Papers for Thursday, Feb 04 2021

The use of Gaussian processes (GPs) as models for astronomical time series datasets has recently become almost ubiquitous, given their ease of use and flexibility. GPs excel in particular at marginalization over the stellar signal in cases where the variability due to starspots rotating in and out of view is treated as a nuisance, such as in exoplanet transit modeling. However, these effective models are less useful in cases where the starspot signal is of primary interest since it is not obvious how the parameters of the GP model are related to the physical properties of interest, such as the size, contrast, and latitudinal distribution of the spots. Instead, it is common practice to explicitly model the effect of individual starspots on the light curve and attempt to infer their properties via optimization or posterior inference. Unfortunately, this process is degenerate, ill-posed, and often computationally intractable when applied to stars with more than a few spots and/or to ensembles of many light curves. In this paper, we derive a closed-form expression for the mean and covariance of a Gaussian process model that describes the light curve of a rotating, evolving stellar surface conditioned on a given distribution of starspot sizes, contrasts, and latitudes. We demonstrate that this model is correctly calibrated, allowing one to robustly infer physical parameters of interest from one or more stellar light curves, including the typical radii and the mean and variance of the latitude distribution of starspots. Our GP has far-ranging implications for understanding the variability and magnetic activity of stars from both light curves and radial velocity (RV) measurements, as well as for robustly modeling correlated noise in both transiting and RV exoplanet searches. Our implementation is efficient, user-friendly, and open source, available as the Python package starry-process.

We introduce a novel approach, the Cosmological Trajectories Method (CTM), to model nonlinear structure formation in the Universe by expanding gravitationally-induced particle trajectories around the Zel'dovich approximation. A new Beyond Zel'dovich approximation is presented, which expands the CTM to leading second-order in the gravitational interaction and allows for post-Born gravitational scattering. In the Beyond Zel'dovich approximation we derive the exact expression for the matter clustering power spectrum. This is calculated to leading order and is available in the CTM MODULE. We compare the Beyond Zel'dovich approximation power spectrum and correlation function to other methods including 1-loop Standard Perturbation Theory (SPT), 1-loop Lagrangian Perturbation Theory (LPT) and Convolution Lagrangian Perturbation Theory (CLPT). We find that the Beyond Zel'dovich approximation power spectrum performs well, matching simulations to within $\pm{10}\%$, on mildly non-linear scales, and at redshifts above $z=1$ it outperforms the Zel'dovich approximation. We also find that the Beyond Zel'dovich approximation models the BAO peak in the correlation function at $z=0$ more accurately, to within $\pm{5}\%$ of simulations, than the Zel'dovich approximation, SPT 1-loop and CLPT.

Recent observations revealed a coherence between the spin vector of a galaxy and the orbital motion of its neighbors. We refer to the phenomenon as "the spin$-$orbit alignment (SOA)" and explore its physical origin via the IllustrisTNG simulation. This is the first study to utilize a cosmological hydrodynamic simulation to investigate the SOA of galaxy pairs. In particular, we identify paired galaxies at $z = 0$ having the nearest neighbor with mass ratios from 1/10 to 10 and calculate the spin$-$orbit angle for each pair. Our results are as follows. (a) There exists a clear preference for prograde orientations (i.e., SOA) for galaxy pairs, qualitatively consistent with observations. (b) The SOA is significant for both baryonic and dark matter spins, being the strongest for gas and the weakest for dark matter. (c) The SOA is stronger for less massive targets and for targets having closer neighbors. (d) The SOA strengthens for galaxies in low-density regions, and the signal is dominated by central$-$satellite pairs in low-mass halos. (e) There is an explicit dependence of the SOA on the duration of interaction with its current neighbor. Taken together, we propose that the SOA witnessed at $z = 0$ has been developed mainly by interactions with a neighbor for an extended period of time, rather than tidal torque from the ambient large-scale structure.

We present the first Faraday rotation measure (RM) grid study of an individual low-mass cluster -- the Fornax cluster -- which is presently undergoing a series of mergers. Exploiting commissioning data for the POlarisation Sky Survey of the Universe's Magnetism (POSSUM) covering a $\sim34$ square degree sky area using the Australian Square Kilometre Array Pathfinder (ASKAP), we achieve an RM grid density of $\sim25$ RMs per square degree from a 280 MHz band centred at 887 MHz, which is similar to expectations for forthcoming GHz-frequency all-sky surveys. We thereby probe the extended magnetoionic structure of the cluster in unprecedented detail. We find that the scatter in the Faraday RM of confirmed background sources is increased by $16.8\pm2.4$ rad m$^{-2}$ within 1 degree (360 kpc) projected distance to the cluster centre, which is 2--4 times more extended than the presently-detectable X-ray-emitting intracluster medium (ICM). The Faraday-active plasma is more massive than the X-ray-emitting ICM, with an average density that broadly matches expectations for the Warm-Hot Intergalactic Medium. The morphology of the Faraday depth enhancement exhibits the classic morphology of an astrophysical bow shock on the southwest side of the main Fornax cluster, and an extended, swept-back wake on the northeastern side. Our favoured explanation is an ongoing merger between the main cluster and a sub-cluster to the southwest. The shock's Mach angle and stand-off distance lead to a self-consistent transonic merger speed with Mach 1.06. The region hosting the Faraday depth enhancement shows a decrement in both total and polarised intensity. We fail to identify a satisfactory explanation for this; further observations are warranted. Generally, our study illustrates the scientific returns that can be expected from all-sky grids of discrete sources generated by forthcoming all-sky radio surveys.

The local escape velocity provides valuable inputs to the mass profile of the Galaxy, and requires understanding the tail of the stellar speed distribution. Following Leonard $\&$ Tremaine (1990), various works have since modeled the tail of the stellar speed distribution as $\propto (v_{\rm{esc}} -v)^k$, where $v_{\rm{esc}}$ is the escape velocity, and $k$ is the slope of the distribution. In such studies, however, these two parameters were found to be largely degenerate and often a narrow prior is imposed on $k$ in order to constrain $v_{\rm{esc}}$. Furthermore, the validity of the power law form is likely to break down in the presence of multiple kinematic substructures. In this paper, we introduce a strategy that for the first time takes into account the presence of kinematic substructure. We model the tail of the velocity distribution as a sum of multiple power laws without imposing strong priors. Using mock data, we show the robustness of this method in the presence of kinematic structure that is similar to the recently-discovered Gaia Sausage. In a companion paper, we present the new measurement of the escape velocity and subsequently the mass of the Milky Way using Gaia DR2 data.

The central (`bulge') region of the Milky Way is teeming with a significant fraction of mildly metal-deficient stars with atmospheres that are strongly enriched in cyanogen ($^{12}$C$^{14}$N). Some of these objects, which are also known as nitrogen-enhanced stars, are hypothesised to be relics of the ancient assembly history of the Milky Way. Although the chemical similarity of nitrogen-enhanced stars to the unique chemical patterns observed in globular clusters has been observed, a direct connection between field stars and globular clusters has not yet been proven. In this work, we report on high-resolution, near-infrared spectroscopic observations of the bulge globular cluster NGC 6723, and the serendipitous discovery of a star, 2M18594405$-$3651518, located outside the cluster (near the tidal radius) but moving on a similar orbit, providing the first clear piece of evidence of a star that was very likely once a cluster member and has recently been ejected. Its nitrogen abundance ratio ([N/Fe]$\gtrsim + 0.94$) is well above the typical Galactic field-star levels, and it exhibits noticeable enrichment in the heavy $s$-process elements (Ce, Nd, and Yb), along with moderate carbon enrichment; all characteristics are known examples in globular clusters. This result suggests that some of the nitrogen-enhanced stars in the bulge likely originated from the tidal disruption of globular clusters.

I simulate the evolution of a stellar system hosting two stellar populations whose initial set up is defined according to the two main scenarios proposed for the origin of multiple populations in Galactic globular clusters: (i) formation of a second generation from a cooling flow of pristine+polluted gas and (ii) accretion of polluted gas onto the proto-stellar disks of a fraction of low-mass stars. For this purpose, Monte Carlo simulations containing from $10^{5}$ up to $3\cdot 10^{6}$ particles have been run including the effect of stellar evolution, binary interactions, external tidal field and a detailed modelling of the proto-stellar disk structure. The early accretion of gas onto proto-stellar disks is unable to produce discrete populations and to alter the chemical composition of a significant ($>10\%$) fraction of stars unless a disk lifetime larger ($t_{disk}\sim20~Myr$) than that predicted by models is assumed. Moreover, in this scenario the mixing timescale of the two populations is too short to reproduce the observed segregation of the chemically enriched population. On the other hand, simulations run within the cooling flow scenario can evolve after a Hubble time into stellar systems with a first-to-second population mass ratio similar to that observed in globular clusters, provided that an initial filling-factor $r_{h}/r_{J}>0.15$ is adopted. However, in the weak tidal field regime a radial segregation of the second population stronger than what observed in Milky Way globular clusters at large Galactocentric distances is predicted. This discrepancy disappears in simulations following eccentric orbits in a realistic axisymmetric potential.

The Laser Interferometer Space Antenna (LISA) will open the mHz frequency window of the gravitational wave (GW) landscape. Among all the new GW sources expected to emit in this frequency band, extreme mass-ratio inspirals (EMRIs) constitute a unique laboratory for astrophysics and fundamental physics. Here we show that EMRIs can also be used to extract relevant cosmological information, complementary to both electromagnetic (EM) and other GW observations. By using the loudest EMRIs (SNR$>$100) detected by LISA as dark standard sirens, statistically matching their sky localisation region with mock galaxy catalogs, we find that constraints on $H_0$ can reach $\sim$1.1% ($\sim$3.6%) accuracy, at the 90% credible level, in our best (worst) case scenario. By considering a dynamical dark energy (DE) cosmological model, with $\Lambda$CDM parameters fixed by other observations, we further show that in our best (worst) case scenario $\sim$5.9% ($\sim$12.3%) relative uncertainties at the 90% credible level can be obtained on $w_0$, the DE equation of state parameter. Besides being relevant in their own right, EMRI measurements will be affected by different systematics compared to both EM and ground-based GW observations. Cross validation with complementary cosmological measurements will therefore be of paramount importance, especially if convincing evidence of physics beyond $\Lambda$CDM emerges from future observations.

This work gives an update to existing reconstructions of the Galactic Faraday rotation sky by processing almost all Faraday rotation data sets available at the end of the year 2020. Observations of extra-Galactic sources in recent years have, among other regions, further illuminated the previously under-constrained southern celestial sky, as well as parts of the inner disc of the Milky Way. This has culminated in an all-sky data set of 55,190 data points, which is a significant expansion on the 41,330 used in previous works, hence making an updated separation of the Galactic component a promising venture. The increased source density allows us to present our results in a resolution of about $1.3\cdot 10^{-2}\, \mathrm{deg}^2$ ($46.8\,\mathrm{arcmin}^2$), which is a twofold increase compared to previous works. As for previous Faraday rotation sky reconstructions, this work is based on information field theory, a Bayesian inference scheme for field-like quantities which handles noisy and incomplete data. In contrast to previous reconstructions, we find a significantly thinner and pronounced Galactic disc with small-scale structures exceeding values of several thousand $\mathrm{rad}\,\mathrm{m}^{-2}$. The improvements can mainly be attributed to the new catalog of Faraday data, but are also supported by advances in correlation structure modeling within numerical information field theory. We furthermore give a detailed discussion on statistical properties of the Faraday rotation sky and investigate correlations to other data sets.

The hot halo gas distribution in the inner Milky Way (MW) contains key fossil records of the past energetic feedback processes in the Galactic center, such as the Fermi and eROSITA bubbles. Here we adopt a variety of spherical and disk-like MW halo gas models as initial conditions in a series of simulations to investigate the formation of the Fermi bubbles in the jet-shock scenario. The simulation results are compared directly with relevant observations of the Fermi bubbles to constrain the halo gas distribution in the inner Galaxy before the Fermi bubble event. Our best-fit gas density distribution can be described by a power law in radius $n_{\rm e}(r)=0.01(r/1 \text{~kpc})^{-1.5}$ cm$^{-3}$. Our study can not determine if there is an inner density core, which if exists, should be very small with size $r_{c} \lesssim 0.5$ kpc. When extrapolating to large radii $r\sim 50-90$ kpc, our derived density distribution lies appreciably below the recently estimated gas densities from ram-pressure stripping calculations, suggesting that the halo gas density profile either flattens out or has one or more discontinuities within $10 \lesssim r \lesssim 50$ kpc. Our derived gas density profile may correspond to the hot gas distribution in the inner 10-kpc region of the eROSITA bubbles about $5$ Myr ago.

The intergalactic medium (IGM) is believed to contain the majority of baryons in the universe and to trace the same dark matter structure as galaxies, forming filaments and sheets. Lya absorbers, which sample the neutral component of the IGM, have been extensively studied at low and high redshift, but the exact relation between Lya absorption, galaxies and the large-scale structure is observationally not well-constrained. In this study, we aim at characterising the relation between Lya absorbers and nearby overdense cosmological structures (galaxy filaments) at recession velocities Delta v \leq 6700 km/s by using archival observational data from various instruments. We analyse 587 intervening Lya absorbers in the spectra of 302 extragalactic background sources obtained with the COS installed on the HST. We combine the absorption-line information with galaxy data of five local galaxy filaments originally mapped by Courtois et al. (2013). Along the 91 sightlines that pass close to a filament, we identify 215 (227) Lya absorption systems (components). Among these, 74 Lya systems are aligned in position and velocity with the galaxy filaments, indicating that these absorbers and the galaxies trace the same large-scale structure. The filament-aligned Lya absorbers have a ~90 percent higher rate of incidence (dN/dz=189 for log N HI \geq 13.2) and a mildly shallower slope (-beta = -1.47) of the column density distribution function than the general Lya population at z=0, reflecting the filaments' matter overdensity. The strongest Lya absorbers are preferentially found near galaxies or close to the axis of a filament, although there is substantial scatter in this relation. Our sample of absorbers clusters more strongly around filament axes than a randomly distributed sample would do (as confirmed by a KS test), but the clustering signal is less pronounced than for the galaxies in the filaments.

I begin this review by first defining what is meant by exoplanet demographics, and then motivating why we would like as broad a picture of exoplanet demographics as possible. I then outline the methodology and pitfalls to measuring exoplanet demographics in practice. I next review the methods of detecting exoplanets, focusing on the ability of these methods to detect wide separation planets. For the purposes of this review, I define wide separation as separations beyond the 'snow line' of the protoplanetary disk, which is at roughly $\sim3$ au for a sunlike star. I note that this definition is somewhat arbitrary, and the practical boundary depends on the host star mass, planet mass and radius, and detection method. I review the approximate scaling relations for the signal-to-noise ratio for the detectability of exoplanets as a function of the relevant physical parameters, including the host star properties. I provide abroad overview of what has already been learned from the transit, radial velocity, direct imaging, and microlensing methods. I outline the challenges to synthesizing the demographics using different methods and discuss some preliminary first steps in this direction. Finally, I describe future prospects for providing a nearly complete statistical census of exoplanets.

We have carried out a set of Monte Carlo simulations to study a number of fundamental aspects of the dynamical evolution of multiple stellar populations in globular clusters with different initial masses, fractions of second generation (2G) stars, and structural properties. Our simulations explore and elucidate: 1) the role of early and long-term dynamical processes and stellar escape in the evolution of the fraction of 2G stars and the link between the evolution of the fraction of 2G stars and various dynamical parameters; 2) the link between the fraction of 2G stars inside the cluster and in the population of escaping stars during a cluster's dynamical evolution; 3) the dynamics of the spatial mixing of the first-generation (1G) and 2G stars and the details of the structural properties of the two populations as they evolve toward mixing; 4) the implications of the initial differences between the spatial distribution of 1G and 2G stars for the evolution of the anisotropy in the velocity distribution and the expected radial profile of the 1G and 2G anisotropy for clusters at different stages of their dynamical history; 5) the variation of the degree of energy equipartition of the 1G and the 2G populations as a function of the distance from the cluster's centre and the cluster's evolutionary phase.

We report the discovery of the third tidally tilted pulsator, TIC 63328020. Observations with the TESS satellite reveal binary eclipses with an orbital period of 1.1057 d, and $\delta$ Scuti-type pulsations with a mode frequency of 21.09533 d$^{-1}$. This pulsation exhibits a septuplet of orbital sidelobes as well as a harmonic quintuplet. Using the oblique pulsator model, the primary oscillation is identified as a sectoral dipole mode with $l = 1, |m| = 1$. We find the pulsating star to have $M_1 \simeq 2.5\, {\rm M}_\odot$, $R_1 \simeq 3 \, {\rm R}_\odot$, and $T_{\rm eff,1} \simeq 8000$ K, while the secondary has $M_2 \simeq 1.1 \, {\rm M}_\odot$, $R_2 \simeq 2 \, {\rm R}_\odot$, and $T_{\rm eff,2} \simeq 5600$ K. Both stars appear to be close to filling their respective Roche lobes. The properties of this binary as well as the tidally tilted pulsations differ from the previous two tidally tilted pulsators, HD74423 and CO Cam, in important ways. We also study the prior history of this system with binary evolution models and conclude that extensive mass transfer has occurred from the current secondary to the primary.

3D detailed radiative transfer is computationally taxing, since the solution of the radiative transfer equation involves traversing the six dimensional phase space of the 3D domain. With modern supercomputers the hardware available for wallclock speedup is rapidly changing, mostly in response to requirements to minimize the cost of electrical power. Given the variety of modern computing architectures, we aim to develop and adapt algorithms for different computing architectures to improve performance on a wide variety of platforms. We implemented the main time consuming kernels for solving 3D radiative transfer problems for vastly different computing architectures using MPI, OpenMP, OpenACC and vector algorithms. Adapted algorithms lead to massively improved speed for all architectures, making extremely large model calculations easily feasible. These calculations would have previously been considered impossible or prohibitively expensive. Efficient use of modern computing devices is entirely feasible, but unfortunately requires the implementation of specialized algorithms for them.

Estimating stellar ages is important for advancing our understanding of stellar and exoplanet evolution and investigating the history of the Milky Way. However, ages for low-mass stars are hard to infer as they evolve slowly on the main sequence. In addition, empirical dating methods are difficult to calibrate for low-mass stars as they are faint. In this work, we calculate ages for Kepler F, G, and crucially K and M dwarfs, using their rotation and kinematic properties. We apply the simple assumption that the velocity dispersion of stars increases over time and adopt an age--velocity--dispersion relation (AVR) to estimate average stellar ages for groupings of coeval stars. We calculate the vertical velocity dispersion of stars in bins of absolute magnitude, temperature, rotation period, and Rossby number and then convert velocity dispersion to kinematic age via an AVR. Using this method, we estimate gyro-kinematic ages for 29,949 Kepler stars with measured rotation periods. We are able to estimate ages for clusters and asteroseismic stars with an RMS of 1.22 Gyr and 0.26 Gyr respectively. With our Astraea machine learning algorithm, which predicts rotation periods, we suggest a new selection criterion (a weight of 0.15) to increase the size of the McQuillian et al. (2014) catalog of Kepler rotation periods by up to 25%. Using predicted rotation periods, we estimated gyro-kinematic ages for stars without measured rotation periods and found promising results by comparing 12 detailed age--element abundance trends with literature values.

In this note we present the starry_process code, which implements an interpretable Gaussian process (GP) for modeling variability in stellar light curves. As dark starspots rotate in and out of view, the total flux received from a distant star will change over time. Unresolved flux time series therefore encode information about the spatial structure of features on the stellar surface. The starry_process software package allows one to easily model the flux variability due to starspots, whether one is interested in understanding the properties of these spots or marginalizing over the stellar variability when it is treated as a nuisance signal. The main difference between the GP implemented here and typical GPs used to model stellar variability is the explicit dependence of our GP on physical properties of the star, such as its period, inclination, and limb darkening coefficients, and on properties of the spots, such as their radius and latitude distributions. This code is the Python implementation of the interpretable GP algorithm developed in Luger, Foreman-Mackey, and Hedges (2021).

Improving the use of Type Ia supernovae (SNIa) as standard candles requires a better approach to incorporate the relationship between SNIa and the properties of their host galaxies. Using a spectroscopically-confirmed sample of $\sim$1600 SNIa, we develop the first empirical model of underlying populations for SNIa light-curve properties that includes their dependence on host-galaxy stellar mass. These populations are important inputs to simulations that are used to model selection effects and correct distance biases within the BEAMS with Bias Correction (BBC) framework. Here we improve BBC to also account for SNIa-host correlations, and we validate this technique on simulated data samples. We recover the input relationship between SNIa luminosity and host-galaxy stellar mass (the mass step, $\gamma$) to within 0.004 mags, which is a factor of 5 improvement over the previous method that results in a $\gamma$-bias of ${\sim}0.02$. We adapt BBC for a novel dust-based model of intrinsic brightness variations, which results in a greatly reduced mass step for data ($\gamma = 0.017 \pm 0.008$), and for simulations ($\gamma =0.006 \pm 0.007$). Analysing simulated SNIa, the biases on the dark energy equation-of-state, $w$, vary from $\Delta w = 0.006(5)$ to $0.010(5)$ with our new BBC method; these biases are significantly smaller than the $0.02(5)$ $w$-bias using previous BBC methods that ignore SNIa-host correlations.

Redshift-space distortions (RSD) offers an exciting opportunity to test the gravity on cosmological scales. In the presence of galaxy bias, however, the RSD measurement at large scales, where the linear theory prediction is safely applied, is known to exhibit a degeneracy between the parameters of structure growth f and fluctuation amplitude sigma8, and one can only constrain the parameters in the form of fsigma8. In order to disentangle this degeneracy, in this paper, we go beyond the linear theory, and consider the model of RSD applicable to a weakly nonlinear regime. Based on the Fisher matrix analysis, we show explicitly that the degeneracy of the parameter fsigma8 can be broken, and sigma8 is separately estimated in the presence of galaxy bias. Performing further the Markov chain Monte Carlo analysis, we verify that our model correctly reproduces the fiducial values of fsigma8 and sigma8, with the statistical errors consistent with those estimated from the Fisher matrix analysis. We show that upcoming galaxy survey of the stage-IV class can unambiguously determine sigma8 at the precision down to 10% at higher redshifts even if we restrict the accessible scales to k<0.16h/Mpc

We present results from a circular polarisation survey for radio stars in the Rapid ASKAP Continuum Survey (RACS). RACS is a survey of the entire sky south of $\delta=+41^\circ$ being conducted with the Australian Square Kilometre Array Pathfinder telescope (ASKAP) over a 288 MHz wide band centred on 887.5 MHz. The data we analyse includes Stokes I and V polarisation products to an RMS sensitivity of 250 $\mu$Jy PSF$^{-1}$. We searched RACS for sources with fractional circular polarisation above 6 per cent, and after excluding imaging artefacts, polarisation leakage, and known pulsars we identified radio emission coincident with 33 known stars. These range from M-dwarfs through to magnetic, chemically peculiar A- and B-type stars. Some of these are well known radio stars such as YZ CMi and CU Vir, but 23 have no previous radio detections. We report the flux density and derived brightness temperature of these detections and discuss the nature of the radio emission. We also discuss the implications of our results for the population statistics of radio stars in the context of future ASKAP and Square Kilometre Array surveys.

We analyze the microlensing event KMT-2019-BLG-0797. The light curve of the event exhibits two anomalous features from a single-lens single-source model, and we aim to reveal the nature of the anomaly. It is found that a model with two lenses plus a single source (2L1S model) can explain one feature of the anomaly, but the other feature cannot be explained. We test various models and find that both anomalous features can be explained by introducing an extra source to a 2L1S model (2L2S model), making the event the third confirmed case of a 2L2S event, following on MOA-2010-BLG-117 and OGLE-2016-BLG-1003. It is estimated that the extra source comprises $\sim 4\%$ of the $I$-band flux from the primary source. Interpreting the event is subject to a close--wide degeneracy. According to the close solution, the lens is a binary consisting of two brown dwarfs with masses $(M_1, M_2)\sim (0.034, 0.021)~M_\odot$, and it is located at a distance of $\dl\sim 8.2$~kpc. According to the wide solution, on the other hand, the lens is composed of an object at the star/brown-dwarf boundary and an M dwarf with masses $(M_1, M_2)\sim (0.06, 0.33)~M_\odot$ located at $\dl\sim 7.7$~kpc. The source is composed of a late-G-dwarf/early-K-dwarf primary and an early-to-mid M-dwarf companion.

The element beryllium is detected for the first time in white dwarf stars. This discovery in the spectra of two helium-atmosphere white dwarfs was made possible only because of the remarkable overabundance of Be relative to all other elements, heavier than He, observed in these stars. The measured Be abundances, relative to chondritic, are by far the largest ever seen in any astronomical object. We anticipate that the Be in these accreted planetary bodies was produced by spallation of one or more of O, C, and N in a region of high fluence of particles of MeV or greater energy.

We present an updated model for the evolution of the orbits of "orphan galaxies" to be used in the SAG semi-analytical model of galaxy formation and evolution. In cosmological simulations, orphan galaxies are those satellite galaxies for which, due to limited mass resolution, halo finders lose track of their dark matter subhalos and can no longer be distinguished as self-bound overdensities within the larger host system. Since the evolution of orphans depends strongly on the orbit they describe within their host halo, a proper treatment of their evolution is crucial in predicting the distribution of subhalos and satellite galaxies. The model proposed takes into account the dynamical friction drag, mass loss by tidal stripping and a proximity merger criterion, also it is simple enough to be inexpensive from a computational point of view. To calibrate this model, we apply it onto a dark matter only simulation and compare the results with a high resolution simulation, considering the halo mass function and the two-point correlation function as constraints. We show that while the halo mass function fails to put tight constraints on the dynamical friction, the addition of clustering information helps to better define the parameters of the model related to the spatial distribution of subhalos. Using the model with the best fit parameters allows us to reproduce the halo mass function to a precision better than 5 per cent, and the two point correlation function at a precision better than 10 per cent.

In this paper we describe the system design and capabilities of the Australian Square Kilometre Array Pathfinder (ASKAP) radio telescope at the conclusion of its construction project and commencement of science operations. ASKAP is one of the first radio telescopes to deploy phased array feed (PAF) technology on a large scale, giving it an instantaneous field of view that covers 31 square degrees at 800 MHz. As a two-dimensional array of 36x12m antennas, with baselines ranging from 22m to 6km, ASKAP also has excellent snapshot imaging capability and 10 arcsecond resolution. This, combined with 288 MHz of instantaneous bandwidth and a unique third axis of rotation on each antenna, gives ASKAP the capability to create high dynamic range images of large sky areas very quickly. It is an excellent telescope for surveys between 700 MHz and 1800 MHz and is expected to facilitate great advances in our understanding of galaxy formation, cosmology and radio transients while opening new parameter space for discovery of the unknown.

We aim to find missing microlensing planets hidden in the unanalyzed lensing events of previous survey data. For this purpose, we conduct a systematic inspection of high-magnification microlensing events, with peak magnifications $A_{\rm peak}\gtrsim 30$, in the data collected from high-cadence surveys in and before the 2018 season. From this investigation, we identify an anomaly in the lensing light curve of the event KMT-2018-BLG-1025. The analysis of the light curve indicates that the anomaly is caused by a very low mass-ratio companion to the lens. We identify three degenerate solutions, in which the ambiguity between a pair of solutions (solutions B) is caused by the previously known close--wide degeneracy, and the degeneracy between these and the other solution (solution A) is a new type that has not been reported before. The estimated mass ratio between the planet and host is $q\sim 0.8\times 10^{-4}$ for the solution A and $q\sim 1.6\times 10^{-4}$ for the solutions B. From the Bayesian analysis conducted with measured observables, we estimate that the masses of the planet and host and the distance to the lens are $(M_{\rm p}, M_{\rm h}, D_{\rm L})\sim (6.1~M_\oplus, 0.22~M_\odot, 6.7~{\rm kpc})$ for the solution A and $\sim (4.4~M_\oplus, 0.08~M_\odot, 7.5~{\rm kpc})$ for the solutions B. The planet mass is in the category of a super-Earth regardless of the solutions, making the planet the eleventh super-Earth planet, with masses lying between those of Earth and the Solar system's ice giants, discovered by microlensing.

A search for laser light from Proxima Centauri was performed, including 107 high-resolution, optical spectra obtained between 2004 and 2019. Among them, 57 spectra contain multiple, confined spectral combs, each consisting of 10 closely-spaced frequencies of light. The spectral combs, as entities, are themselves equally spaced with a frequency separation of 5800 GHz, rendering them unambiguously technological in origin. However, the combs do not originate at Proxima Centauri. Otherwise, the 107 spectra of Proxima Centauri show no evidence of technological signals from lasers or any optical light in a narrow range of wavelengths. This search would have revealed lasers pointed toward Earth having a power of 20 to 120 kilowatts and located within the 1.3au field of view centered on Proxima Centauri, assuming a benchmark laser launcher having a 10-meter aperture.

We present a catalog of eclipsing binaries in the northern Galactic Plane from the Kiso Wide-Field Camera Intensive Survey of the Galactic Plane (KISOGP). We visually identified 7055 eclipsing binaries spread across $\sim$330 square degrees, including 4197 W Ursa Majoris/EW-, 1458 $\beta$ Lyrae/EB-, and 1400 Algol/EA-type eclipsing binaries. For all systems, $I$-band light curves were used to obtain accurate system parameters. We derived the distances and extinction values for the EW-type objects from their period--luminosity relation. We also obtained the structure of the thin disk from the distribution of our sample of eclipsing binary systems, combined with those of high-mass star-forming regions and Cepheid tracers. We found that the thin disk is inhomogeneous in number density as a function of Galactic longitude. Using this new set of distance tracers, we constrain the detailed structure of the thin disk. Finally, we report a global parallax zero-point offset of $ \Delta \pi=-42.1\pm1.9\mbox{(stat.)}\pm12.9\mbox{(syst.)}$ $\mu$as between our carefully calibrated EW-type eclipsing binary positions and those provided by Gaia Early Data Release 3. Implementation of the officially recommended parallax zero-point correction results in a significantly reduced offset. Additionally, we provide a photometric characterization of our EW-type eclipsing binaries that can be applied to further analyses.

It has been shown that temperature cycles on airless bodies of our Solar System can cause damaging of surface materials. Nevertheless, propagation mechanisms in the case of space objects are still poorly understood. Present work combines a thermoelasticity model together with linear elastic fracture mechanics theory to predict fracture propagation in the presence of thermal gradients generated by diurnal temperature cycling and under conditions similar to those existing on the asteroid Bennu. The crack direction is computed using the maximal strain energy release rate criterion, which is implemented using finite elements and the so-called G$\theta$ method (Uribe-Su\'arez et al. 2020. Eng. Fracture Mech. 227:106918). Using the implemented methodology, crack propagation direction for an initial crack tip in different positions and for different orientations is computed. It is found that cracks preferentially propagate in the North to South (N-S), in the North-East to South-West (NE-SW) and in the North-West to South-East (NW-SE) directions. Finally, thermal fatigue analysis was performed in order to estimate the crack growth rate. Computed value is in good agreement with available experimental evidence.

We present a search for radio afterglows from long gamma-ray bursts using the Australian Square Kilometre Array Pathfinder (ASKAP). Our search used the Rapid ASKAP Continuum Survey, covering the entire celestial sphere south of declination $+41^\circ$, and three epochs of the Variables and Slow Transients Pilot Survey (Phase 1), covering $\sim 5,000$ square degrees per epoch. The observations we used from these surveys spanned a nine-month period from 2019 April 21 to 2020 January 11. We crossmatched radio sources found in these surveys with 779 well-localised (to $\leq 15''$) long gamma-ray bursts occurring after 2004 and determined whether the associations were more likely afterglow- or host-related through the analysis of optical images. In our search, we detected one radio afterglow candidate associated with GRB 171205A, a local low-luminosity gamma-ray burst with a supernova counterpart SN 2017iuk, in an ASKAP observation 511 days post-burst. We confirmed this detection with further observations of the radio afterglow using the Australia Telescope Compact Array at 859 days and 884 days post-burst. Combining this data with archival data from early-time radio observations, we showed the evolution of the radio spectral energy distribution alone could reveal clear signatures of a wind-like circumburst medium for the burst. Finally, we derived semi-analytical estimates for the microphysical shock parameters of the burst: electron power-law index $p = 2.84$, normalised wind-density parameter $A_* = 3$, fractional energy in electrons $\epsilon_{e} = 0.3$, and fractional energy in magnetic fields $\epsilon_{B} = 0.0002$.

Sulfur is a volatile chemical element that plays an important role in tracing the chemical evolution of galaxies. However, its nucleosynthesis origin and abundance variations are still unclear. The goal of the present article is to accurately and precisely study the S-content of large number of stars located in the solar neighbourhood. We use the parametrisation of thousands of HR stellar spectra provided by the AMBRE Project, and combine it with the automated abundance determination GAUGUIN to derive LTE sulfur abundances for 1855 slow-rotating FGK-type stars. This is the largest and most precise catalogue of S-abundances published to date. It covers a metallicity domain as high as ~2.5dex starting at [M/H]~-2.0dex. We find that the [S/M] abundances ratio is compatible with a plateau-like distribution in the metal-poor regime, and then starts to decrease continuously at [M/H]~-1.0dex. This decrease continues towards negative values for supersolar metallicity stars as recently reported for Mg and as predicted by Galactic chemical evolution models. Moreover, sulfur-rich stars having [M/H] in the range [-1.0,-0.5] have very different kinematical and orbital properties with respect to more metal-rich and sulfur-poor ones. Two disc components, associated with the thin and thick discs, are thus seen independently in kinematics and sulfur abundances. The sulfur radial gradients in the Galactic discs have also been estimated. Finally, the enrichment in sulfur with respect to iron is nicely correlated with stellar ages: older metal-poor stars have higher [S/M] ratios than younger metal-rich ones. This work has confirmed that sulfur is an alfa-element that could be considered to explore the Galactic populations properties.

Spatial gaseous structures in the Beta Lyrae system have been studied with the fact of change in the longitudinal component of the donor's magnetic field during the orbital period in mind. The investigation was based primarily on the study of the dynamics of the circumstellar structures surrounding the binary system as a whole. The special emphasis was placed on the study of complex helium lines, in particular those arising from metastable levels. A number of different observable facts from the ultraviolet to the red spectral region were analyzed. The configuration of the donor magnetic field is a factor that not only enhances mass transfer and influences the formation of spatial gas structures between stellar components but, to some extent, also affects the outflow of matter and the formation of external gas structures around this interacting binary system. Together with previous articles \citep{Skulskyy2020a, Skulskyy2020b}, the pieces of evidence of this work, confirming the reflection of magnetically controlled matter in circumbinary structures, define the basis for a coherent picture of the mass exchange between components and outflows of matter outwards

Using TESS photometry and Rozhen spectra of the Be/gamma-ray binaries MWC 148 and MWC 656, we estimate the projected rotational velocity ($ {v} \sin i$), the rotational period (P$_{\rm rot}$), radius (R$_{\rm 1}$), and inclination ($i$) of the mass donor. For MWC 148 we derive P$_{\rm rot} = 1.10 \pm 0.03$~d, R$_{\rm 1}= 9.2 \pm 0.5$~R$_\odot$, $i = 40^\circ \pm 2^\circ$, and $ {v} \sin i =272 \pm 5$~km~s$^{-1}$. For MWC 656 we obtain P$_{\rm rot} = 1.12 \pm 0.03$~d, R$_{\rm 1}= 8.8 \pm 0.5$~R$_\odot$, $i = 52^\circ \pm 3^\circ$, and $ {v} \sin i =313 \pm 3$~km~s$^{-1}$. For MWC 656 we also find that the rotation of the mass donor is coplanar with the orbital plane.

IDeF-X HD is a 32-channel analog front-end with self-triggering capability optimized for the readout of 16 x 16 pixels CdTe or CdZnTe pixelated detectors to build low power micro gamma camera. IDeF-X HD has been designed in the standard AMS CMOS 0.35 microns process technology. Its power consumption is 800 micro watt per channel. The dynamic range of the ASIC can be extended to 1.1 MeV thanks to the in-channel adjustable gain stage. When no detector is connected to the chip and without input current, a 33 electrons rms ENC level is achieved after shaping with 10.7 micro seconds peak time. Spectroscopy measurements have been performed with CdTe Schottky detectors. We measured an energy resolution of 4.2 keV FWHM at 667 keV (137-Cs) on a mono-pixel configuration. Meanwhile, we also measured 562 eV and 666 eV FWHM at 14 keV and 60 keV respectively (241-Am) with a 256 small pixel array and a low detection threshold of 1.2 keV. Since IDeF-X HD is intended for space-borne applications in astrophysics, we evaluated its radiation tolerance and its sensitivity to single event effects. We demonstrated that the ASIC remained fully functional without significant degradation of its performances after 200 krad and that no single event latch-up was detected putting the Linear Energy Transfer threshold above 110 MeV/(mg/cm2). Good noise performance and radiation tolerance make the chip well suited for X-rays energy discrimination and high-energy resolution. The chip is space qualified and flies on board the Solar Orbiter ESA mission launched in 2020.

Using the Hamilton Echelle Spectrograph at Lick Observatory, we have obtained precise radial velocities (RVs) of a sample of 373 G- and K-giant stars over more than 12 years, leading to the discovery of several single and multiple planetary systems. The RVs of the long-period (~53 years) spectroscopic binary $\epsilon$ Cyg (HIP 102488) are found to exhibit additional regular variations with a much shorter period (~291 days). We intend to improve the orbital solution of the $\epsilon$ Cyg system and attempt to identify the cause of the nearly periodic shorter period variations, which might be due to an additional substellar companion. We used precise RV measurements of the K-giant star $\epsilon$ Cyg from Lick Observatory, in combination with a large set of RVs collected more recently with the SONG telescope, as well as archival data sets. Our Keplerian model to the RVs characterizes the orbit of the spectroscopic binary to higher precision than achieved previously, resulting in a semi-major axis of $a = 15.8 \mathrm{AU}$, an eccentricity of $e = 0.93$, and a minimum mass of the secondary of $m \sin i = 0.265 M_\odot$. Additional short-period RV variations closely resemble the signal of a Jupiter-mass planet orbiting the evolved primary component with a period of $291 \mathrm{d}$, but the period and amplitude of the putative orbit change strongly over time. Furthermore, in our stability analysis of the system, no stable orbits could be found in a large region around the best fit. Both of these findings deem a planetary cause of the RV variations unlikely. Most of the investigated alternative scenarios, such as an hierarchical triple or stellar spots, also fail to explain the observed variability convincingly. Due to its very eccentric binary orbit, it seems possible, however, that $\epsilon$ Cyg could be an extreme example of a heartbeat system.

This article discusses the physical and kinematical characteristics of planetary nebulae accompanying PG1159 central stars. The study is based on the parallax and proper motion measurements recently offered by Gaia space mission. Two approaches were used to investigate the kinematical properties of the sample. The results revealed that most of the studied nebulae arise from progenitor stars of mass range; $0.9-1.75$\,M$_{\odot}$. Furthermore, they tend to live within the Galactic thick-disk and moving with an average peculiar velocity of $61.7\pm19.2$\,km\,s$^{-1}$ at a mean vertical height of $469\pm79$ pc. The locations of the PG1159 stars on the H-R diagram indicate that they have an average final stellar mass and evolutionary age of $0.58\pm0.08$\,M$_{\odot}$ and $25.5\pm5.3 \rm{x}10^3$ yr, respectively. We found a good agreement between the mean evolutionary age of the PG1159 stars and the mean dynamical age of their companion planetary nebulae ($28.0\pm6.4 \rm{x}10^3$ yr).

The values of Hubble constant between the direct measurements from various independent local observations and that inferred from the cosmic microwave background with $\Lambda$-cold-dark-matter model are in tension with persistent significance. In this Letter, we propose a late-time inhomogeneous resolution that a chameleon field coupled to a local overdensity of matter could be trapped at a higher potential energy density as an effective cosmological constant driving the local expansion rate faster than that of the background with lower matter density. We illustrate this mechanism in a toy model that a region with only $20\%$ overdensity of matter is sufficient to resolve the Hubble tension, and the Hubble constant measured with the local distance ladders is enhanced by the chameleon coupled to the Great-Wall overdensities discovered in the large scale structure surveys.

Galactic black hole candidate (BHC) GX~339-4 underwent several outbursting phases in the past two and a half decades at irregular intervals of $2-3$ years. Nature of these outbursts in terms of the duration, number of peaks, maximum peak intensity, etc. varies. We present a possible physical reason behind the variation of outbursts. From a physical point of view, if the supply of matter from the companion is roughly constant, the total energy release in an outburst is expected to be proportional to the quiescence period prior to the outburst when the matter is accumulated. We use archival data of RXTE/ASM from January 1996 to June 2011, and MAXI/GSC from August 2009 to July 2020 data. Initial five outbursts of GX~339-4 between 1997 and 2011 were observed by ASM and showed a good linear relation between the accumulation period and the amount of energy released in each outburst, but the outbursts after 2013 behaved quite differently. The 2013, $2017-18$, and $2018-19$ outbursts were of short duration, and incomplete or `failed' in nature. We suggest that the matter accumulated during the quiescence periods prior to these outbursts were not cleared through accretion due to lack of viscosity. The leftover matter was cleared in the immediate next outbursts. Our study thus sheds light on long term accretion dynamics in outbursting sources.

We collect data at all frequencies for the new sources classified as unknown active galactic nuclei (AGNs) in the latest Burst Alert Telescope (BAT) all-sky hard X-ray catalog. Focusing on the 36 sources with measured redshift, we compute their spectral energy distribution (SED) from radio to $\gamma$-rays with the aim to classify these objects. We apply emission models that attempt to reproduce the obtained SEDs, including: i) a standard thin accretion disk together with an obscuring torus and a X-ray corona; ii) a two temperature thick advection-dominated flow; iii) an obscured AGN model, accounting for absorption along the line of sight at kiloelectronvolt energies and in the optical band; and iv) a phenomenological model to describe the jet emission in blazar-like objects. We integrate the models with the SWIRE template libraries to account for the emission of the host galaxy. For every source we found a good agreement between data and our model. Considering that the sources were selected in the hard X-ray band, which is rather unaffected by absorption, we expected and found a large fraction of absorbed radio-quiet AGNs (31 out of 36) and some additional rare radio-loud sources (5 out of 36), since the jet emission in hard X-rays is important for aligned jets owing to the boost produced by the beaming effect. With our work we can confirm the hypothesis that a number of galaxies, whose optical spectra lack AGN emission features, host an obscured active nucleus. The approach we used proved to be efficient in rapidly identifying objects, which commonly used methods were not able to classify.

Massive stars die an explosive death as a core-collapse supernova (CCSN). The exact physical processes that cause the collapsing star to rebound into an explosion are not well-understood, and the key in resolving this issue may lie in the measurement of the shape of CCSNe ejecta. Spectropolarimetry is the only way to perform this measurement for CCSNe outside of the Milky Way and Magellanic Clouds. We present an infrared (IR) spectropolarimetric detection of a CCSN, enabled by the new highly sensitive WIRC+Pol instrument at Palomar Observatory, that can observe CCSNe (M = -17 mags) out to 20 Mpc to ~0.1% polarimetric precision. IR spectropolarimetry is less affected than optical by dust scattering in the circumstellar and interstellar media, thereby providing a more unbiased probe of the intrinsic geometry of the SN ejecta. SN 2018hna, a SN 1987A-like explosion, shows 2.0+-0.3% continuum polarization in the J band oriented at ~160 degree on-sky at 182 d after the explosion. Assuming prolate geometry like in SN 1987A, we infer an ejecta axis ratio of <0.48 with the axis of symmetry pointing at 70 degree position angle. The axis ratio is similar to that of SN 1987A suggesting that they may share intrinsic geometry and inclination angle. Our data do not rule out oblate ejecta. We also observe one other core-collapse and two thermonuclear SNe in the J band. SN 2020oi, a stripped-envelope Type Ic SN in Messier 100 has p = 0.37+-0.09% at peak light, indicative of either a 10% asymmetry or host interstellar polarization. The SNe Ia, 2019ein and 2020ue have p < 0.33% and < 1.08% near peak light, indicative of asymmetries of less than 10% and 20%, respectively.

The formation of the Galactic disc is an enthusiastically debated issue. Numerous studies and models seek to identify the dominant physical process(es) that shaped its observed properties. Taking advantage of the improved coverage of the inner Milky Way provided by the SDSS DR16 APOGEE catalogue and of the ages published in the APOGEE-AstroNN Value Added Catalogue (VAC), we examine the radial evolution of the chemical and age properties of the Galactic stellar disc, with the aim to better constrain its formation. Using a sample of 199,307 giant stars with precise APOGEE abundances and APOGEE-astroNN ages, selected in a +/-2 kpc layer around the galactic plane, we assess the dependency with guiding radius of: (i) the median metallicity, (ii) the ridge lines of the [Fe/H]-[Mg/Fe] and age-[Mg/Fe] distributions and (iii) the Age Distribution Function (ADF). The giant star sample allows us to probe the radial behaviour of the Galactic disc from Rg = 0 to 14-16 kpc. The thick disc [Fe/H]-[Mg/Fe] ridge lines follow closely grouped parallel paths, supporting the idea that the thick disc did form from a well-mixed medium. However, the ridge lines present a small drift in [Mg/Fe], which decreases with increasing guiding radius. At sub-solar metallicity, the intermediate and outer thin disc [Fe/H]-[Mg/Fe] ridge lines follow parallel sequences shifted to lower metallicity as the guiding radius increases. We interpret this pattern, as the signature of a dilution of the inter-stellar medium from Rg~6 kpc to the outskirt of the disc, which occured before the onset of the thin disc formation. The APOGEE-AstroNN VAC provides stellar ages for statistically significant samples of thin disc stars from the Galactic centre up to Rg~14 kpc. An important result provided by this dataset, is that the thin disc presents evidence of an inside-out formation up to R_g~10-12 kpc.(Abridged)

The propagating intensity disturbances (PIDs) in plumes are still poorly understood and their identity (magnetoacoustic waves or flows) remains an open question. We investigate PIDs in five plumes located in the northern polar coronal hole observed during the 2017 total solar eclipse. Three plumes are associated with coronal bright points, jets and macrospicules at their base (active plumes) and the other two plumes are not (quiet plumes). The electron temperature at the base of the plumes is obtained from the filter ratio of images taken with the X-ray Telescope on board Hinode and the passband ratio around 400 nm from an eclipse instrument, the Diagnostic Coronagraph Experiment (DICE). The phase speed (v_r), frequency (omega), and wavenumber (k) of the PIDs in the plumes are obtained by applying a Fourier transformation to the space-time (r-t plane) plots in images taken with the Atmospheric Imaging Assembly (AIA) in three different wavelength channels (171 A, 193 A, and 211 A). We found that the PIDs in the higher temperature AIA channels, 193 and 211 A, are faster than that of the cooler AIA 171 A channel. This tendency is more significant for the active plumes than the quiet ones. The observed speed ratio (~1.3) between the AIA 171 and 193 A channels is similar to the theoretical value (1.25) of a slow magnetoacoustic wave. Our results support the idea that PIDs in plumes represent a superposition of slow magnetoacoustic waves and plasma outflows that consist of dense cool flows and hot coronal jets.

In [1] we highlighted the fact that the log polynomial expansion employed in Nature Astron. 3, no.3, 272-277 (2019) [2] is a poor approximation to flat $\Lambda$CDM, so using it to infer deviations from flat $\Lambda$CDM is not well-motivated. The "orthogonalized logarithmic polynomials" recently presented in arXiv:2101.08278 [3] are an attempt to respond to the earlier criticism [1]. Here we demonstrate that this new technique [3] - interesting though it may be - fails to address the fundamental problem raised in [1]. Unfortunately, the claim made in [2] may still be lost in the expansion.

The Simons Observatory (SO) will be a cosmic microwave background (CMB) survey experiment with three small-aperture telescopes and one large-aperture telescope, which will observe from the Atacama Desert in Chile. In total, SO will field over 60,000 transition-edge sensor (TES) bolometers in six spectral bands centered between 27 and 280 GHz in order to achieve the sensitivity necessary to measure or constrain numerous cosmological quantities, as outlined in The Simons Observatory Collaboration et al. (2019). The 6~m Large Aperture Telescope (LAT), which will target the smaller angular scales of the CMB, utilizes a cryogenic receiver (LATR) designed to house up to 13 individual optics tubes. Each optics tube is comprised of three silicon lenses, IR blocking filters, and three dual-polarization, dichroic TES detector wafers. The scientific objectives of the SO project require these optics tubes to achieve high-throughput optical performance while maintaining exquisite control of systematic effects. We describe the integration and testing program for the SO LATR optics tubes that will verify the design and assembly of the optics tubes before they are shipped to the SO site and installed in the LATR cryostat. The program includes a quick turn-around test cryostat that is used to cool single optics tubes and validate the cryogenic performance and detector readout assembly. We discuss the optical design specifications the optics tubes must meet to be deployed on sky and the suite of optical test equipment that is prepared to measure these requirements.

We analyze two sets of observations of Dione's co-orbital satellite Helene taken by Cassini's Composite Infrared Spectrometer (CIRS). The first observation was a CIRS FP3 (600 to 1100cm-1, 9.1 to 16.7 ${\mu}$m) stare of Helene's trailing hemisphere, where two of the ten FP3 pixels were filled. The daytime surface temperatures derived from these observations were 83.3${\pm}$0.9 K and 88.8${\pm}$0.8 K at local times 223${\deg}$ to 288${\deg}$ and 180${\deg}$ to 238${\deg}$ respectively. When these temperatures were compared to a 1-D thermophysical model only albedos between 0.25 and 0.70 were able to fit the data, with a mean and standard deviation of 0.43${\pm}$0.12. All thermal inertias tested between 1 and 2000 J m$^{-2}$ K$^{-1}$ s$^{-1/2}$ could fit the data (i.e. thermal inertia was not constrained). The second observation analyzed was a FP3 and FP4 (1100 to 1400cm-1, 7.1 to 9.1 ${\mu}m)$ scan of Helene's leading hemisphere. Temperatures between 77 and 89 K were observed with FP3, with a typical error between 5 and 10 K. The surface temperatures derived from FP4 were higher, between 98 and 106 K, but with much larger errors (between 10 and 30 K) and thus the FP3- and FP4-derived temperature largely agree within their uncertainty. Dione's disk-integrated bolometric Bond albedos have been found to be between 0.63${\pm}$0.15 (Howett et al., 2010) and 0.44${\pm}$0.13 (Howett et al., 2014). Thus Helene may be darker than Dione, which is the opposite of the trend found at shorter wavelengths (c.f. Hedman et al., 2020; Royer et al., 2020). However few conclusions can be drawn since the albedos of Dione and Helene agree within their uncertainty.

We establish a quantitative relationship between photometric and spectroscopic detections of solar-like oscillations using ab initio, three-dimensional (3D), hydrodynamical numerical simulations of stellar atmospheres. We present a theoretical derivation as proof of concept for our method. We perform realistic spectral line formation calculations to quantify the ratio between luminosity and radial velocity amplitude for two case studies: the Sun and the red giant $\epsilon$ Tau. Luminosity amplitudes are computed based on the bolometric flux predicted by 3D simulations with granulation background modelled the same way as asteroseismic observations. Radial velocity amplitudes are determined from the wavelength shift of synthesized spectral lines with methods closely resembling those used in BiSON and SONG observations. Consequently, the theoretical luminosity to radial velocity amplitude ratios are directly comparable with corresponding observations. For the Sun, we predict theoretical ratios of 21.0 and 23.7 ppm/[m/s] from BiSON and SONG respectively, in good agreement with observations 19.1 and 21.6 ppm/[m/s]. For $\epsilon$ Tau, we predict K2 and SONG ratios of 48.4 ppm/[m/s], again in good agreement with observations 42.2 ppm/[m/s], and much improved over the result from conventional empirical scaling relations which gives 23.2 ppm/[m/s]. This study thus opens the path towards a quantitative understanding of solar-like oscillations, via detailed modelling of 3D stellar atmospheres.

Observational astronomers survey the sky in great detail to gain a better understanding of many types of astronomical phenomena. In particular, the formation and evolution of galaxies, including our own, is a wide field of research in astronomy. Three dimensional (spatial) scientific visualisation is typically limited to simulated galaxies, due to the inherently two dimensional spatial resolution of Earth-based observations. We present a novel approach to reconstruct and visualise 3D representations of galaxies based on observational data, using the scientific visualisation software Splotch to generate high quality visual representations that provide a new perspective of galaxies nearby the Milky Way.

We combine observations from ALMA, ATCA, MUSE, andHerschel to study gas-to-dust ratios in 15 Fornax cluster galaxies detected in the FIR/sub-mm by Herschel and observed by ALMA as part of the ALMA Fornax Cluster Survey (AlFoCS). The sample spans a stellar mass range of 8.3 $\leq$ log (M$_*$ / M$_\odot$) $\leq$ 11.16, and a variety of morphological types. We use gas-phase metallicities derived from MUSE observations (from the Fornax3D survey) to study these ratios as a function of metallicity, and to study dust-to-metal ratios, in a sub-sample of nine galaxies. We find that gas-to-dust ratios in Fornax galaxies are systematically lower than those in field galaxies at fixed stellar mass/metallicity. This implies that a relatively large fraction of the metals in these Fornax systems is locked up in dust, which is possibly due to altered chemical evolution as a result of the dense environment. The low ratios are not only driven by HI deficiencies, but H$_2$-to-dust ratios are also significantly decreased. This is different in the Virgo cluster, where low gas-to-dust ratios inside the virial radius are driven by low HI-to-dust ratios, while H$_2$-to-dust ratios are increased. Resolved observations of NGC1436 show a radial increase in H$_2$-to-dust ratio, and show that low ratios are present throughout the disc. We propose various explanations for the low H$_2$-to-dust ratios in the Fornax cluster, including the more efficient stripping of H$_2$ compared to dust, more efficient enrichment of dust in the star formation process, and altered ISM physics in the cluster environment.

Neutrino-matter interactions play an important role in core-collapse supernova (CCSN) explosions as they contribute to both lepton number and/or four-momentum exchange between neutrinos and matter, and thus act as the agent for neutrino-driven explosions. Due to the multiscale nature of neutrino transport in CCSN simulations, an implicit treatment of neutrino-matter interactions is desired, which requires solutions of coupled nonlinear systems in each step of the time integration scheme. In this paper we design and compare nonlinear iterative solvers for implicit systems with energy coupling neutrino-matter interactions commonly used in CCSN simulations. Specifically, we consider electron neutrinos and antineutrinos, which interact with static matter configurations through the Bruenn~85 opacity set. The implicit systems arise from the discretization of a non-relativistic two-moment model for neutrino transport, which employs the discontinuous Galerkin (DG) method for phase-space discretization and an implicit-explicit (IMEX) time integration scheme. In the context of this DG-IMEX scheme, we propose two approaches to formulate the nonlinear systems -- a coupled approach and a nested approach. For each approach, the resulting systems are solved with Anderson-accelerated fixed-point iteration and Newton's method. The performance of these four iterative solvers has been compared on relaxation problems with various degree of collisionality, as well as proto-neutron star deleptonization problems with several matter profiles adopted from spherically symmetric CCSN simulations. Numerical results suggest that the nested Anderson-accelerated fixed-point solver is more efficient than other tested solvers for solving implicit nonlinear systems with energy coupling neutrino-matter interactions.

We investigate the ringdown waveform and reflectivity of a Lifshitz scalar field around a fixed Schwarzschild black hole. The radial wave equation is modified due to the Lorentz breaking terms, which leads to a diversity of ringdown waveforms. Also, it turns out that Lifshitz waves scattered by the Schwarzschild black hole exhibits superradiance. The Lorentz breaking terms lead to superluminal propagation and high-frequency modes can enter and leave the interior of the Killing horizon where negativity of energy is not prohibited. This allows the Lifshitz waves to carry out additional positive energy to infinity while leaving negative energy inside the Killing horizon, similar to the Penrose process in the ergosphere of a Kerr spacetime. Another interesting phenomenon is emergence of long-lived quasinormal modes, associated with roton-type dispersion relations. These effects drastically modify the greybody factor of a microscopic black hole, whose Hawking temperature is comparable with or higher than the Lifshitz energy scale.

Measuring the solar neutrino flux over gigayear timescales could provide a new window to inform the Solar Standard Model as well as studies of the Earth's long-term climate. We demonstrate the feasibility of measuring the time-evolution of the $^8$B solar neutrino flux over gigayear timescales using paleo detectors, naturally occurring minerals which record neutrino-induced recoil tracks over geological times. We explore suitable minerals and identify track lengths of 15--30 nm to be a practical window to detect the $^8$B solar neutrino flux. A collection of ultra-radiopure minerals of different ages, each some 0.1 kg by mass, can be used to probe the rise of the $^8$B solar neutrino flux over the recent gigayear of the Sun's evolution. We also show that models of the solar abundance problem can be distinguished based on the time-integrated tracks induced by the $^8$B solar neutrino flux.

We discuss the energy scales of the explicit breaking terms of the global symmetries \USW~ needed for the quinessential axion (QA) and the ultra-light axion (ULA). The appropriate scale of QA is about $10^{8}$ GeV.

The role of dense-matter properties in the tidal deformability of a cold nonaccreted neutron star is further investigated. Using the set of Brussels-Montreal unified equations of state, we have computed the gravitoelectric Love numbers $k_\ell$ and the gravitomagnetic Love numbers $j_\ell$ up to $\ell=5$. Their relative importance and their sensitivity to the symmetry energy and the neutron-matter stiffness are numerically assessed. Their impact on the phase of the gravitational-wave signal emitted by binary neutron star inspirals is also discussed.

In this work, we investigate the effects of the torsion-fermionic interaction on the energy levels of fermions within a Riemann-Cartan geometry using a model-independent approach. We consider the case of fermions minimally coupled to the background torsion as well as non-minimal extensions via additional couplings with the vector and axial fermionic currents which include parity-breaking interactions. In the limit of zero-curvature, and for the cases of constant and spherically symmetric torsion, we find a Zeeman-like effect on the energy levels of fermions and anti-fermions depending on whether they are aligned/anti-aligned with respect to the axial vector part of the torsion (or to specific combination of torsion quantities), and determine the corresponding fine-structure energy transitions. We also discuss non-minimal couplings between fermionic fields and torsion within the Einstein-Cartan theory and its extension to include the (parity-breaking) Holst term. Finally we elaborate on the detection of torsion effects related to the splitting of energy levels in astrophysics, cosmology and solid state physics using current capabilities.

The existing methods detect the cloud scenes are applied at relatively small spectral range within shortwave upwelling radiative wavelength flux. We have reported a new method for detection of the cloud scenes based on the Radiance Enhancement (RE). This method can be used to cover a significantly wider spectral range from 1100 nm to 1700 nm (Siddiqui et al., 2015) by using datasets from the space-orbiting micro-spectrometer Argus 1000. Due to high sunlight reflection of the smoke originated from the forest or field fires the proposed RE method can also be implemented for detection of combustion aerosols. The approach can be a promising technique for efficient detection and continuous monitor of the seasonal forest and field fires. To the best of our knowledge this is the first report showing how a cloud method can be generalized for efficient detection of the forest fires due to combustion-originated reflectance.