $r$-II stars found in our simulation is also commensurate with observations from the RPA, and the distribution of the predicted [Eu/Fe] for halo $r$-II stars well matches that observed. These results demonstrate that RPE stars can also be valuable probes of the early stages of their formation.

One promising way to extract information about stellar astrophysics from gravitational wave catalogs is to compare the catalog to the outputs of stellar population synthesis modeling with varying physical assumptions. The parameter space of physical assumptions in population synthesis is high-dimensional and the choice of parameters that best represents the evolution of a binary system may depend in an as-yet-to-be-determined way on the system's properties. Here we propose a pipeline to simultaneously infer zero-age main sequence properties and population synthesis parameter settings controlling modeled binary evolution from individual gravitational wave observations of merging compact binaries. Our pipeline can efficiently explore the high-dimensional space of population synthesis settings and progenitor system properties for each system in a catalog of gravitational wave observations. We apply our pipeline to observations in the third third LIGO-Virgo Gravitational-Wave Transient Catalog. We showcase the effectiveness of this pipeline with a detailed study of the progenitor properties and population synthesis settings that produce mergers like the observed GW150914. Our pipeline permits a measurement of the variation of population synthesis parameter settings with binary properties, if any; we present inferences for the recent GWTC-3 transient catalog that suggest that the stable mass transfer efficiency parameter may vary with primary black hole mass.

The origin of our universe's cosmological magnetic fields remains a mystery. In this study, we consider whether these magnetic fields could have been generated in the early universe by a population of charged, spinning primordial black holes. To this end, we calculate the strength of the magnetic fields generated by this population, and describe their evolution up to the current epoch. We find that extremal black holes in the mass range $ M \sim 10^{28} -10^{36} \, {\rm g}$ could potentially produce magnetic fields with present day values as large as $B \sim 10^{-20} - 10^{-15} \, {\rm G}$. While we remain largely agnostic as to the origin of these spinning, charged black holes, we do briefly discuss how new physics may have induced a chemical potential which could have briefly maintained the black holes in an electrically charged state in the early universe.

The Colours of the Outer Solar System Origins Survey (Col-OSSOS) has gathered high quality, near-simultaneous (g-r) and (r-J) colours of 92 Kuiper Belt Objects (KBOs) with (u-g) and (r-z) gathered for some. We present the current state of the survey and data analysis. Recognizing that the optical colours of most icy bodies broadly follow the reddening curve, we present a new projection of the optical-NIR colours, which rectifies the main non-linear features in the optical-NIR along the ordinates. We find evidence for a bifurcation in the projected colours which presents itself as a diagonal empty region in the optical-NIR. A reanalysis of past colour surveys reveals the same bifurcation. We interpret this as evidence for two separate surface classes: the BrightIR class spans the full range of optical colours and broadly follows the reddening curve, while the FaintIR objects are limited in optical colour, and are less bright in the NIR than the BrightIR objects. We present a two class model. Objects in each class consist of a mix of separate blue and red materials, and span a broad range in colour. Spectra are modelled as linear optical and NIR spectra with different slopes, that intersect at some transition wavelength. The underlying spectral properties of the two classes fully reproduce the observed structures in the UV-optical-NIR colour space ($0.4\lesssim\lambda\lesssim1.4 \mbox{ $\mu$m}$), including the bifurcation observed in the Col-OSSOS and H/WTSOSS datasets, the tendency for cold classical KBOs to have lower (r-z) colours than excited objects, and the well known bimodal optical colour distribution.

The supernova remnant (SNR) candidate G 116.6-26.1 is one of the few high Galactic latitude ($|b| > 15^o$) remnants detected so far in several wavebands. It was discovered recently in the SRG/eROSITA all-sky X-ray survey and displays also a low-frequency weak radio signature. In this study, we report the first optical detection of G 116.6-26.1 through deep, wide-field and higher resolution narrowband imaging in $\rm H\alpha$, [S II] and [O III] light. The object exhibits two major and distinct filamentary emission structures in a partial shell-like formation. The optical filaments are found in excellent positional match with available X-ray, radio and UV maps, can be traced over a relatively long angular distance (38' and 70') and appear unaffected by any strong interactions with the ambient interstellar medium. We also present a flux-calibrated, optical emission spectrum from a single location, with Balmer and several forbidden lines detected, indicative of emission from shock excitation in a typical evolved SNR. Confirmation of the most likely SNR nature of G 116.6-26.1 is provided from the observed value of the line ratio $\rm [S\, II] / H\alpha = 0.56 \pm 0.06$, which exceeds the widely accepted threshold 0.4, and is further strengthened by the positive outcome of several diagnostic tests for shock emission. Our results indicate an approximate shock velocity range $70-100\, km\, s^{-1}$ at the spectroscopically examined filament, which, when combined with the low emissivity in $\rm H\alpha$ and other emission lines, suggest that G 116.6-26.1 is a SNR at a mature evolutionary stage.

Integral Field Spectrographs (IFS) often require non-trivial calibration techniques to process raw data. The OH Suppressing InfraRed Imaging Spectrograph (OSIRIS) at the W. M. Keck Observatory is a lenslet-based IFS that requires precise methods to associate the flux on the detector with both a wavelength and a position on the detector. During calibration scans, a single column lenslet mask is utilized to keep light from adjacent lenslet columns separate from the primary lenslet column, in order to uniquely determine spectral response of individual lenslets on the detector. Despite employing a single column lenslet mask, an issue associated with such calibration schemes may occur when light from adjacent masked lenslet columns leaks into the primary lenslet column. Incorrectly characterizing the flux due to additional light in the primary lenslet column results in one form of crosstalk between lenslet columns, which most clearly manifest as non-physical artifacts in the spectral dimension of the reduced data. We treat the problem of potentially blended calibration scans as a source separation problem and implement Non-negative Matrix Factorization (NMF) as a way to separate blended calibration scan spectra. After applying NMF to calibration scan data, extracted spectra from calibration scans show reduced crosstalk of up to 26.7$\pm$0.5$\%$ while not adversely impacting the signal-to-noise ratio. Additionally, we determined the optimal number of calibration scans per lenslet column needed to create NMF factors, finding that greatest reduction crosstalk occurs when NMF factors are created using one calibration scan per lenslet column.

We analyze high-cadence data from the Transiting Exoplanet Survey Satellite (TESS) of the ambiguous nuclear transient (ANT) ASASSN-18el. The optical changing-look phenomenon in ASASSN-18el has been argued to be due to either a drastic change in the accretion rate of the existing active galactic nucleus (AGN) or the result of a tidal disruption event (TDE). Throughout the TESS observations, short-timescale stochastic variability is seen, consistent with an AGN. We are able to fit the TESS light curve with a damped-random-walk (DRW) model and recover a rest-frame variability amplitude of $\hat{\sigma} = 0.93 \pm 0.02$ mJy and a rest-frame timescale of $\tau_{DRW} = 20^{+15}_{-6}$ days. We find that the estimated $\tau_{DRW}$ for ASASSN-18el is broadly consistent with an apparent relationship between the DRW timescale and central supermassive black hole mass. The large-amplitude stochastic variability of ASASSN-18el, particularly during late stages of the flare, suggests that the origin of this ANT is likely due to extreme AGN activity rather than a TDE.

The true 3-dimensional (3D) morphology of the Musca molecular cloud is a topic that has received significant attention lately. Given that Musca does not exhibit intense star-formation activity, unveiling its shape has the potential of also revealing crucial information regarding the physics that dictates the formation of the first generation of stars within molecular clouds. Here, we revisit the shape of Musca and we present a comprehensive array of evidence pointing towards a shape that is extended along the line-of-sight dimension: (a) 3D maps of differential extinction; (b) new non-local thermodynamic equilibrium radiative transfer simulations of CO rotational transitions from a sheet-like, magnetically-dominated simulated cloud; (c) an effective/critical density analysis of available CO observations; (d) indirect consequences that a filamentary structure would have had, from a theoretical star-formation perspective. We conclude that the full collection of observational evidence strongly suggests that Musca has a sheet-like geometry.

Astrophysical sources of very high energy (VHE; $>100$ GeV) $\gamma$ rays are rare, since GeV and TeV photons can be only emitted in extreme circumstances involving interactions of relativistic particles with local radiation and magnetic fields. In the context of the Fermi Large Area Telescope (LAT), only a few sources are known to be VHE emitters, where the largest fraction belongs to the rarest class of active galactic nuclei: the blazars. In this work, we explore Fermi-LAT data for energies $>100$ GeV and Galactic latitudes $b > |50^{\circ}|$ in order to probe the origin of the extragalactic isotropic $\gamma$-ray emission. Since the production of such VHE photons requires very specific astrophysical conditions, we would expect that the majority of the VHE photons from the isotropic $\gamma$-ray emission originate from blazars or other extreme objects like star-forming galaxies, $\gamma$-ray bursts, and radio galaxies, and that the detection of a single VHE photon at the adopted Galactic latitudes would be enough to unambiguously trace the presence of such a counterpart. Our results suggest that blazars are, by far, the dominant class of source above 100 GeV, although they account for only $22.8^{+4.5}_{-4.1}\%$ of the extragalactic VHE photons. The remaining $77^{+4.1}_{-4.5}\%$ of the VHE photons still have an unknown origin.

Carbon-enhanced metal-poor (CEMP) stars are a unique resource for Galactic archaeology because they are closely connected to the First Stars, and/or allow investigating binary interactions at very low metallicity. Comparing the fractions and properties of CEMP stars in different Galactic environments can provide us with unique insights into the formation and evolution of the Milky Way halo and its building blocks. In this work, we investigate whether directly comparing fractions of CEMP stars from different literature samples of very metal-poor ([Fe/H] < -2.0) stars is valid. We compiled published CEMP fractions and samples of Galactic halo stars from the past 25 years, and find that they are not all consistent with each other. Focusing on giant stars, we find significant differences between various surveys when comparing their trends of [Fe/H] versus [C/Fe] and their distributions of CEMP stars. To test the role of the analysis pipelines for low-resolution spectroscopic samples, we re-analysed giant stars from various surveys with the SSPP and FERRE pipelines. We found systematic differences in [C/Fe] of ~0.1-0.4 dex, partly independent of degeneracies with the stellar atmospheric parameters. These systematics are likely due to the different pipeline approaches, different assumptions in the employed synthetic grids, and/or the comparison of different evolutionary phases. We conclude that current biases in (the analysis of) very metal-poor samples limit the conclusions one can draw from comparing different surveys. We provide some recommendations and suggestions that will hopefully aid the community to unlock the full potential of CEMP stars for Galactic archaeology.

Cosmic rays have been shown to be extremely important in the dynamics of diffuse gas in galaxies, helping to maintain hydrostatic equilibrium, and serving as a regulating force in star formation. In this paper, we address the influence of cosmic rays on galaxies by re-examining the theory of a cosmic ray Eddington limit, first proposed by Socrates et al. (2008) and elaborated upon by Crocker et al. (2021a) and Huang & Davis (2022). A cosmic ray Eddington limit represents a maximum cosmic ray energy density above which the interstellar gas cannot be in hydrostatic equilibrium, resulting in a wind. In this paper, we continue to explore the idea of a cosmic ray Eddington limit by introducing a general framework that accounts for the circumgalactic environment and applying it to five galaxies that we believe to be a good representative sample of the star forming galaxy population, using different cosmic ray transport models to determine what gives each galaxy the best chance to reach this limit. We show that while an Eddington limit for cosmic rays does exist, for our five galaxies, the limit either falls at star formation rates that are much larger or gas densities that are much lower than each galaxy's measured values. This suggests that cosmic ray pressure is not the main factor limiting the luminosity of starburst galaxies.

The distribution of surface classes of resonant trans-Neptunian objects (TNOs) provides constraints on the proto-planetesimal disk and giant planet migration. To better understand the surfaces of TNOs, the Colours of the Outer Solar System Origins Survey (Col-OSSOS) acquired multi-band photometry of 92 TNOs, and found that the surfaces of TNOs can be well described by two surface classifications, BrightIR and FaintIR. These classifications both include optically red members and are differentiated predominantly based on whether their near-infrared spectral slope is similar to their optical spectral slope. The vast majority of cold classical TNOs, with dynamically unexcited orbits, have the FaintIR surface classification, and we infer that TNOs in other dynamical classifications with FaintIR surfaces share a common origin with the cold classical TNOs. Comparison between the resonant populations and the possible parent populations of cold classical and dynamically excited TNOs reveal that the 3:2 has minimal contributions from the FaintIR class, consistent with the $\nu_8$ secular resonance clearing the region near the 3:2 before any sweeping capture occurred. Conversely, the FaintIR class is over-represented in the 4:3 resonance, 2:1 resonance, and the resonances within the cold classical belt, implying that the FaintIR surface formed in the protoplanetary disk between ~<34.6 au to ~>47 au, though the outer bound depends on the degree of resonance sweeping during migration. The presence and absence of the FaintIR surfaces in Neptune's resonances provides critical constraints for the history of Neptune's migration, the evolution of the $\nu_8$, and the surface class distribution in the initial planetesimal disk.

Wide-field searches for young stellar objects (YSOs) can place useful constraints on the prevalence of clustered versus distributed star formation. The Spitzer/IRAC Candidate YSO (SPICY) catalog is one of the largest compilations of such objects (~120,000 candidates in the Galactic midplane). Many SPICY candidates are spatially clustered, but, perhaps surprisingly, approximately half the candidates appear spatially distributed. To better characterize this unexpected population and confirm its nature, we obtained Palomar/DBSP spectroscopy for 26 of the optically-bright (G<15 mag) "isolated" YSO candidates. We confirm the YSO classifications of all 26 sources based on their positions on the Hertzsprung-Russell diagram, H and Ca II line-emission from over half the sample, and robust detection of infrared excesses. This implies a contamination rate of <10% for SPICY stars that meet our optical selection criteria. Spectral types range from B4 to K3, with A-type stars most common. Spectral energy distributions, diffuse interstellar bands, and Galactic extinction maps indicate moderate to high extinction. Stellar masses range from ~1 to 7 $M_\odot$, and the estimated accretion rates, ranging from $3\times10^{-8}$ to $3\times10^{-7}$ $M_\odot$ yr$^{-1}$, are typical for YSOs in this mass range. The 3D spatial distribution of these stars, based on Gaia astrometry, reveals that the "isolated" YSOs are not evenly distributed in the Solar neighborhood but are concentrated in kpc-scale dusty Galactic structures that also contain the majority of the SPICY YSO clusters. Thus, the processes that produce large Galactic star-forming structures may yield nearly as many distributed as clustered YSOs.

The SETI Ellipsoid is a geometric method for prioritizing technosignature observations based on the strategy of receiving signals synchronized to conspicuous astronomical events. Precise distances to nearby stars from Gaia makes constraining Ellipsoid crossing times possible. Here we explore the utility of using the Gaia Catalog of Nearby Stars to select targets on the SN 1987A SETI Ellipsoid, as well the Ellipsoids defined by 278 classical novae. Less than 8% of stars within the 100 pc sample are inside the SN 1987A SETI Ellipsoid, meaning the vast majority of nearby stars are still viable targets for monitoring over time. We find an average of 734 stars per year within the 100 pc volume will intersect the Ellipsoid from SN 1987A, with ~10% of those having distance uncertainties from Gaia better than 0.1 lyr.

We report on VLT/FORS2 imaging polarimetry observations in the $R_{\rm special}$ band of WISE J011601.41-050504.0 (W0116-0505), a heavily obscured hyper-luminous quasar at $z=3.173$ classified as a Hot, Dust-Obscured Galaxy (Hot DOG) based on its mid-IR colors. Recently, Assef et al. (2020) identified W0116-0505 as having excess rest-frame optical/UV emission, and concluded this excess emission is most likely scattered light from the heavily obscured AGN. We find that the broad-band rest-frame UV flux is strongly linearly polarized (10.8$\pm$1.9\%, with a polarization angle of 74$\pm$9~deg), confirming this conclusion. We analyze these observations in the context of a simple model based on scattering either by free electrons or by optically thin dust, assuming a classical dust torus with polar openings. Both can replicate the degree of polarization and the luminosity of the scattered component for a range of geometries and column densities, but we argue that optically thin dust in the ISM is the more likely scenario. We also explore the possibility that the scattering medium corresponds to an outflow recently identified for W0116-0505. This is a feasible option if the outflow component is bi-conical with most of the scattering occurring at the base of the receding outflow. In this scenario the quasar would still be obscured even if viewed face on, but might appear as a reddened type 1 quasar once the outflow has expanded. We discuss a possible connection between blue-excess Hot DOGs, extremely red quasars (ERQs), reddened type 1 quasars, and unreddened quasars that depends on a combination of evolution and viewing geometry.

Type Ia Supernovae (SNe Ia) are securely understood to come from the thermonuclear explosion of a white dwarf as a result of binary interaction, but the nature of that binary interaction and the secondary object is uncertain. Recently, a double white dwarf model known as the dynamically driven double-degenerate double-detonation (D6) model has become a promising explanation for these events. One realization of this scenario predicts that the companion may survive the explosion and reside within the remnant as a fast moving ($V_{peculiar} >1000$ km s$^{-1}$), overluminous ($L > 0.1 L_\odot$) white dwarf. Recently, three objects which appear to have these unusual properties have been discovered in the Gaia survey. We obtained photometric observations of the SN Ia remnant SN 1006 with the Dark Energy Camera over four years to attempt to discover a similar star. We present a deep, high precision astrometric proper motion survey of the interior stellar population of the remnant. We rule out the existence of a high proper motion object consistent with our tested realization of the D6 scenario ($V_{transverse} > 600$ km s$^{-1}$ with $m_r < 21$ corresponding to an intrinsic luminosity of $L > 0.0176 L_\odot$). We conclude that such a star does not exist within the remnant, or is hidden from detection by either strong localized dust or the unlikely possibility of ejection from the binary system near parallel to the line of sight.

In the present-day Kuiper Belt, the number of compositional classes and the orbital distributions of these classes hold important cosmogonic implications for the Solar System. In a companion paper by Fraser et al., we demonstrate that the observed color distribution of small (H>6) Trans-Neptunian Objects (TNOs) can be accounted for by the existence of only two composition classes, named brightIR and faintIR, where the range of colors in each class is governed by a mixture of two material end members. Here, we investigate the orbital distribution of the two color classes identified by Fraser et al. and find that the orbital inclinations of the brightIR class objects are correlated with their optical colors. Using the output of numerical simulations investigating the orbital evolution of TNOs during their scattering phase with Neptune, we show that this correlation could reflect a composition gradient in the early protoplanetary disk, in the range of heliocentric distances over which TNOs from the brightIR class accreted. However, tensions between this interpretation and the existence of blue contaminants among cold classical TNOs, and possible alternative origins for the detected correlation, currently bear uncertainty on our proposed interpretation.

Despite the theoretical indication that fast neutrino-flavor conversion (FFC) ubiquitously occurs in core-collapse supernova and binary neutron star merger, the lack of global simulations has been the greatest obstacle to study their astrophysical consequences. In this Letter, we present the first global simulation of FFC in spherical symmetry by using a novel approach, in which the injected number of neutrinos into simulation box is systematically changed, and then we explore general characteristics of FFC in global scale. We find that FFC in all models achieves quasi-steady state in the non-linear regime, and its saturation property of FFC is universal. We also find that temporal- and spatial variations of FFC are smeared out at large radii due to phase cancellation through neutrino self-interactions. Finally, we provide a new diagnostic quantity, ELN-XLN angular crossing, to assess the non-linear saturation of FFC.

We developed a new general-relativistic quantum-kinetics neutrino transport code, GRQKNT, for numerical studies of quantum kinetics of non-equilibrium neutrinos in six-dimensional phase space. This code is intended for use in both local and global simulations of neutrino transport in core-collapse supernova and binary neutron star merger. It has been widely recognized that global simulations of collective neutrino oscillations, in particular fast neutrino-flavor conversions (FFC), require unfeasible computational resources due to large disparity of scales between flavor conversion and astrophysical phenomena. We propose a novel approach to tackle the issue. This paper is devoted to describe the philosophy, design, and numerical implementation of GRQKNT with a number of tests ensuring correct implementation of each module. The code is based on a discrete-ordinate Sn method, finite-difference realization of mean-field quantum kinetic equation. The transport equation is solved based on a conservative formalism, and we use a fifth-order weighted essentially non-oscillatory scheme with fourth-order TVD Runge-Kutta time-integration. The transport module is designed to work with arbitrary spacetimes and currently three different stationary spacetimes (flat spacetime, Schwarzschild black hole, and Kerr black hole) are implemented. The collision term including neutrino emission, absorption, and momentum-exchanged scatterings are also implemented into our code. The oscillation Hamiltonian consists of vacuum, matter, and self-interactions. Both two- and three neutrino-flavor scenarios can be applied. Fluid-velocity dependences in transport-, collision-, and oscillation modules, are also treated self-consistently by using two-energy-grid technique, that has been already established in our another code with full Boltzmann neutrino transport.

While Gaia has observed the phase space coordinates of over a billion stars in the Galaxy, in the overwhelming majority of cases it has only obtained five of the six coordinates, the missing dimension being the radial (line-of-sight) velocity. Using a realistic mock dataset, we show that Bayesian neural networks are highly capable of `learning' these radial velocities as a function of the other five coordinates, and thus filling in the gaps. For a given star, the network outputs are not merely point predictions, but full posterior distributions encompassing the intrinsic scatter of the stellar phase space distribution, the observational uncertainties on the network inputs, and any `epistemic' uncertainty stemming from our ignorance about the stellar phase space distribution. Applying this technique to the real Gaia data, we generate and publish a catalogue of posteriors for the radial velocities of 16 million Gaia DR2/EDR3 stars in the magnitude range 6<G<14.5. Many of these gaps will be filled in very soon by Gaia DR3, which will serve to test our blind predictions. Thus, the primary use of our published catalogue will be to validate our method, justifying its future use in generating an updated catalogue of posteriors for radial velocities missing from Gaia DR3.

Using Athena++, we perform 3D Radiation-Hydrodynamic calculations of the radiative breakout of the shock wave in the outer envelope of a red supergiant (RSG) which has suffered core collapse and will become a Type IIP supernova. The intrinsically 3D structure of the fully convective RSG envelope yields key differences in the brightness and duration of the shock breakout (SBO) from that predicted in a 1D stellar model. First, the lower-density `halo' of material outside of the traditional photosphere in 3D models leads to a shock breakout at lower densities than 1D models. This would prolong the duration of the shock breakout flash at any given location on the surface to $\approx$1-2 hours. However, we find that the even larger impact is the intrinsically 3D effect associated with large-scale fluctuations in density that cause the shock to break out at different radii at different times. This substantially prolongs the SBO duration to $\approx$3-6 hours and implies a diversity of radiative temperatures, as different patches across the stellar surface are at different stages of their radiative breakout and cooling at any given time. These predicted durations are in better agreement with existing observations of SBO. The longer durations lower the predicted luminosities by a factor of 3-10 ($L_\mathrm{bol}\sim10^{44}\mathrm{erg\ s^{-1}}$), and we derive the new scalings of brightness and duration with explosion energies and stellar properties. These intrinsically 3D properties eliminate the possibility of using observed rise times to measure the stellar radius via light-travel time effects.

Large surveys of star-forming regions have unveiled power-law correlations between the stellar mass and the disc parameters, such as the disc mass $M_{\mathrm{d}} \propto {M_{\star}}^{\lambda_{\mathrm{m}}}$ and the accretion rate $\dot M \propto {M_{\star}}^{\lambda_{\mathrm{acc}}}$. The observed slopes appear to be increasing with time, but the reason behind the establishment of these correlations and their subsequent evolution is still uncertain. We conduct a theoretical analysis of the impact of viscous evolution on power-law initial conditions for a population of protoplanetary discs. We find that, for evolved populations, viscous evolution enforces the two correlations to have the same slope, $\lambda_{\mathrm{m}}$ = $\lambda_{\mathrm{acc}}$, and that this limit is uniquely determined by the initial slopes $\lambda_{\mathrm{m}, 0}$ and $\lambda_{\mathrm{acc}, 0}$. We recover the increasing trend claimed from the observations when the difference in the initial values, $\delta_0 = \lambda_{\mathrm{m}, 0} - \lambda_{\mathrm{acc}, 0}$, is larger than $1/2$; moreover, we find that this increasing trend is a consequence of a positive correlation between the viscous timescale and the stellar mass. We also present the results of disc population synthesis numerical simulations, that allow us to introduce a spread and analyse the effect of sampling, which show a good agreement with our analytical predictions. Finally, we perform a preliminary comparison of our numerical results with observational data, which allows us to constrain the parameter space of the initial conditions to $\lambda_{\mathrm{m}, 0} \in [1.2, 2.1]$, $\lambda_{\mathrm{acc}, 0} \in [0.7, 1.5]$.

The O'Connell effect - the presence of unequal maxima in eclipsing binaries - remains an unsolved riddle in the study of close binary systems. The Kepler space telescope produced high precision photometry of nearly 3,000 eclipsing binary systems, providing a unique opportunity to study the O'Connell effect in a large sample and in greater detail than in previous studies. We have characterized the observational properties - including temperature, luminosity, and eclipse depth - of a set of 212 systems (7.3% of Kepler eclipsing binaries) that display a maxima flux difference of at least 1%, representing the largest sample of O'Connell effect systems yet studied. We explored how these characteristics correlate with each other to help understand the O'Connell effect's underlying causes. We also describe some system classes with peculiar light curve features aside from the O'Connell effect (~30% of our sample), including temporal variation and asymmetric minima. We found that the O'Connell effect size's correlations with period and temperature are inconsistent with Kouzuma's starspot study. Up to 20% of systems display the parabolic eclipse timing variation signal expected for binaries undergoing mass transfer. Most systems displaying the O'Connell effect have the brighter maximum following the primary eclipse, suggesting a fundamental link between which maximum is brighter and the O'Connell effect's physical causes. Most importantly, we find that the O'Connell effect occurs exclusively in systems where the components are close enough to significantly affect each other, suggesting that the interaction between the components is ultimately responsible for causing the O'Connell effect.

We present spatially resolved observations of Betelgeuse (Alpha Orionis) obtained with the Karl G. Jansky Very Large Array (VLA) at wavelengths of ~7mm (44~GHz) and ~1.3cm (22~GHz) on 2019 August 2, just prior to the onset of the historical optical dimming that occurred between late 2019 and early 2020. Our measurements suggest recent changes in the temperature and density structure of the atmosphere between radii r~2-3R*. At 7mm the star is ~20% dimmer than in previously published observing epochs between 1996--2004. We measure a mean gas temperature of T_B = 2270 +\- 260 K at r~2.1R*, where R* is the canonical photospheric radius. This is ~2 sigma lower than previously reported temperatures at comparable radii and >1200K lower than predicted by previous semi-empirical models of the atmosphere. The measured brightness temperature at r~2.6R* (T_B = 2580 +\- 260 K) is also cooler than expected based on trends in past measurements. The stellar brightness profile in our current measurements appears relatively smooth and symmetric, with no obvious signatures of giant convective cells or other surface features. However, the azimuthally averaged brightness profile is found to be more complex than a uniform elliptical disk. Our observations were obtained approximately six weeks before spectroscopic measurements in the ultraviolet revealed evidence of increases in the chromospheric electron density in the southern hemisphere of Betelgeuse, coupled with a large-scale outflow. We discuss possible scenarios linking these events with the observed radio properties of the star, including the passage of a strong shock wave.

Gaia used a large sample of photometrically selected active galactic nuclei (AGNs) and quasars to remove the residual spin of its global proper motion system in order to achieve a maximally inertial reference frame. A small fraction of these reference objects have statistically significant astrometric proper motions in Gaia EDR3. We compile a source sample of $105,593$ high-fidelity AGNs with accurate spectroscopically determined redshifts above 0.5 from the SDSS and normalized proper motions below 4. The rate of genuinely perturbed proper motions is at least 0.17\%. A smaller high completeness sample of 152 quasars with excess proper motions at a confidence level of 0.9995 is examined in detail. Pan-STARRS images and Gaia-resolved pairs reveal that 29\% of the sample are either double sources or gravitationally lensed quasars. An Anderson--Darling test on parameters of a smaller high-reliability sample and their statistical controls reveals 17 significant factors that favor multiplicity and multi-source structure as the main cause of perturbed astrometry. Using a nearest neighbor distance statistical analysis and counts of close companions in Gaia on a much larger initial sample of AGNs, an excess of closely separated sources in Gaia is detected. At least 0.33\% of all optical quasars are genuinely double or multiply imaged. We provide a list of 44 candidate double or multiple AGNs and four previously known gravitational lenses. Many proper motion quasars may be more closely separated, unresolved doubles exhibiting the variability imposed motion (VIM) effect, and a smaller fraction may be chance alignments with foreground stars causing weak gravitational lensing.

Theoretical models suggest the existence of a dark matter spike surrounding the supermassive black holes that lie at the center of galaxies. The spike density is thought to obey a power law that starts at a few times the black hole horizon radius and extends to a distance, $R_\text{sp}$, of the order of a kiloparsec. In this paper, we use the Tolman-Oppenheimer-Volkoff equations to construct the spacetime metric representing a black hole surrounded by such a dark matter spike. We consider the dark matter to be a perfect fluid, but make no other assumption about its nature. The assumed power law density provides in principle three parameters with which to work: the power law exponent $\gamma_\text{sp}$, the external radius $R_\text{sp}$, and the spike density $\rho_\text{DM}^\text{sp}$ at $R_\text{sp}$. These in turn determine the total mass of the spike. We focus on Sagittarius A* and M87 for which some theoretical and observational bounds exist on the DM spike parameters. Using these bounds in conjunction with the metric obtained from the Tolman-Oppenheimer-Volkoff equations, we investigate the possibility of detecting the dark matter spikes surrounding these black holes via the gravitational waves emitted at the ringdown phase of black hole perturbations. Our results suggest that if the DM spike to black hole mass ratio is roughly constant, greater mass black holes require relatively smaller spike densities in order to yield potentially observable signals. In particular, the detection of the dark matter spike in M87 through the ringdown waveform may soon be within reach.

We report the discovery of a bright (g = 14.5 ABmag, K = 11.9 Vegamag) quasar at redshift z=0.83 -- the optically brightest (unbeamed) quasar at z>0.4. SMSS J114447.77-430859.3, at a Galactic latitude of b=+18.1deg, was identified by its optical colours from the SkyMapper Southern Survey (SMSS) during a search for symbiotic binary stars. Optical and near-infrared spectroscopy reveals broad MgII, H-beta, H-alpha, and Pa-beta emission lines, from which we measure a black hole mass of log(M_BH / M_Sun) = 9.4 +/- 0.5. With its high luminosity, L_bol = (4.7 +/- 1.0) * 10^47 erg/s or M_i(z=2) = -29.74 mag, we estimate an Eddington ratio of ~1.4. As the most luminous quasar known over the last ~9 Gyr of cosmic history, having a luminosity 8 times greater than 3C 273, the source offers a range of potential follow-up opportunities.

The observations of GW170817/AT2017gfo have provided us with evidence that binary neutron star mergers are sites of $r$-process nucleosynthesis. However, the observed signatures in the spectra of GW170817/AT2017gfo have not been fully decoded especially in the near-infrared (NIR) wavelengths. In this paper, we investigate the kilonova spectra over the entire wavelength range with the aim of elemental identification. We systematically calculate the strength of bound-bound transitions by constructing a hybrid line list that is accurate for important strong transitions and complete for weak transitions. We find that the elements on the left side of the periodic table, such as Ca, Sr, Y, Zr, Ba, La, and Ce, tend to produce prominent absorption lines in the spectra. This is because such elements have a small number of valence electrons and low-lying energy levels, resulting in strong transitions. By performing self-consistent radiative transfer simulations for the entire ejecta, we find that La III and Ce III appear in the NIR spectra, which can explain the absorption features at $\lambda \sim$ 12000-14000 A in the spectra of GW170817/AT2017gfo. The mass fractions of La and Ce are estimated to be $>2\times 10^{-6}$ and $\sim$ (1-100)$\times 10^{-5}$, respectively. An actinide element Th can also be a source of absorption as the atomic structure is analogous to that of Ce. However, we show that Th III features are less prominent in the spectra because of the denser energy levels of actinides compared to those of lanthanides.

We present the results of fitting a flexible stellar stream density model to a collection of thirteen streams around the Milky Way, using photometric data from DES, DECaLS, and Pan-STARRS. We construct density maps for each stream and characterise their tracks on the sky, width, and distance modulus curves along the length of each stream. We use these measurements to compute lengths and total luminosities of streams and identify substructures. Several streams show prominent substructures, such as stream broadening, gaps, large deviations of stream tracks and sharp changes in stream densities. Examining the group of streams as a population, as expected we find that streams with globular cluster progenitors are typically narrower than those with dwarf galaxy progenitors, with streams around 100 pc wide showing overlap between the two populations. We also note the average luminosity of globular cluster streams is significantly lower than the typical luminosity of intact globular clusters. The likely explanation is that observed globular cluster streams preferentially come from lower luminosity and lower density clusters. The stream measurements done in a uniform manner presented here will be helpful for more detailed stream studies such as identifying candidate stream members for spectroscopic follow up and stellar stream dynamical modeling.

HCN is among the most commonly detected molecules in star- and planet-forming regions. It is of broad interest as a tracer of star-formation physics, a probe of nitrogen astrochemistry, and an ingredient in prebiotic chemical schemes. Despite this, one of the most fundamental astrochemical properties of HCN remains poorly characterized: its thermal desorption behavior. Here, we present a series of experiments to characterize the thermal desorption of HCN in astrophysically relevant conditions, with a focus on predicting the HCN sublimation fronts in protoplanetary disks. We derive HCN-HCN and HCN-H2O binding energies of 3207\pm197 K and 4192\pm68 K, which translate to disk midplane sublimation temperatures around 85 K and 103 K. For a typical midplane temperature profile, HCN should only begin to sublimate ~1-2 au exterior to the H2O snow line. Additionally, in H2O-dominated mixtures (20:1 H2O:HCN), we find that the majority of HCN remains trapped in the ice until H2O crystallizes. Thus, HCN may be retained in disk ices at almost all radii where H2O-rich planetesimals form. This implies that icy body impacts to planetary surfaces should commonly deliver this potential prebiotic ingredient. A remaining unknown is the extent to which HCN is pure or mixed with H2O in astrophysical ices, which impacts the HCN desorption behavior as well as the outcomes of ice-phase chemistry. Pure HCN and HCN:H2O mixtures exhibit distinct IR bands, raising the possibility that the James Webb Space Telescope will elucidate the mixing environment of HCN in star- and planet-forming regions and address these open questions.

Strong nebular emission lines are an important diagnostic tool for tracing the evolution of star-forming galaxies across cosmic time. However, different observational setups can affect these lines, and the derivation of the physical nebular properties. We analyze 12 local star-forming galaxies from the COS Legacy Spectroscopy SurveY (CLASSY) to assess the impact of using different aperture combinations on the determination of the physical conditions and gas-phase metallicity. We compare optical spectra observed with the SDSS aperture, which has a 3" of diameter similar to COS, to IFU and longslit spectra, including new LBT/MODS observations of five CLASSY galaxies. We calculate the reddening, electron densities and temperatures, metallicities, star formation rates, and equivalent widths (EWs). We find that measurements of the electron densities and temperatures, and metallicity remained roughly constant with aperture size, indicating that the gas conditions are relatively uniform for this sample. However, using the IFU observations of 3 galaxies, we find that the E(B-V) values derived from the Balmer ratios decrease ( by up to 53%) with increasing aperture size. The values change most significantly in the center of the galaxies, and level out near the COS aperture diameter of 2.5". We examine the relative contributions from the gas and stars using the H$\alpha$ and [OIII] $\lambda$5007 EWs as a function of aperture light fraction, but find little to no variations within a given galaxy. These results imply that the optical spectra provide nebular properties appropriate for the FUV CLASSY spectra, even when narrow 1.0" long-slit observations are used.

The detection of cyclotron resonance scattering features (CRSFs) is the only way to directly and reliably measure the magnetic field near the surface of a neutron star (NS). The broad energy coverage and large collection area of \emph{Insight}-HXMT in the hard X-ray band allowed us to detect the CRSF with the highest energy known to date, reaching about 146 keV during the 2017 outburst of the first galactic pulsing ultraluminous X-ray source (pULX) Swift~J0243.6+6124. During this outburst, the CRSF was only prominent close to the peak luminosity $\sim 2\times10^{39}$ erg s$^{-1}$, the highest to date in any of the Galactic pulsars. The CRSF is most significant in the spin phase region corresponding to the main pulse of the pulse profile, and its centroid energy evolves with phase from 120 to 146 keV. We identify this feature as the fundamental CRSF, since no spectral feature exists at $60-70$ keV. This is the first unambiguous detection of an electron CRSF from an ULX. We also estimate a surface magnetic field $\sim1.6\times10^{13}$ G for Swift~J0243.6+6124. Considering that the dipole magnetic field strengths, inferred from several independent estimates of magnetosphere radius, are at least an order of magnitude lower than our measurement, we argue that the detection of the highest energy CRSF reported here unambiguously proves the presence of multipole field components close to the surface of the neutron star. Such a scenario has previously been suggested for several pulsating ULXs, including Swift J0243.6+6124, and our result represents the first direct confirmation of this scenario.

Massive stars born in star clusters terminate star cluster formation by ionizing the surrounding gas. This process is considered to be prevalent in young star clusters containing massive stars. The Orion Nebula is an excellent example associated with a forming star cluster including several massive stars (the Orion Nebula Cluster; ONC) and a 2-pc size H{\sc ii} region (ionized bubble) opening toward the observer; however, the other side is still covered with dense molecular gas. Recent astrometric data acquired by the Gaia satellite revealed the stellar kinematics in this region. By comparing this data with star cluster formation simulation results, we demonstrate that massive stars born in the ONC center were ejected via three-body encounters. Further, orbit analysis indicates that $\theta^2$ Ori A, the second massive star in this region, was ejected from the ONC center toward the observer and is now returning to the cluster center. Such ejected massive stars can form a hole in the dense molecular cloud and contribute to the formation of the 2-pc bubble. Our results demonstrate that the dynamics of massive stars are essential for the formation of star clusters and H{\sc ii} regions that are not always centered by massive stars.

Abridged Context: Snowlines during star and disk formation are responsible for a range of effects during the evolution of protostars, such as setting the chemical composition of the envelope and disk. This in turn influences the formation of planets by changing the elemental compositions of solids and affecting the collisional properties and outcomes of dust grains. Snowlines can also reveal accretion bursts, providing insight into the formation process of stars. Methods: A numerical chemical network coupled with a grid of cylindrical-symmetric physical models was used to identify what physical parameters alter the CO and H$_2$O snowline locations. The investigated parameters are the initial molecular abundances, binding energies of CO and H$_2$O, heating source, cloud core density, outflow cavity opening angle, and disk geometry. Simulated molecular line emission maps were used to quantify the change in the snowline location with each parameter. Conclusions: The models presented in this work show that the CO and H$_2$O snowline locations do not occur at a single, well-defined temperature as is commonly assumed. Instead, the snowline position depends on luminosity, cloud core density, and whether a disk is present or not. Inclination and spatial resolution affect the observability and successful measurement of snowline locations. We note that N$_2$H$^+$ and HCO$^+$ emission serve as good observational tracers of CO and H$_2$O snowline locations. However, constraints on whether or not a disk is present, the observation of additional molecular tracers, and estimating envelope density will help in accurately determining the cause of the observed snowline position. Plots of the N$_2$H$^+$ and HCO$^+$ peak emission radius versus luminosity are provided to compare the models with observations of deeply embedded protostars aiming to measure the CO and H$_2$O snowline locations.

MOdified Newtonian Dynamics (MOND) is an alternative to the standard Cold Dark Matter (CDM) paradigm which proposes an alteration of Newton's laws of motion at low accelerations, characterized by a universal acceleration scale a_0. It attempts to explain observations of galactic rotation curves and predicts a specific scaling relation of the baryonic and total acceleration in galaxies, referred to as the Rotational Acceleration Relation (RAR), which can be equivalently formulated as a Mass Discrepancy Acceleration Relation (MDAR). The appearance of these relations in observational data such as SPARC has lead to investigations into the existence of similar relations in cosmological simulations using the standard {\Lambda}CDM model. Here, we report the existence of an RAR and MDAR similar to that predicted by MOND in {\Lambda}CDM using a large sample of galaxies extracted from a cosmological, hydrodynamical simulation (Magneticum). Furthermore, by using galaxies in Magneticum at different redshifts, a prediction for the evolution of the inferred acceleration parameter a_0 with cosmic time is derived by fitting a MOND force law to these galaxies. In Magneticum, the best fit for a_0 is found to increase by a factor of approximately 3 from redshift z = 0 to z = 2. This offers a powerful test from cosmological simulations to distinguish between MOND and {\Lambda}CDM observationally.

The Sgr\,B region, including Sgr\,B1 and Sgr\,B2, is one of the most active star-forming regions in the Galaxy. Hasegawa et al. (1994) originally proposed that Sgr\,B2 was formed by a cloud-cloud collision (CCC) between two clouds with velocities of $\sim$45 km~s$^{-1}$ and $\sim$75 km~s$^{-1}$. However, some recent observational studies conflict with this scenario. We have re-analyzed this region, by using recent, fully sampled, dense-gas data and by employing a recently developed CCC identification methodology, with which we have successfully identified more than 50 CCCs and compared them at various wavelengths. We found two velocity components that are widely spread across this region and that show clear signatures of a CCC, each with a mass of $\sim$10$^6$ $M_\odot$. Based on these observational results, we suggest an alternative scenario, in which contiguous collisions between two velocity features with a relative velocity of $\sim$20 km~s$^{-1}$ created both Sgr\,B1 and Sgr\,B2. The physical parameters, such as the column density and the relative velocity of the colliding clouds, satisfy a relation that has been found to apply to the most massive Galactic CCCs, meaning that the triggering of high-mass star formation in the Galaxy and starbursts in external galaxies can be understood as being due to the same physical CCC process.

Solid body tides provide key information on the interior structure, evolution, and origin of the planetary bodies. Our Solar system harbours a very diverse population of planetary bodies, including those composed of rock, ice, gas, or a mixture of all. While a rich arsenal of geophysical methods has been developed over several years to infer knowledge about the interior of the Earth, the inventory of tools to investigate the interiors of other Solar-system bodies remains limited. With seismic data only available for the Earth, the Moon, and Mars, geodetic measurements, including the observation of the tidal response, have become especially valuable and therefore, has played an important role in understanding the interior and history of several Solar system bodies. To use tidal response measurements as a means to obtain constraints on the interior structure of planetary bodies, appropriate understanding of the viscoelastic reaction of the materials from which the planets are formed is needed. Here, we review the fundamental aspects of the tidal modeling and the information on the present-day interior properties and evolution of several planets and moons based on studying their tidal response. We begin with an outline of the theory of viscoelasticity and tidal response. Next, we proceed by discussing the information on the tidal response and the inferred structure of Mercury, Venus, Mars and its moons, the Moon, and the largest satellites of giant planets, obtained from the analysis of the data that has been provided by space missions. We also summarise the upcoming possibilities offered by the currently planned missions.

The propagation of Galactic cosmic rays is well understood in the context of the solar system but is poorly studied for M dwarf systems. Quantifying the flux of cosmic rays reaching exoplanets is important since cosmic rays are relevant in the context of life. Here, we calculate the Galactic cosmic ray fluxes in AU Mic and Prox Cen planetary systems. We propagate the Galactic cosmic rays using a 1D cosmic ray transport model. We find for Prox Cen b, AU Mic b and AU Mic c that the Galactic cosmic ray fluxes are strongly suppressed and are lower than the fluxes reaching Earth. We include in our models, for the first time for a star other than the Sun, the effect of radial particle drift due to gradients and curvatures in the stellar magnetic field. For Prox Cen we find that the inclusion of particle drift leads to less suppression of Galactic cosmic rays fluxes than when it is excluded from the model. In the case of AU Mic we explore two different wind environments, with a low and high stellar wind mass-loss rate. For AU Mic, the particle drift also leads to less suppression of the Galactic cosmic ray fluxes but it is only significant for the high mass-loss rate scenario. However, both wind scenarios for AU Mic suppress the Galactic cosmic rays strongly. Overall, careful modelling of stellar winds is needed to calculate the Galactic cosmic ray fluxes reaching exoplanets. The results found here can be used to interpret future exoplanet atmosphere observations and in atmospheric models.

We show how astrometric and spectroscopic errors introduced by an unresolved binary system can be combined to give estimates of the binary period and mass ratio. This can be performed analytically if we assume we see one or more full orbits over our observational baseline, or numerically for any period. We show how these errors behave for a wide range of systems and what we can infer from them. We apply this method to Gaia eDR3 data, combining the radial velocities from the second data release with the most recent astrometric data. We compare predicted periods and mass ratios to known binaries in APOGEE, finding good agreement between inferred values calculated with our method and measured values. Finally, we use this method to search the whole Gaia RVS dataset for compact object candidates. We select sources with significant astrometric and spectroscopic errors ($RUWE_{ast}>1.25$ and $RUWE_{spec}>3$), with large inferred mass ratios, and large inferred companion masses ($q>1$ and $M_c>3 M_\odot$) giving a catalogue of 2,601 candidate Main Sequence+Compact Object pairs. We apply more stringent cuts, and impose low levels of photometric variability to remove triples ($RUWE_{phot}<2$) producing a gold sample of 182 candidates.

In this work we performed a polarimetric study of a fast and wide coronal mass ejection (CME) observed on 12 July 2012 by the COR1 and COR2 instruments onboard Solar TErrestrial RElations Observatory (STEREO) mission. The CME source region was an X1.4 flare located at approximately S15W01 on the solar disk as observed from the Earth's perspective. The position of the CME as derived from the 3D Graduated Cylindrical Shell (GCS) reconstruction method was at around S18W00 at 2.5 solar radii and S07W00 at 5.7 solar radii, meaning that the CME was deflected towards the Equator while propagating outward in the corona. The projected speed of the leading edge of the CME also evolved from around 200 km s$^{-1}$ in the lower corona to around 1000 km s$^{-1}$ in the COR2 field of view. The degree of polarisation of the CME is around 65 % but it can go as high as 80 % in some CME regions. The CME showed deviation of the polarisation angle from the tangential in the range of 10$^\circ$ - 15$^\circ$ (or more). Our analysis showed that this is mostly due to the fact that the sequence of three polarised images from where the polarised parameters are derived is not taken simultaneously, but at a difference of few seconds in time. In this interval of time, the CME is moving by at least two pixels in the FOV of the instruments and this displacement results in uncertainties in the polarisation parameters (degree of polarisation, polarisation angle, etc.). We propose some steps forward to improve the derivation of the polarisation. This study is important for analysing the future data from instruments with polarisation capabilities.

Planets have been detected in circumbinary orbits in several different systems, despite the additional challenges faced during their formation in such an environment. We investigate the possibility of planetary formation in the spectroscopic binary CS Cha by analyzing its circumbinary disk. The system was studied with high angular resolution ALMA observations at 0.87mm. Visibilities modeling and Keplerian fitting are used to constrain the physical properties of CS Cha, and the observations were compared to hydrodynamic simulations. Our observations are able to resolve the disk cavity in the dust continuum emission and the 12CO J:3-2 transition. We find the dust continuum disk to be azimuthally axisymmetric (less than 9% of intensity variation along the ring) and of low eccentricity (of 0.039 at the peak brightness of the ring). Under certain conditions, low eccentricities can be achieved in simulated disks without the need of a planet, however, the combination of low eccentricity and axisymmetry is consistent with the presence of a Saturn-like planet orbiting near the edge of the cavity.

We conducted a detailed long-term spectral and temporal study of flat spectrum radio quasar 4C +01.02, by using the multi-wavelength observations from Fermi-LAT, Swift-XRT, and Swift-UVOT. The $2$-day bin $\gamma$-ray lightcurve in the 2014-2017 active state displays $14$ peak structures with a maximum integral flux $(\rm E > 100 \ MeV)$ of $\rm (2.5 \pm 0.2) \times 10^{-6}\ ph\ cm^{-2}\ s^{-1}$ at MJD 57579.1, which is approximately $61$ times higher than the base flux of $\rm (4.1 \pm 0.3) \times 10^{-8}\ ph\ cm^{-2}\ s^{-1}$, calculated by averaging the flux points when the source was in quiescent state. The shortest $\gamma$-ray variability of $0.66 \pm 0.08$ days is observed for the source. The correlation study between $\gamma$-ray spectral index and flux suggests that the source deviates from the usual trend of harder when brighter feature shown by blazars. To understand the likely physical scenario responsible for the flux variation, we performed a detailed broadband spectral analysis of the source by selecting different flux states from the multi-wavelength lightcurve. A single zone leptonic model was able to reproduce the broadband spectral energy distribution (SED) of each state. The parameters of the model in each flux state are determined using a $\chi^2$ fit. We observed that the synchrotron, synchrotron-self-Compton (SSC), and External-Compton (EC) processes produce the broadband SED under varied flux states. The adjoining contribution of the seed photons from the broad-line region (BLR) and the IR torus for the EC process are required to provide adequate fits to the GeV spectrum in all the chosen states.

The present work aims to build a new statistical distance scale for planetary nebulae (PNe) based on a rigorous calibration sample. The distances of the calibration sample are derived from the trigonometric parallax method using the recent measurements of Gaia early third data release (Gaia EDR3). The new distance scale is created by applying the well-known linear relationship between the radio surface brightness temperature and the nebular radius. The calibration sample is made up of 96 PNe of accurately computed distances with uncertainties less than $20\%$. Earlier ground- and space-based trigonometric parallaxes of PNe display inconsistency with those of Gaia, particularly the HIPPARCOS results. In addition, these measurements have appreciably lower precision than that of Gaia. When compared to the trigonometric technique, the expansion and kinematic methods exhibited more consistency than the spectroscopic, extinction, gravity, and photo-ionization methods. Furthermore, contrary to earlier results in the literature, the extinction and gravity methods, on average, underestimate and slightly overestimate the PN distances. As a byproduct of extracting the Gaia parallaxes, we detect the radial velocity and variability for 14 and 3 PN central stars (CSs), respectively. To our knowledge, the variability of Hen 2-447 CS has been determined for the first time.

We present a follow-up study on the recent detection of two X-ray flaring events by MAXI/GSC observations in soft and hard X-rays from MAXI J0709-159 in the direction of HD 54786 (LY CMa), on 2022 January 25. The X-ray luminosity during the flare was around 10^(37) erg/s (MAXI), which got reduced to 10^(32) erg/s (NuSTAR) after the flare. We took low-resolution spectra of HD 54786 from HCT and VBT facilities in India, on 2022 February 1 and 2. In addition to H-alpha emission, we found emission lines of He I in the optical spectrum of this star. By comparing our spectrum of the object with those from literature we found that He I lines show variability. Using photometric study we estimate that the star is having effective temperature of 20000 K. Although HD 54786 is reported as a supergiant in previous studies, our analysis favours it to be evolving off the main sequence in the Color-Magnitude Diagram. We could not detect any infrared excess, ruling out the possibility of IR emission from a dusty circumstellar disc. Our present study suggests that HD 54786 is a Be/X-ray binary system with a compact object companion, possibly a neutron star.

We attempt to model magnetic reconnection during the two-ribbon flare in the gravitationally stratified solar atmosphere with the Lundquist number of $S=10^6$ using 2D simulations. We found that the tearing mode instability leads to the inhomogeneous turbulence inside the reconnecting current sheet (CS) and invokes the fast phase of reconnection. Fast reconnection brings an extra dissipation of magnetic field which enhances the reconnection rate in an apparent way. The energy spectrum in the CS shows the power-law pattern and the dynamics of plasmoids governs the associated spectral index. We noticed that the energy dissipation occurs at a scale $l_{ko}$ of 100-200~km, and the associated CS thickness ranges from 1500 to 2500~km, which follows the Taylor scale $l_T=l_{ko} S^{1/6}$. The termination shock(TS) appears in the turbulent region above flare loops, which is an important contributor to heating flare loops. Substantial magnetic energy is converted into both kinetic and thermal energies via TS, and the cumulative heating rate is greater than the rate of the kinetic energy transfer. In addition, the turbulence is somehow amplified by TS, of which the amplitude is related to the local geometry of the TS.

Theory suggests that mergers play an important role in shaping galactic disks and stellar haloes, which was observationally confirmed in the MW thanks to the Gaia data. In this work, aiming to probe the contribution of mergers to the in-situ stellar halo formation, we analyze six M31/MW analogues from the HESTIA suite of cosmological hydrodynamical zoom-in simulations of the Local Group. We found that all the HESTIA galaxies experience from 1 to 4 mergers with stellar mass ratios between 0.2 and 1 relative to the host at the time of the merger. These significant mergers, with a single exception, happened 7-11 Gyr ago. The overall impact of the most massive mergers in HESTIA is clearly seen as a sharp increase of the orbital eccentricity (and a corresponding decrease of the Vphi) of preexisting disc stars of the main progenitor, thus reproducing well the Splash/Plume-like feature discovered in the MW. We do find a correlation between mergers/close pericentric passages of massive satellites and bursts of the star formation in the in-situ component. Massive mergers sharply increase the disc velocity dispersion of the in-situ stars, however, the latest significant merger often heats up the disk up to the numbers when the contribution of the previous ones is less prominent in the age-velocity dispersion relation. In the HESTIA galaxies, the in-situ halo is an important component of the inner stellar halo where its fraction is about 30-40%, while in the outer parts it typically does not exceed ~5% beyond 15 kpc. The simulations suggest that this component of the stellar haloes continues to grow well after mergers conclude; however, the most significant contribution comes from stars formed recently before the merger. The orbital analysis of the HESTIA galaxies suggests that wedges in Rmax-Zmax space are mainly populated by the stars born in between significant mergers.

In the Milky Way, recent progress in the exploration of its assembly history is driven by the tremendous amount of high-quality data delivered by Gaia, which has revealed a number of substructures potentially linked to several ancient accretion events. In this work, aiming to explore the phase-space structure of accreted stars, we analyze six M31/MW analogues from the HESTIA suite of cosmological hydrodynamics zoom-in simulations of the Local Group. We found that all the HESTIA galaxies experience a few dozen mergers but only 1-4 mergers have the stellar mass ratio >0.2 where, depending on the halo definition, the most massive merger contributes from 20% to 70% of the total stellar halo. Individual merger remnants show diverse density distributions at z=0, significantly overlapping with each other and with the in-situ stars in the ELz, UV and RVphi coordinates. The mergers debris often change their position in the ELz with time due to the galactic mass growth and the non-axisymmetry of the potential. In agreement with previous works, we show that even individual merger debris exhibit a number of distinct ELz features. In the UV plane, all HESTIA galaxies reveal radially hot, non-rotating or weakly counter-rotating, Gaia-Sausage-like features. We found an age gradient in Elz space for the individual debris, where the youngest stars, formed in the inner regions of accreting systems, deposit to the innermost regions of the host. The bulk of these stars is being formed during the last stages of accretion, making it possible to date the merger. In actions space (Jr, Jz, J\phi), the mergers debris do not appear as isolated substructures but are instead scattered over a large parameters area and overlapping with the in-situ stars. We also introduce a purely kinematic space (Jz/Jr-eccentricity), where different merger debris can be disentangled better from each other and from the in-situ stars.

We present a numerical study on the stability of the 1/2, 2/1 and 1/1 retrograde mean motion resonances in the 3-body problem composed of a solar mass star, a Jupiter mass planet and an additional body with zero mass (elliptic restricted 3-body problem) or masses corresponding to either Neptune, Saturn or Jupiter (planetary 3-body problem). For each system we obtain stability maps using the n-body numerical integrator REBOUND and computing the chaos indicator mean exponential growth factor of nearby orbits (MEGNO). We show that families of periodic orbits exist in all configurations and they correspond to the libration of either a single resonant argument or all resonant arguments (fixed points). We compare the results obtained in the elliptic restricted 3-body problem with previous results in the literature and we show the differences and similarities between the phase space topology for these retrograde resonances in the circular restricted, elliptic restricted and planetary 3-body problems.

A deep learning method for the particle trajectory reconstruction with the DAMPE experiment is presented. The developed algorithms constitute the first fully machine-learned track reconstruction pipeline for space astroparticle missions. Significant performance improvements over the standard hand-engineered algorithms are demonstrated. Thanks to the better accuracy, the developed algorithms facilitate the identification of the particle absolute charge with the tracker in the entire energy range, opening a door to the measurements of cosmic ray proton and helium spectra at extreme energies, towards the PeV scale, hardly achievable with the standard track reconstruction methods. In addition, the developed approach demonstrates an unprecedented accuracy in the particle direction reconstruction with the calorimeter at high deposited energies, above a few hundred GeV for hadronic showers and above a few tens GeV for electromagnetic showers.

We analyse the distribution of Mira variable stars in the central region of the Milky Way. We find that with increasing period, i.e. decreasing age, the Miras shift towards negative Galactic longitudes $\ell$. Comparing to a cosmological zoom simulation of a barred galaxy, we find that this shift with age can be explained by an age-morphology dependence of the boxy peanut/bulge. Owing to a combination of projection effects and the limitation of the range of Galactic longitudes, the near hump at $\ell>0$ is more truncated for younger populations, and the far hump at $\ell<0$ dominates the observed distributions.

We study the thermal evolution of axisymmetric rotating neutron stars in full general relativity. To this aim we develop "NSCool 2D Rot", a major upgrade of the 1D neutron stars thermal evolution code "NSCool" by D. Page. As a first application of our new code we address the standard cooling of isolated neutron stars with rotation frequencies up to the mass shedding limit. We investigate the effects of the equation of state (EOS) by considering different combinations of core and crust EOSs. The results indicate complex time-dependent evolution of temperature distribution throughout the whole volume of the star and, in particular, in the crust. We show that most of that complexity can be attributed to the formation of a "heat blob" in the crust and to the latitude dependence of the heat diffusion timescale through the crust.

Energetic X-ray radiations emitted from various accretion systems are widely considered to be produced by Comptonization in the hot corona. The corona and its interaction with the disc play an essential role in the evolution of the system and are potentially responsible for many observed features. However many intrinsic properties of the corona are still poorly understood, especially for the geometrical configurations. The traditional spectral fitting method is not powerful enough to distinguish various configurations. In this paper we intent to investigate the possible configurations by modeling the polarization properties of X-ray radiations. The geometries of the corona include the slab, sphere and cylinder. The simulations are implemented through the publicly available code, LEMON, which can deal with the polarized radiative transfer and different electron distributions readily. The results demonstrate clearly that the observed polarizations are dependent on the geometry of the corona heavily. The slab-like corona produces the highest polarization degrees, the following are the cylinder and sphere. One of the interesting things is that the polarization degrees first increase gradually and then decrease with the increase of photon energy. For slab geometry there exists a zero point where the polarization vanishes and the polarization angle rotates for $90^\circ$. These results may potentially be verified by the upcoming missions for polarized X-ray observations, such as $IXPE$ and $eXTP$.

Through the relationship between dispersion measures (DM) and redshifts, fast radio bursts (FRBs) are considered to be very promising cosmological probes. In this paper, we attempted to use the DM-z relationship of FRBs to study the helium abundance ($Y_{\rm He}$) in the universe. First, we used 17 current FRBs with known redshifts for our study. Due to their low redshifts and the strong degeneracy between $Y_{\rm He}$ and $\Omega_bh^2$, however, this catalog could not provide a good constraint on the helium abundance. Then, we simulated 500 low redshift FRB mock data with $z\in[0,\,1.5]$ to forecast the constraining ability on $Y_{\rm He}$. In order to break the degeneracy between $Y_{\rm He}$ and $\Omega_bh^2$ further, we introduced the shift parameters of the Planck measurement $(R,l_A,\Omega_bh^2)$ as a prior, where $\Omega_bh^2$ represents the baryon density parameter, and $R$ and $l_A$ correspond to the scaled distance to recombination and the angular scale of the sound horizon at recombination, respectively. We obtained the standard deviation for the helium abundance: $\sigma({Y_{\rm He}}) = 0.025$. Finally, we considered 2000 higher redshift FRB data with the redshift distribution of $[0,\,3]$ and found that the constraining power for $Y_{\rm He}$ would be improved by more than 2 times, $\sigma({Y_{\rm He}}) = 0.011$, which indicates that the FRB data with high redshift can provide a better constraint on the helium abundance. Hopefully, large FRB samples with high redshift from the Square Kilometre Array can provide high-precision measurements of the helium abundance in the near future.

We present the results of a density-based clustering analysis of the 6-dimensional XYZ Galactic positions and UVW space velocities of nearby ($\leq$ 200 pc) Gaia EDR3 stars with radial velocities using HDBSCAN, in opposition to previous studies that only included positions and tangential velocities. Among the 241 recovered clusters, we identify more than 50 known associations, 32 new candidate stellar streams aged 100 Myr-3 Gyr, 9 extensions of known Theia groups uncovered by Kounkel & Covey (2019), and 8 newly recognized coronae around nearby open clusters. Three confirmed exoplanet-hosting stars and three more TESS transiting exoplanet candidates are part of the new groups discovered here, including TOI-1807 and TOI-2076 from Hedges et al. (2021) that were suspected to belong to a yet unidentified moving group. The new groups presented here were not previously recognized because of their older ages, low spatial density, and projection effects that spread out the tangential velocities of their nearby co-moving members. Several newly identified structures reach distances within 60 pc of the Sun, providing new grounds for the identification of isolated planetary-mass objects. The nearest member of the newly recognized corona of Volans-Carina is V419 Hya, a known young debris disk star at a distance of 22 pc. This study outlines the importance of further characterization of young associations in the immediate Solar neighborhood, which will provide new laboratories for the precise age calibration of nearby stars, exoplanets and substellar objects.

We present a chemodynamical study of the Grus I ultra-faint dwarf galaxy (UFD) from medium-resolution ($R\sim11,000$) Magellan/IMACS spectra of its individual member stars. We identify eight confirmed members of Grus I, based on their low metallicities and coherent radial velocities, and four candidate members for which only velocities are derived. In contrast to previous work, we find that Grus I has a very low mean metallicity of $\langle$[Fe/H]$\rangle = -2.62 \pm 0.11$ dex, making it one of the most metal-poor UFDs. Grus I has a systemic radial velocity of $-143.5\pm1.2$ km s$^{-1}$ and a velocity dispersion of $\sigma_{\text{rv}} = 2.5^{+1.3}_{-0.8}$ km s$^{-1}$ which results in a dynamical mass of $M_{1/2}(r_h) = 8^{+12}_{-4} \times 10^5$ M$_{\odot}$ and a mass-to-light ratio of M/L$_V$ = $440^{+650}_{-250}$ M$_\odot$/L$_\odot$. Our analysis confirms that Grus I is a dark-matter-dominated UFD (M/L $> 80$ M$_\odot$/L$_\odot$). However, we do not resolve a metallicity dispersion ($\sigma_{\text{[Fe/H]}} < 0.44$ dex). Our results indicate that Grus I is a fairly typical UFD with parameters that agree with mass-metallicity and metallicity-luminosity trends for faint galaxies. This agreement suggests that Grus I has not lost an especially significant amount of mass from tidal encounters with the Milky Way, in line with its orbital parameters. Intriguingly, Grus I has among the lowest central density ($\rho_{1/2} \sim 3.5_{-2.1}^{+5.7} \times 10^7$ M$_\odot$ kpc$^{-3}$) of the UFDs that are not known to be tidally disrupting. Models of the formation and evolution of UFDs will need to explain the diversity of these central densities, in addition to any diversity in the outer regions of these relic galaxies.

We explore the possibility of using machine learning to estimate physical parameters directly from AGN X-ray spectra without needing computationally expensive spectral fitting. Specifically, we consider survey quality data, rather than long pointed observations, to ensure that this approach works in the regime where it is most likely to be applied. We simulate Athena WFI spectra of AGN with warm absorbers, and train simple neural networks to estimate the ionisation and column density of the absorbers. We find that this approach can give comparable accuracy to spectral fitting, without the risk of outliers caused by the fit sticking in a false minimum, and with an improvement of around three orders of magnitude in speed. We also demonstrate that using principal component analysis to reduce the dimensionality of the data prior to inputting it into the neural net can significantly increase the accuracy of the parameter estimation for negligible computational cost, while also allowing a simpler network architecture to be used.

Here we present our current updates of the gas-phase chemical reaction rates and molecular lines in the spectral synthesis code CLOUDY, and its implications in spectroscopic modelling of various astrophysical environments. We include energy levels, radiative and collisional rates for HF, CF$^+$, HC$_3$N, ArH$^+$, HCl, HCN, CN, CH, and CH$_2$. Simultaneously, we expand our molecular network involving these molecules. For this purpose, we have added 561 new reactions and have updated the existing 165 molecular reaction rates involving these molecules. As a result, CLOUDY now predicts all the lines arising from these nine molecules. In addition, we also update H$_2$--H$_2$ collisional data up to rotational levels $J$=31 for $v$=0. We demonstrate spectroscopic simulations of these molecules for a few astrophysical environments. Our existing model for globules in the Crab nebula successfully predicts the observed column density of ArH$^+$. Our model predicts a detectable amount of HeH$^+$, OH$^+$, and CH$^+$ for the Crab nebula. We also model the ISM towards HD185418, W31C, NGC 253, and our predictions match with most of the observed column densities within the observed error bars. Very often molecular lines trace various physical conditions. Hence, this update will be very supportive for spectroscopic modelling of various astrophysical environments, particularly involving sub-millimeter and mid-infrared observations using ALMA and JWST, respectively.

That active galactic nuclei (AGN) with jets can alternately enhance as well as suppress star formation rates, explains the location and slope of radio loud AGN on the star formation rate-stellar mass plane. Here, we explore 860 type 1 and 2 AGN at z<0.2 from the ROSAT-2XRS survey in order to understand both different location and lower slopes for non-jetted AGN in the star formation rate-stellar mass plane. We describe the nature of these differences in terms of different degrees of black hole feedback, with relatively weak negative feedback from non-jetted AGN compared to both relatively strong positive and negative feedback from jetted AGN. The validity of these ideas brings us a step closer towards understanding the black hole scaling relation across space and time.

We present a solution of the Schr\"odinger-Poisson system based on the WKB ansatz for the wave function. In this way we obtain a description of a gravitationally bound clump of axion dark matter by a superposition of energy eigenstates with random phases. It can be applied to any self-consistent pair of radial density distribution and phase space density $f(E)$ related by Eddington's formula. We adopt this as a model for axion miniclusters in our galaxy and use it to study the mass loss due to a star encounter by using standard perturbation theory methods known from quantum mechanics. Finally, we perform a Monte Carlo study to estimate the surviving fraction of axion miniclusters in the dark matter halo of our galaxy. We find that the reaction to perturbations and the survival probability depend crucially on the density profile. Weakly bound clusters are heated up and eventually destroyed, whereas more strongly bound systems get even more compact as a result of perturbations and are driven towards an axion star configuration.

We model the local stellar velocity field using position and velocity measurements for 4M stars from the second data release of Gaia. We determine the components of the mean or bulk velocity in ~27k spatially-defined bins. Our assumption is that these quantities constitute a Gaussian process where the correlation between the bulk velocity at different locations is described by a simple covariance function or kernel. We use a sparse Gaussian process algorithm based on inducing points to construct a non-parametric, smooth, and differentiable model for the underlying velocity field. We estimate the Oort constants A, B, C, and K and find values in excellent agreement with previous results. Maps of the velocity field within 2 kpc of the Sun reveal complicated substructures, which provide clear evidence that the local disk is in a state of disequilibrium. We present the first 3D map of the divergence of the stellar velocity field and identify regions of the disk that may be undergoing compression and rarefaction.

We start by reviewing our previous work on retrograde orbital configurations and on modeling and identifying retrograde resonances. Then, we present new results regarding the enhanced stability of retrograde configurations with respect to prograde configurations in the low mass ratio regime of the planar circular restricted 3-body problem. Motivated by the recent discovery of small bodies which are in retrograde resonance with the Solar System's giant planets we then explore the case with mass ratio 0.001 and show new stability maps in a grid of semi-major axis versus eccentricity for the 2/1 and 1/2 retrograde resonances. Finally, we explain how the stability borders of the 2/1 and 1/2 retrograde resonances are related to the resonant orbits' geometry.

To quantify the role of radio jets for Intra-Night Optical Variability (INOV) in Radio-Loud Narrow-Line Seyfert 1 (RLNLSy1) galaxies, we report the first systematic comparative INOV study of 23 RLNLSy1 galaxies, with 15 RLNLSy1s having confirmed detection of jets (jetted) and the remaining 8 RLNLSy1s having no detection of jets (non-jetted) based on their Very Long Baseline Array observations. We have monitored these two samples, respectively, in 37 and 16 sessions of a minimum 3-hour duration each. Based upon F$^{\eta}$-test at 99\% confidence level with a typical INOV amplitude ($\psi$) detection threshold of $>$ 3\%, we find the INOV duty cycles of 12\% for the sample of jetted RLNLSy1s, however, none of the sources showed INOV in the sample of non-jetted RLNLSy1s. Among the jetted RLNLSy1s, we find that the Duty Cycle (DC) for jetted $\gamma$-ray detected ($\gamma$-ray) RLNLSy1s is found to be 34\% in contrast to null INOV detection in the case of non-$\gamma$-ray RLNLSy1s. It suggests that instead of the mere presence of a jet, relativistic beaming plays a significant role for INOV in the case of low-luminous high accreting AGNs such as NLSy1s in which dilution of the AGN's non-thermal optical emission by the (much steadier) optical emission contributed by the nuclear accretion disc is quite likely. Our study of jetted $\gamma$-ray RLNLSy1s shows more frequent INOV detection for sources with higher apparent jet speed. Further, our results also suggest that among the NLSy1s, only jetted $\gamma$-ray RNLSy1 galaxies DC approaches blazar like DC.

We analyzed spectropolarimetric data from the Swedish 1-meter Solar Telescope to investigate physical properties of small-scale magnetic cancellations in the quiet Sun photosphere. Specifically, we looked at the full Stokes polarization profiles along the Fe I 557.6 nm and of the Fe I 630.1 nm lines measured by CRisp Imaging SpectroPolarimeter (CRISP) to study temporal evolution of the line-of-sight (LOS) magnetic field during 42.5 minutes of quiet Sun evolution. From this magnetogram sequence, we visually identified 38 cancellation events. We then used Yet Another Feature Tracking Algorithm (YAFTA) to characterize physical properties of these magnetic cancellations. We found on average $1.6\times10^{16}$ Mx of magnetic flux cancelled in each event with an average cancellation rate of $3.8\times10^{14}$ Mx s$^{-1}$. The derived cancelled flux is associated with strong downflows, with an average speed of $V_\mathrm{LOS}\approx1.1$ km s$^{-1}$. Our results show that the average lifetime of each event is $9.2$ minutes with an average $44.8\%$ of initial magnetic flux being cancelled. Our estimates of magnetic fluxes provide a lower limit since studied magnetic cancellation events have magnetic field values that are very close to the instrument noise level. We observed no horizontal magnetic fields at the cancellation sites and therefore can not conclude whether the events are associated structures that could cause magnetic reconnection.

The gravitational pull of an unseen companion to a luminous star is well-known to cause deviations to the parallax and proper motion of a star. In a previous paper in this series, we argue that the astrometric mission Gaia can identify long-period binaries by precisely measuring these arcs. An arc in a star's path can also be caused by a fly-by -- the hyperbolic encounter with another massive object. We quantify the apparent acceleration over time induced by a companion star as a function of the impact parameter, velocity of interaction, and companion mass. In principle, Gaia could be used to astrometrically identify the contribution of massive compact halo objects to the local dark matter potential of the Milky Way. However, after quantifying their rate and Gaia's sensitivity, we find that fly-bys are so rare that Gaia will probably never observe one. Therefore every star in the Gaia database exhibiting astrometric acceleration is likely in a long-period binary with another object. Nevertheless, we show how intermediate mass black holes, if they exist in the Solar Neighborhood, could be detected by the anomalously large accelerations they induce on nearby stars.

The presence of large-scale magnetic fields and ultra-relativistic electrons in the intra-cluster medium (ICM) is confirmed through the detection of diffuse radio synchrotron sources, so-called radio halos and relics. Due to their steep-spectrum nature, these sources are rarely detected at frequencies above a few GHz, especially in low-mass systems. The aim of this study is to discover and characterise diffuse radio sources in low-mass galaxy clusters in order to understand their origin and their scaling with host cluster properties. We searched for cluster-scale radio emission from low-mass galaxy clusters in the Low Frequency Array (LOFAR) Two-metre Sky Survey - Data Release 2 (LoTSS-DR2) fields. We made use of existing optical (Abell, DESI, WHL) and X-ray (comPRASS, MCXC) catalogues. The LoTSS-DR2 data were processed further to improve the quality of the images that are used to detect and characterize diffuse sources. We have detected diffuse radio emission in 28 galaxy clusters. The number of confirmed (candidates) halos and relics are six (seven) and 10 (three), respectively. Among these, 11 halos and 10 relics, including candidates, are newly discovered by LOFAR. Beside these, five diffuse sources are detected in tailed radio galaxies and are probably associated with mergers during the formation of the host clusters. We are unable to classify other 13 diffuse sources. We compare our newly detected, diffuse sources to known sources by placing them on the scaling relation between the radio power and the mass of the host clusters.

In both particle physics and muon applications, a high-resolution muon momentum measurement capability plays a significant role not only in providing valuable information on the properties of subatomic particles but also in improving the utilizability of cosmic ray muons. Typically, muon momentum is measured by reconstructing a curved muon path using a strong magnetic field and muon trackers. Alternatively, a time-of-flight and Cherenkov ring imager are less frequently applied, especially when there is a need to avoid a magnetic field. However, measurement resolution is much less than that of magnetic spectrometers, approximately 20% whereas it is nearly 4% or less when using magnets and trackers. Here, we propose a different paradigm to estimate muon momentum that utilizes multiple pressurized gas Cherenkov radiators. Using the fact that the refractive index of gas medium varies depending on its pressure and temperature, we can optimize the muon Cherenkov threshold momentum levels for which a muon signal will be detected. In this work, we demonstrate that muon momentum can be estimated with mean resolution of {sigma_p}/p < 20% and mean classification rate of 90.08% in the momentum range of 0.1 to 10.0 GeV/c by analyzing optical photon signals from each Cherenkov radiator. We anticipate our new spectrometer will significantly improve quality of imaging and reduce scanning time in cosmic ray muon applications by being incorporated with existing instruments.

Information of interest can often only be extracted from data by model fitting. When the functional form of such a model can not be deduced from first principles, one has to make a choice between different possible models. A common approach in such cases is to minimise the information loss in the model by trying to reduce the number of fit variables (or the model flexibility, respectively) as much as possible while still yielding an acceptable fit to the data. Model selection via the Akaike Information Criterion (AIC) provides such an implementation of Occam's razor. We argue that the same principles can be applied to optimise the penalty-strength of a penalised maximum-likelihood model. However, while in typical applications AIC is used to choose from a finite, discrete set of maximum-likelihood models the penalty optimisation requires to select out of a continuum of candidate models and these models violate the maximum-likelihood condition. We derive a generalised information criterion AICp that encompasses this case. It naturally involves the concept of effective free parameters which is very flexible and can be applied to any model, be it linear or non-linear, parametric or non-parametric, and with or without constraint equations on the parameters. We show that the generalised AICp allows an optimisation of any penalty-strength without the need of separate Monte-Carlo simulations. As an example application, we discuss the optimisation of the smoothing in non-parametric models which has many applications in astrophysics, like in dynamical modeling, spectral fitting or gravitational lensing.

We study background dynamics and the growth of matter perturbations in the extended quasi-dilation setup of massive gravity. For the analysis of perturbations, we first choose a scalar field matter component and obtain the conditions under which all scalar perturbations are stable. We work in unitary gauge for the matter field, which allows us to directly map to known results in the limit of general relativity. By performing a parameter search, we find that the perturbations are unstable in general, while a particular choice of potential, where the scalar field effectively behaves like pressureless matter, allows for stable perturbations. We next consider the growth of matter perturbations in a cold dark matter-dominated Universe. Working in conformal Newtonian gauge, we obtain evolution equations for various observables including the growth factor and growth rate, and find scale-independent growth in the quasi-static and sub-horizon approximations. We finally show how the Hubble parameter and matter perturbations evolve in massive gravity for a specific choice of parameter values, and how this evolution compares to the standard cosmological model consisting of a cosmological constant and cold dark matter.

Massive stars are crucial to galactic chemical evolution for elements heavier than iron. Their contribution at early times in the evolution of the Universe, however, is unclear due to poorly constrained nuclear reaction rates. The competing $^{17}$O($\alpha,\gamma$)$^{21}$Ne and $^{17}$O($\alpha,n$)$^{20}$Ne reactions strongly impact weak s-process yields from rotating massive stars at low metallicities. Abundant $^{16}$O absorbs neutrons, removing flux from the s-process, and producing $^{17}$O. The $^{17}$O($\alpha,n$)$^{20}$Ne reaction releases neutrons, allowing continued s-process nucleosynthesis, if the $^{17}$O($\alpha,\gamma$)$^{21}$Ne reaction is sufficiently weak. While published rates are available, they are based on limited indirect experimental data for the relevant temperatures and, more importantly, no uncertainties are provided. The available nuclear physics has been evaluated, and combined with data from a new study of astrophysically relevant $^{21}$Ne states using the $^{20}$Ne($d,p$)$^{21}$Ne reaction. Constraints are placed on the ratio of the ($\alpha,n$)/($\alpha,\gamma$) reaction rates with uncertainties on the rates provided for the first time. The new rates favour the ($\alpha,n$) reaction and suggest that the weak s-process in rotating low-metallicity stars is likely to continue up to barium and, within the computed uncertainties, even to lead.

Observations across the heliosphere typically rely on in situ spacecraft observations producing time-series data. While often this data is analysed visually, it lends itself more naturally to our sense of sound. The simplest method of converting oscillatory data into audible sound is audification -- a one-to-one mapping of data samples to audio samples -- which has the benefit that no information is lost, thus is a true representation of the original data. However, audification can make some magnetospheric ULF waves observations pass by too quickly for someone to realistically be able to listen to effectively. For this reason, we detail various existing audio time scale modification techniques developed for music, applying these to ULF wave observations by spacecraft and exploring how they affect the properties of the resulting audio. Through a public dialogue we arrive at recommendations for ULF wave researchers on rendering these waves audible and discuss the scientific and educational possibilities of these new methods.

The characteristic features and mechanisms of the formation of a deep ozone mini-hole (OMH) in winter 2015/2016 over Siberia were carried out using AIRS and CALIOP satellite data. The depletion in the total column ozone was caused mainly by a strong decrease in ozone mixing ratio in the lower stratosphere, reaching 50% near the pressure level of 70 hPa. The formation of OMH was closely related to the dynamic factors including an increase in the tropopause height and advection in the troposphere of ozone-depleted subtropical air, which were associated with atmospheric blocking. Also, an important factor of OMH formation was ozone decrease in the stratosphere due to increased outflow of ozone from the area of the OMH. The contribution of chemical destruction of stratospheric ozone, due to catalytic reactions with halogen-containing compounds on the surface of polar stratospheric clouds to the OMH formation, was evaluated.

In this work, we study the shadow of Kerr black hole surrounded by an axisymmetric plasma, whose density takes an Gaussian distribution in the angular direction. Along the radial direction, we consider two models: in model A the density of the plasma decays in a power law; in model B the density obeys a logarithmic Gaussian distribution. Using the numerical backward ray-tracing method, we find that the size of the shadow is sensitive to the inclination angle of the observer due to the angular distribution of the density of the plasma. In particular, we pay special attention to the model B and investigate the influence of the radial position of maximum density, the decay rate of the density towards the event horizon and the opening angle of the plasma on the shape and size of the Kerr black hole shadow. The effects of the plasmas studied in this work can be qualitatively explained by taking the plasmas as convex lenses with the refractive index being less than $1$.

A neutron star is one of the possible end states of a massive star. It is compressed by gravity and stabilized by the nuclear degeneracy pressure. Despite its name, the composition of these objects is not exactly known. However, from the inferred densities, neutrons will most likely compose a significant fraction of the star's interior. While all neutron stars are expected to have a magnetic field, some neutron stars (''magnetars'') are much more highly magnetized than others with inferred magnetar surface magnetic field is between $10^{14}$ to $10^{15}$ gauss. While neutron stars are macroscopic objects, due to the extreme value of the stars' energy, pressure, and magnetic field the thermodynamics on the microscopic scale can be imprinted on the star's large scale behaviour. This contribution focusses on describing the thermodynamics of magnetized dense neutron matter, its equation of state and to explore conditions of a possible ferromagnetic state, contributions from the magnetized vacuum, as well as possible observational implications.

In this work, the early evolution of low-mass fully convective stars is studied in the context of DHOST (degenerate higher order scalar-tensor) theories of gravity. Although it is known that the hydrostatic equilibrium equation is modified for scalar-tensor gravity, the consequent modifications to the early evolution phases of a star were not explored in this framework. With this in mind, we consider three evolutionary phases - contraction to the main sequence, lithium burning and entrance to the main sequence - and investigate how each of these phases is affected by the theory's parameter. Taking these effects into account, we are able to show, among other things, that the Hayashi tracks are shifted and the star's age is considerably modified.