Papers for Wednesday, Aug 25 2021

While Euclid is an ESA mission specifically designed to investigate the nature of Dark Energy and Dark Matter, the planned unprecedented combination of survey area ($\sim15\,000$ deg$^2$), spatial resolution, low sky-background, and depth also make Euclid an excellent space observatory for the study of the low surface brightness Universe. Scientific exploitation of the extended low surface brightness structures requires dedicated calibration procedures yet to be tested. We investigate the capabilities of Euclid to detect extended low surface brightness structure by identifying and quantifying sky background sources and stray-light contamination. We test the feasibility of generating sky flat-fields to reduce large-scale residual gradients in order to reveal the extended emission of galaxies observed in the Euclid Survey. We simulate a realistic set of Euclid/VIS observations, taking into account both instrumental and astronomical sources of contamination, including cosmic rays, stray-light, zodiacal light, ISM, and the CIB, while simulating the effects of the presence of background sources in the FOV. We demonstrate that a combination of calibration lamps, sky flats and self-calibration would enable recovery of emission at a limiting surface brightness magnitude of $\mu=29.5^{+0.08}_{-0.27} $ mag arcsec$^{-2}$ ($3\sigma$, $10\times10$ arcsec$^2$) in the Wide Survey, reaching regions 2 magnitudes deeper in the Deep Surveys. Euclid/VIS has the potential to be an excellent low surface brightness observatory. Covering the gap between pixel-to-pixel calibration lamp flats and self-calibration observations for large scales, the application of sky flat-fielding will enhance the sensitivity of the VIS detector at scales of larger than 1 degree, up to the size of the FOV, enabling Euclid to detect extended surface brightness structures below $\mu=31$ mag arcsec$^{-2}$ and beyond.

Stellar mergers are important processes in stellar evolution, dynamics, and transient science. However, it is difficult to identify merger remnant stars because they cannot easily be distinguished from single stars based on their surface properties. We demonstrate that merger remnants can potentially be identified through asteroseismology of red giant stars using measurements of the gravity mode period spacing together with the asteroseismic mass. For mergers that occur after the formation of a degenerate core, remnant stars have over-massive envelopes relative to their cores, which is manifested asteroseismically by a g~mode period spacing smaller than expected for the star's mass. Remnants of mergers which occur when the primary is still on the main sequence or whose total mass is less than $\approx\! 2 \, M_\odot$ are much harder to distinguish from single stars. Using the red giant asteroseismic catalogs of Vrard et al. 2016 and Yu et al. 2018, we identify $15$ promising candidates for merger remnant stars. In some cases, merger remnants could also be detectable using only their temperature, luminosity, and asteroseismic mass, a technique that could be applied to a larger population of red giants without a reliable period spacing measurement.

The microwave radiometer aboard the Juno spacecraft provided a measurement of the water abundance found to range between 1 and 5.1 times the protosolar abundance of oxygen in the near-equatorial region of Jupiter. Here, we aim to combine this up-to-date oxygen determination, which is likely to be more representative of the bulk abundance than the Galileo probe subsolar value, with the other known measurements of elemental abundances in Jupiter, to derive the formation conditions and initial composition of the building blocks agglomerated by the growing planet, and that determine the heavy element composition of its envelope. We investigate several cases of icy solids formation in the protosolar nebula, from the condensation of pure ices to the crystallization of mixtures of pure condensates and clathrates in various proportions. Each of these cases correspond to a distinct solid composition whose amount is adjusted in the envelope of Jupiter to match the O abundance measured by Juno. The volatile enrichments can be matched by a wide range of planetesimal compositions, from solids exclusively formed from pure condensates or from nearly exclusively clathrates, the latter case providing a slightly better fit. The total mass of volatiles needed in the envelope of Jupiter to match the observed enrichments is within the 4.3-39 Mearth range, depending on the crystallization scenario considered in the protosolar nebula. A wide range of masses of heavy elements derived from our fits is found compatible with the envelope's metallicity calculated from current interior models.

Precise cosmic web classification of observed galaxies in massive spectroscopic surveys can be either highly uncertain or computationally expensive. As an alternative, we explore a fast Machine Learning-based approach to infer the underlying dark matter tidal cosmic web environment of a galaxy distribution from its $\beta$-skeleton graph. We develop and test our methodology using the cosmological magnetohydrodynamic simulation Illustris-TNG at $z=0$. We explore three different tree-based machine-learning algorithms to find that a random forest classifier can best use graph-based features to classify a galaxy as belonging to a peak, filament or sheet as defined by the T-Web classification algorithm. The best match between the galaxies and the dark matter T-Web corresponds to a density field smoothed over scales of $2$ Mpc, a threshold over the eigenvalues of the dimensionless tidal tensor of $\lambda_{\rm{th}}=0.0$ and galaxy number densities around $8\times 10^{-3}$ Mpc$^{-3}$. This methodology results on a weighted F1 score of 0.728 and a global accuracy of 74\%. More extensive tests that take into account lightcone effects and redshift space distortions (RSD) are left for future work. We make one of our highest ranking random forest models available on a public repository for future reference and reuse.

Accurate radiative transfer coefficients (emissivities, absorptivities, and rotativities) are needed for modeling radiation from relativistically hot, magnetized plasmas such as those found in Event Horizon Telescope sources. Here we review, update, and correct earlier work on radiative transfer coefficients. We also describe an improved method for numerically evaluating rotativities and provide convenient fitting formulae for the relativistic \kdf{} distribution of electron energies.

We compute rotating 1D stellar evolution models that include a modified temperature gradient in convection zones and criterion for convective instability inspired by rotating 3D hydrodynamical simulations performed with the MUSIC code. In those 3D simulations we found that convective properties strongly depend on the Solberg-H{\o}iland criterion for stability. We therefore incorporated this into 1D stellar evolution models by replacing the usual Schwarzschild criterion for stability and also modifying the temperature gradient in convection zones. We computed a grid of 1D models between 0.55 and 1.2 stellar masses from the pre-main sequence to the end of main sequence in order to study the problem of lithium depletion in low-mass main sequence stars. This is an ideal test case because many of those stars are born as fast rotators and the rate of lithium depletion is very sensitive to the changes in the stellar structure. Additionally, observations show a correlation between slow rotation and lithium depletion, contrary to expectations from standard models of rotationally driven mixing. By suppressing convection, and therefore decreasing the temperature at the base of the convective envelope, lithium burning is strongly quenched in our rapidly rotating models to an extent sufficient to account for the lithium spread observed in young open clusters.

Obliquity measurements for stars hosting relatively long-period giant planets with weak star-planet tidal interactions may play a key role in distinguishing between formation theories for shorter-period hot Jupiters. Few such obliquity measurements have been made to date due to the relatively small sample of known wide-orbiting, transiting Jovian-mass planets and the challenging nature of these targets, which tend to have long transit durations and orbit faint stars. We report a measurement of the Rossiter-McLaughlin effect across the transit of K2-140 b, a Jupiter-mass planet with period $P=6.57$ days orbiting a $V=12.6$ star. We find that K2-140 is an aligned system with projected spin-orbit angle $\lambda=0.5\pm9.7$ degrees, suggesting a dynamically cool formation history. This observation builds towards a population of tidally detached giant planet spin-orbit angles that will enable a direct comparison with the distribution of close-orbiting hot Jupiter orbital configurations, elucidating the prevalent formation mechanisms of each group.

Observational astrophysics consists of making inferences about the Universe by comparing data and models. The credible intervals placed on model parameters are often as important as the maximum a posteriori probability values, as the intervals indicate concordance or discordance between models and with measurements from other data. Intermediate statistics (e.g. the power spectrum) are usually measured and inferences made by fitting models to these rather than the raw data, assuming that the likelihood for these statistics has multivariate Gaussian form. The covariance matrix used to calculate the likelihood is often estimated from simulations, such that it is itself a random variable. This is a standard problem in Bayesian statistics, which requires a prior to be placed on the true model parameters and covariance matrix, influencing the joint posterior distribution. As an alternative to the commonly-used Independence-Jeffreys prior, we introduce a prior that leads to a posterior that has approximately frequentist matching coverage. This is achieved by matching the covariance of the posterior to that of the distribution of true values of the parameters around the maximum likelihood values in repeated trials, under certain assumptions. Using this prior, credible intervals derived from a Bayesian analysis can be interpreted approximately as confidence intervals, containing the truth a certain proportion of the time for repeated trials. Linking frequentist and Bayesian approaches that have previously appeared in the astronomical literature, this offers a consistent and conservative approach for credible intervals quoted on model parameters for problems where the covariance matrix is itself an estimate.

We present a detailed analysis of the Galaxy structure using an unWISE wide-field image at $3.4\mu$m. We perform a 3D photometric decomposition of the Milky Way taking into account i) the projection of the Galaxy on the celestial sphere and ii) that the observer is located within the Galaxy at the solar radius. We consider a large set of photometric models starting with a pure disc model and ending with a complex model which consists of thin and thick discs plus a boxy-peanut-shaped bulge. In our final model, we incorporate many observed features of the Milky Way, such as the disc flaring and warping, several over-densities in the plane, and the dust extinction. The model of the bulge with the corresponding X-shape structure is obtained from N-body simulations of a Milky Way-like galaxy. This allows us to retrieve the parameters of the aforementioned stellar components, estimate their contribution to the total Galaxy luminosity, and constrain the position angle of the bar. The mass of the thick disc in our models is estimated to be 0.4-1.3 of that for the thin disc. The results of our decomposition can be directly compared to those obtained for external galaxies via multicomponent photometric decomposition.

Exploration of asteroid (101955) Bennu by the OSIRIS-REx mission has provided an in-depth look at this rubble-pile near-Earth asteroid. In particular, the measured gravity field and the detailed shape model of Bennu indicate significant heterogeneities in its interior structure, compatible with a lower density at its center. Here we combine gravity inversion methods with a statistical rubble-pile model to determine the density and size-frequency distribution (SFD) index of the rubble that constitutes Bennu. The best-fitting models indicate that the SFD of the interior is consistent with that observed on the surface, with a cumulative SFD index of approximately $-2.9$. The rubble bulk density is approximately $1.35$ g/cm$^3$, corresponding to a $12$% macro-porosity. We find the largest rubble particle to be approximately $145$ m, whereas the largest void is approximately $10$ m.

We present observations (with NAO Rozhen and AS Vidojevica telescopes) of the AM Canum Venaticorum (AM CVn) type binary star CR Bootis (CR Boo) in the UBV bands. The data were obtained in two nights in July 2019, when the V band brightness was in the range of 16.1-17.0 mag. In both nights, a variability for a period of $25 (\pm 1)$ min and amplitude of about 0.2 magnitudes was visible. These brightness variations are most likely indications of "humps". During our observational time, they appear for a period similar to the CR Boo orbital period. A possible reason of their origin is the phase rotation of the bright spot, placed in the contact point of the infalling matter and the outer disc edge. We estimated some of the parameters of the binary system, on the base of the observational data.

We present the results of 3 GHz radio continuum observations of 23 superluminous supernovae (SLSNe) and their host galaxies by using the Karl G. Jansky Very Large Array conducted 5-21 years after the explosions. The sample consists of 15 Type I and 8 Type II SLSNe at z < 0.3, providing one of the largest sample of SLSNe with late-time radio data. We detected radio emission from one SLSN (PTF10hgi) and 5 hosts with a significance of >5$\sigma$. No time variability is found in late-time radio light curves of the radio-detected sources in a timescale of years except for PTF10hgi, whose variability is reported in a separate study. Comparison of star-formation rates (SFRs) derived from the 3 GHz flux densities with those derived from SED modeling based on UV-NIR data shows that four hosts have an excess of radio SFRs, suggesting obscured star formation. Upper limits for undetected hosts and stacked results show that the majority of the SLSN hosts do not have a significant obscured star formation. By using the 3 GHz upper limits, we constrain the parameters for afterglows arising from interaction between initially off-axis jets and circumstellar medium (CSM). We found that the models with higher energies ($E_{\rm iso} \gtrsim$ several $\times 10^{53}$ erg) and CSM densities ($n \gtrsim 0.01$ cm$^{-3}$) are excluded, but lower energies or CSM densities are not excluded with the current data. We also constrained the models of pulsar wind nebulae powered by a newly born magnetar for a subsample of SLSNe with model predictions in the literature.

We present the first comparison of observed stellar continuum spectra of high-redshift galaxies and mock galaxy spectra generated from hydrodynamical simulations. The mock spectra are produced from the IllustrisTNG TNG100 simulation combined with stellar population models and take into account dust attenuation and realistic observational effects (aperture effects and noise). We compare the simulated $D_n4000$ and EW(H$\delta$) of galaxies with $10.5 \leq \log(M_\ast/M_\odot) \leq 11.5$ at $0.6 \leq z \leq 1.0$ to the observed distributions from the LEGA-C survey. TNG100 globally reproduces the observed distributions of spectral indices, implying that the age distribution of galaxies in TNG100 is generally realistic. Yet there are small but significant differences. For old galaxies, TNG100 shows small $D_n4000$ when compared to LEGA-C, while LEGA-C galaxies have larger EW(H$\delta$) at fixed $D_n4000$. There are several possible explanations: 1) LEGA-C galaxies have overall older ages combined with small contributions (a few percent in mass) from younger ($<1$~Gyr) stars, while TNG100 galaxies may not have such young sub-populations; 2) the spectral mismatch could be due to systematic uncertainties in the stellar population models used to convert stellar ages and metallicities to observables. In conclusion, the latest cosmological galaxy formation simulations broadly reproduce the global age distribution of galaxies at $z\sim1$ and, at the same time, the high quality of the latest observed and simulated datasets help constrain stellar population synthesis models as well as the physical models underlying the simulations.

Using a time-dependent one-zone leptonic model that incorporates both shock acceleration and stochastic acceleration processes, we investigate the formation of the narrow spectral feature at $\sim3$ TeV of Mrk 501 which was observed during the X-ray and TeV flaring activity in July 2014. It is found that the broadband spectral energy distribution (SED) can be well interpreted as the synchrotron and synchrotron-self-Compton emission from the electron energy distribution (EED) that is composed by a power-law (PL) branch and a pileup branch. The PL branch produces synchrotron photons which are scattered by the electrons of the pileup branch via inverse-Compton scattering and form the narrow spectral feature observed at the TeV energies. The EED is produced by two injection episodes, and the pileup branch in EED is caused by shock acceleration rather than stochastic acceleration.

Gaia Data Release 2 (Gaia DR2) provides high accuracy and precision astrometric parameters (position, parallax, and proper motion) for more than 1 billion sources and is revolutionizing astrometry. For a fast-moving target such as an asteroid, with many stars in the field of view that are brighter than the faint limit magnitude of Gaia (21 Gmag), its measurement accuracy and precision can be greatly improved by taking advantage of Gaia reference stars. However, if we want to study the relative motions of cluster members, we could cross-match them in different epochs based on pixel positions. For both types of targets, the determination of optical field-angle distortion or called geometric distortion (GD) in this paper is important for image calibration especially when there are few reference stars to build a high-order plate model. For the former, the GD solution can be derived based on the astrometric catalogue's position, while for the latter, a reference system called 'master frame' is constructed from these observations in pixel coordinates, and then the GD solution is derived. But, are the two GD solutions in agreement with each other? In this paper, two types of GD solutions, which are derived either from the Gaia DR2 catalogue or from the self-constructed master frame, are applied respectively for the observations taken by 1-m telescope at Yunnan Observatory. It is found that two GD solutions enable the precision to achieve a comparable level (~10 mas) but their GD patterns are different. Synthetic distorted positions are generated for further investigation into the discrepancy between the two GD solutions. We aim to find the correlation and distinction between the two types of GD solutions and their applicability in high precision astrometry.

Planetesimal formation is a crucial yet poorly understood process in planet formation. It is widely believed that planetesimal formation is the outcome of dust clumping by the streaming instability (SI). However, recent analytical and numerical studies have shown that the SI can be damped or suppressed by external turbulence, and at least the outer regions of protoplanetary disks are likely weakly turbulent due to magneto-rotational instability (MRI). We conduct high-resolution local shearing-box simulations of hybrid particle-gas magnetohydrodynamics (MHD), incorporating ambipolar diffusion as the dominant non-ideal MHD effect, applicable to outer disk regions. We first show that dust backreaction enhances dust settling towards the midplane by reducing turbulence correlation time. Under modest level of MRI turbulence, we find that dust clumping is in fact easier than the conventional SI case, in the sense that the threshold of solid abundance for clumping is lower. The key to dust clumping includes dust backreaction and the presence of local pressure maxima, which in our work is formed by the MRI zonal flows overcoming background pressure gradient. Overall, our results support planetesimal formation in the MRI-turbulent outer protoplanetary disks, especially in ring-like substructures.

Supernovae classes have been defined phenomenologically, based on spectral features and time series data, since the specific details of the physics of the different explosions remain unrevealed. However, the number of these classes is increasing as objects with new features are observed, and the next generation of large-surveys will only bring more variety to our attention. We apply the machine learning technique of multi-label classification to the spectra of supernovae. By measuring the probabilities of specific features or `tags' in the supernova spectra, we can compress the information from a specific object down to that suitable for a human or database scan, without the need to directly assign to a reductive `class'. We use logistic regression to assign tag probabilities, and then a feed-forward neural network to filter the objects into the standard set of classes, based solely on the tag probabilities. We present STag, a software package that can compute these tag probabilities and make spectral classifications.

Pulsar glitches are the sudden increase in their spin frequency, most accompanied with a long timescale recovery process. A permanent shift would be remained in the first order derivative of spin frequency with time. Relevant data fitting research about this persistent shift was performed in this essay, we have found a more suitable fitting strategy by choosing a fitting function form $k\ln(ax + b)$ and demonstrated that would be more meaningful in pure mathematical aspect in describe the correlation between the time scale of Delayed-Spin-Up $\tau_{d}$ (so as the persistent shift $\Delta \dot{\nu}_{p}$) and glitch size $\Delta \nu$.Some possible physical ideas about this fitting also have been presented while the clear physical mechanism behind this strategy still remain unknown.

We search for isotropic stochastic gravitational-wave background including non-tensorial polarizations allowed in general metric theories of gravity in the Parkes Pulsar Timing Array (PPTA) second data release (DR2). We find no statistically significant evidence that the common process reported by the PPTA collaboration has the tensor transverse (TT), scalar transverse (ST), vector longitudinal (VL), or scalar longitudinal (SL) correlations in PPTA DR2. Therefore, we place $95\%$ upper limit on the amplitude of each polarization mode as $\mathcal{A}_{\mathrm{TT}} \lesssim 3.2\times 10^{-15}$, $\mathcal{A}_{\mathrm{ST}} \lesssim 1.8\times 10^{-15}$, $\mathcal{A}_{\mathrm{VL}}\lesssim 3.5\times 10^{-16}$ and $\mathcal{A}_{\mathrm{SL}}\lesssim 4.2\times 10^{-17}$; or equivalently, the $95\%$ upper limit on the energy density parameter per logarithm frequency as $\Omega_{\mathrm{GW}}^{\mathrm{TT}} \lesssim 1.4\times 10^{-8}$, $\Omega_{\mathrm{GW}}^{\mathrm{ST}} \lesssim 4.5\times 10^{-9}$, $\Omega_{\mathrm{GW}}^{\mathrm{VL}} \lesssim 1.7\times 10^{-10}$ and $\Omega_{\mathrm{GW}}^{\mathrm{SL}} \lesssim 2.4\times 10^{-12}$ at frequency of 1/year.

We mapped the kinetic temperature structure of two massive star-forming regions, N113 and N159W, in the Large Magellanic Cloud (LMC). We have used $\sim$1\hbox{$\,.\!\!^{\prime\prime}$}6\,($\sim$0.4\,pc) resolution measurements of the para-H$_2$CO\,$J_{\rm K_ aK_c}$\,=\,3$_{03}$--2$_{02}$, 3$_{22}$--2$_{21}$, and 3$_{21}$--2$_{20}$ transitions near 218.5\,GHz to constrain RADEX non-LTE models of the physical conditions. The gas kinetic temperatures derived from the para-H$_2$CO line ratios 3$_{22}$--2$_{21}$/3$_{03}$--2$_{02}$ and 3$_{21}$--2$_{20}$/3$_{03}$--2$_{02}$ range from 28 to 105\,K in N113 and 29 to 68\,K in N159W. Distributions of the dense gas traced by para-H$_2$CO agree with those of the 1.3\,mm dust and \emph{Spitzer}\,8.0\,$\mu$m emission, but do not significantly correlate with the H$\alpha$ emission. The high kinetic temperatures ($T_{\rm kin}$\,$\gtrsim$\,50\,K) of the dense gas traced by para-H$_2$CO appear to be correlated with the embedded infrared sources inside the clouds and/or YSOs in the N113 and N159W regions. The lower temperatures ($T_{\rm kin}$\,$<$\,50\,K) are measured at the outskirts of the H$_2$CO-bearing distributions of both N113 and N159W. It seems that the kinetic temperatures of the dense gas traced by para-H$_2$CO are weakly affected by the external sources of the H$\alpha$ emission. The non-thermal velocity dispersions of para-H$_2$CO are well correlated with the gas kinetic temperatures in the N113 region, implying that the higher kinetic temperature traced by para-H$_2$CO is related to turbulence on a $\sim$0.4\,pc scale. The dense gas heating appears to be dominated by internal star formation activity, radiation, and/or turbulence. It seems that the mechanism heating the dense gas of the star-forming regions in the LMC is consistent with that in Galactic massive star-forming regions located in the Galactic plane.

We analyze the global structure of the Milky Way (MW)'s stellar halo including its dominant subcomponent, Gaia-Sausage-Enceladus (GSE). The method to reconstruct the global distribution of this old stellar component is to employ the superposition of the orbits covering over the large MW's space, where each of the orbit-weighting factor is assigned following the probability that the star is located at its currently observed position. The selected local, metal-poor sample with ${\rm [Fe/H]}<-1$ using {\it Gaia} EDR3 and SDSS DR16 shows that the global shape of the halo is systematically rounder at all radii in more metal-poor ranges, such that an axial ratio, $q$, is nearly 1 for ${\rm [Fe/H]}<-2.2$ and $\sim 0.7$ for $-1.4<{\rm [Fe/H]}<-1.0$. It is also found that a halo in relatively metal-rich range of ${\rm [Fe/H]}>-1.8$ actually shows a boxy/peanut-like shape, suggesting a major merger event. The distribution of azimuthal velocities shows a disk-like flattened structure at $-1.4<{\rm [Fe/H]}<-1.0$, which is thought to be the metal-weak thick disk. For the subsample of stars showing GSE-like kinematics and at ${\rm [Fe/H]}>-1.8$, its global density distribution is more spherical with $q \sim 0.9$ than the general halo sample, having an outer ridge at $r\sim20$~kpc. This spherical shape is consistent with the feature of accreted halo components and the ridge suggests that the orbit of GSE's progenitor has an apocenter of $\sim 20$~kpc. Implications for the formation of the stellar halo are also presented.

According to the scheme of action of the solar dynamo, the poloidal magnetic field can be considered a source of production of the toroidal magnetic field by the solar differential rotation. From the polar magnetic field proxies, it is natural to expect that solar Cycle 25 will be weak as recorded in sunspot data. We suggest that there are parameters of the zonal harmonics of the solar surface magnetic field, such as the magnitude of the $\ell$=3 harmonic or the effective multipole index, that can be used as a reasonable addition to the polar magnetic field proxies. We discuss also some specific features of solar activity indices in Cycles 23 and 24.

We have derived high-spatial-resolution metallicity maps covering $\sim$105~deg$^2$ across the Large Magellanic Cloud (LMC) using near-infrared passbands from the VISTA Survey of the Magellanic Clouds. We attempt to understand the metallicity distribution and gradients of the LMC up to a radius of $\sim$ 6~kpc. We identify red giant branch (RGB) stars in spatially distinct $Y, (Y-K_{\rm s})$ colour-magnitude diagrams. In any of our selected subregions, the RGB slope is used as an indicator of the average metallicity, based on calibration to metallicity using spectroscopic data. The mean LMC metallicity is [Fe/H] = $-$0.42~dex ($\sigma$[Fe/H] = 0.04~dex). We find the bar to be mildly metal-rich compared with the outer disc, showing evidence of a shallow gradient in metallicity ($-0.008 \pm 0.001$ dex kpc$^{-1}$) from the galaxy's centre to a radius of 6~kpc. Our results suggest that the LMC's stellar bar is chemically similar to the bars found in large spiral galaxies. The LMC's radial metallicity gradient is asymmetric. It is metal-poor and flatter towards the southwest, in the direction of the Bridge. This hints at mixing and/or distortion of the spatial metallicity distribution, presumably caused by tidal interactions between the Magellanic Clouds.

This paper calls attention to the relevance of Raman scattering by atomic hydrogen to three optical and near/mid-infrared spectral features of HI clouds: extended red emission (ERE), diffuse interstellar bands (DIBs), and the unidentified infrared bands (UIBs). DIBs, ERE, and UIBs are observed predominantly at the edge of HI clouds, are manifestly related, and remain poorly understood. Their salient properties correspond to two major characteristics of HI Raman scattering: unusual line broadenings and a concentration of the Raman scattered ultraviolet continuum in the vicinity of hydrogen's optical and infrared transitions. Raman scattering by atomic hydrogen has now been detected in several object classes where the spectral features are observed, and I argue that it can account for all three features. I further identify three factors that condition observation of Raman scattering in HI clouds, and thus of DIBs, ERE, and UIBs: the hardness of the radiation field, interstellar dust extinction, and the geometry of the observation. The geometry determines whether complete forward scattering, yielding DIBs, or scattering at large angles, yielding ERE in the vicinity of H{\alpha} and UIBs in the infrared spectrum, will be observed. ERE results from Raman scattering of photons near Ly\b{eta} and UIBs from excitation of hydrogen atoms close to the ionization limit. DIBs, ERE, UIBs are thus different facets of the same interstellar phenomenon: Raman scattering by atomic hydrogen.

We present the results obtained from detailed spectral and timing studies of extra-galactic black hole X-ray binaries LMC~X--1 and LMC~X--3, using simultaneous observations with {\it Nuclear Spectroscopic Telescope Array (NuSTAR)} and {\it Neil Gehrels Swift} observatories. The combined spectra in the $0.5-30$~keV energy range, obtained between 2014 and 2019, are investigated for both sources. We do not find any noticeable variability in $0.5-30$~keV light curves, with $0.1-10$~Hz fractional rms estimated to be $<2$\%. No evidence of quasi-periodic oscillations is found in the power density spectra. The sources are found to be in the high soft state during the observations with disc temperature $T_{\rm in}\sim 1$~keV, photon index, $\Gamma > 2.5$ and thermal emission fraction, $f_{\rm disc}>80$\%. An Fe K$\alpha$ emission line is detected in the spectra of LMC~X--1, though no such feature is observed in the spectra of LMC~X--3. From the spectral modelling, the spins of the black holes in LMC~X--1 and LMC~X--3 are estimated to be in the range of $0.92-0.95$ and $0.19-0.29$, respectively. The accretion efficiency is found to be, $\eta \sim 0.13$ and $\eta \sim 0.04$ for LMC~X--1 and LMC~X--3, respectively.

Context. Radio halos are megaparsec-scale diffuse radio sources{ mostly} located at the centres of merging galaxy clusters. The common mechanism invoked to explain their origin is the re-acceleration of relativistic particles caused by large-scale turbulence. Aims. Current re-acceleration models predict that a significant number of halos at high redshift should be characterised by very steep spectra ($\alpha<-1.5$) because of increasing inverse Compton energy losses. In this paper, we investigate the spectral index properties of a sample of nine clusters selected from the second Planck Sunyaev-Zel'dovich catalogue showing diffuse radio emission with the Low Frequency Array (LOFAR) in the 120-168 MHz band. This is the first time that radio halos discovered at low frequencies are followed up at higher frequencies. Methods. We analysed upgraded Giant Metrewave Radio Telescope (uGMRT) observations in Bands 3 and 4, that is, 250-500 and 550-900 MHz respectively. These observations were combined with existing LOFAR data to obtain information on the spectral properties of the diffuse radio emission. Results. We find diffuse radio emission in the uGMRT observations for five of the nine high-$z$ radio halos previously discovered with LOFAR. For those, we measure spectral indices in the range of $-1$ to $-1.4$. For the uGMRT non-detections, we estimated that the halos should have a spectral index steeper than $-1.5$. We also confirm the presence of one candidate relic. Conclusions. Despite the small number of clusters, we find evidence that about half of the massive and merging clusters at high redshift host radio halos with a very steep spectrum. This is in line with theoretical predictions, although larger statistical samples are necessary to test models.

As the sensitivity and observing time of gravitational-wave detectors increase, a more diverse range of signals is expected to be observed from a variety of sources. Especially, long-lived gravitational-wave transients have received interest in the last decade. Because most of long-duration signals are poorly modeled, detection must rely on generic search algorithms, which make few or no assumption on the nature of the signal. However, the computational cost of those searches remains a limiting factor, which leads to sub-optimal sensitivity. Several detection algorithms have been developed to cope with this issue. In this paper, we present a new data analysis pipeline to search for un-modeled long-lived transient gravitational-wave signals with duration between 10 and 1000 s, based on an excess cross-power statistic in a network of detectors. The pipeline implements several new features that are intended to reduce computational cost and increase detection sensitivity for a wide range of signal morphologies. The method is generalized to a network of an arbitrary number of detectors and aims to provide a stable interface for further improvements. Comparisons with a previous implementation of a similar method on simulated and real gravitational-wave data show an overall increase in detection efficiency depending on the signal morphology, and a computing time reduced by at least a factor 10.

We have performed a search for flares and Quasi-Periodic Pulsations (QPPs) from low mass M dwarf stars using TESS 2 min cadence data. We find seven stars which show evidence of QPPs. Using Fourier and Empirical Mode Decomposition techniques, we confirm the presence of 11 QPPs in these seven stars with a period between 10.2 and 71.9 min, including an oscillation with strong drift in the period and a double-mode oscillation. The fraction of flares we examined which showed QPPs (7 percent) is higher than other studies of stellar flares, but is very similar to the fraction of Solar C-class flares. Based on the stellar parameters taken from the TESS Input Catalog, we determine the lengths and magnetic field strengths of the flare coronal loops using the period of the QPPs and various assumptions about the origin of the QPPs. We also use a scaling relationship based on flares from Solar and Solar-type stars and the observed energy, plus the duration of the flares, finding that the different approaches predict loop lengths which are consistent to a factor of $\sim$2. We also discuss the flare frequency of the seven stars determining whether this could result in ozone depletion or abiogenesis. Three of our stars have a sufficiently high rate of energetic flares which are likely to cause abiogenesis. However, two of them are also in the range where ozone depletion is likely to occur. We speculate on the implications for surface life on these stars and the effects of the loop lengths and QPPs on potential exoplanets in the habitable zone.

Fast radio bursts (FRBs) are bright radio transients with short durations and extremely high brightness temperatures, and their physical origins are still unknown. Recently, a repeating source, FRB 20200120E, was found in a globular cluster in the very nearby M81 galaxy. The associated globular cluster has an age of $\sim9.13~{\rm Gyr}$, and hosts an old population of stars. In this work, we consider that an FRB source is in a close binary system with a low-mass main sequence star as its companion. Due to the large burst energy of the FRB, when the companion star stops the FRB, its surface would be heated by the radiation-induced shock, and make re-emission. For a binary system with a solar-like companion star and an orbital period of a few days, we find that the re-emission is mainly at optical band, and with delays of a few seconds after the FRB. Its luminosity is several times larger than the solar luminosity, and the duration is about hundreds of seconds. Such a transient might be observable in the future multiwavelength follow-up observation for Galactic FRB sources.

Faraday tomography of a field centred on the extragalactic point source 3C 196 with the LOw Frequency ARray (LOFAR) revealed an intertwined structure of diffuse polarised emission with straight depolarisation canals and tracers of the magnetized and multi-phase interstellar medium (ISM), such as dust and line emission from atomic hydrogen (HI). This study aims at extending the multi-tracer analysis of LOFAR data to three additional fields in the surroundings of the 3C 196 field. For the first time, we study the three-dimensional structure of the LOFAR emission by determining the distance to the depolarisation canals. We use the Rolling Hough Transform to compare the orientation of the depolarisation canals with that of the filamentary structure seen in HI and, based on starlight and dust polarisation data, with that of the plane-of-the-sky magnetic field. Stellar parallaxes from $Gaia$ complement the starlight polarisation with the corresponding distances. Faraday tomography of the three fields shows a rich network of diffuse polarised emission at Faraday depths between $-10~{\rm rad~m^{-2}}$ and $+15~{\rm rad~m^{-2}}$. A complex system of straight depolarisation canals resembles that of the 3C 196 field. The depolarisation canals align both with the HI filaments and with the magnetic field probed by dust. The observed alignment suggests that an ordered magnetic field organises the multiphase ISM over a large area ($\sim$20$^{\circ}$). In one field, two groups of stars at distances below and above 200 pc, respectively, show distinct magnetic-field orientations. These are both comparable with the orientations of the depolarisation canals in the same field. We conclude that the depolarisation canals likely trace the same change of the magnetic field as probed by the stars, which corresponds to the edge of the Local Bubble.

The infrared signature of polycyclic aromatic hydrocarbons (PAHs) are present in many protostellar disks and these speciesare thought to play an important role in heating of the gas in the photosphere. We aim to consider PAH cluster formation as one possible cause for non-detections of PAH features in protoplanetary disks. We test the necessary conditions for cluster formation and cluster dissociation by stellar optical and FUV photons in protoplanetarydisks using a Herbig Ae/Be and a T Tauri star disk model. We perform Monte-Carlo (MC) and statistical calculations to determine dissociation rates for coronene, circumcoronene and circumcoronene clusters with sizes between 2 and 200 cluster members. By applying general disk models to our Herbig Ae/Be and T Tauri star model, we estimate the formation rate of PAH dimers and compare these with the dissociation rates. We show that the formation of PAH dimers can take place in the inner 100 AU of protoplanetary disks in sub-photospheric layers. Dimer formation takes seconds to years allowing them to grow beyond dimer size in a short time. We further demonstrate that PAH cluster increase their stability while they grow if they are located beyond a critical distance that depends on stellar properties and PAH species. The comparison with the local vertical mixing time scale allows a determination of the minimum cluster size necessaryfor survival of PAH clusters. Considering the PAH cluster formation sites, cluster survival in the photosphere of the inner disk of Herbig stars isunlikely because of the high UV radiation. For the T Tauri stars, survival of coronene, circumcoronene and circumcircumcoronene clusters is possible and cluster formation should be considered as one possible explanation for low PAH detection rates in T Tauri star disks.

Gravitational waves from the coalescence of compact-binary sources are now routinely observed by Earth bound detectors. The most sensitive search algorithms convolve many different pre-calculated gravitational waveforms with the detector data and look for coincident matches between different detectors. Machine learning is being explored as an alternative approach to building a search algorithm that has the prospect to reduce computational costs and target more complex signals. In this work we construct a two-detector search for gravitational waves from binary black hole mergers using neural networks trained on non-spinning binary black hole data from a single detector. The network is applied to the data from both observatories independently and we check for events coincident in time between the two. This enables the efficient analysis of large quantities of background data by time-shifting the independent detector data. We find that while for a single detector the network retains $91.5\%$ of the sensitivity matched filtering can achieve, this number drops to $83.9\%$ for two observatories. To enable the network to check for signal consistency in the detectors, we then construct a set of simple networks that operate directly on data from both detectors. We find that none of these simple two-detector networks are capable of improving the sensitivity over applying networks individually to the data from the detectors and searching for time coincidences.

Imaging data from upcoming radio telescopes requires distributing processing at large scales. This paper presents a distributed Fourier transform algorithm for radio interferometry processing. It generates arbitrary grid chunks with full non-coplanarity corrections while minimising memory residency, data transfer and compute work. We utilise window functions to isolate the influence between regions of grid and image space. This allows us to distribute image data between nodes and construct parts of grid space exactly when and where needed. The developed prototype easily handles image data terabytes in size, while generating visibilities at great throughput and accuracy. Scaling is demonstrated to be better than cubic in baseline length, reducing the risk involved in growing radio astronomy processing to the Square Kilometre Array and similar telescopes.

The Polstar mission will provide for a space-borne 60cm telescope operating at UV wavelengths with spectropolarimetric capability capturing all four Stokes parameters (intensity, two linear polarization components, and circular polarization). Polstar's capabilities are designed to meet its goal of determining how circumstellar gas flows alter massive stars' evolution, and finding the consequences for the stellar remnant population and the stirring and enrichment of the interstellar medium, by addressing four key science objectives. In addition, Polstar will determine drivers for the alignment of the smallest interstellar grains, and probe the dust, magnetic fields, and environments in the hot diffuse interstellar medium, including for the first time a direct measurement of the polarized and energized properties of intergalactic dust. Polstar will also characterize processes that lead to the assembly of exoplanetary systems and that affect exoplanetary atmospheres and habitability. Science driven design requirements include: access to ultraviolet bands: where hot massive stars are brightest and circumstellar opacity is highest; high spectral resolution: accessing diagnostics of circumstellar gas flows and stellar composition in the far-UV at 122-200nm, including the NV, SiIV, and CIV resonance doublets and other transitions such as NIV, AlIII, HeII, and CIII; polarimetry: accessing diagnostics of circumstellar magnetic field shape and strength when combined with high FUV spectral resolution and diagnostics of stellar rotation and distribution of circumstellar gas when combined with low near-UV spectral resolution; sufficient signal-to-noise ratios: ~1000 for spectropolarimetric precisions of 0.1% per exposure; ~100 for detailed spectroscopic studies; ~10 for exploring dimmer sources; and cadence: ranging from 1-10 minutes for most wind variability studies.

The redshift drift is a model-independent probe of fundamental cosmology, but choosing a fiducial model one can also use it to constrain the model parameters. We compare the constraining power of redshift drift measurements by the Extremely Large Telescope (ELT), as studied by Liske {\it et al.} (2008), with that of two recently proposed alternatives: the cosmic accelerometer of Eikenberry {\it et al.} (2020), and the differential redshift drift of Cooke (2020). We find that the cosmic accelerometer with a 6-year baseline leads to weaker constraints than those of the ELT (by $60\%$), but with identical time baselines it outperforms the ELT by up to a factor of 6. The differential redshift drift always performs worse that the standard approach if the goal is to constrain the matter density, but it can perform significantly better than it if the goal is to constrain the dark energy equation of state. Our results show that accurately measuring the redshift drift and using these measurements to constrain cosmological parameters are different merit functions: an experiment optimized for one of them will not be optimal for the other. These non-trivial trade-offs must be kept in mind as next generation instruments enter their final design and construction phases.

We aim to constrain the sizes of the CO circumstellar envelopes (CSEs) of 16 S-type stars, along with an additional 7 and 4 CSEs of C-type and M-type AGB stars, respectively. We map the emission from the CO J=2-1 and 3-2 lines observed with the Atacama Compact Array (ACA) and its total power (TP) antennas, and fit with a Gaussian distribution in the uv- and image planes for ACA-only and TP observations, respectively. The major axis of the fitted Gaussian for the CO(2-1) line data gives a first estimate of the size of the CO-line-emitting CSE. We investigate possible signs of deviation from spherical symmetry by analysing the line profiles, the results from visibility fitting, and by investigating the deconvolved images. The sizes of the CO-line-emitting CSEs of low-mass-loss-rate (low-MLR) S-stars fall between the sizes of the CSEs of C-stars, which are larger, and those of M-stars, which are smaller, as expected because of the differences in their respective CO abundances. The sizes of the low-MLR S-type stars show no dependence on circumstellar density, while a steeper density dependence is observed at high MLR. Furthermore, our results show that the CO CSEs of most of the S-stars in our sample are consistent with a spherically symmetric and smooth outflow. The CO envelope sizes obtained in this paper will be used to constrain detailed radiative transfer modelling to directly determine more accurate MLR estimates for the stars in our sample. For several of our sources that present signs of deviation from spherical symmetry, further high-resolution observations would be necessary to investigate the nature of, and the physical processes behind, these asymmetrical structures. This will provide further insight into the mass-loss process and its related chemistry in S-type AGB stars.

Plateau inflation is an experimentally consistent framework in which the scale of inflation can be kept relatively low. Close to the edge of the plateau, scalar perturbations are subject to a strong tachyonic instability. Tachyonic preheating is realized when, after inflation, the oscillating inflaton repeatedly re-enters the plateau. We develop the analytic theory of this process and expand the linear approach by including backreaction between the coherent background and growing perturbations. For a family of plateau models, the analytic predictions are confronted with numerical estimates. Our analysis shows that the inflaton fragments in a fraction of an $e$-fold in all examples supporting tachyonic preheating, generalizing the results of previous similar studies. In these scenarios, the scalar-to-tensor ratio is tiny, $r<10^{-7}$.

IRAS 20319+3958 in Cygnus X South is a rare example of a free-floating globule (mass ~240 Msun, length ~1.5 pc) with an internal HII region created by the stellar feedback of embedded intermediate-mass stars, in particular, one Herbig Be star. Here, we present a Herschel/HIFI CII 158 mu map of the whole globule and a large set of other FIR lines (mid-to high-J CO lines observed with Herschel/PACS and SPIRE, the OI 63 mu line and the CO 16-15 line observed with upGREAT on SOFIA), covering the globule head and partly a position in the tail. The CII map revealed that the whole globule is probably rotating. Highly collimated, high-velocity CII emission is detected close to the Herbig Be star. We performed a PDR analysis using the KOSMA-tau PDR code for one position in the head and one in the tail. The observed FIR lines in the head can be reproduced with a two-component model: an extended, non-clumpy outer PDR shell and a clumpy, dense, and thin inner PDR layer, representing the interface between the HII region cavity and the external PDR. The modelled internal UV field of ~2500 Go is similar to what we obtained from the Herschel FIR fluxes, but lower than what we estimated from the census of the embedded stars. External illumination from the ~30 pc distant Cyg OB2 cluster, producing an UV field of ~150-600 G0 as an upper limit, is responsible for most of the CII emission. For the tail, we modelled the emission with a non-clumpy component, exposed to a UV-field of around 140 Go.

Supernova remnants (SNRs) are known to accelerate particles to relativistic energies, on account of their nonthermal emission. The observational progress from radio to gamma-ray observations reveals more and more morphological features that need to be accounted for when modeling the emission from those objects. We use our time-dependent acceleration code RATPaC to study the formation of extended gamma-ray halos around supernova remnants and the morphological implications that arise when the high-energetic particles start to escape from the SNRs. We performed spherically symmetric 1D simulations in which we simultaneously solved the transport equations for cosmic rays, magnetic turbulence, and the hydrodynamical flow of the thermal plasma. Our simulations span 25,000 years, thus covering the free-expansion and the Sedov-Taylor phase of the SNR's evolution. We find a strong difference in the morphology of the gamma-ray emission from SNRs at later stages dependent on the emission process. At early times, both the inverse-Compton and the Pion-decay morphology are shell-like. However, as soon as the maximum-energy of the freshly accelerated particles starts to fall, the inverse-Compton morphology starts to become center-filled, whereas the Pion-decay morphology keeps its shell-like structure. Escaping high-energy electrons start to form an emission halo around the SNR at this time. There are good prospects for detecting this spectrally hard emission with the future Cerenkov Telescope Array, as there are for detecting variations in the gamma-ray spectral index across the interior of the SNR. Further, we find a constantly decreasing nonthermal X-ray flux that makes a detection of X-ray unlikely after the first few thousand years of the SNR's evolution. The radio flux is increasing throughout the SNR's lifetime and changes from a shell-like to a more center-filled morphology later on.

Modeling the extragalactic astroparticle skies involves reconstructing the 3D distribution of the most extreme sources in the Universe. Full-sky tomographic surveys at near-infrared wavelengths have already enabled the astroparticle community to bind the density of sources of astrophysical neutrinos and ultra-high cosmic rays (UHECRs), constrain the distribution of binary black-hole mergers and identify some of the components of the extragalactic gamma-ray background. This contribution summarizes the efforts of cleaning and complementing the catalogs developed by the gravitational-wave and near-infrared communities, in order to obtain a cosmographic view on stellar mass ($M_*$) and star formation rate (SFR). Unprecedented cosmography is offered by a sample of about 400,000 galaxies within 350 Mpc, with a 50-50 ratio of spectroscopic and photometric distances, $M_*$, SFR and corrections for incompleteness with increasing distance and decreasing Galactic latitude. The inferred 3D distribution of $M_*$ and SFR is consistent with Cosmic Flows. The $M_*$ and SFR densities converge towards values compatible with deep-field observations beyond 100 Mpc, suggesting a close-to-isotropic distribution of more distant sources. In addition to highlighting relevant applications for the four astroparticle communities, this contribution explores the distribution of $B$-fields at Mpc scales deduced from the 3D distribution of matter, which is believed to be crucial in shaping the ultra-high-energy sky. These efforts provide a new basis for modeling UHECR anisotropies, which bodes well for the identification of their long-sought sources.

In light of the most recent observations of late afterglows produced by the merger of compact objects or by the core-collapse of massive dying stars, we research the evolution of the afterglow produced by an off-axis top-hat jet and its interaction with a surrounding medium. The medium is parametrized by a power law distribution of the form $n(r)\propto r^{-k}$ is the stratification parameter and contains the development when the surrounding density is constant ($k=0$) or wind-like ($k=2$). We develop an analytical synchrotron forward-shock model when the outflow is viewed off-axis, and it is decelerated by a stratified medium. Using the X-ray data points collected by a large campaign of orbiting satellites and ground telescopes, we have managed to apply our model and fit the X-ray spectrum of the GRB afterglow associated to SN 2020bvc with conventional parameters. Our model predicts that its circumburst medium is parametrized by a power law with stratification parameter $k=1.5$.

Transit and radial velocity models were applied to archival data in order to examine exoplanet properties, in particular for the recently discovered super-Earth GJ 357b. There is however considerable variation in estimated model parameters across the literature, and especially their uncertainty estimates. This applies even for relatively uncomplicated systems and basic parameters. Some published accuracy values thus appear highly over-optimistic. We present our reanalyses with these variations in mind and specify parameters with appropriate confidence intervals for the exoplanets Kepler-1b, -2b, -8b, -12b, -13b, -14b, -15b, -40b \& -77b and 51 Peg. More sophisticated models in WinFitter, EXOFAST, and DACE were applied, leading to mean planet densities for Kepler-12b, -14b, -15b, and -40b as: $0.11 \pm 0.01$, $4.04 \pm 0.58$, $0.43 \pm 0.05$, and $1.19^{+0.31}_{-0.36}$ g per cc respectively. We confirm a rocky mean density for the Earth-like GJ357b, although we urge caution about the modelling given the low S/N data. We cannot confidently specify parameters for the other two proposed planets in this system.

We simulate the influence of the energy that the merger process of two neutron stars (NSs) releases inside a red supergiant (RSG) star on the RSG envelope inner to the merger location. In the triple star common envelope evolution (CEE) that we consider a tight binary system of two NSs spirals-in inside an RSG envelope and because of mass accretion and dynamical friction the two NS merge. We deposit merger-explosion energies of 3e50 and 1e51 erg at distances of 25Ro and 50Ro from the center of the RSG, and with the three-dimensional hydrodynamical code FLASH we follow the evolution of the RSG envelope in inner regions. For the parameters we explore we find that more than 90 per cent of the RSG envelope mass inner to the merger site stays bound to the RSG. NSs that experience a CEE are likely to accrete RSG envelope mass through an accretion disk that launches jets. These jets power a luminous transient event, a common envelope jets supernova (CEJSN). The merger process adds to the CEJSN energy. Our finding implies that the interaction of the merger product, a massive NS or a BH, with the envelope can continue to release more energy, both by further in-spiral and by mass accretion by the merger product. Massive RSG envelopes can force the merger product to spiral-in into the core of the RSG, leading to an even more energetic CEJSN.

We investigate the evolution of the afterglow produced by the deceleration of the non-relativistic material due to its surroundings. The ejecta mass is launched into the circumstellar medium with equivalent kinetic energy expressed as a power-law velocity distribution $E\propto (\Gamma\beta)^{-\alpha}$. The density profile of this medium follows a power law $n(r)\propto r^{-k}$ with $k$ the stratification parameter, which accounts for the usual cases of a constant medium ($k=0$) and a wind-like medium ($k=2$). A long-lasting central engine, which injects energy into the ejected material as ($E\propto t^{1-q}$) was also assumed. With our model, we show the predicted light curves associated with this emission for different sets of initial conditions and notice the effect of the variation of these parameters on the frequencies, timescales and intensities. The results are discussed in the Kilonova scenario.

We study observational constraints on the non-metricity $f(Q)$-gravity which reproduces an exact $\Lambda$CDM background expansion history while modifying the evolution of linear perturbations. To this purpose we use Cosmic Microwave Background (CMB) radiation, baryonic acoustic oscillations (BAO), redshift-space distortions (RSD), supernovae type Ia (SNIa), galaxy clustering (GC) and weak gravitational lensing (WL) measurements. We set stringent constraints on the parameter of the model controlling the modifications to the gravitational interaction at linear perturbation level. We find the model to be statistically preferred by data over the $\Lambda$CDM according to the $\chi^2$ and deviance information criterion statistics for the combination with CMB, BAO, RSD and SNIa. This is mostly associated to a better fit to the low-$\ell$ tail of CMB temperature anisotropies.

We present new MMT/Hectochelle spectroscopic measurements for 257 stars observed along the line of sight to the ultra-faint dwarf galaxy Triangulum II. Combining with results from previous Keck/DEIMOS spectroscopy, we obtain a sample that includes 16 likely members of Triangulum II, with up to 10 independent redshift measurements per star. To this multi-epoch kinematic data set we apply methodology that we develop in order to infer binary orbital parameters from sparsely sampled radial velocity curves with as few as two epochs. For a previously-identified (spatially unresolved) binary system in Tri~II, we infer an orbital solution with period $296.0_{-3.3}^{+3.8} \rm~ days$ , semi-major axis $1.12^{+0.41}_{-0.24}\rm~AU$, and a systemic velocity $ -380.0 \pm 1.7 \rm~km ~s^{-1}$ that we then use in the analysis of Tri~II's internal kinematics. Despite this improvement in the modeling of binary star systems, the current data remain insufficient to resolve the velocity dispersion of Triangulum II. We instead find a 95% confidence upper limit of $\sigma_{v} \lesssim 3.4 \rm ~km~s^{-1}$.

We measure the 1D Ly$\,\alpha$ power spectrum \poned from Keck Observatory Database of Ionized Absorption toward Quasars (KODIAQ), The Spectral Quasar Absorption Database (SQUAD) and XQ-100 quasars using the optimal quadratic estimator. We combine KODIAQ and SQUAD at the spectrum level, but perform a separate XQ-100 estimation to control its large resolution corrections in check. Our final analysis measures \poned at scales $k<0.1\,$s$\,$km$^{-1}$ between redshifts $z=$ 2.0 -- 4.6 using 538 quasars. This sample provides the largest number of high-resolution, high-S/N observations; and combined with the power of optimal estimator it provides exceptional precision at small scales. These small-scale modes ($k\gtrsim 0.02\,$s$\,$km$^{-1}$), unavailable in Sloan Digital Sky Survey (SDSS) and Dark Energy Spectroscopic Instrument (DESI) analyses, are sensitive to the thermal state and reionization history of the intergalactic medium, as well as the nature of dark matter. As an example, a simple Fisher forecast analysis estimates that our results can improve small-scale cut off sensitivity by more than a factor of 2.

We study the cosmological propagation of gravitational waves (GWs) beyond general relativity (GR) across homogeneous and isotropic backgrounds. We consider scenarios in which GWs interact with an additional tensor field and use a parametrized phenomenological approach that generically describes their coupled equations of motion. We analyze four distinct classes of derivative and non-derivative interactions: mass, friction, velocity, and chiral. We apply the WKB formalism to account for the cosmological evolution and obtain analytical solutions to these equations. We corroborate these results by analyzing numerically the propagation of a toy GW signal. We then proceed to use the analytical results to study the modified propagation of realistic GWs from merging compact binaries, assuming that the GW signal emitted is the same as in GR. We generically find that tensor interactions lead to copies of the originally emitted GW signal, each one with its own possibly modified dispersion relation. These copies can travel coherently and interfere with each other leading to a scrambled GW signal, or propagate decoherently and lead to echoes arriving at different times at the observer that could be misidentified as independent GW events. Depending on the type of tensor interaction, the detected GW signal may exhibit amplitude and phase distortions with respect to a GW waveform in GR, as well as birefringence effects. We discuss observational probes of these tensor interactions with both individual GW events, as well as population studies for both ground- and space-based detectors.

The chemical abundances of a galaxy's metal-poor stellar population can be used to investigate the earliest stages of its formation and chemical evolution. The Magellanic Clouds are the most massive of the Milky Way's satellite galaxies and are thought to have evolved in isolation until their recent accretion by the Milky Way. Unlike the Milky Way's less massive satellites, little is know about the Magellanic Clouds' metal-poor stars. We have used the mid-infrared metal-poor star selection of Schlaufman & Casey (2014) and archival data to target nine LMC and four SMC giants for high-resolution Magellan/MIKE spectroscopy. These nine LMC giants with $-2.4\lesssim[\text{Fe/H}]\lesssim-1.5$ and four SMC giants with $-2.6\lesssim[\text{Fe/H}]\lesssim-2.0$ are the most metal-poor stars in the Magellanic Clouds yet subject to a comprehensive abundance analysis. While we find that at constant metallicity these stars are similar to Milky Way stars in their $\alpha$, light, and iron-peak elemental abundances, both the LMC and SMC are enhanced relative to the Milky Way in the $r$-process element europium. These abundance offsets are highly significant, equivalent to$3.9\sigma$ for the LMC, $2.7\sigma$ for the SMC, and $5.0\sigma$ for the complete Magellanic Cloud sample. We propose that the $r$-process enhancement of the Magellanic Clouds' metal-poor stellar population is a result of the Magellanic Clouds' isolated chemical evolution and long history of accretion from the cosmic web combined with $r$-process nucleosynthesis on a timescale longer than the core-collapse supernova timescale but shorter than or comparable to the thermonuclear (i.e., Type Ia) supernova timescale.

We closely investigate NN potentials based upon the Delta-full version of chiral effective field theory. We find that recently constructed NN potentials of this kind, which (when applied together with three-nucleon forces) were presented as predicting accurate binding energies and radii for a range of nuclei from A=16 to A=132 and providing accurate equations of state for nuclear matter, yield a chi^2/datum of 60 for the reproduction of the pp data below 100 MeV laboratory energy. We compare this result with the first semi-quantitative $NN$ potential ever constructed in the history of mankind: the Hamada-Johnston potential of the year of 1962. It turns out that the chi^2 for the new Delta-full potentials is more than three times what was already achieved some 60 years ago. In fact, there has not been any known NN potential during the entire history of nuclear forces with a chi^2 as large as the ones of these recent Delta-full potentials of the Gothenburg-Oak Ridge group of the year of 2020. We perceive this historical fact as highly disturbing in view of the current trend for which the term "precision" has become the most frequently used label to characterize contemporary advances in microscopic nuclear structure physics. We are able to trace the very large chi^2 as well as the apparent success of the potentials in nuclear structure to unrealistic predictions for P-wave states, in which the Delta-full NNLO potentials are off by up to 40 times the NNLO truncation errors. In fact, we show that, the worse the description of the P-wave states, the better the predictions in nuclear structure. Misleading results of the above kind are unhelpful to the community's efforts in microscopic nuclear structure, because they obscure a correct understanding of the nature of the remaining problems and, thus, hamper sincere attempts towards genuine solutions.

We perform numerical simulations of fast collective neutrino flavor conversions in an one-dimensional box mimicking a system with the periodic boundary condition in one spatial direction and translation symmetry in the other two dimensions. We evolve the system over several thousands of the characteristic timescale (inverse of the interaction strength) with different initial $\bar\nu_e$ to $\nu_e$ number density ratios and different initial seed perturbations. We find that small scale structures are formed due to the interaction of the flavor waves. This results in nearly flavor depolarization in a certain neutrino phase space, when averaged over the entire box. Specifically, systems with initially equal number of $\nu_e$ and $\bar\nu_e$ can reach full flavor depolarization for the entire neutrino electron lepton number ($\nu$ELN) angular spectra. For systems with initially unequal $\nu_e$ and $\bar\nu_e$, flavor depolarization can only be reached in one side of the $\nu$ELN spectra, dictated by the net neutrino $e-x$ lepton number conservation. Quantitatively small differences depending on the initial perturbations are also found when different perturbation seeds are applied. Our numerical study here provides new insights for efforts aiming to include impact of fast flavor conversions in astrophysical simulations while calls for better analytical understanding accounting for the evolution of fast flavor conversions.

The primordial irreducible gravitational-wave background due to quantum vacuum tensor fluctuations produced during inflation spans a large range of frequencies with an almost scale-invariant spectrum but is too low to be detected by the next generation of gravitational-wave interferometers. We show how this signal is enhanced by a short temporary kination era in the cosmological history (less than 10 e-folds), that can arise at any energy scale between a GeV and the inflationary scale $10^{16}$ GeV. We argue that such kination era is naturally generated by a spinning axion before it gets trapped by its potential. It is usually assumed that the axion starts oscillating around its minimum from its initially frozen position. However, the early dynamics of the Peccei-Quinn field can induce a large kinetic energy in the axion field, triggering a kination era, either before or after the axion acquires its mass, leading to a characteristic peak in the primordial gravitational-wave background. This represents a smoking-gun signature of axion physics as no other scalar field dynamics is expected to trigger such a sequence of equations of state in the early universe. We derive the resulting gravitational-wave spectrum, and present the parameter space that leads to such a signal as well as the detectability prospects, in particular at LISA, Einstein Telescope, Cosmic Explorer and Big Bang Observer. We show both model-independent predictions and present as well results for two specific well-motivated UV completions for the QCD axion dark matter where this dynamics is built-in.

The scattering of light dark matter off thermal electrons inside the Sun produces a "fast" sub-component of the dark matter flux that may be detectable in underground experiments. We update and extend previous work by analyzing the signatures of dark matter candidates which scatter via light mediators. Using numerical simulations of the dark matter-electron interaction in the solar interior, we determine the energy spectrum of the reflected flux, and calculate the expected rates for direct detection experiments. We find that large Xenon-based experiments (such as XENON1T) provide the strongest direct limits for dark matter masses below a few MeV, reaching a sensitivity to the effective dark matter charge of $\sim 10^{-9}e$.

Chameleon gravity is an example of a model that gives rise to interesting phenomenology on cosmological scales while simultaneously possessing a screening mechanism, allowing it to avoid solar system constraints. Such models result in non-linear field equations, which can be solved analytically only in simple highly symmetric systems. In this work we study the equation of motion of a scalar-tensor theory with chameleon screening using the finite element method. More specifically, we solve the field equation for spherical and triaxial NFW cluster-sized halos. This allows a detailed investigation of the relationship between the NFW concentration and the virial mass parameters and the magnitude of the chameleon acceleration, as measured at the virial radius. In addition, we investigate the effects on the chameleon acceleration due to halo triaxiality. We focus on the parameter space regions that are still allowed by the observational constraints. We find that given our dataset, the largest allowed value for the chameleon-to-NFW acceleration ratio at the virial radius is $\sim 10^{-7}$. This result strongly indicates that the chameleon models that are still allowed by the observational constraints would not lead to any measurable effects on galaxy cluster scales. Nonetheless, we also find that there is a direct relationship between the NFW potential and the chameleon-to-NFW acceleration ratio at the virial radius. Similarly, there is a direct (yet a much more complicated) relationship between the NFW concentration, the virial mass and the acceleration ratios at the virial radius. Finally, we find that triaxiality introduces extra directional effects on the acceleration measurements. These effects in combination could potentially be used in future observational searches for fifth forces.

With an increasing number of expected gravitational-wave detections of binary neutron star mergers, it is essential that gravitational-wave models employed for the analysis of observational data are able to describe generic compact binary systems. This includes systems in which the individual neutron stars are millisecond pulsars for which spin effects become essential. In this work, we perform numerical-relativity simulations of binary neutron stars with aligned and anti-aligned spins within a range of dimensionless spins of $\chi \sim [-0.28,0.58]$. The simulations are performed with multiple resolutions, show a clear convergence order and, consequently, can be used to test existing waveform approximants. We find that for very high spins gravitational-wave models that have been employed for the interpretation of GW170817 and GW190425 are not capable of describing our numerical-relativity dataset. We verify through a full parameter estimation study in which clear biases in the estimate of the tidal deformability and effective spin are present. We hope that in preparation of the next gravitational-wave observing run of the Advanced LIGO and Advanced Virgo detectors our new set of numerical-relativity data can be used to support future developments of new gravitational-wave models.

We provide a refined and much more simplified Einstein-Gauss-Bonnet inflationary theoretical framework, which is compatible with the GW170817 observational constraints on the gravitational wave speed. As in previous works, the constraint that the gravitational wave speed is $c_T^2=1$ in natural units, results to a constraint differential equation that relates the coupling function of the scalar field to the Gauss-Bonnet invariant $\xi(\phi)$ and the scalar potential $V(\phi)$. Adopting the slow-roll conditions for the scalar field and the Hubble rate, and in contrast to previous works, by further assuming that $\kappa \frac{\xi '}{\xi''}\ll 1$, which is motivated by slow-roll arguments, we succeed in providing much more simpler expressions for the slow-roll indices and for the tensor and scalar spectral indices and for the tensor-to-scalar ratio. We exemplify our refined theoretical framework by using an illustrative example with a simple power-law scalar coupling function $\xi(\phi)\sim \phi^{\nu}$ and as we demonstrate the resulting inflationary phenomenology is compatible with the latest Planck data. Moreover, this particular model produces a blue-tilted tensor spectral index, so we discuss in brief the perspective of describing the NANOGrav result with this model as is indicated in the recent literature.

The recent claim by the NANOGrav collaboration of a possible detection of an isotropic gravitational wave background stimulated a series of investigations searching for the origin of such a signal. The QCD phase transition appears as a natural candidate and in this paper the gravitational spectrum generated during the conversion of quarks into hadrons is calculated. Here, contrary to recent studies, equations of state for the quark-gluon plasma issued from the lattice approach were adopted. The duration of the transition, an important parameter affecting the amplitude of the gravitational wave spectrum, was estimated self-consistently with the dynamics of the universe controlled by the Einstein equations. The gravitational signal generated during the transition peaks around 0,28 \mu Hz, being unable to explain the claimed NANOGrav signal. However, the expected QCD gravitational wave background could be detected by the planned spatial interferometer Big Bang Observer in its advanced version for frequencies above 1.0 mHz. This possible detection assumes that algorithms recently proposed will be able to disentangle the cosmological signal from that expected for the astrophysical background generated by black hole binaries.

In this work we show that the excess of antiprotons in the range $E_{K}=10-20 ~GeV$ reported by several groups in the analysis of the AMS-02 Collaboration data, can be explained by the production of antiprotons in the annihilation of dark matter with a $(1,0)\oplus (0,1)$ space-time structure (tensor dark matter). First, we calculate the proton and antiproton flux from conventional mechanisms and fit our results to the AMS-02 data, confirming the antiproton excess. Then we calculate the antiproton production in the annihilation of tensor dark matter. For the window $M\in [62.470,62.505] ~ GeV$ to which the measured relic density, XENO1T results and the gamma ray excess from the galactic center constrain the values of the tensor dark matter mass, we find sizable contributions of antiprotons in the excess region from the annihilation into $\bar{b}b$ and smaller contributions from the $\bar{c}c$ channel. We fit our results to the AMS-02 data, finding an improvement of the fit for these values of $M$.

Studies of shocks have long suggested that a shock can undergo cyclically self-reformation in a time scale of ion cyclotron period. This process has been proposed as a primary mechanism for energy dissipation and energetic particle acceleration at shocks. Unambiguous observational evidence, however, has remained elusive. Here, we report direct observations for the self-reformation process of a collisionless, high Mach number, quasi-perpendicular shock using MMS measurements. We find that reflected ions by the old shock ramp form a clear phase-space vortex, which gives rise to a new ramp. The new ramp observed by MMS2 has not yet developed to a mature stage during the self-reformation, and is not strong enough to reflect incident ions. Consequently, these ions are only slightly slowed down and show a flat velocity profile from the new ramp all the way to the old one. The present results provide direct evidence for shock self-reformation, and also shed light on energy dissipation and energetic particle acceleration at collisionless shocks throughout the universe.