Papers for Friday, Mar 11 2022

Ground-based, high-resolution spectrographs are providing us with an unprecedented view of the dynamics and chemistry of the atmospheres of planets outside the Solar System. While there is a large number of stable and precise high-resolution spectrographs on modest-size telescopes, it is the spectrographs at observatories with apertures larger than 3.5 metres that dominate the atmospheric follow-up of exoplanets. In this work, we explore the potential of characterising exoplanetary atmospheres with FIES, a high-resolution spectrograph at the 2.56 metre Nordic Optical Telescope. We observed two transits of MASCARA-2 b (also known as KELT-20 b) and one transit of KELT-9 b to search for atomic iron, a species that has been recently discovered in both neutral and ionised forms in the atmospheres of these ultra-hot Jupiters using large telescopes. Using a cross-correlation method, we detect a signal of Fe II at the $4.5\sigma$ and $4.0\sigma$ level in the transits of MASCARA-2 b. We also detect Fe II in the transit of KELT-9 b at the $8.5\sigma$ level. Although we do not find any significant Doppler shift in the signal of MASCARA-2 b, we do measure a moderate blueshift (3-6 km/s) of the feature in KELT-9 b, which might be a manifestation of high-velocity winds transporting Fe II from the planetary dayside to the nightside. Our work demonstrates the feasibility of investigating exoplanet atmospheres with FIES, potentially unlocking a wealth of additional atmosphere detections with this and other high-resolution spectrographs mounted on similar-size telescopes.

Tidally tilted pulsators (TTPs) are an intriguing new class of oscillating stars in binary systems; in such stars, the pulsation axis coincides with the line of apsides, or semi-major axis, of the binary. All three TTPs discovered so far have been $\delta$~Scuti stars. In this Letter, we report the first conclusive discovery of tidally tilted pulsations in a subdwarf B (sdB) star. HD 265435 is an sdB--white dwarf binary with a 1.65-hr period that has been identified and characterized as the nearest potential Type Ia supernova progenitor. Using TESS 20-s cadence data from Sectors 44 and 45, we show that the pulsation axis of the sdB star has been tidally tilted into the orbital plane and aligned with the tidal axis of the binary. We identify 31 independent pulsation frequencies, 27 of which have between 1 and 7 sidebands separated by the orbital frequency ($\nu_{\rm orb}$), or multiples thereof. Using the observed amplitude and phase variability due to tidal tilting, we assign $\ell$ and $m$ values to most of the observed oscillation modes and use these mode identifications to generate preliminary asteroseismic constraints. Our work significantly expands our understanding of TTPs, as we now know that (i) they can be found in stars other than $\delta$~Scuti pulsators, especially highly-evolved stars that have lost their H-rich envelopes, and (ii) tidally tilted pulsations can be used to probe the interiors of stars in very tight binaries.

The emission region of $\rm \gamma$-ray bursts (GRBs) is poorly constrained. The uncertainty on the size of the dissipation site spans over 4 orders of magnitude ($\rm 10^{12}-10^{16}$ cm) depending on the unknown energy composition of the GRB jets. The joint multi-band analysis from soft X-rays to high energies (up to $\rm \sim$ 1 GeV) of one of the most energetic and distant GRB 220101A (z = 4.618) allows us for an accurate distinction between prompt and early afterglow emissions. The enormous amount of energy released by GRB 220101A ($\rm E_{iso} \approx 3 \times10^{54}$ erg) and the spectral cutoff at $\rm E_{cutoff} = 80_{-14}^{+44}$ MeV observed in the prompt emission spectrum constrains the parameter space of GRB dissipation site. We put stringent constraints on the prompt emission site, requiring $\rm \Gamma_0 \sim 900$ and $\rm R_\gamma \sim 4.5 \times 10^{13}$ cm. Our findings favor the proton synchrotron model, also consistent with the observed spectral shape. Deeper measurements of the time variability of GRBs together with accurate high-energy observations (MeV-GeV) would unveil the nature of the prompt emission.

We discuss gravitational waves (GWs) induced by a heavy spectator field that starts to oscillate during inflation. During the oscillation of the spectator field, its effective mass can also oscillate in some potentials. This mass oscillation can resonantly amplify the spectator field fluctuations. We show that these amplified fluctuations can induce GWs, which could be investigated by future gravitational wave observations. This kind of induced GWs can be produced even if the spectator field does not have any interaction with other fields except for gravitational interaction.

We investigate the ionizing properties of the pair of bright Ly$\alpha$ emitting galaxies BDF521 and BDF2195 at z=7.012 in order to constrain their contribution to the formation of the BDF "reionized bubble". We obtain constraints on UV emission lines (CIV$\lambda 1548$ doublet, HeII$\lambda 1640$, OIII]$\lambda 1660$ doublet, and CIII]$\lambda 1909$ doublet) from deep VLT-XSHOOTER observations and compare them to those available for other high-redshift objects, and to models with mixed stellar and AGN emission. We use this spectroscopic information together with the photometry available in the field to constrain the physical properties of the two objects using the spectro-photometric fitting code BEAGLE. We do not detect any significant emission at the expected position of UV lines, with 3$\sigma$ upper limits of EW$\lesssim$2-7 AA rest-frame. We find that the two objects have lower CIII] emission than expected on the basis of the correlation between the Ly$\alpha$ and CIII] EWs. The EW limits on CIV and HeII emission exclude pure AGN templates at $\sim2-3\sigma$ significance, and only models with a $\lesssim$40% AGN contribution are compatible with the observations. The two objects are found to be relatively young ($\sim$20-30 Myrs) and metal-poor ($\lesssim 0.3 Z_{\odot}$) with stellar masses of a few $10^9M_{\odot}$. Their production rate of hydrogen ionizing photons per intrinsic UV luminosity is log($\xi_{ion}^*$/Hz erg$^{-1}$)=25.02-25.26, consistent with values typically found in high-redshift galaxies, but more than twice lower than values measured in $z>$7 galaxies with strong CIII] and/or optical line emission ($\simeq$25.6-25.7). The two BDF emitters have no evidence of higher than average ionizing capabilities and are not capable of reionizing their surroundings by their own means under realistic assumptions on the escape fraction of ionizing photons. (abridged)

The hot intracluster medium (ICM) is thought to be quiescent with low observed velocity dispersions. Surface brightness fluctuations of the ICM also suggest that its turbulence is subsonic with a Kolmogorov scaling relation, indicating that the viscosity is suppressed and the kinetic energy cascades down the length scales unscathed. However, recent observations of the cold gas filaments in galaxy clusters find that the scaling relations are steeper than that of the hot plasma, signaling kinetic energy losses and the presence of supersonic flows. In this work we use high-resolution simulations to explore the turbulent velocity structure of the cold filaments at the cores of galaxy clusters. Our results indicate that supersonic turbulent structures can be "frozen" in the cold gas that cools and fragments out of a fast outflow driven by the central active galactic nucleus (AGN), when the cooling time is shorter than the dynamical sound-crossing time. After the cold gas formation, however, the slope of the velocity structure function (VSF) flattens significantly over short, 10-Myr timescales. The lack of flattened VSF in observations of H$\alpha$ filaments indicates that the H$\alpha$-emitting phase is short-lived for the cold gas in galaxy clusters. On the other hand, the ubiquity of supersonic structures in the cold filaments strongly suggests that supersonic outflows are an integral part of AGN-ICM interaction, and that AGN activity plays a crucial role at driving turbulence in galaxy clusters.

REQUIEM-2D (REsolving QUIEscent Magnified galaxies with 2D grism spectroscopy) is comprised of a sample of 8 massive ($\log M_*/M_\odot > 10.6$) strongly lensed quiescent galaxies at $z\sim2$. REQUIEM-2D combines the natural magnification from strong gravitational lensing with the high spatial-resolution grism spectroscopy of \emph{Hubble Space Telescope} through a spectrophotometric fit to study spatially resolved stellar populations. We show that quiescent galaxies in the REQUIEM-2D survey have diverse formation histories manifesting as a gradient in stellar ages, including examples of (1) a younger central region supporting outside-in formation, (2) flat age gradients that show evidence for both spatially-uniform early formation or inside-out quenching, and (3) regions at a fixed radial distance having different ages (such asymmetries cannot be recovered when averaging stellar population measurements azimuthally). The typical dust attenuation curve for the REQUIEM-2D galaxies is constrained to be steeper than Calzetti's law in the UV and generally consistent with $A_V<1$. Combined together and accounting for the different physical radial distances and formation time-scales, we find that the REQUIEM-2D galaxies that formed earlier in the universe exhibit slow and uniform growth in their inner core, whereas the galaxies that formed later have rapid inner growth in their inner core with younger ages relative to the outskirts. These results challenge the currently accepted paradigm of how massive quiescent galaxies form, where the earliest galaxies are thought to form most rapidly. Significantly larger samples close to the epoch of formation with similar data quality and higher spectral resolution are required to validate this finding.

We use accurate estimates of aluminium abundance provided as part of the APOGEE Data Release 17 and Gaia Early Data Release 3 astrometry to select a highly pure sample of stars with metallicity $-1.5\lesssim {\rm [Fe/H]}\lesssim 0.5$ born in-situ in the Milky Way proper. We show that the low-metallicity ([Fe/H]$\lesssim -1.3$) in-situ component that we dub Aurora is kinematically hot with an approximately isotropic velocity ellipsoid and a modest net rotation. Aurora stars exhibit large scatter in metallicity and in a number of element abundance ratios. The median tangential velocity of the in-situ stars increases sharply with increasing metallicity between [Fe/H]$=-1.3$ and $-0.9$, the transition that we call the spin-up. The observed and theoretically expected age-metallicity correlations imply that this increase reflects a rapid formation of the Milky Way disk over $\approx 1-2$ Gyrs. The transformation of the stellar kinematics as a function of [Fe/H] is accompanied by a qualitative change in chemical abundances: the scatter drops sharply once the Galaxy builds up a disk during later epochs corresponding to [Fe/H]$>-0.9$. Results of galaxy formation models presented in this and other recent studies strongly indicate that the trends observed in the Milky Way reflect generic processes during the early evolution of progenitors of MW-sized galaxies: a period of chaotic pre-disk evolution, when gas is accreted along cold narrow filaments and when stars are born in irregular configurations, and subsequent rapid disk formation. The latter signals formation of a stable hot gaseous halo around the MW progenitor, which changes the mode of gas accretion and allows development of coherently rotating disk.

The first directly observed gravitational wave event, GW150914, featuring the merger of two massive black holes, highlighted the need to determine how these systems of compact remnant binaries are formed. We use the binary population synthesis code COSMIC (Compact Object Synthesis and Monte Carlo Investigation Code) to predict the types of massive stars that will show significant radial velocity variations, indicative of a potential compact object (i.e. a black hole or neutron star) orbiting the star. We "observe" the binaries generated in the populations with a similar number of epochs and RV accuracy as planned for the Milky Way Mapper. In this analysis, we are especially interested in systems where a compact remnant is orbiting a massive O or B star as these systems survived the first supernova and neutron star kick. We test the ability of the Milky Way Mapper observing strategy to distinguish among different mass loss and kick prescriptions. We find that Wolf-Rayet stars or hot subdwarfs in binaries could be detectable (i.e. luminous, high delta RV max), viable progenitors of such objects, while the different prescriptions primarily affect the number of sources.

Observations of the high redshift universe provide a promising avenue for constraining the nature of the dark matter (DM). This will be even more true following the now successful launch of the James Webb Space Telescope (JWST). We run cosmological simulations of galaxy formation as a part of the Effective Theory of Structure Formation (ETHOS) project to compare the properties of high redshift galaxies in Cold (CDM) and alternative DM models which have varying relativistic coupling and self-interaction strengths. Phenomenologically, the interacting DM scenarios result in a cutoff in the linear power spectrum on small-scales, followed by a series of "dark acoustic oscillations" (DAOs). We find that DM interactions suppress the abundance of galaxies below $M_\star \sim 10^8\, M_\odot$ for the models considered. The cutoff in the linear power spectrum generally causes a delay in structure formation relative to CDM. Objects in ETHOS that end up at the same final masses as their CDM counterparts are characterised by a more vigorous phase of early star formation. While galaxies with $M_\star \lesssim 10^6\,{M_\odot}$ make up more than 60 per cent of star formation in CDM at $z\approx 10$, they contribute only about half the star formation density in ETHOS. These differences in star formation diminish with decreasing redshift. We find that the effects of DM self-interactions are negligible compared to effects of relativistic coupling (i.e. the effective initial conditions for galaxy formation) in all properties of the galaxy population we examine. Finally, we show that the clustering strength of galaxies at high redshifts depends sensitively on DM physics, although these differences are manifest on scales that may be too small to be measurable by JWST.

The nature of the sources powering nebular HeII emission in star-forming galaxies remains debated, and various types of objects have been considered, including Wolf-Rayet stars, X-ray binaries, and Population III stars. Modern X-ray observations show the ubiquitous presence of hot gas filling star-forming galaxies. We use a collisional ionization plasma code to compute the specific HeII ionizing flux produced by hot gas and show that if its temperature is not too high (less than 2.5 MK), then the observed levels of soft diffuse X-ray radiation could explain HeII ionization in galaxies. To gain a physical understanding of this result, we propose a model that combines the hydrodynamics of cluster winds and hot superbubbles with observed populations of young massive clusters in galaxies. We find that in low-metallicity galaxies, the temperature of hot gas is lower and the production rate of HeII ionizing photons is higher compared to high-metallicity galaxies. The reason is that the slower stellar winds of massive stars in lower-metallicity galaxies input less mechanical energy in the ambient medium. Furthermore, we show that ensembles of star clusters up to 10-20 Myr old in galaxies can produce enough soft X-rays to induce nebular HeII emission. We discuss observations of the template low-metallicity galaxy I Zw 18 and suggest that the HeII nebula in this galaxy is powered by a hot superbubble. Finally, appreciating the complex nature of stellar feedback, we suggest that soft X-rays from hot superbubbles are among the dominant sources of HeII ionizing flux in low-metallicity star-forming galaxies.

We investigate the effect of radio-frequency interference (RFI) excision in estimating the cosmological \hi\ 21 cm power spectrum. Flagging of RFI-contaminated channels results in a non-uniform sampling of the instrumental bandpass response. Hence, the Fourier transformation (FT) of visibilities from frequency to delay domain contaminates the higher foreground-free delay modes, and separating the spectrally fluctuating \hi\ signal from spectrally smooth foregrounds becomes challenging. We have done a comparative analysis between two algorithms, one-dimensional CLEAN and Least Square Spectral Analysis (LSSA), which have been used widely to solve this issue in the literature. We test these algorithms using the simulated SKA-1 low observations in the presence of different RFI flagging scenarios. We find that in the presence of random flagging of data, both algorithms perform well and can mitigate the foreground leakage issue. But, CLEAN fails to restrict the foreground leakage in the presence of periodic and periodic plus broadband RFI flagging and gives an extra bias to the estimated power spectrum. However, LSSA can restrict the foreground leakage for these RFI flagging scenarios and gives an unbiased estimate of the \hi\ 21 cm power spectrum. We have also applied these algorithms to the upgraded GMRT observation and found that both CLEAN and LSSA give consistent results in the presence of realistic random flagging scenarios for this observed data set. This comparative analysis demonstrates the effectiveness and robustness of these two algorithms in estimating the \hi\ 21 cm power spectrum from the data set affected by different RFI scenarios.

Using high cadence observations from the Hydrogen-alpha Rapid Dynamics camera imaging system on the Dunn Solar Telescope, we present an investigation of the statistical properties of transverse oscillations in spicules captured above the solar limb. At five equally separated atmospheric heights, spanning approximately 4900-7500 km, we have detected a total of 15 959 individual wave events, with a mean displacement amplitude of 151 +/- 124 km, a mean period of 54 +/- 45 s, and a mean projected velocity amplitude of 21 +/- 13 km s^-1. We find that both the displacement and velocity amplitudes increase with height above the solar limb, ranging from 132 +/- 111 km and 17.7 +/- 10.6 km s^-1 at 4900 km, and 168 +/- 125 km and 26.3 +/- 14.1 km s^-1 at 7500 km, respectively. Following the examination of neighboring oscillations in time and space, we find 45% of the waves to be upwardly propagating, 49% to be downwardly propagating, and 6% to be standing, with mean absolute phase velocities for the propagating waves on the order of 75-150 km s^-1. While the energy flux of the waves propagating downwards does not appear to depend on height, we find the energy flux of the upwardly propagating waves decreases with atmospheric height at a rate of -13 200 +/- 6500 W m^-2 /Mm. As a result, this decrease in energy flux as the waves propagate upwards may provide significant thermal input into the local plasma.

In the canonical theory of stellar magnetic dynamo, the tachocline in partially convective stars serves to arrange small-scale fields, generated by stochastic movement of plasma into a coherent large-scale field. Mid-to-late M-dwarfs, which are fully convective, show more magnetic activity than classical magnetic dymano theory predicts. However, mid-to-late M-dwarfs show tight correlations between rotation and magnetic activity, consistent with elements of classical dynamo theory. We use data from Magellan Inamori Kyocera Echelle (MIKE) Spectrograph to detail the relation between Ca II H\&K flux and rotation period for these low-mass stars. We measure $R'_{HK}$ values for 53 spectroscopically identified M-dwarfs selected from the MEarth survey; these stars span spectral classes from M5.0 to M3.5 and have rotation periods ranging from hours to months. We present the rotation--activity relationship as traced through these data. We find power law and saturated regimes consistent to within one sigma of previously published results and observe a mass dependence in $R'_{HK}$.

In this paper we use HST/WFC3 observations of 6 galaxies from the DYNAMO survey, combined with stellar population modelling of the SED, to determine the stellar masses of DYNAMO clumps. The DYNAMO sample has been shown to have properties similar to $z\approx1.5$ turbulent, clumpy disks. DYNAMO sample clump masses offer a useful comparison for studies of $z>1$ in that the galaxies have the same properties, yet the observational biases are significantly different. Using DYNAMO we can more easily probe rest-frame near-IR wavelengths and also probe finer spatial scales. We find that the stellar mass of DYNAMO clumps is typically $10^{7}-10^8 \mathrm{M}_\odot$. We employ a technique that makes non-parametric corrections in removal of light from nearby clumps, and carries out a locally determined disk subtraction. The process of disk subtraction is the dominant effect, and can alter clump masses at the 0.3~dex level. Using these masses, we investigate the stellar mass function of clumps in DYNAMO galaxies. DYNAMO stellar mass functions follow a declining power law with slope $\alpha \approx -1.4$, which is slightly shallower than, but similar to what is observed in $z>1$ lensed galaxies. We compare DYNAMO clump masses to results of simulations. The masses and galactocentric position of clumps in DYNAMO galaxies are more similar to long-lived clumps in simulations. Similar to recent DYNAMO results on the stellar population gradients, these results are consistent with simulations that do not employ strong "early" radiative feedback prescriptions.

We present a variational-Bayes solution to compute non-Gaussian posteriors from extremely expensive likelihoods. Our approach is an alternative for parameter inference when MCMC sampling is numerically prohibitive or conceptually unfeasible. For example, when either the likelihood or the theoretical model cannot be evaluated at arbitrary parameter values, but only previously selected values, then traditional MCMC sampling is impossible, whereas our variational-Bayes solution still succeeds in estimating the full posterior. In cosmology, this occurs e.g. when the parametric model is based on costly simulations that were run for previously selected input parameters. We demonstrate our posterior construction on the KiDS-450 weak lensing analysis, where we reconstruct the original KiDS MCMC posterior at 0.6% of its former numerical cost. The reduction in numerical cost implies that systematic effects which formerly exhausted the numerical budget could now be included.

Spectroscopic multiplicity surveys of O stars in young clusters and OB associations have revealed that a large portion ($\sim$ 70%) of these massive stars (M$_{i}$ $\gt$ 15 $M_{\odot}$) belong to close and short-period binaries (physical separation d $\lt$few au). Despite the recent and significant progress, the formation mechanisms leading to such close massive multiple systems remain to be elucidated. As a result, young massive close binaries (or higher-order multiple systems) are unique laboratories to figure out the pairing mechanism of high-mass stars. We present the first VLTI/GRAVITY observations of six young O stars in the M17 star-forming region ($\lesssim$ 1 Myr) and two additional foreground stars. From the interferometric model fitting of visibility amplitudes and closure phases, we search for companions and measure their positions and flux ratios. Combining the resulting magnitude difference with atmosphere models and evolutionary tracks, we further constrain the masses of the individual components. All of the six high-mass stars are in multiple systems, leading to a multiplicity fraction (MF) of 100%, yielding a 68% confidence interval of 94-100%. We detect a total number of 9 companions with separations up to 120 au. Including previously identified spectroscopic companions, the companion fraction of the young O stars in our sample reaches 2.3$\pm$0.6. The derived masses span a wide range from 2.5 to 50 $M_{\odot}$, with a great tendency towards high-mass companions. While based on a modest sample, our results clearly indicate that the origin of the high degree of multiplicity is rooted in their star formation mechanism. No clear evidence for one of the competing concepts of massive star formation (core accretion or competitive accretion) could be found. However, our results are compatible with migration as a scenario for the formation of close massive binaries.

In many investigations involving accretion on a central point mass, ranging from observational studies to cosmological simulations, including semi-analytical modelling, the classical Bondi accretion theory is the standard tool widely adopted. Previous works generalised the theory to include the effects of the gravitational field of the galaxy hosting a central black hole, and of electron scattering in the optically thin limit. Here we apply this extended Bondi problem, in the general polytropic case, to a class of new two-component galaxy models recently presented. In these models, a Jaffe stellar density profile is embedded in a dark matter halo such that the total density distribution follows a $r^{-3}$ profile at large radii; the stellar dynamical quantities can be expressed in a fully analytical way. The hydrodynamical properties of the flow are set by imposing that the gas temperature at infinity is proportional to the virial temperature of the stellar component. The isothermal and adiabatic (monoatomic) cases can be solved analytically, in the other cases we explore the accretion solution numerically. As non-adiabatic accretion inevitably leads to an exchange of heat with the ambient, we also discuss some important thermodynamical properties of the polytropic Bondi accretion, and provide the expressions needed to compute the amount of heat exchanged with the environment, as a function of radius. The results can be useful for the subgrid treatment of accretion in numerical simulations, as well as for the interpretation of observational data.

Homestake, Gallex and GNO data reveal variability of the solar neutrino flux. Kamiokande records for 1996-2001 reveal oscillations at 9.43 and 12.6 yr$^{-1}$, well within a range (6-16 yr$^{-1}$) that, according to helioseismology, may be related to internal solar rotation. A nuclear-decay experiment at Brookhaven National Laboratory (for 1982-86) reveals strong oscillations at 11.2 and 13.2 yr$^{-1}$. Similar oscillations are found in nuclear-decay measurements conducted by A. Parkhomov. By contrast, S. Pomme points out that nuclear-decay experiments at standards laboratories tend not to exhibit variability. The most extensive series of nuclear-decay measurements comes from an experiment initiated by G. Steinitz at the Geological Survey of Israel (2007-16), which recorded 340,000 radon-related measurements from each of 3 gamma detectors and 3 environmental sensors. Analysis of a subset of 85,000 hourly gamma measurements reveals a number of oscillation frequencies compatible with influences of internal solar rotation. There is no correlation between the gamma and environmental measurements. The solar internal magnetic field may lead to neutrino modulation by the RSFP (Resonant Spin-Flavor Precession) mechanism. A triplet of oscillations (7.43, 8.43 and 9.43 yr$^{-1}$) may be attributed to an internal region (presumably the core) with a sidereal rotation rate of 8.43 yr$^{-1}$ and a rotation axis roughly orthogonal to that of the photosphere. This suggests that the Sun had its origin in more than one stage of condensation of interplanetary material (one on top of another), which could lead to present-day layers with different metallicities, rotation rates and axes. The peak modulation occurs near local midnight in early June, suggestive of a role of cosmic neutrinos. These neutrinos could provide the mass attributed to dark matter for a neutrino mass of order 0.1 eV.

As engineered systems grow in complexity, there is an increasing need for automatic methods that can detect, diagnose, and even correct transient anomalies that inevitably arise and can be difficult or impossible to diagnose and fix manually. Among the most sensitive and complex systems of our civilization are the detectors that search for incredibly small variations in distance caused by gravitational waves -- phenomena originally predicted by Albert Einstein to emerge and propagate through the universe as the result of collisions between black holes and other massive objects in deep space. The extreme complexity and precision of such detectors causes them to be subject to transient noise issues that can significantly limit their sensitivity and effectiveness. In this work, we present a demonstration of a method that can detect and characterize emergent transient anomalies of such massively complex systems. We illustrate the performance, precision, and adaptability of the automated solution via one of the prevalent issues limiting gravitational-wave discoveries: noise artifacts of terrestrial origin that contaminate gravitational wave observatories' highly sensitive measurements and can obscure or even mimic the faint astrophysical signals for which they are listening. Specifically, we demonstrate how a highly interpretable convolutional classifier can automatically learn to detect transient anomalies from auxiliary detector data without needing to observe the anomalies themselves. We also illustrate several other useful features of the model, including how it performs automatic variable selection to reduce tens of thousands of auxiliary data channels to only a few relevant ones; how it identifies behavioral signatures predictive of anomalies in those channels; and how it can be used to investigate individual anomalies and the channels associated with them.

Hill et al. (2022, arXiv:2203.00221) recently published analysis of the intermediate polar DO Dra (YY Dra) using TESS, ASAS-SN and ZTF data. They also attempted a search for the "lost" variable YY Dra using modern catalogs of variable stars and found no corresponding one. This search drew our renewed attention and we studied the original discovery paper of YY Dra by Tsesevich (Zessewitch). We found that two out of four variables reported by him were either lost or improperly studied. The coordinate offset from the correct position in another object was much larger than the expected error. Using the information of the published period and epoch of YY Dra, we suspect that Tsesevich used a couple of plates on which the object was invisible to derive the period rather than from a completely phased light curve. DO Dra sometimes spends high states around 14 mag for a month to several months and it would not be surprising if Tsesevich observed DO Dra in such a state and suspected it to be an Algol, urging him to examine the plate archive to obtain the moments when the variable was undetected. We suspect that Tsesevich indeed observed DO Dra, rather than a different, lost eclipsing variable. The final conclusion of this matter is almost impossible to reach due to the consequence of the World War II, destructing the large part of plate collections. Until the humanity becomes wise enough to restore this destruction and wise enough to be able to avoid further destruction of human achievements, the designation YY Dra would better be conserved as a record of our negative history and unambiguous DO Dra would better be used to designate the intermediate polar 3A 1148+719.

We present the discovery and the very first analysis of four stellar systems showing two periods of eclipses, that are the objects classified as doubly eclipsing systems. Some of them were proved to orbit each other thanks to their eclipse-timing-variations (ETVs) of both pairs, hence they really constitute rare quadruples with two eclipsing pairs. Some of them do not, as we are still waiting for more data to detect their mutual movement. Their light curves and period changes were analysed. All of them are detached and near-contact, but none of them contact; moreover, to our knowledge none of these stars can be considered as blend of two spatially unresolved close components on the sky. These systems are CzeV2647 (0.5723296 + 0.9637074 days), proved to orbit with 4.5-year periodicity; CzeV1645 (1.0944877 + 1.6594641 days), with a rather questionable detection of ETV; CzeV3436 (0.6836870 + 0.3833930 days); and, finally, OGLE SMC-ECL-1758 (0.9291925 + 3.7350826 days), proved to move on its 30-year orbit. Even more surprising is the fact that most of these systems show the ratio of their two orbital periods close to coupling near some resonant values of small integers, namely CzeV2647, with only 1% from 3:5 resonance, CzeV1645 1% from 2:3 resonance, and OGLE SMC-ECL-1758 with only 0.49% from 1:4 resonance. The nature of these near-resonant states still remains a mystery.

We present the full data release for the Southern Parkes Large-Area Survey in Hydroxyl (SPLASH), a sensitive, unbiased single-dish survey of the Southern Galactic Plane in all four ground-state transitions of the OH radical at 1612, 1665, 1667 and 1720 MHz. The survey covers the inner Galactic Plane, Central Molecular Zone and Galactic Centre over the range $|b|<$ 2$^{\circ}$, 332$^{\circ}$ $< l <$ 10$^{\circ}$, with a small extension between 2$^{\circ}$ $< b <$ 6$^{\circ}$, 358$^{\circ}$ $< l <$ 4$^{\circ}$. SPLASH is the most sensitive large-scale survey of OH to-date, reaching a characteristic root-mean-square sensitivity of $\sim15$ mK for an effective velocity resolution of $\sim0.9$ km/s. The spectral line datacubes are optimised for the analysis of extended, quasi-thermal OH, but also contain numerous maser sources, which have been confirmed interferometrically and published elsewhere. We also present radio continuum images at 1612, 1666 and 1720 MHz. Based on initial comparisons with $^{12}$CO(J=1-0), we find that OH rarely extends outside CO cloud boundaries in our data, but suggest that large variations in CO-to-OH brightness temperature ratios may reflect differences in the total gas column density traced by each. Column density estimation in the complex, continuum-bright Inner Galaxy is a challenge, and we demonstrate how failure to appropriately model sub-beam structure and the line-of-sight source distribution can lead to order-of-magnitude errors. Anomalous excitation of the 1612 and 1720 MHz satellite lines is ubiquitous in the inner Galaxy, but is disabled by line overlap in and around the Central Molecular Zone.

We introduce a systematic and quantitative methodology for establishing the presence of neutrino oscillatory signals due to the hadron-quark phase transition (PT) in failing core-collapse supernovae from the observed neutrino event rate in water- or ice-based neutrino detectors. The methodology uses a likelihood ratio in the frequency domain as a test-statistic; it is also employed to estimate the frequency, amplitude, starting time, and duration of the PT-induced oscillatory signal present in the neutrino events. Assuming a core-collapse simulation of a 17 solar-mass star by Zha \emph{et al.} (2021) can be used as representative of a future PT-induced oscillatory signal in the two detectors, we find that the presence of a PT can be identified with high confidence for a core-collapse supernovae out to a distance of $\sim 10$ kpc for IceCube and to $\sim 5$ kpc for a 0.4 Mt mass water Cherenkov detector. This methodology will aid the investigation of a future galactic supernova and the study of hadron-quark matter phase in the core of massive stars.

We studied the IW And star V507 Cyg using ASAS-SN data, ZTF data and our snapshot photometry. The star has been found to be in a long standstill in 2020 May-2022 March (and it still continues now). Such long-lasting standstills have been found in a few other IW And stars in the past literature. We found that this system was systematically fainter by 0.3 mag between 2018 March and 2019 January when it showed dwarf nova-type variations, including IW And-type states. This is one of the clearest pieces of evidence that the dwarf nova-type state in Z Cam stars (in a broader sense) is associated with a decrease in the mass-transfer rate (~25% for a duration of 300 d in this case). The object also showed IW And-type phenomena in 2019, when the system was as bright as in the current long standstill. This finding suggests that the condition whether the IW And-type phenomenon occurs or not is subtle under the same mass-transfer rate.

Imaging data is the principal observable required to use galaxy-scale strong lensing in a multitude of applications in extragalactic astrophysics and cosmology. In this paper, we develop Lensing Exposure Time Calculator (LensingETC) to optimize the efficiency of telescope time usage when planning multi-filter imaging campaigns for galaxy-scale strong lenses. This tool simulates realistic data tailored to specified instrument characteristics and then automatically models them to assess the power of the data in constraining lens model parameters. We demonstrate a use case of this tool by optimizing a two-filter observing strategy (in IR and UVIS) within the limited exposure time per system allowed by a Hubble Space Telescope (HST) Snapshot program. We find that higher resolution is more advantageous to gain constraining power on the lensing observables, when there is a trade-off between signal-to-noise ratio and resolution; e.g., between the UVIS and IR filters of the HST. We also find that, whereas a point spread function (PSF) with sub-Nyquist sampling allows the sample mean for a model parameter to be robustly recovered for both galaxy-galaxy and point-source lensing systems, a sub-Nyquist sampled PSF introduces a larger scatter than a Nyquist sampled one in the deviation from the ground truth for point-source lens systems.

We report 541 new open cluster candidates in Gaia EDR3 through revisiting the cluster results from an earlier analysis of the Gaia DR2, which revealed nearly a thousand open cluster candidates in the solar neighborhood (mostly d < 3 kpc) resideing at Galactic latitudes |b| < 20 degrees. A subsequent comparison with lists of known clusters shows a large increases of the cluster samples within 2 kpc from the Sun. We assign membership probabilities to the stars through the open source pyUPMASK algorithm, and also estimate the physical parameters through isochrone fitting for each candidate. Most of the new candidates show small total proper motion dispersions and clear features in the color-magnitude diagrams. Besides, the metallicity gradient of the new candidates is consistent with those found in the literature. The cluster parameters and member stars are available at CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.128.5) or via https://cdsarc.unistra.fr/viz-bin/cat/J/ApJS. The discovery of these new objects shows that the open cluster samples in Gaia data is still not complete, and more discoveries are expected in the future researches.

Coronal Mass Ejections (CMEs) are energetic storms in the Sun that result in the ejection of large-scale magnetic clouds (MCs) in interplanetary space that contain enhanced magnetic fields with coherently changing field direction. The severity of geomagnetic perturbations depends on the direction and strength of the interplanetary magnetic field (IMF), as well as the speed and duration of passage of the storm. The coupling between the heliospheric environment and Earth's magnetosphere is the strongest when the IMF direction is persistently southward for a prolonged period. Predicting the magnetic profile of such Earth-directed CMEs is crucial for estimating their geomagnetic impact. We aim to build upon and integrate diverse techniques towards development of a comprehensive magnetic cloud prediction (MCP) model that can forecast the magnetic field vectors, Earth-impact time, speed and duration of passage of solar storms. A novelty of our scheme is the ability to predict the passage duration of the storm without recourse to computationally intensive, time-dependent dynamical equations. Our methodology is validated by comparing the MCP model output with observations of ten MCs at 1 AU. In our sample, we find that eight MCs show a root mean square deviation of less than 0.1 between predicted and observed magnetic profiles and the passage duration of seven MCs fall within the predicted range. Based on the success of this approach, we conclude that predicting the near-Earth properties of MCs based on analysis and modelling of near-Sun CME observations is a viable endeavor with potential benefits for space weather assessment.

The continuous nanohertz gravitational waves (GWs) from individual supermassive binary black holes (SMBBHs) can be encoded in the timing residuals of pulsar timing arrays (PTAs). For each pulsar, the residuals actually contain an Earth term and a pulsar term, but usually only the Earth term is considered as signal and the pulsar term is dropped, which leads to parameter-estimation biases (PEBs) for the SMBBHs, and currently there are no convenient evaluations of the PEBs. In this article, we formulate the PEBs for a SMBBH with an eccentric orbit. In our analyses, the unknown phases of pulsar terms are treated as random variables obeying the uniform distribution $U[0,2\pi)$, due to the fact that pulsar distances are generally poorly measured. Our analytical results are in accordance with the numerical work by Zhu et. al. (2016) at $1.5\sigma$ level, implying that our formulae are effective in estimating magnitudes of the PEBs. Additionally, we find that for two parameters -- Earth term phase $\varphi^E$ and orbital eccentricity $e$, their biases $\Delta \varphi^E$ and $\Delta e/e$ monotonically decrease as $e$ increases, which partly confirms a hypothesis in our previous work Chen & Zhang (2018). Furthermore, we also calculate the PEBs caused by the recently observed common-spectrum process (CSP), finding that if the strain amplitude of the continuous GW is significantly stronger ($3$ times larger, in our cases) than the stochastic GW background, the PEBs from pulsar terms are larger than those from the CSP. Our formulae of the PEBs can be conveniently applied in the future PTA data analyses.

Machine learning, through the use of convolutional and recurrent neural networks is a promising avenue for the improvement of background rejection performance in imaging atmospheric Cherenkov telescopes. However, it is of paramount importance for science analysis that their performance remains stable against a wide range of observing conditions and instrument states. We investigate the stability of convolutional recurrent networks by applying them to background rejection in a toy Monte Carlo simulation of a Cherenkov telescope array. We then vary a range of observation and instrument parameters in the simulation. In general, most of the resulting systematics are at a level not much greater than conventional analyses. However, a strong dependence of the neural network predictions on the noise level within the camera was found, with differences of up to 50% in the gamma-ray acceptance rate in very noisy environments. It is clear from the performance differences seen in these studies that these observational effects must be considered in the training step of the final analysis when using such networks for background rejection in Cherenkov telescope observations.

We investigate the fine-structure [C${\rm \scriptsize II}$] line at $158\,\mu$m as a molecular gas tracer by analyzing the relationship between molecular gas mass ($M_{\rm mol}$) and [C${\rm \scriptsize II}$] line luminosity ($L_{\rm [CII]}$) in 11,125 $z\simeq 6$ star-forming, main sequence galaxies from the SIMBA simulations, with line emission modeled by S\'IGAME. Though most ($\sim 50-100\,\%$) of the gas mass in our simulations is ionized, the bulk ($> 50\,\%$) of the [C${\rm \scriptsize II}$] emission comes from the molecular phase. We find a sub-linear (slope $0.78\pm 0.01$) $\log L_{\rm [CII]}-\log M_{\rm mol}$ relation, in contrast with the linear relation derived from observational samples of more massive, metal-rich galaxies at $z \lesssim 6$. We derive a median [C${\rm \scriptsize II}$]-to-$M_{\rm mol}$ conversion factor of $\alpha_{\rm [CII]} \simeq 18\,{\rm M_{\rm \odot}/L_{\rm \odot}}$. This is lower than the average value of $\simeq 30\,{\rm M_{\rm \odot}/L_{\rm \odot}}$ derived from observations, which we attribute to lower gas-phase metallicities in our simulations. Thus, a lower, luminosity-dependent, conversion factor must be applied when inferring molecular gas masses from [C${\rm \scriptsize II}$] observations of low-mass galaxies. For our simulations, [C${\rm \scriptsize II}$] is a better tracer of the molecular gas than CO $J=1-0$, especially at the lowest metallicities, where much of the gas is 'CO-dark'. We find that $L_{\rm [CII]}$ is more tightly correlated with $M_{\rm mol}$ than with star-formation rate (${\rm SFR}$), and both the $\log L_{\rm [CII]}-\log M_{\rm mol}$ and $\log L_{\rm [CII]}-\log {\rm SFR}$ relations arise from the Kennicutt-Schmidt relation. Our findings suggest that $L_{\rm [CII]}$ is a promising tracer of the molecular gas at the earliest cosmic epochs.

Barium stars have been studied extensively over the past few decades, yet our current understanding of how these intriguing objects formed leaves much to be desired. Many trends observed in systems containing barium stars cannot be satisfactorily explained by classical binary evolution models, naturally raising the question of whether triples and other higher-order multiples can give rise to such exotic objects. In this paper, we study the possibility that a Roche Lobe overflow from a tertiary in a hierarchical triple system can potentially lead to surface barium enrichment within the inner binary, while at the same time causing the inner binary to merge, thereby producing a barium star. This possibility has the potential to form a large proportion of Barium stars, as Roche Lobe overflow from a tertiary is typically much more stable for close orbits than that from a binary companion. Various formation channels and mechanisms by which this can be achieved are considered, and constraints on relative formation rates are placed on each scenario. We conclude that a significant, if not dominant, proportion of barium stars are formed from hierarchical triple systems, and that further studies are required in this area before a complete understanding of Barium star populations can be achieved.

We generate probabilistic predictions of the low-redshift ($z < 0.2$) synchrotron Cosmic Web for half of the Northern Sky. In particular, we predict the contribution to the specific intensity function at $\nu_\mathrm{obs} = 150\ \mathrm{MHz}$ from merger shocks in clusters and accretion shocks in filaments, both of which arise during large-scale structure formation. We assume a primordial magnetogenesis scenario, but our method is general enough to allow for an exploration of alternative magnetogenesis scenarios - and even alternative radiation mechanisms and spectral windows. In the future, by comparing different predictions, one could infer the most plausible physical model from a synchrotron Cosmic Web detection. Our method combines Bayesian large-scale structure reconstructions, snapshots of an MHD cosmological simulation, a Gaussian random field, and a ray tracing approach. The results help to select targets for deep observations and can be used in actual detection experiments. We highlight predictions for the Hercules Cluster, the Coma Cluster, Abell 2199, Abell 2255, the Lockman Hole and the Ursa Major Supercluster. At degree-scale resolution, the median specific intensity reaches $m_{I_\nu} \sim 10^{-1}\ \xi_e\ \mathrm{Jy\ deg^{-2}}$, where $\xi_e$ is the electron acceleration efficiency.

Coherent radio emission from pulsars originates from excited plasma waves in an ultra-relativistic and strongly magnetized electron-positron pair plasma streaming along the open magnetic field lines of the pulsar. Traditional coherent radio emission models have relied on instabilities in this pair plasma. Recently alternative models have been suggested. These models appeal to direct coupling of the external electromagnetic field to the superluminal O-mode ($lt_2$ mode) during the time-dependent pair cascade process at the polar gap. The objective of this work is to provide generic constraints on plasma models based on $lt_2$ mode using realistic pulsar parameters. We find that the very short timescale associated with pair cascades does not allow $lt_{2}$ mode to be excited at radio frequencies and the impulsive energy transfer can only increase the kinetic spread ("temperature") of the pair plasma particles. Moreover, under homogeneous plasma conditions, plasma waves on both branches of O-mode (i.e. superluminal $lt_2$ and subluminal $lt_1$) cannot escape the plasma. In the strongly magnetized pair plasma, only the extraordinary mode ($t$ mode) can escape freely. We show that any generic fictitious mechanisms does not result in the wave electric field of $t$ mode to have predominant orientation either or perpendicular to the magnetic field plane as observed. Such fictitious mechanisms will inevitably lead to depolarization of signals and cannot account for the highly polarized single pulses observed in pulsars. We suggest coherent curvature radiation as a promising candidate for pulsar radio emission mechanism.

Observations of the eclipsing binary system V471 Tau show that the time of the primary eclipses varies in an apparent periodic way. With growing evidence that the magnetically active K2 dwarf component might be responsible for driving the eclipse timing variations (ETVs), it is necessary to monitor the star throughout the predicted ~ 35 yr activity cycle that putatively fuels the observed ETVs. We contribute to this goal with this paper by analysing spectropolarimetric data obtained with ESPaDOnS at the Canada-France-Hawaii Telescope in December 2014 and January 2015. Using Zeeman-Doppler Imaging, we reconstruct the distribution of brightness inhomogeneities and large-scale magnetic field at the surface of the K2 dwarf. Compared to previous tomographic reconstructions of the star carried out with the same code, we probe a new phase of the ETVs cycle, offering new constraints for future works exploring whether a magnetic mechanism operating in the K2 dwarf star is indeed able to induce the observed ETVs of V471 Tau.

Cosmological constraints from current and upcoming galaxy cluster surveys are limited by the accuracy of cluster mass calibration. In particular, optically identified galaxy clusters are prone to selection effects that can bias the weak lensing mass calibration. We investigate the selection bias of the stacked cluster lensing signal associated with optically selected clusters, using as case study clusters identified by the redMaPPer algorithm in the Buzzard simulations. We find that at a given cluster halo mass, the residuals of redMaPPer richness and weak lensing signal are positively correlated. As a result, for a given richness selection, the stacked lensing signal is biased high compared with what we would expect from the underlying halo mass probability distribution. The cluster lensing selection bias can thus lead to overestimated mean cluster mass and biased cosmology results. We show that this selection bias largely originates from spurious member galaxies within +/-20 to 60 Mpc/h along the line of sight, highlighting the importance of quantifying projection effects associated with the broad redshift distribution of member galaxies in photometric cluster surveys. While our results qualitatively agree with those in the literature, precise quantitative modelling of selection bias is needed to achieve the goals of cluster lensing cosmology. An accurate calibration of the cluster lensing selection bias will require synthetic catalogues covering a wide range of galaxy-halo connection models.

We propose a new method for retrieving the atmospheric number density profile in the lower thermosphere, based on the X-ray Earth occultation of the Crab Nebula with the Hard X-ray Modulation Telescope (\emph{Insight}-HXMT) Satellite. The absorption and scattering of X-rays by the atmosphere result in changes in the X-ray energy, and the Earth's neutral atmospheric number density can be directly retrieved by fitting the observed spectrum and spectrum model at different altitude ranges during the occultation process. The pointing observations from LE/\emph{Insight}-HXMT on 16 November 2017 are analyzed to obtain high-level data products such as lightcurve, energy spectrum and detector response matrix. The results show that the retrieved results based on the spectrum fitting in the altitude range of 90--200 km are significantly lower than the atmospheric density obtained by the NRLMSISE-00 model, especially in the altitude range of 110--120 km, where the retrieved results are 34.4\% lower than the model values. The atmospheric density retrieved by the new method is qualitatively consistent with previous independent X-ray occultation results (Determan et al., 2007; Katsuda et al., 2021), which are also lower than empirical model predictions. In addition, the accuracy of atmospheric density retrieved results decreases with the increase of altitude in the altitude range of 150--200 km, and the accurate quantitative description will be further analyzed after analyzing a large number of X-ray occultation data in the future.

This paper describes a collaborative experience to empower organized communities to produce, curate and disseminate environmental data. A particular emphasis is done on the description of open hardware & software architecture and the processes of commissioning of the low cost Arduino-Raspberry-Pi weather station which measures: atmospheric pressure, temperature, humidity, precipitation, cloudiness, and illuminance/irradiance. The idea is to encourage more people to replicate this open-science initiative. We have started this experience training students & teachers from seven mid secondary schools through a syllabus of 12 two-hours lectures with a web-based support which exposes them to basic concepts and practices of Citizen Science and Open Data Science.

We explore the structural and kinematic properties of the outskirts of the Large Magellanic Cloud (LMC) using data from the Magellanic Edges Survey (MagES) and Gaia EDR3. Even at large galactocentric radii ($8^\circ<R<11^\circ$), we find the north-eastern LMC disk is relatively unperturbed: its kinematics are consistent with a disk of inclination ~$36.5^\circ$ and line-of-nodes position angle ~$145^\circ$ east of north. In contrast, fields at similar radii in the southern and western disk are significantly perturbed from equilibrium, with non-zero radial and vertical velocities, and distances significantly in front of the disk plane implied by our north-eastern fields. We compare our observations to simple dynamical models of the Magellanic/Milky Way system which describe the LMC as a collection of tracer particles within a rigid potential, and the Small Magellanic Cloud (SMC) as a rigid Hernquist potential. A possible SMC crossing of the LMC disk plane ~400 Myr ago, in combination with the LMC's infall to the Milky Way potential, can qualitatively explain many of the perturbations in the outer disk. Additionally, we find the claw-like and arm-like structures south of the LMC have similar metallicities to the outer LMC disk ([Fe/H]~-1), and are likely comprised of perturbed LMC disk material. The claw-like substructure is particularly disturbed, with out-of-plane velocities >60 km s$^{-1}$ and apparent counter-rotation relative to the LMC's disk motion. More detailed N-body models are necessary to elucidate the origin of these southern features, potentially requiring repeated interactions with the SMC prior to ~1 Gyr ago.

We report the discovery and characterization of a new symbiotic star of the accreting-only variety, which we observed in the optical/near-infrared (NIR) with VLT/X-Shooter and in the X-rays/ultraviolet with Swift/UVOT+XRT. The new symbiotic star, THA 15-31, was previously described as a pre-main sequence star belonging to the Lupus~3 association. Our observations, ancillary data, and Gaia EDR3 parallax indicate that THA 15-31 is a symbiotic star composed of an M6III red giant and an accreting companion, is subject to E(B-V)=0.38 reddening, and is located at a distance of ~12 kpc and at 1.8 kpc above the Galactic plane in the outskirts of the Bulge. The luminosity of the accreting companion is ~100 Lsun, placing THA 15-31 among the symbiotic stars accreting at a high rate (2.5e-08 Msun/yr if the accretion is occurring on a white dwarf of 1 Msun). The observed emission lines originate primarily from HI, HeI, and FeII, with no HeII or other high-excitation lines observed; a sharp central absorption superimposed on the Balmer emission lines is observed, while all other lines have a simple Gaussian-like profile. The emission from the companion dominates over the M6III red giant at $U$ and $B$-band wavelengths, and is consistent with an origin primarily in an optically thick accretion disk. No significant photometric variability is observed at optical or NIR wavelengths, suggesting either a face-on orbital orientation and/or that the red giant is far from Roche-lobe filling conditions. The profile of emission lines supports a low orbital inclination if they form primarily in the accretion disk. An excess emission is present in AllWISE W3 (12 micron) and W4 (22 micron) data, radiating a luminosity ~35 Lsun, consistent with thermal emission from optically thin circumstellar dust.

Observatory end-to-end science operations is the overall process starting with a scientific question, represented by a proposal requesting observing time, and ending with the analysis of observation data addressing that question, and including all the intermediate steps needed to plan, schedule, obtain, and process these observations. Increasingly complex observing facilities demand a highly efficient science operations approach and at the same time be user friendly to the astronomical user community and enable the highest possible scientific return. Therefore, this process is supported by a collection of tools. In this paper, we describe the overall end-to-end process and its implementation for the three upcoming extremely large telescopes (ELTs), ESO's ELT, the Thirty Meter Telescope (TMT), and the Giant Magellan Telescope (GMT).

Observations of astrophysical transients have brought many novel discoveries and provided new insights into physical processes at work under extreme conditions in the Universe. Multi-wavelength and multi-messenger observations of variable objects require dedicated procedures and follow-up systems capable of digesting and reacting to external alerts to execute coordinated follow-ups. The main functions of such follow-up systems are the processing, filtering, and ranking of incoming alerts, the fully automated rapid execution of the observations according to an observation strategy tailored to the instrument, and real-time data analysis with feedback to the operators and other instruments. H.E.S.S. has been searching for transient phenomena since its inauguration in 2003. In this paper, we describe the transients follow-up system of H.E.S.S, which became operational in 2016. The transients follow-up system allows H.E.S.S. to conduct a more versatile, optimised, and largely autonomous transient follow-up program, combining all major functionalities in one systematic approach. We describe the design, central functionalities, and interfaces of the transients follow-up system in general and its three main components in detail: the Target of Opportunity (ToO) alert system, the data acquisition and central control system, and the real-time analysis. We highlight architectural decisions and detailed features that enable fully automatic ToO follow-up and indicate key performance metrics of the sub-systems. We discuss the system's capabilities and highlight the need for a fine-tuned interplay of the different sub-systems to react quickly and reliably. Lessons learnt from the development, integration, and operation of the H.E.S.S. transients follow-up system are reviewed in light of new and large science infrastructures and associated challenges in this exciting new era of interoperable astronomy.

We present [K/Fe] abundance ratios for a sample of 450 stars in Omega Centauri, using high resolution spectra acquired with the multi-object spectrograph FLAMES@VLT. Abundances for Fe, Na and Mg were also derived. We detected intrinsic K variations in the analysed stars. Moreover, [K/Fe] shows a significant correlation with [Na/Fe] and anti-correlation with [Mg/Fe]. The presence of a clear-cut Mg-K anti-correlation makes Omega Centauri the third stellar system, after NGC 2419 and NGC 2808, hosting a sub-population of stars with [Mg/Fe]<0.0 dex, K-enriched in the case of Omega Centauri by ~0.3 dex with respect to the Mg-rich stars ([Mg/Fe]>0.0 dex). The correlation/anti-correlation between K and other light elements involved in chemical anomalies supports the idea that the spread in [K/Fe] can be associated to the same self-enrichment process typical of globular clusters. We suggest that significant variations in K abundances perhaps can be found in the most massive and/or metal-poor globular clusters as manifestation of an extreme self-enrichment process. Theoretical models face problems to explain the K production in globular clusters. Indeed, models where asymptotic giant branch stars are responsible for the Mg-K anti-correlation only qualitatively agree with the observations. Finally, we discovered a peculiar star with an extraordinary K overabundance ([K/Fe]=+1.60 dex) with respect to the other stars with similar [Mg/Fe]. We suggest that this K-rich star could be formed from the pure ejecta of AGB stars before dilution with pristine material.

Large scale surveys open the possibility to investigate Galactic evolution both chemically and kinematically, however, reliable stellar ages remain a major challenge. Detailed chemical information provided by high-resolution spectroscopic surveys of the stars in clusters can be used as a means to calibrate recently developed chemical tools for age-dating field stars. Using data from the Open Cluster Abundances and Mapping (OCCAM) survey, based on the SDSS/APOGEE-2 survey, we derive a new empirical relationship between open cluster stellar ages and the carbon-to-nitrogen ([C/N]) abundance ratios for evolved stars, primarily those on the red giant branch. With this calibration, [C/N] can be used a chemical clock for evolved field stars to investigate the formation and evolution of different parts of our Galaxy. We explore how mixing effects at different stellar evolutionary phases, like the red clump, affect the derived calibration. We have established the [C/N]-age calibration for APOGEE DR17 giant star abundances to be $\log[Age({\rm yr})]_{\rm DR17} = 10.14 \, (\pm 0.08) + 2.23\,(\pm 0.19) \, {\rm [C/N]}$, usable for $8.62 \leq \log(Age[{\rm yr}]) \leq 9.82$, derived from a uniform sample of 49 clusters observed as part of APOGEE DR17 applicable primarily to metal-rich, thin and thick disk giant stars. This measured [C/N]-age APOGEE DR17 calibration is also shown to be consistent with astereoseismic ages derived from Kepler photometry.

The mean apparent magnitude and the mean of magnitudes adjusted to a standard distance are reported. The illumination phase function for OneWeb satellites is determined and it differs strongly from that of VisorSat spacecraft. Brightness flares are characterized and the mean rate of magnitude variation during a pass is determined. Tools for planning observations that minimize interference from bright satellites are illustrated and discussed.

We present the first detailed study on the Galactic supernova remnant (SNR) G46.8-0.3 and its environment since its discovery more than 50 years ago. With new flux measurements from radio surveys plus a compilation from the literature we created an improved integrated radio spectrum of G46.8-0.3, which is well fitted by a simple power-law with an index alpha = -0.535 +/- 0.012, then excluding the presence of absorption by abundant ionised gas in the line of sight, or in the SNR's proximity. The analysis of local changes in the radio spectral index across G46.8-0.3 suggests a slight steepening at about 1 GHz, which does not impact on the integrated spectrum of the source. From atomic hydrogen (HI) spectra we placed the remnant at 8.7 +/- 1.0 kpc, and revisited the distance to the nearby HII region G046.495-00.241 to 7.3 +/- 1.2 kpc. From evolutionary models and our distance estimate, we conclude G46.8-0.3 is a middle-aged ($\sim$1 x 10^4 yr) SNR. We recognised several 12CO and 13CO molecular structures in the proximity of the remnant and used combined CO-HI profiles to derive the kinematic distances to these features and characterise their physical properties. We also provided compelling evidences for environmental molecular clouds physically linked to G46.8-0.3 at its centre, on its eastern edge, and towards the northern and southwestern rims on the far side of the SNR shell. Our study does not confirm that the remnant is embedded in a molecular cavity as previously suggested. G46.8-0.3 shows a line-of-sight coincidence with the gamma-ray source 4FGL J1918.1+1215c, detected at GeV energies by the space telescope Fermi. A rough analysis based on the properties of the interstellar matter close G46.8-0.3 indicates that the GeV gamma-rays photons detected in direction to the SNR can be plausibly attributed to hadronic collisions and/or bremsstrahlung radiation.

Some important predictions from 4 main models of spiral arm formation are tested here, using observational data acquired for the Milky Way galaxy. Many spiral arm models (density wave, tidal wave, nuclear Lyapunov tube, or dynamic transient wave) have some consistencies with some of the observations, and some inconsistencies. Our 4 tests consist of the relative locations and relative speeds of different arm tracers away from the dust lane, and the global arm pitch angle as obtained over two Galactic quadrants and several Galactic radii, as well as the arm's continuity of shape from Galactic quadrant IV to Galactic quadrant I. In the Milky Way, an age gradient is observed from different arm tracers, amounting to 12.9 +/-1.1 Myrs/kpc, or a relative speed away from the dust lane of 76 +/-10 km/s. The presence of an age gradient is predicted by the density waves, but is not consistent with the predictions of the tidal waves, of the nuclear Lyapunov tubes, nor of the dynamic transient recurrent waves.

With the inception of gravitational wave astronomy, astrophysical studies using interferometric techniques have begun to probe previously unknown parts of the universe. In this work, we investigate the potential of a new interferometric experiment to study a unique group of gravitationally interacting sources within our solar system: binary asteroids. We present the first study into binary asteroid detection via gravitational signals. We identify the interferometer sensitivity necessary for detecting a population of binary asteroids in the asteroid belt. We find that the space-based gravitational wave detector LISA will have negligible ability to detect these sources as these signals will be well below the LISA noise curve. Consequently, we propose a 4.6 AU and a 1 AU arm-length interferometers specialized for binary asteroid detection, targeting frequencies between $10^{-6}$ and $10^{-4}$ Hz. Our results demonstrate that the detection of binary asteroids with space-based gravitational wave interferometers is possible though very difficult, requiring substantially improved interferometric technology over what is presently proposed for space-based missions. If that threshold can be met, an interferometer may be used to map the asteroid belt, allowing for new studies into the evolution of our solar system.

We present a $z = 0.94$ quasar, SDSS J004846.45-004611.9, discovered in the SDSS-III BOSS survey. A visual analysis of this spectrum reveals highly broadened and blueshifted narrow emission lines, in particular [Ne~V]$\lambda3426$ and [O~III]$\lambda5007$, with outflow velocities of 4000 km s$^{-1}$, along with unusually large [Ne V]$\lambda3426$/[Ne III]$\lambda3869$ ratios. The gas shows higher ionization at higher outflow velocities, indicating a connection between the powerful outflow and the unusual strength of the high ionization lines. The SED and the $i - \text{W3}$ color of the source reveal that it is likely a "core" Extremely Red Quasar (core ERQ); a candidate population of young AGN that are violently "blowing out" gas and dust from their centers. The dominance of host galaxy light in its spectrum and its fortuitous position in the SDSS S82 region allows us to measure its star formation history and investigate for variability for the first time in an ERQ. Our analysis indicates that SDSS J004846.45-004611.9 underwent a short-lived starburst phase 400 Myr ago and was subsequently quenched, possibly indicating a time-lag between star formation quenching and the onset of AGN activity. We also find that the strong extinction can be uniquely attributed to the AGN and does not persist in the host galaxy, contradicting a scenario where the source has recently transitioned from being a dusty sub-mm galaxy. In our relatively shallow photometric data, the source does not appear to be variable at $0.24-2.4~\mu$m in the restframe, most likely due to the dominant contribution of host galaxy starlight at these wavelengths.

Despite the increasing sophistication of numerical models of hot Jupiter atmospheres, the large time-scale separation required in simulating the wide range in electrical conductivity between the dayside and nightside has made it difficult to run fully consistent magnetohydrodynamic (MHD) models. This has led to many studies that resort to drag parametrizations of MHD. In this study, we revisit the question of the Lorentz force as an effective drag by running a series of direct numerical simulations of a weakly rotating, poorly conducting flow in the presence of a misaligned, strong background magnetic field. We find that the drag parametrization fails once the time-scale associated with the Lorentz force becomes shorter than the dynamical time-scale in the system, beyond which the effective drag coefficient remains roughly constant, despite orders-of-magnitude variation in the Lorentz (magnetic) time-scale. We offer an improvement to the drag parametrization by considering the relevant asymptotic limit of low conductivity and strong background magnetic field, known as the quasi-static MHD approximation of the Lorentz force. This approximation removes the fast time-scale associated with magnetic diffusion, but retains a more complex version of the Lorentz force, which could be utilized in future numerical models of hot Jupiter atmospheric circulation.

We study binary systems in which a stellar mass compact object spirals into a massive black hole, known as extreme mass ratio inspirals, in scenarios with a new fundamental scalar field. Earlier work has shown that, in most interesting such scenarios and to leading order in the mass ratio, the massive black holes can be adequately approximated by the Kerr metric and the imprint of the scalar field on the waveform is fully controlled by the scalar charge of the stellar mass object. Here we use this drastic simplification in the inspiral modelling and consider eccentric equatorial orbits. We study how the scalar charge affects the orbital evolution for different eccentricities and different values of the black hole spin. We then determine how changes in the orbital evolution get imprinted on the waveform and assess LISA's capability to detect or constrain the scalar charge.

The Standard Model of Particle Physics cannot explain the observed baryon asymmetry of the Universe. This observation is a clear sign of new physics beyond the Standard Model. There have been many recent theoretical developments to address this question. Critically, many new physics models that generate the baryon asymmetry have a wide range of repercussions for many areas of theoretical and experimental particle physics. This white paper provides an overview of such recent theoretical developments with an emphasis on experimental testability.

The process of Compton scattering by a free electron with subsequent reemission of one or two photons is considered in the assumption of finite interaction time. The corresponding cross sections are obtained in the framework of relativistic quantum electrodynamics using a modified form of fermion propagator with complex transmitted momentum. It is shown that finite time effects can be observable at sufficiently low energies of scattered photons. The proposed method also regularizes arising infrared divergence in the cross section of the double Compton effect. Possible experimental verification of considered theoretical approach is discussed.

We discuss gauge theories of scale invariance beyond the Standard Model (SM) and Einstein gravity. We show that the non-metricity of their underlying 4D geometry is at the origin of mass generation and discuss phenomenological implications. Examples of such theories are Weyl's original quadratic gravity theory and its Palatini formulation. Non-metricity leads to spontaneous breaking of this gauged scale symmetry to Einstein gravity. All mass scales: the Planck scale, the cosmological constant and the mass ($m_\omega$) of the Weyl gauge boson of scale symmetry ($\omega_\mu$) are proportional to a scalar field vev that has a (non-metric) geometric origin, in the $\tilde R^2$ term. With $\omega_\mu$ of geometric origin, the SM Higgs field has a (non-metric) geometric origin too, being generated by Weyl boson fusion in the early Universe. This appears as a microscopic realisation of "matter creation from geometry" discussed in the thermodynamics of open systems applied to cosmology. Unlike in a locally scale invariant theory (no $\omega_\mu$ present) with an underlying (metric) pseudo-Riemannian geometry, here there are no ghost degrees of freedom or additional fields beyond the SM and their underlying Weyl/Palatini geometry, the cosmological constant is predicted positive and their connection shares the symmetry of the action. An intuitive picture of non-metricity in solid state physics is also provided, where it is associated with point defects (metric anomalies) of the crystalline structure.

The study of the equation of state (EOS) for nuclear matter has been still a challenging problem, although the EOS is essential for determining the properties of neutron stars. In order to constrain the EOS, several studies have been based on astronomical observations with the X-ray and gravitational waves, which mainly cover the higher density of neutron star matter. In this study, focusing on the relatively lower density region, we show an allowed area in the neutron-star mass and radius relation by using the constraints on the density-dependence of the nuclear symmetry energy obtained via the recent nuclear experiments with different projects (i.e., S$\pi$RIT and PREX-II) together with the experiment at RCNP. Each region predicted by these experiments is still consistent with the area in the higher density allowed by the various astronomical observations. Our results show that terrestrial nuclear experiments must provide further constraints on the EOS for neutron stars, complementing astronomical observations.

We review the study of dissociative recombination and ro-vibrational excitation of diatomic and small polyatomic molecular ions initiating complex organic molecules formation. In particular, we show how Multichannel Quantum Defect Theory (MQDT) and R-matrix methods are used to compute cross sections and rate coefficients for cations in well defined ro-vibrational levels of the ground electronic state, from sub-meV up to few eV collision energies. The most recent MQDT results are compared with either other theoretical data, or with measured data obtained in storage-ring experiments.