Papers for Thursday, Jun 10 2021

The extents of proximity zones of high-redshift quasars enable constraints on the timescales of quasar activity, which are fundamental for understanding the growth of the supermassive black holes (SMBHs) that power the quasars' emission. In this study, we obtain precise estimates for the ultraviolet (UV) luminous lifetimes of ten quasars at $5.8< z< 6.5$. These objects were pre-selected to have short lifetimes based on preliminary measurements of their proximity zone sizes, and were then targeted for high quality follow-up sub-mm, optical, and infrared observations required to increase the measurements' precision and securely determine their lifetimes. By comparing these proximity zone sizes to mock quasar spectra generated from radiative transfer simulations at a range of different lifetimes, we deduce extremely short lifetimes $t_{\rm Q}<10^4$ yr for four objects in our sample, whereas the remaining quasars are consistent with longer lifetimes of $t_{\rm Q}\gtrsim 10^5$ yr. These young objects with small proximity zones represent $\lesssim10\%$ of the quasar population as a whole. We compare our results in detail to other studies on timescales of quasar activity, which point towards an average lifetime of $t_{\rm Q}\sim10^6$ yr for the quasar population. This is consistent with finding newly turned on quasars approximately $\sim 1-10\%$ of the time. These young quasars represent an unique opportunity to study triggering and feedback mechanisms of SMBHs, since the onset of their UV luminous quasar phase happened only recently, and therefore traces of this process might still be observable.

The evolution of satellite galaxies is shaped by their constant interaction with the circum galactic medium surrounding central galaxies, which in turn may be affected by gas and energy ejected from the central supermassive black hole. However, the nature of this coupling between black holes and galaxies is highly debated and observational evidence remains scarce. Here we report an analysis of archival data on 124,163 satellite galaxies in the potential wells of 29,631 dark matter halos with masses between 10$^{12}$ and $10^{14}$ solar masses. We find that quiescent satellites are relatively less frequent along the minor axis of their central galaxies. This observation might appear counterintuitive as black hole activity is expected to eject mass and energy preferentially in the direction of the minor axis of the host galaxy. However, we show that the observed signal results precisely from the ejective nature of black hole feedback in massive halos, as active galactic nuclei-powered outflows clear out the circumgalactic medium, reducing the ram pressure and thus preserving star formation. This interpretation is supported by the IllustrisTNG suite of cosmological numerical simulations, where a similar modulation is observed even though the sub-grid implementation of black hole feedback is effectively isotropic. Our results provide compelling observational evidence for the role of black holes in regulating galaxy evolution over spatial scales differing by several orders of magnitude.

We investigate and quantify the impact of mixed (cold and warm) dark matter models on large-scale structure observables. In this scenario, dark matter comes in two phases, a cold one (CDM) and a warm one (WDM): the presence of the latter causes a suppression in the matter power spectrum which is allowed by current constraints and may be detected in present-day and upcoming surveys. We run a large set of $N$-body simulations in order to build an efficient and accurate emulator to predict the aforementioned suppression with percent precision over a wide range of values for the WDM mass, $M_\mathrm{wdm}$, and its fraction with respect to the totality of dark matter, $f_\mathrm{wdm}$. The suppression in the matter power spectrum is found to be independent of changes in the cosmological parameters at the 2% level for $k\lesssim 10 \ h/$Mpc and $z\leq 3.5$. In the same ranges, by applying a baryonification procedure on both $\Lambda$CDM and CWDM simulations to account for the effect of feedback, we find a similar level of agreement between the two scenarios. We examine the impact that such suppression has on weak lensing and angular galaxy clustering power spectra. Finally, we discuss the impact of mixed dark matter on the shape of the halo mass function and which analytical prescription yields the best agreement with simulations. We provide the reader with an application to galaxy cluster number counts.

Non-thermal desorption of ices on interstellar grains is required to explain observations of molecules that are not synthesized efficiently in the gas phase in cold dense clouds. Perhaps the most important non-thermal desorption mechanism is one induced by cosmic rays (CRs), which, when passing through a grain, heat it transiently to a high temperature - the grain cools back to its original equilibrium temperature via the (partial) evaporation of the ice. Current cosmic-ray-induced desorption (CRD) models assume that the ice consists of a homogeneous layer of a generic CO-like volatile molecule, leading to a fixed grain cooling time. In this work we present a revised description of CRD in which the desorption efficiency depends dynamically on the ice content. We apply the revised desorption scheme to two-phase and three-phase chemical models in physical conditions corresponding to starless and prestellar cores, and to molecular clouds surrounding the cores. We find that inside starless and prestellar cores, introducing dynamic CRD in general decreases gas-phase abundances in two-phase chemical models, and increases gas-phase abundances in three-phase chemical models - dynamic CRD helps to retain appreciable gas-phase abundances in three-phase chemical models. In molecular cloud conditions, we find variations in ice abundances that can exceed five orders of magnitude; dynamic CRD suppresses the formation of lightly-bound molecules in the ice at low visual extinctions. Further improved CRD models need to take into account additional effects in the transient heating of the grains, introduced for example by the adoption of a spectrum of CR energies.

We explore an alternative method to the usual shear correlation function approach for the estimation of aperture mass statistics in weak lensing survey data. Our approach builds on the direct estimator method. In this paper, we extend our analysis to statistics of arbitrary order and to the multiscale aperture mass statistics. We show that there always exists a linear order algorithm to retrieve any of these generalised aperture mass statistics from shape catalogs when the direct estimator approach is adopted. We validate our approach through application to a large number of Gaussian mock lensing surveys where the true answer is known and we do this up to 10th order statistics. We then apply our estimators to an ensemble of real-world mock catalogs obtained from N-body simulations - the SLICS mocks, and show that one can expect to retrieve detections of higher order clustering up to fifth order in a KiDS-1000 like survey. We expect that these methods will be of most utility for future wide-field surveys like Euclid and the Rubin Telescope.

The IR emission of dust heated by stars provides critical information for galaxy evolution studies. Unfortunately, observations are often limited to the MIR, making templates a necessity. Previously published templates were based on small samples of luminous galaxies, not necessarily representative of normal star-forming galaxies. We construct new dust templates, including instrument-specific relations and software tools that facilitate the estimation of the TIR luminosity and SFR based on one or several fluxes up to z=4. For the first time the templates include a dependence on both TIR luminosity and the sSFR, thereby increasing their reliability and utility. We also provide formulae for calculating TIR luminosities and SFR from JWST F2100W observations at 0<z<2. Our templates are based on 2584 normal star-forming galaxies spanning a wide range of stellar mass and sSFR, including sSFRs typical at higher redshifts. IR spectra and properties are obtained using CIGALE and the Draine & Li (2007) dust models. The photometry from the GALEX-SDSS-WISE Legacy Catalog is supplemented with 2MASS and H-ATLAS, from FUV to 500 microns. The shape of the dust spectrum varies with TIR luminosity, but also independently with sSFR. Remarkably precise estimates of the dust luminosity are possible with a single band over the rest-frame 12-17 and 55-130 microns. We validate single-band estimates on diverse populations, including local LIRGs, and find no significant systematic errors. Using two or more bands simultaneously yields unbiased estimation of the TIR luminosity even of star-forming dwarfs. We obtain fresh insights regarding the interplay between monochromatic IR luminosities, spectral shapes and physical properties, and construct new templates and estimators of the dust luminosity and SFR. We provide software for generating templates and estimating these quantities based on 1-4 bands up to z=4.

Integrated photonic spectrographs offer an avenue to extreme miniaturization of astronomical instruments, which would greatly benefit extremely large telescopes and future space missions. These devices first require optimization for astronomical applications, which includes design, fabrication and field-testing. Given the high costs of photonic fabrication, Multi-Project Wafer (MPW) SiN offerings, where a user purchases a portion of a wafer, provide a convenient and affordable avenue to develop this technology. In this work we study the potential of two commonly used SiN waveguide geometries by MPW foundries, i.e. square and rectangular profiles to determine how they affect the performance of mid-high resolution arrayed waveguide grating spectrometers around 1.5 $\mu$m. Specifically, we present results from detailed simulations on the mode sizes, shapes, and polarization properties, and on the impact of phase errors on the throughput and cross talk as well as some laboratory results of coupling and propagation losses. From the MPW-run tolerances and our phase-error study, we estimate that an AWG with R $\sim$ 10,000 can be developed with the MPW runs and even greater resolving power is achievable with more reliable, dedicated fabrication runs. Depending on the fabrication and design optimizations, it is possible to achieve throughputs $\sim 60\%$ using the SiN platform. Thus, we show that SiN MPW offerings are highly promising and will play a key role in integrated photonic spectrograph developments for astronomy.

Absorption-selected galaxies offer an effective way to study low-mass galaxies at high redshift. However, the physical properties of the underlying galaxy population remains uncertain. In particular, the multiphase circum-galactic medium is thought to hold key information on gas flows into and out of galaxies that are vital for galaxy evolution models. Here we present ALMA observations of CO molecular gas in host galaxies of H_2-bearing absorbers. In our sample of six absorbers we detect molecular gas-rich galaxies in five absorber fields although we did not target high-metallicity (>50 per cent solar) systems for which previous studies reported the highest detection rate. Surprisingly, we find that the majority of the absorbers are associated with multiple galaxies rather than single haloes. Together with the large impact parameters these results suggest that the H_2-bearing gas seen in absorption is not part of an extended disk, but resides in dense gas pockets in the circum-galactic and intra-group medium.

Our knowledge of white dwarf planetary systems predominately arises from the region within a few Solar radii of the white dwarfs, where minor planets break up, form rings and discs, and accrete onto the star. The entry location, angle and speed into this Roche sphere has rarely been explored but crucially determines the initial geometry of the debris, accretion rates onto the photosphere, and ultimately the composition of the minor planet. Here we evolve a total of over 10^5 asteroids with single-planet N-body simulations across the giant branch and white dwarf stellar evolution phases to quantify the geometry of asteroid injection into the white dwarf Roche sphere as a function of planetary mass and eccentricity. We find that lower planetary masses increase the extent of anisotropic injection and decrease the probability of head-on (normal to the Roche sphere) encounters. Our results suggest that one can use dynamical activity within the Roche sphere to make inferences about the hidden architectures of these planetary systems.

Type Iax supernovae represent the largest class of peculiar white-dwarf supernovae. The type Iax SN 2012Z in NGC 1309 is the only white dwarf supernova with a detected progenitor system in pre-explosion observations. Deep Hubble Space Telescope images taken before SN 2012Z show a luminous, blue source that we have interpreted as a helium-star companion (donor) to the exploding white dwarf. We present here late-time HST observations taken ~1400 days after the explosion to test this model. We find the SN light curve can empirically be fit by an exponential decay model in magnitude units. The fitted asymptotic brightness is within 10% of our latest measurements and approximately twice the brightness of the pre-explosion source. The decline of the light curve is too slow to be powered by $^{56}$Co or $^{57}$Co decay. Interaction with circumstellar material may play a role, as may shock heating of the companion star. Companion-star models underpredict the observed flux in the optical, producing most of their flux in the UV at these epochs. A radioactively-heated bound remnant, left after only a partial disruption of the white dwarf, can produce the excess late-time flux, but no models we tested could explain both the early and late-time light curves of SN 2012Z. Our analysis suggests that the total ejecta + remnant mass is consistent with the Chandrasekhar mass for a range of type Iax supernovae.

Communities of practice in science communication can make important contributions to public engagement with science but are under-researched. In this article, we look at the perspectives of a community of practice in astronomy communication regarding (relations with) their public(s). Most participants in this study consider that public(s) have several deficits and vulnerabilities. Moreover, practitioners have little to no contact with (and therefore make no use of) academic research on science communication. We argue that collaboration between science communication researchers and practitioners could benefit the science-public relationship and that communities of practice may be critical to that purpose.

The Vertical Shear Instability is an axisymmetric effect suggested to drive turbulence in the magnetically inactive zones of protoplanetary accretion disks. Here we examine its physical mechanism in analytically tractable ``minimal models" in three settings that include a uniform density fluid, a stratified atmosphere, and a shearing-box section of a protoplanetary disk. Each of these analyses show that the vertical shear instability's essence is similar to the slantwise convective symmetric instability in the mid-latitude Earth atmosphere, in the presence of vertical shear of the baroclinic jet stream, as well as mixing in the top layers of the Gulf Stream. We show that in order to obtain instability the fluid parcels' slope should exceed the slope of the mean absolute momentum in the disk radial-vertical plane. We provide a detailed and mutually self-consistent physical explanation from three perspectives: in terms of angular momentum conservation, as a dynamical interplay between a fluid's radial and azimuthal vorticity components, and from an energy perspective involving a generalized Solberg-H{\o}iland Rayleigh condition. Furthermore, we explain why anelastic dynamics yield oscillatory unstable modes and isolate the oscillation mechanism from the instability one.

Ionization of gas-phase organic molecules such as polycyclic aromatic hydrocarbons (PAHs) requires vacuum ultraviolet photons at wavelengths shorter than 200 nm (~6-9 eV). We present here for the first time that visible photons - accessible through sunlight - can cause photoionization of trapped PAHs in cryogenic water-ice, accounting for 4.4 eV less ionization energy than in the gas phase. This finding opens up new reaction pathways involving low-energy ionization in many environments where water and organic matter coexist. This include the interstellar medium, molecular clouds, protoplanetary disks, and planetary surfaces and atmospheres (including Earth).

The internal heat flows of both Uranus and Neptune remain major outstanding problems in planetary science. Uranus' surprisingly cold effective temperature is inconsistent with adiabatic thermal evolution models, while Neptune's substantial internal heat flow is twice its received insolation. In this work we constrain the magnitude of influence condensation, including latent heat and inhibition of convection, can have on the thermal evolution of these bodies. We find that while the effect can be significant, it is insufficient to solve the Uranus faintness problem on its own. Self-consistently considering the effects of both latent heat release and stable stratification, methane condensation can speed up the cool down time of Uranus and Neptune by no more than 15%, assuming 5% molar methane abundance. Water condensation works in the opposite direction; water condensation can slow down the cool down timescale of Uranus and Neptune by no more than 15% assuming 12% molar water abundance. We also constrain the meteorological implications of convective inhibition. We demonstrate that sufficiently abundant condensates will relax to a state of radiative-convective equilibrium requiring finite activation energy to disrupt. We also comment on the importance of considering convective inhibition when modeling planetary interiors.

Metallicity is a fundamental probe for understanding the baryon physics in a galaxy. Since metals are intricately associated with radiative cooling, star formation, and feedback, reproducing the observed metal distribution through numerical experiments will provide a prominent way to examine our understandings of galactic baryon physics. In this study, we analyze the dependence of the galactic metal distribution on the numerical schemes and quantify the differences in the metal mixing among modern galaxy simulation codes (the mesh-based code Enzo and the particle-based codes Gadget-2 and Gizmo-PSPH). In particular, we examine different stellar feedback strengths and an explicit metal diffusion scheme in particle-based codes, as a way to alleviate the well-known discrepancy in metal transport between mesh-based and particle-based simulations. We demonstrate that a sufficient number of gas particles are needed in the gas halo to properly investigate the metal distribution therein. Including an explicit metal diffusion scheme does not significantly affect the metal distribution in the galactic disk but does change the amount of low-metallicity gas in the hot-diffuse halo. We also find that the spatial distribution of metals depends strongly on how the stellar feedback is modeled. We demonstrate that the previously reported discrepancy in metals between mesh-based and particle-based simulations can be mitigated with our proposed prescription, enabling these simulations to be reliably utilized in the study of metals in galactic halos and the circumgalactic medium.

We present a multi-instrument spectroscopic analysis of the unique Li/Na-rich giant star 25664 in Omega Centauri using spectra acquired with FLAMES-GIRAFFE, X-SHOOTER, UVES and HARPS. Li and Na abundances have been derived from the UVES spectrum using transitions weakly sensitive to non-local thermodynamic equilibrium and assumed isotopic ratio. This new analysis confirms the surprising Li and Na abundances of this star (A(Li) =+2.71+-0.07 dex, [Na/Fe]=+1.00+-0.05 dex). Additionally, we provide new pieces of evidence for its chemical characterisation. The 12C/13C isotopic ratio (15+-2) shows that this star has not yet undergone the extra-mixing episode usually associated with the red giant branch bump. Therefore, we can rule out the scenario of efficient deep extra-mixing during the red giant branch phase envisaged to explain the high Li and Na abundances. Also, the star exhibits high abundances of both C and N ([C/Fe]=+0.45+-0.16 dex and [N/Fe]=+0.99+-0.20 dex), not compatible with the typical C-N anticorrelation observed in globular cluster stars. We found evidence of a radial velocity variability in 25664, suggesting that the star could be part of a binary system, likely having accreted material from a more massive companion when the latter was evolving in the AGB phase. Viable candidates for the donor star are AGB stars with 3-4 Msun and super-AGB stars (~7-8 Msun), both able to produce Li- and Na-rich material. Alternatively, the star could be formed from the pure ejecta of a super-AGB stars, before the dilution with primordial gas occurs.

We analyze the range rate residual data from Cassini's gravity experiment that cannot be explained with a static, zonally symmetric gravity field. In this paper we reproduce the data using a simple forward model of gravity perturbations from normal modes. To do this, we stack data from multiple flybys to improve sensitivity. We find a partially degenerate set of normal mode energy spectra which successfully reproduce the unknown gravity signal from Cassini's flybys. Although there is no unique solution, we find that the models most likely to fit the data are dominated by gravitational contributions from p-modes between 500-700uHz. Because f-modes at lower frequencies have stronger gravity signals for a given amplitude, this result would suggest strong frequency dependence in normal mode excitation on Saturn. We predict peak amplitudes for p-modes on the order of several kilometers, at least an order of magnitude larger than the peak amplitudes inferred by Earth-based observations of Jupiter. The large p-mode amplitudes we predict on Saturn, if they are indeed present and steady state, would imply weak damping with a lower bound of Q>1e7 for these modes, consistent with theoretical predictions.

In this work, we consider four $f(R)$ gravity models -- the Hu-Sawicki, Starobinsky, Exponential and Tsujikawa models -- and use a range of cosmological data, together with Markov Chain Monte Carlo sampling techniques, to constrain the associated model parameters. Our main aim is to compare the results we get when $\Omega_{k,0}$ is treated as a free parameter with their counterparts in a spatially flat scenario. The bounds we obtain for $\Omega_{k,0}$ in the former case are compatible with a flat geometry. It appears, however, that a higher value of the Hubble constant $H_0$ allows for more curvature. Indeed, upon including in our analysis a Gaussian likelihood constructed from the local measurement of $H_0$, we find that the results favor an open universe at a little over $1\sigma$. This is perhaps not statistically significant, but it underlines the important implications of the Hubble tension for the assumptions commonly made about spatial curvature. We note that the late-time deviation of the Hubble parameter from its $\Lambda$CDM equivalent is comparable across all four models, especially in the non-flat case. When $\Omega_{k,0}=0$, the Hu-Sawicki model admits a smaller mean value for $\Omega_{\text{cdm},0}h^2$, which increases the said deviation at redshifts higher than unity. We also study the effect of a change in scale by evaluating the growth rate at two different wavenumbers $k_\dagger$. Any changes are, on the whole, negligible, although a smaller $k_\dagger$ does result in a slightly larger average value for the deviation parameter $b$.

This article presents the results of a study concerning interstellar molecules which are useful for the bookkeeping of the organic content of the universe and for providing a glimpse into prebiotic conditions on Earth and in other environments in the universe. We explored production channels for astrobiological relevant nitrogen-bearing cyclic molecules (N-heterocycles), e. g. pyrrole and pyridine. The present simulations demonstrate how the exploration of a few possible routes of production of N-heterocycles resulted in significant abundances for these species. One particularly efficient class of channels for the production of N-heterocycles incorporates polycyclic aromatic hydrocarbons (PAHs) as catalysts. Thereby, an exploration of a variety of production paths should reveal more species to be target of astrophysical observations.

We present the first PSP-observed CME that hits a second spacecraft before the end of the PSP encounter, providing an excellent opportunity to study short-term CME evolution. The CME was launched from the Sun on 10 October 2019 and was measured in situ at PSP on 13 October 2019 and at STEREO-A on 14 October 2019. The small, but not insignificant, radial (~0.15 au) and longitudinal (~8 deg) separation between PSP and STEREO-A at this time allows for observations of both short-term radial evolution as well as investigation of the global CME structure in longitude. Although initially a slow CME, magnetic field and plasma observations indicate that the CME drove a shock at STEREO-A and also exhibited an increasing speed profile through the CME (i.e. evidence for compression). We find that the presence of the shock and other compression signatures at 1 au are due to the CME having been overtaken and accelerated by a high speed solar wind stream (HSS). We estimate the minimum interaction time between the CME and the HSS to be about 2.5 days, indicating the interaction started well before the CME arrival at PSP and STEREO-A. Despite alterations of the CME by the HSS, we find that the CME magnetic field structure is similar between the vantage points, with overall the same flux rope classification and the same field distortions present. These observations are consistent with the fact that coherence in the magnetic structure is needed for steady and continued acceleration of the CME.

\noindent Recently, it has been discovered that gaseous nickel and iron is present in most comets. To evaluate the state of the laboratory data in support of these identifications, we re-analyzed archived spectra of comet C/1996 B2 (Hyakutake), one of the nearest and brightest comets of the last century, using a combined experimental and computational approach. We developed a new, many-level fluorescence model that indicates that the fluorescence emission of Fe I and Ni I vary greatly with heliocentric velocity. Combining this model with laboratory spectra of an Fe-Ni plasma, we identified 23 lines of Fe I and 14 lines of Ni I in the spectrum of Hyakutake. Using Haser models, we estimate the nickel and iron production rates as $Q_\textrm{Ni} = 2.6 - 4.1\times10^{22}$~s$^{-1}$ and $Q_\textrm{Fe} = 0.4 - 2.6\times10^{23}$~s$^{-1}$. From derived column densities the Ni/Fe abundance ratio log$_{10}$[Ni/Fe] = $-0.38\pm0.06$ deviates significantly from solar, and it is consistent with the ratios observed in solar system comets. Spectra from several offset distances show profiles consistent with a short-lived parent and/or emissive photodissociation of an unknown parent species. Possible production and emission mechanisms are analyzed in context of existing laboratory measurements. Based on the observed spatial distributions, excellent fluorescence model agreement, and Ni/Fe ratio, our findings support an origin consisting of dissociation of an unknown parent followed by fluorescence emission. Our findings suggest that the strong heliocentric velocity dependence of the fluorescence efficiencies can provide a meaningful test of the physical process responsible for the Fe I and Ni I emission.

We present a detailed analysis of XMM-Newton X-ray spectra of the Narrow-Line Seyfert 1 galaxy Mrk 1044. We find robust evidence for a multi-phase, ultra-fast outflow, traced by four separate components in the grating spectrum. One component has high column density and ionization state, and is outflowing at 0.15c. The other three wind components have lower temperature, lower column density, and have outflow velocities 0.08c. This wind structure is strikingly similar to that found in IRAS 17020+4544, suggesting that stratified winds may be a common feature of ultra-fast outflows. Such structure is likely produced by fluid instabilities that form when the nuclear wind shocks the ambient medium. We show that in an energy-driven wind scenario, the wind in Mrk 1044 might carry enough energy to produce significant feedback on its host galaxy. We further discuss the implications of the presence of a fast wind in yet another NLS1 galaxy with high Eddington ratio.

Cometary outbursts offer a valuable window into the composition of comet nuclei with their forceful ejection of dust and volatiles in explosive events, revealing the interior components of the comet. Understanding how different types of outbursts influence the dust properties and volatile abundances to better interpret what signatures can be attributed to primordial composition and what features are the result of processing is an important task best undertaken with a multi-instrument approach. The European Space Agency \textit{Rosetta} mission to 67P/Churyumov-Gerasimenko carried a suite of instruments capable of carrying out this task in the near-nucleus coma with unprecedented spatial and spectral resolution. In this work we discuss two outbursts that occurred November 7 2015 and were observed by three instruments on board: the Alice ultraviolet spectrograph, the Visual Infrared and Thermal Imaging Spectrometer (VIRTIS), and the Optical, Spectroscopic, and Infrared Remote Imaging System (OSIRIS). Together the observations show that mixed gas and dust outbursts can have different spectral signatures representative of their initiating mechanisms, with the first outburst showing indicators of a cliff collapse origin and the second more representative of fresh volatiles being exposed via a deepening fracture. This analysis opens up the possibility of remote spectral classification of cometary outbursts with future work.

The Alice ultraviolet spectrograph on board the \textit{Rosetta} orbiter provided the first near-nucleus ultraviolet observations of a cometary coma from arrival at comet 67P/Churyumov-Gerasimenko in 2014 August through 2016 September. The characterization of atomic and molecular emissions in the coma revealed the unexpected contribution of dissociative electron impact emission at large heliocentric distances and during some outbursts. This mechanism also proved useful for compositional analysis, and Alice observed many cases that suggested elevated levels of the supervolatile \ce{O2}, identifiable in part to their emissions resulting from dissociative electron impact. In this paper we present the first two-dimensional UV maps constructed from Alice observations of atomic emission from 67P during an increase in cometary activity on 2015 November 7-8. Comparisons to observations of background coma and of an earlier collimated jet are used to describe possible changes to the near-nucleus coma and plasma. To verify the mapping method and place the Alice observations in context, comparisons to images derived from the MIRO and VIRTIS-H instruments are made. The spectra and maps we present show an increase in dissociative electron impact emission and an \ce{O2}/\ce{H2O} ratio of $\sim$0.3 for the activity; these characteristics have been previously identified with cometary outbursts seen in Alice data. Further, UV maps following the increases in activity show the spatial extent and emission variation experienced by the near-nucleus coma, informing future UV observations of comets that lack the same spatial resolution.

The vertical current sheet (VCS) trailing coronal mass ejections (CMEs) is the key place where the flare energy release and the CME buildup take place through magnetic reconnection. It is often studied from the edge-on perspective for the morphological similarity with the two-dimensional ``standard'' picture, but its three dimensional structure can only be revealed when the flare arcade is observed side on. The structure and dynamics in the so-called supra-arcade region thus contain important clues to the physical processes in flares and CMEs. Here we focus on the supra-arcade spikes (SASs), interpreted as the VCS viewed side-on, to study their spatiotemporal structures. By identifying each individual spike during the decay phase of four selected flares, in which the associated CME is traversed by a near-Earth spacecraft, we found that the widths of spikes are log-normal distributed, while the Fourier power spectra of the overall supra-arcade EUV emission, including bright spikes and dark downflows as well as the diffuse background, are power-law distributed, in terms of either spatial frequency $k$ or temporal frequency $\nu$, which reflects the fragmentation of the VCS. We demonstrate that coronal emission-line intensity observations dominated by Kolmogorov turbulence would exhibit a power spectrum of $E(k)\sim k^{-13/3}$ or $E(\nu)\sim \nu^{-7/2}$, which is consistent with our observations. By comparing the number of SASs and the turns of field lines as derived from the ICMEs, we found a consistent axial length of $\sim\,$3.5 AU for three events with a CME speed of $\sim\,$1000 km/s in the inner heliosphere, but a much longer axial length $\sim\,$8 AU) for the fourth event with an exceptionally fast CME speed of $\sim\,$1500 km/s, suggesting that this ICME is flattened and its `nose' has well passed the Earth when the spacecraft traversed its leg.

The open star clusters (OSC) are important tracers for understanding the Galactic evolution. The parametric study of these astronomical-objects is crucial task due to the appearing sequence of the members of OSC. These members are defined through the various approaches such as photometric, statistical, kinematics etc. In the present paper, we have been using the photometric colours of the identified stars for categorized them into the blue and red component groups and identification of these groups is possible through (B-V) vs V colour magnitude diagram (CMD). Furthermore, the influence/effect of these groups is also examined in the estimation of cluster parameters. The stellar enhancement of cluster NGC 6866 is found through the blue-component-stars (BCS) and the linear solution of best fitted values of King Models of the radial-densityprofile (RDP) gives the core radius as 5.22+/-0.29 arcmin. The good agreement of present estimated parameters of the cluster with the literature seems to be an effective evidence to consider BCS as the true representative of the cluster. The stellar distribution of the cluster shows continuous phenomena of the mass segregation. An effect of the incompleteness of photometric data is related to the mass-function slope values, which is found to be -3.80+/-0.11 and also shows the incremental nature with the incompleteness.

The flare-associated stellar coronal mass ejection (CME) in solar-like and late type stars is quite essential for the habitability of an exoplanet. In this paper, we report detection of flare-associated CMEs in two M-dwarfs, thanks to the high cadence survey carried out by the Ground Wide-angle Camera system and the fast photometric and spectroscopic follow-ups. The flare energy in $R-$band is determined to be $1.6\times10^{35}\ \mathrm{erg}$ and $8.1\times10^{33}\ \mathrm{erg}$ based on the modeling of their light curves. The time-resolved spectroscopyic observations start at about 20 and 40 minutes after the trigger in both cases. The large projected maximum velocity of $\sim500-700\ \mathrm{km\ s^{-1}}$ suggests that the high velocity wing of their H$\alpha$ emission lines are most likely resulted from a CME event in both stars, after excluding the possibility of chromospheric evaporation and coronal rain. The masses of the CMEs are estimated to be $1.5-4.5\times10^{19}\ \mathrm{g}$ and $7.1\times10^{18}\ \mathrm{g}$.

This paper presents an investigation of an old age open cluster King 11 using Gaia's Early Data Release 3 (EDR3) data. Considering the stars with membership probability ($P_{\mu}$) $> 90\%$, we identified 676 most probable cluster members within the cluster's limiting radius. The mean proper motion (PM) for King 11 is determined as: $\mu_{x}=-3.391\pm0.006$ and $\mu_{y}=-0.660\pm0.004$ mas yr$^{-1}$. The blue straggler stars (BSS) of King 11 show a centrally concentrated radial distribution. The values of limiting radius, age, and distance are determined as 18.51 arcmin, 3.63$\pm$0.42 Gyr and $3.33\pm0.15$ kpc, respectively. The cluster's apex coordinates ($A=267.84^{\circ} \pm 1.01^{\circ}$, $D=-27.48^{\circ} \pm 1.03^{\circ}$) are determined using the apex diagram (AD) method and verified using the ($\mu_U$,$\mu_T$) diagram. We also obtained the orbit that the cluster follows in the Galaxy and estimated its tentative birthplace in the disk. The resulting spatial velocity of King 11 is 60.2 $\pm$ 2.16 km s$^{-1}$. A significant oscillation along the $Z$-coordinate up to 0.556$\pm$0.022~kpc is determined.

A relativistic electron-positron ($e^{+}e^{-}$) pair wind from a rapidly rotating, strongly magnetized neutron star (NS) would interact with a gamma-ray burst (GRB) external shock and reshapes afterglow emission signatures. Assuming that the merger remnant of GW170817 is a long-lived NS, we show that a relativistic $e^{+}e^{-}$ pair wind model with a simple top-hat jet viewed off-axis can reproduce multi-wavelength afterglow lightcurves and superluminal motion of GRB 170817A. The Markov chain Monte Carlo (MCMC) method is adopted to obtain the best-fitting parameters, which give the jet half-opening angle $\theta_{j}\approx0.11$ rad, and the viewing angle $\theta_{v}\approx0.23$ rad. The best-fitting value of $\theta_{v}$ is close to the lower limit of the prior which is chosen based on the gravitational-wave and electromagnetic observations. In addition, we also derive the initial Lorentz factor $\Gamma_{0}\approx47$ and the isotropic kinetic energy $E_{\rm K,iso}\approx2\times10^{52}\rm\ erg$. A consistence between the corrected on-axis values for GRB 170817A and typical values observed for short GRBs indicates that our model can also reproduce the prompt emission of GRB 170817A. An NS with a magnetic field strength $B_{p}\approx1.6\times10^{13}\rm\ G$ is obtained in our fitting, indicating that a relatively low thermalization efficiency $\eta\lesssim10^{-3}$ is needed to satisfy observational constraints on the kilonova. Furthermore, our model is able to reproduce a late-time shallow decay in the X-ray lightcurve and predicts that the X-ray and radio flux will continue to decline in the coming years.

It has been recognized that the observed galaxy distribution is susceptible to long-wavelength density and tidal fluctuations whose wavelengths exceed the accessible scale of a finite-volume observation, referred to as the super-sample modes. The super-sample modes modulate the growth and expansion rate of local structures, thus affecting the cosmological information encoded in the statistics of galaxy clustering data. In this paper, based on the Lagrangian perturbation theory, we develop a new formalism to systematically compute the response of a biased tracer of matter distribution to the super-sample modes at the field level. The formalism presented here reproduces the power spectrum responses that have been previously derived, and beyond the leading order, it also enables us to proceed to a higher-order calculation. As an application, we consider the statistics of the intrinsic alignments of galaxies and halos, and derive the field response of the galaxy/halo ellipticity to the super-sample modes. Possible impacts of the long-mode contributions on the covariance of the power spectra are also discussed, and the signal-to-noise ratios are estimated.

Magnetars have been proposed to be the origin of FRBs soon after its initial discovery. The detection of the first Galactic FRB 20200428 from SGR 1935+2154 has made this hypothesis more convincing. In October 2020, this source was supposed to be in an extremely active state again. We then carried out a 1.6-hours follow-up observation of SGR 1935+2154 using the new ultra-wideband low (UWL) receiver of the Parkes 64\,m radio telescope covering a frequency range of 704$-$4032 MHz. However, no convincing signal was detected in either of our single pulse or periodicity searches. We obtained a limit on the flux density of periodic signal of $\rm 3.6\,\mu Jy$ using the full 3.3GHz bandwidth data sets, which is the strictest limit for that of SGR 1935+2154. Our full bandwidth limit on the single pulses fluence is 35mJy ms, which is well below the brightest single pulses detected by the FAST radio telescope just two before our observation. Assuming that SGR 1935+2154 is active during our observation, our results suggest that its radio bursts are either intrinsically narrowband or show a steep spectrum.

Two new equations of motion for a supernova remnant (SNR) are derived in the framework of energy conservation for the thin-layer approximation. The first one is based on an inverse square law for the surrounding density and the second one on a non-cubic dependence of the swept mass. Under the assumption that the observed radio-flux scales as the flux of kinetic energy, two scaling laws are derived for the temporal evolution of the surface brightness of SNRs. The astrophysical applications cover two galactic samples of surface brightness and an extragalactic one.

The Lyman-alpha forest is the large-scale structure probe for which we appear to have modeling control to the highest wavenumbers, which makes it of great interest for constraining the warmness/fuzziness of the dark matter and the timing of reionization processes. However, the standard statistic, the Lyman-alpha forest power spectrum, is unable to strongly constrain the IGM temperature-density relation, and this inability further limits how well other high wavenumber-sensitive parameters can be constrained. With the aim of breaking these degeneracies, we measure the power spectrum of the Lyman-beta forest and its cross correlation with the coeveal Lyman-alpha forest using the one hundred spectra of z=3.5-4.5 quasars in the VLT/X-Shooter XQ-100 Legacy Survey, motivated by the Lyman-beta transition's smaller absorption cross section that makes it sensitive to somewhat higher densities relative to the Lyman-alpha transition. Our inferences from this measurement for the IGM temperature-density relation appear to latch consistently onto the recent tight lower-redshift Lyman-alpha forest constraints of arXiv:2009.00016v1 [astro-ph.CO]. The z=3.4-4.7 trends we find using the Lyman-alpha--Lyman-beta cross correlation show a flattening of the slope of the temperature-density relation with decreasing redshift. This is the trend anticipated from ongoing HeII reionization and there being sufficient time to reach the asymptotic temperature-density slope after hydrogen reionization completes. Furthermore, our measurements provide a consistency check on IGM models that explain the Lyman-alpha forest, with the cross correlation being immune to systematics that are uncorrelated between the two forests, such as metal line contamination.

We analyze the effect of polarized diffuse emission in the calibration of wide-beam mm-wave polarimeters, when using the Crab Nebula as a reference source for both polarized brightness and polarization angle. We show that, for CMB polarization experiments aiming at detecting B-mode in a scenario with a tensor to scalar ratio $r \sim 0.001$, wide (a few degrees in diameter), precise ($\sigma_Q$ , $\sigma_U$ $\sim$ 20 $\mu$$K_{CMB}$ arcmin), high angular resolution ($< \mathrm{FWHM}$) reference maps are needed to properly take into account the effects of diffuse polarized emission and avoid significant bias in the calibration.

The Laser Interferometer Gravitational-wave Observatory Scientific Collaboration and Virgo Collaboration (LVC) sent out 56 gravitational-wave (GW) notices during the third observing run (O3). Japanese collaboration for Gravitational wave ElectroMagnetic follow-up (J-GEM) performed optical and near-infrared observations to identify and observe an electromagnetic (EM) counterpart. We constructed web-based system which enabled us to obtain and share information of candidate host galaxies for the counterpart, and status of our observations. Candidate host galaxies were selected from the GLADE catalog with a weight based on the three-dimensional GW localization map provided by LVC. We conducted galaxy-targeted and wide-field blind surveys, real-time data analysis, and visual inspection of observed galaxies. We performed galaxy-targeted follow-ups to 23 GW events during O3, and the maximum probability covered by our observations reached to 9.8%. Among them, we successfully started observations for 10 GW events within 0.5 days after the detection. This result demonstrates that our follow-up observation has a potential to constrain EM radiation models for a merger of binary neutron stars at a distance of up to $\sim$100~Mpc with a probability area of $\leq$ 500~deg$^2$.

High-velocity neutron stars (HVNSs) that were kicked out from their birth location can be potentially identified with their large proper motions, and possibly with large parallax, when they come across the solar neighborhood. In this paper, we study the feasibility of hunting isolated HVNSs in wide-area optical surveys by modeling the evolution of NS luminosity taking into account spin-down and thermal radiation. Assuming the upcoming 10-year VRO LSST observation, our model calculations predict that about 10 HVNSs mainly consisting of pulsars with ages of $10^4$--$10^5$ yr and thermally emitting NSs with $10^5$--$10^6$ yr are detectable. We find that a few NSs with effective temperature $< 5 \times 10^5$ K, which are likely missed in the current and future X-ray surveys, are also detectable. In addition to the standard neutron star cooling models, we consider a dark matter heating model. If such a strong heating exists we find that the detectable HVNSs would be significantly cooler, i.e., $\lesssim 5\times 10^5$ K. Thus, the future optical observation will give an unique NS sample, which can provide essential constraints on the NS cooling and heating mechanisms. Moreover, we suggest that providing HVNS samples with optical surveys is helpful for understanding the intrinsic kick-velocity distribution of NSs.

Standard stellar evolution model predicts a severe depletion of lithium (Li) abundance during the first dredge-up process (FDU). Yet a small fraction of giant stars are still found to preserve a considerable amount of Li in their atmospheres after FDU. Those giants are usually identified as Li-rich by a widely used criterion, A(Li) $ > 1.5$\,{\it dex}. A large number of works dedicated to search for and investigate this minority of the giant family, and the amount of Li-rich giants has been largely expanded, especially in the era of big data. In this paper, we present a catalog of Li-rich giants found from the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) survey with Li abundances derived from a template matching method developed for LAMOST low-resolution spectra. The catalog contains $10,535$ Li-rich giants with Li abundances from $\sim 1.5$\,{\it dex} to $\sim 4.9$\,{\it dex}. We also confirm that the ratio of Li-rich phenomenon among giant stars is about one percent, or for a more expression, $1.29\%$ from our statistically important sample. This is the largest Li-rich giant sample ever reported to date, which significantly exceeds amount of all the reported Li-rich giants combined. The catalog will help the community to better understand the Li-rich phenomenon in giant stars.

The underlying plasma composition of relativistic extragalactic jets remains largely unknown. Relativistic magnetohydrodynamic (RMHD) models are able to reproduce many of the observed macroscopic features of these outflows. The nonthermal synchrotron emission detected by very long baseline interferometric (VLBI) arrays, however, is a by-product of the kinetic-scale physics occurring within the jet, physics that is not modeled directly in most RMHD codes. This paper attempts to discern the radiative differences between distinct plasma compositions within relativistic jets using small-scale 3D relativistic particle-in-cell (PIC) simulations. We generate full Stokes imaging of two PIC jet simulations, one in which the jet is composed of an electron-proton ($e^{-}$-$p^{+}$) plasma (i.e., a normal plasma jet), and the other in which the jet is composed of an electron-positron ($e^{-}$-$e^{+}$) plasma (i.e., a pair plasma jet). We examined the differences in the morphology and intensity of the linear polarization (LP) and circular polarization (CP) emanating from these two jet simulations. We find that the fractional level of CP emanating from the $e^{-}$-$p^{+}$ plasma jet is orders of magnitude larger than the level emanating from an $e^{-}$-$e^{+}$ plasma jet of a similar speed and magnetic field strength. In addition, we find that the morphology of both the linearly and circularly polarized synchrotron emission is distinct between the two jet compositions. We also demonstrate the importance of slow-light interpolation and we highlight the effect that a finite light-crossing time has on the resultant polarization when ray-tracing through relativistic plasma.

Aims. In this paper, we aim to study the time dependence of sunspot group areas in a large sample composed of various databases spanning over 130 years, used state-of-the-art statistical methods. Methods. For a carefully selected but unbiased sample, we use Bayesian modelling to fit the temporal evolution of the combined umbral and penumbral area of spot groups with a skew-normal function to determine the existence of any asymmetry in spot growth or decay. Our primary selection criteria guaranteed that only spot groups with a well-defined maximum area were taken into account. We also analysed the covariance of the resulting model parameters and their correlations with the physical parameters of the sunspots and the ongoing solar cycle. Results. Our results show that the temporal evolution of well-observed sunspot groups that reach at least 50 millionths of a solar hemisphere (MSH) at their maximum can be fitted surprisingly well with our model. Furthermore, we show significant asymmetry - described by a skew parameter of fitted curves - between the growing and decaying phases of analysed sunspot groups. In addition, we found a weak correlation between the values of skew parameters and the maximum area of sunspot groups and their hemispherical latitude.

Nearby radio galaxies, containing jets, are extensively studied with VLBI, addressing jet launching and the physical mechanisms at play around massive black holes. 3C 84 is unique in this regard, because the combination of its proximity and large SMBH mass provides a high spatial resolution to resolve the complex structure at the jet base. For 3C 84 an angular scale of 50 ${\mu}$as corresponds to 200 - 250 Schwarzschild radii ($R_s$). Recent RadioAstron VLBI imaging at 22 GHz revealed an east-west elongated feature at the northern end of the VLBI jet, which challenges interpretations. Here we propose instead that the jet apex is not located within the 22 GHz VLBI core region but more upstream of the jet. We base our arguments on a 2D cross-correlation analysis of quasi-simultaneously obtained VLBI images at 15, 43, and 86 GHz, which measures the opacity shift of the VLBI core in 3C 84. With the assumption of the power law index ($k_r$) of the core shift being set to 1, we find the jet apex to be located $83 \pm 7$ ${\mu}$as north (upstream) of the 86 GHz VLBI core. Depending on the assumptions for $k_r$ and the particle number density power law index n, we find a mixed toroidal/poloidal magnetic field configuration, consistent with a region which is offset from the central engine by about 400-1500 $R_s$. The measured core shift is then used to estimate the magnetic field strength, which amounts to B = 1.80 - 4.0 G near the 86 GHz VLBI core. We discuss some physical implications of these findings.

The physical conditions leading the sunspot penumbra decay are poorly understood so far. We investigate the photospheric magnetic and velocity properties of a sunspot penumbra during the decay phase to advance the current knowledge of the conditions leading to this process. A penumbral decay was observed with the CRISP instrument at the Swedish 1m Solar Telescope on 2016 September 4 and 5 in active region NOAA 12585. During these days, full-Stokes spectropolarimetric scans along the Fe I 630 nm line pair were acquired over more than one hour. We inverted these observations with the VFISV code in order to obtain the evolution of the magnetic and velocity properties. We complement the study with data from instruments onboard the Solar Dynamics Observatory and Hinode space missions. The studied penumbra disappears progressively in both time and space. The magnetic flux evolution seems to be linked to the presence of Moving Magnetic Features (MMFs). Decreasing Stokes V signals are observed. Evershed flows and horizontal fields were detected even after the disappearance of the penumbral sector. The analyzed penumbral decay seems to result from the interaction between opposite polarity fields in type III MMFs and penumbra, while the presence of overlying canopies rules the evolution in the different penumbral sectors.

Stellar winds govern the spin-down of Solar-type stars as they age, and play an important role in determining planetary habitability, as powerful winds can lead to atmospheric erosion. We calculate three-dimensional stellar wind models for five young Solar-type stars in the Hyades cluster, using TOUPIES survey stellar magnetograms and state-of-the-art Alfv\'en wave driven wind modelling. The stars have the same 0.6-Gyr age and similar fundamental parameters, and we account for the uncertainty in and underestimation of absolute field strength inherent in Zeeman-Doppler imaging by adopting both unscaled and scaled (by a factor of five) field strengths. For the unscaled fields, the resulting stellar wind mass loss is 2-4 times greater and the angular momentum loss 2-10 times greater than for the Sun today, with the scaled results correspondingly greater. We compare our results with a range published of wind models and for the Alfv\'en wave driven modelling see evidence of mass loss saturation at about $10 \dot M_\odot$.

We propose a new model to determine the ages and masses of red giant branch (RGB) stars from the low-resolution large sky area multi-object fiber spectroscopic telescope (LAMOST) spectra. The ages of RGB stars are difficult to determine using classical isochrone fitting techniques in the Hertzsprung-Russell diagram, because isochrones of RGB stars are tightly crowned. With the help of the asteroseismic method, we can determine the masses and ages of RGB stars accurately. Using the ages derived from the asteroseismic method, we train a deep learning model based on DenseNet to calculate the ages of RGB stars directly from their spectra. We then apply this model to determine the ages of 512 272 RGB stars from LAMOST DR7 spectra (see this http URL). The results show that our model can estimate the ages of RGB stars from low-resolution spectra with an accuracy of 24.3%. The results on the open clusters M 67, Berkeley 32, and NGC 2420 show that our model performs well in estimating the ages of RGB stars. Through comparison, we find that our method performs better than other methods in determining the ages of RGB stars. The proposed method can be used in the stellar parameter pipeline of upcoming large surveys such as 4MOST, WEAVES, and MOONS.

We investigate the damping of Alfv\'en waves generated by the cosmic ray resonant streaming instability in the context of the cosmic ray escape and propagation in the proximity of supernova remnants. We consider ion-neutral damping, turbulent damping and non linear Landau damping in the warm ionized and warm neutral phases of the interstellar medium. For the ion-neutral damping, up-to-date damping coefficients are used. We investigate in particular whether the self-confinement of cosmic rays nearby sources can appreciably affect the grammage. We show that the ion-neutral damping and the turbulent damping effectively limit the residence time of cosmic rays in the source proximity, so that the grammage accumulated near sources is found to be negligible. Contrary to previous results, this also happens in the most extreme scenario where ion-neutral damping is less effective, namely in a medium with only neutral helium and fully ionized hydrogen. Therefore, the standard picture, in which CR secondaries are produced during the whole time spent by cosmic rays throughout the Galactic disk, need not to be deeply revisited.

High-resolution cosmological hydrodynamic simulations are currently limited to relatively small volumes due to their computational expense. However, much larger volumes are required to probe rare, overdense environments, and measure clustering statistics of the large scale structure. Typically, zoom simulations of individual regions are used to study rare environments, and semi-analytic models and halo occupation models applied to dark matter only (DMO) simulations are used to study the Universe in the large-volume regime. We propose a new approach, using a machine learning framework to explore the halo-galaxy relationship in the periodic EAGLE simulations, and zoom C-EAGLE simulations of galaxy clusters. We train a tree based machine learning method to predict the baryonic properties of galaxies based on their host dark matter halo properties. The trained model successfully reproduces a number of key distribution functions for an infinitesimal fraction of the computational cost of a full hydrodynamic simulation. By training on both periodic simulations as well as zooms of overdense environments, we learn the bias of galaxy evolution in differing environments. This allows us to apply the trained model to a larger DMO volume than would be possible if we only trained on a periodic simulation. We demonstrate this application using the $(800 \; \mathrm{Mpc})^3$ P-Millennium simulation, and present predictions for key baryonic distribution functions and clustering statistics from the EAGLE model in this large volume.

Exoplanet searches through space-based photometric time series have shown to be very efficient in the past years. However, follow-up efforts on the detected planet candidates have demonstrated to be critical to uncover the true nature of the transiting objects. In this paper we show a detailed analysis of one of those false positives hidden as planetary signals. In this case, the candidate KOI-3886.01 showed clear evidence of a planetary nature from different techniques. Indeed, the properties of the fake planet set it among the most interesting and promising ones for the study of planetary evolution as the star leaves the main sequence. To unveil the true nature of this system, we present a complete set of observational techniques including high-spatial resolution imaging, high-precision photometric time series (showing eclipses, phase curve variations and asteroseismology signals), high-resolution spectroscopy and derived radial velocities, to unveil the true nature of this planet candidate. We find that KOI-3886.01 is an interesting false positive case: a hierarchical triple system composed by a $\sim$K2III giant star (KOI-3886A) accompanied by a close-in eclipsing binary formed by a sub-giant $\sim$G4IV star (KOI-3886B) and a brown dwarf (KOI-3886C). In particular, KOI-3886C is one of the most irradiated brown dwarfs known to date, showing the largest radius in this substellar regime. It is also the first eclipsing brown dwarf known around an evolved star. In this paper we highlight the relevance of complete sets of follow-up observations to extrasolar planets detected by the transit technique using large-pixel photometers like Kepler and TESS and in the future PLATO. Specially, the multi-color high-spatial resolution imaging was the first hint towards ruling out the planet scenario in this system.

We present a new method to model the mass distribution of galaxy clusters that combines a parametric and a free-form approach to reconstruct cluster cores with strong lensing constraints. It aims at combining the advantages of both approaches, by keeping the robustness of the parametric component with an increased flexibility thanks to a free-form surface of B-spline functions. We demonstrate the capabilities of this new approach on the simulated cluster Hera, which has been used to evaluate lensing codes for the analysis of the Frontier Fields clusters. The method leads to better reproduction of the constraints, with an improvement by a factor $\sim3-4$ on the root-mean-square error on multiple-image positions, when compared to parametric-only approaches. The resulting models show a better accuracy in the reconstruction of the amplitude of the convergence field while conserving a high fidelity on other lensing observables already well reproduced. We make this method publicly available through its implementation in the Lenstool software.

The persistent thermal luminosity of magnetars and their outbursts suggest the existence of some internal heat sources located in their outer crust. The compression of matter accompanying the decay of the magnetic field may trigger exothermic electron captures and, possibly, pycnonuclear fusions of light elements that may have been accreted onto the surface from the fallback of supernova debris, from a disk or from the interstellar medium. This scenario bears some resemblance to deep crustal heating in accreting neutron stars, although the matter composition and the thermodynamic conditions are very different. The maximum possible amount of heat that can be released by each reaction and their locations are determined analytically taking into account the Landau--Rabi quantization of electron motion. Numerical results are also presented using experimental, as well as theoretical nuclear data. Whereas the heat deposited is mainly determined by atomic masses, the locations of the sources are found to be very sensitive to the magnetic field strength, thus providing a new way of probing the internal magnetic field of magnetars. Most sources are found to be concentrated at densities $10^{10}-10^{11}$ g cm$^{-3}$ with heat power $W^\infty\sim 10^{35}-10^{36}$ erg/s, as found empirically by comparing cooling simulations with observed thermal luminosity. The change of magnetic field required to trigger the reactions is shown to be consistent with the age of known magnetars. This suggests that electron captures and pycnonuclear fusion reactions may be a viable heating mechanism in magnetars. The present results provide consistent microscopic inputs for neutron star cooling simulations, based on the same model as that underlying the Brussels-Montreal unified equations of state.

Every 19 years, Saturn passes through Jupiter's 'flapping' magnetotail. Here, we report Chandra X-ray observations of Saturn planned to coincide with this rare planetary alignment and to analyse Saturn's magnetospheric response when transitioning to this unique parameter space. We analyse three Director's Discretionary Time (DDT) observations from the High Resolution Camera (HRC-I) on-board Chandra, taken on November 19, 21 and 23 2020 with the aim to find auroral and/or disk emissions. We infer the conditions in the kronian system by looking at coincident soft X-ray solar flux data from the Geostationary Operational Environmental Satellite (GOES) and Hubble Space Telescope (HST) observations of Saturn's ultraviolet (UV) auroral emissions. The large Saturn-Sun-Earth angle during this time would mean that most flares from the Earth-facing side of the Sun would not have impacted Saturn. We find no significant detection of Saturn's disk or auroral emissions in any of our observations. We calculate the 3$\sigma$ upper band energy flux of Saturn during this time to be 0.9 - 3.04 $\times$ 10$^{14}$ erg cm$^{-2}$ s$^{-1}$ which agrees with fluxes found from previous modelled spectra of the disk emissions. We conclude by discussing the implications of this non-detection and how it is imperative that the next fleet of X-ray telescope (such as Athena and the Lynx mission concept) continue to observe Saturn with their improved spatial and spectral resolution and very enhanced sensitivity to help us finally solve the mysteries behind Saturn's apparently elusive X-ray aurora.

Stars in multiple systems offer a unique opportunity to learn about stellar formation and evolution. As they settle down into stable configurations, multiple systems occur in a variety of hierarchies and a wide range of separations between the components. We examine 11 known and 11 newly discovered multiple systems including at least one M dwarf with the latest astrometric data from Gaia Early Data Release 3 (EDR3). We find that the individual components of systems at very wide separations are often multiple systems themselves.

We present a new model to describe the star formation process in galaxies, which includes the description of the different gas phases -- molecular, atomic, and ionized -- together with its metal content. The model, which will be coupled to cosmological simulations of galaxy formation, will be used to investigate the relation between the star formation rate (SFR) and the formation of molecular hydrogen. The model follows the time evolution of the molecular, atomic and ionized phases in a gas cloud and estimates the amount of stellar mass formed, by solving a set of five coupled differential equations. As expected, we find a positive, strong correlation between the molecular fraction and the initial gas density, which manifests in a positive correlation between the initial gas density and the SFR of the cloud.

This special issue is dedicated to starshades: science, engineering, technology and programmatics. Our reasons for organizing this special issue are several fold. First as a new technology and with research accomplished in many institutions, recent results are widely scattered in the literature. As such, we see great value in co-locating many of the most recent results. This guest editorial summarizes the 19 contributed papers as the result of a special call for papers. Since this is a rapidly maturing technology, we wanted to co-locate a primer with the most current work in the field. It is hoped that this primer will provide a tutorial to the starshade concept and pathway to the literature not in this issue. In doing so, we hope to widen the starshade community in terms of engineering and scientific engagements. This tutorial takes the form of a dialog, where frequently asked questions are answered.

The magnetar SGR J1745-2900 located in the vicinity of the supermassive black hole Sgr A$^{\star}$ was detected during its X-ray outburst with the Swifht/XRT telescope in April 2013. For several months after its detection the source was observed with the NuSTAR observatory, which allowed pulsations with a period $\sim3.76$ s to be recorded. Using these observations, we have studied in detail the dependence of the pulse profile and the pulsed fraction on the energy and intensity of the magnetar. The pulsed fraction in the 3-5 and 5-10 keV energy bands is shown to be 40-50%, slightly increasing with decreasing flux. We have performed phase-resolved spectroscopy for the source in the energy band from 3 to $\sim$40 keV and show that the temperature of the emitting regions remains fairly stable during the pulse, while their apparent size changes significantly with phase.

Future ground-based telescopes will expand our capabilities for simultaneous multi-line polarimetric observations in a wide range of wavelengths, from the near-ultraviolet to the near-infrared. This creates a strong demand to compare candidate spectral lines to establish a guideline of the lines that are most appropriate for each observation target. We focused in this first work on Zeeman-sensitive photospheric lines in the visible and infrared. We first examined their polarisation signals and response functions using a 1D semi-empirical atmosphere. Then we studied the spatial distribution of the line core intensity and linear and circular polarisation signals using a realistic 3D numerical simulation. We ran inversions of synthetic profiles, and we compared the heights at which we obtain a high correlation between the input and the inferred atmosphere. We also used this opportunity to revisit the atomic information we have on these lines and computed the broadening cross-sections due to collisions with neutral hydrogen atoms for all the studied spectral lines. The results reveal that four spectral lines stand out from the rest for quiet-Sun and network conditions: Fe I 5250.2, 6302, 8468, and 15648 A. The first three form higher in the atmosphere, and the last line is mainly sensitive to the atmospheric parameters at the bottom of the photosphere. However, as they reach different heights, we strongly recommend using at least one of the first three candidates together with the Fe I 15648 A line to optimise our capabilities for inferring the thermal and magnetic properties of the lower atmosphere.

Studies of the stellar and the HI gas kinematics in dwarf and Low Surface Brightness (LSB) galaxies are essential for deriving constraints on their dark matter distribution. Moreover, a key component to unveil in the evolution of LSBs is why some of them can be classified as superthin. We aim to investigate the nature of the proto-typical superthin galaxy Fourcade-Figueroa (FF), to understand the role played by the dark matter halo in forming its superthin shape and to investigate the mechanism that explains the observed disruption in the approaching side of the galaxy. Combining new HI 21-cm observations obtained with the Giant Metrewave Radio Telescope with archival data from the Australia Telescope Compact Array we were able to obtain sensitive HI observations of the FF galaxy. These data were modeled with a 3D tilted ring model in order to derive the rotation curve and surface brightness density of the neutral hydrogen. We subsequently used this model, combined with a stellar profile from the literature, to derive the radial distribution of the dark matter in the FF galaxy. For the FF galaxy the Navarro-Frenk-White dark matter distribution provides the best fit to the observed rotation curve. However, the differences with a pseudo-isothermal halo are small. Both models indicate that the core of the dark matter halo is compact. Even though the FF galaxy classifies as superthin, the gas thickness about the galactic centre exhibits a steep flaring of the gas which is in agreement with the edge of the stellar disk. As suggested previously in the literature, the compact dark matter halo might be the main responsible for the superthin structure of the stellar disk in FF. This idea is strengthened through the detection of the mentioned disruption; the fact that the galaxy is disturbed also seems to support the idea that it is not isolation that cause its superthin structure.

The paper presents the results of numerical simulation of the propagation of a sequence of plasma knots in laboratory conditions and the astrophysical environment. The physical and geometric parameters of the simulation have been chosen close to the parameters of the PF-3 facility (Kurchatov Institute) and the jet of the star RW Aur. We found that the low-density region formed after the first knot propagation plays an important role for collimation of the subsequent ones. Assuming only the thermal expansion of the subsequent emissions, qualitative estimates of the time taken to fill this area with the surrounding matter and the angle of jet scattering have been made. These estimates are consistent with observations and results of our modeling.

We investigate the viability of producing galaxy mock catalogues with COmoving Lagrangian Acceleration (COLA) simulations in Modified Gravity (MG) models employing the Halo Occupation Distribution (HOD) formalism. In this work, we focus on two theories of MG: $f(R)$ gravity with the chameleon mechanism, and a braneworld model (nDGP) that incorporates the Vainshtein mechanism. We use a suite of full $N$-body simulations in MG as a benchmark to test the accuracy of COLA simulations. At the level of Dark Matter (DM), we show that COLA accurately reproduces the matter power spectrum up to $k \sim 1 h {\rm Mpc}^{-1}$, while it is less accurate in reproducing the velocity field. To produce halo catalogues, we find that the ROCKSTAR halo-finder does not perform well with COLA simulations. On the other hand, using a simple Friends-of-Friends (FoF) finder and an empirical mass conversion from FoF to spherical over-density masses, we are able to produce halo catalogues in COLA that are in good agreement with those in $N$-body simulations. To consider the effects of the MG fifth force on the halo profile, we derive simple fitting formulae for the concentration-mass and the velocity dispersion-mass relations that we calibrate using ROCKSTAR halo catalogues in $N$-body simulations. We then use these results to extend the HOD formalism to modified gravity simulations in COLA. We use an HOD model with five parameters that we tune to obtain galaxy catalogues in redshift space. We find that despite the great freedom of the HOD model, MG leaves characteristic imprints in the redshift space power spectrum multipoles and these features are well captured by the COLA galaxy catalogues.

Dust in spiral galaxies produces emission in the far-infrared (FIR) and internal absorption in visible wavelengths. However, the relation of the two amounts is not trivial because optical absorption may saturate, but the FIR emission does not. Moreover, the volume concentration of dust plays a role in the relation of absorption and emission, which depends on the size of the galaxy. We explore the relation of these three quantities. In order to understand the geometrical problem, we developed a model of dust distribution. We also investigated the relation of the three variables with real data of spiral galaxies at z<0.2 using the spectroscopic SDSS and FIR AKARI surveys. Internal absorptions were derived with two different methods: the ratio of emission lines H$_\alpha $ and H$_\beta $, and a previously calibrated relation based on the color variations as a function of absolute magnitude and concentration index. We find that in our low-z sample, the dependence of the average internal attenuation on galaxy size is negligible on average. It allows us to derive the internal attenuation of the galaxy, $A_V$, even when we only know its FIR flux. This attenuation approximately depends on the inclination of the galaxy $i$ as $\overline {A_V}=\gamma_V \log _{10}\left(\frac{1}{\cos i}\right)$, where $\gamma_V$ is a constant. We found that $\gamma_V$ has a maximum value of $1.45\pm 0.27$ magnitudes. When similar properties of dust are assumed, a general expression can be used at any $z$. For cases of nonsaturation, this might be used as a cosmological test. Although the present-day sensitivity of FIR or mm surveys does not allow us to carry out this cosmological test at z>2 within the standard model, it may be used in the future. For much lower z or different cosmological models, a test might be feasible at present.

We report 272 radial velocities for 19 RR Lyrae variables. For most of the stars we have radial velocities for the complete pulsation cycle. These data are used to determine robust center--of--mass radial velocities that have been compared to values from the literature in a search for evidence of binary systems. Center--of--mass velocities were determined for each star using Fourier Series and Template fits to the radial velocities. Our center--of--mass velocities have uncertainties from $\pm0.16$ km s$^{-1}$ to $\pm$2.5 km s$^{-1}$, with a mean uncertainty of $\pm$0.92 km s$^{-1}$. We combined our center--of--mass velocities with values from the literature to look for deviations from the mean center--of--mass velocity of each star. Fifteen RR Lyrae show no evidence of binary motion (BK And, CI And, Z CVn, DM Cyg, BK Dra, RR Gem, XX Hya, SZ Leo, BX Leo, TT Lyn, CN Lyr, TU Per, U Tri, RV UMa, and AV Vir). In most cases this conclusion is reached due to the sporadic sampling of the center--of--mass velocities over time. Three RR Lyrae show suspicious variation in the center--of--mass velocities that may indicate binary motion but do not prove it (SS Leo, ST Leo, and AO Peg). TU UMa was observed by us near a predicted periastron passage (at 0.14 in orbital phase) but the absence of additional center--of--mass velocities near periastron make the binary detection, based on radial velocities alone, uncertain. Two stars in our sample show $H\gamma$ emission in phases 0.9--1.0: SS Leo and TU UMa.

When does the presence of an outlier in some measured property indicate that the outlying object differs qualitatively, rather than quantitatively, from other members of its apparent class? Historical examples include the many types of supernov\ae\ and short {\it vs.\/} long Gamma Ray Bursts. There may be only one parameter and one outlier, so that principal component analyses are inapplicable. A qualitative difference implies that some parameter has a characteristic scale, and hence its distribution cannot be a power law (that can have no such scale). If the distribution is a power law the objects differ only quantitatively. The applicability of a power law to an empirical distribution may be tested by comparing the most extreme member to its next-most extreme. The probability distribution of their ratio is calculated, and compared to data for stars, radio and X-ray sources, and the fluxes, fluences and rotation measures of Fast Radio Bursts.

Stripped-envelope supernovae (Type IIb, Ib, Ic) showing little or no hydrogen are one of the main classes of explosions of massive stars. Their origin and the evolution of their progenitors are not fully understood as yet. Very massive single stars stripped by their own winds ($\gtrsim 25-30 M_{\odot}$ at solar metallicity) are considered viable progenitors of these events. However, recent 1D core-collapse simulations show that some massive stars may collapse directly onto black holes after a failed explosion, with weak or no visible transient. In this letter, we estimate the effect of direct collapse onto a black hole on the rates of stripped-envelope supernovae that arise from single stars. For this, we compute single star MESA models at solar metallicity and map their final state to their core-collapse outcome following prescriptions commonly used in population synthesis. According to our models, no single stars that have lost their entire hydrogen-rich envelope are able to explode, and only a fraction of progenitors with a thin hydrogen envelope left (IIb progenitor candidates) do, unless we invoke increased wind mass-loss rates. This result increases the existing tension between the single-star scenario for stripped-envelope supernovae and their observed rates and properties. At face value, our results point towards an even higher contribution of binary progenitors for stripped-envelope supernovae. Alternatively, they may suggest inconsistencies in the common practice of mapping different stellar models to core-collapse outcomes and/or higher overall mass loss in massive stars.

We present the largest sample of brown dwarf (BD) protoplanetary disk spectral energy distributions modeled to date. We compile 46 objects with ALMA observations from four star-forming regions: $\rho$ Ophiuchus, Taurus, Lupus, and Upper Scorpius. Studying multiple regions with various ages enables us to probe disk evolution over time. Specifically, from our models we obtain values for dust grain sizes, dust settling, and disk mass; we compare how each of these parameters vary between the regions. We find that disk mass generally decreases with age, though the youngest region, Ophiuchus, has the lowest disk masses. We find evidence of disk evolution (i.e., grain growth and significant dust settling) in all four regions, indicating that planet formation and disk evolution may begin to occur at earlier stages. We generally find these disks contain too little mass to form planetary companions, though we cannot rule out that planet formation may have already occurred. Finally, we examine the disk mass -- host mass relationship and find that BD disks are largely consistent with previously-determined relationships for disks around T Tauri stars.

In this work we present a new catalogue of Cosmic Filaments obtained from the latest Sloan Digital Sky Survey (SDSS) public data. In order to detect filaments, we implement a version of the Subspace-Constrained Mean-Shift algorithm, boosted by Machine Learning techniques. This allows us to detect cosmic filaments as one-dimensional maxima in the galaxy density distribution. Our filament catalogue uses the cosmological sample of SDSS, including Data Release 16, so it inherits its sky footprint (aside from small border effects) and redshift coverage. In particular, this means that, taking advantage of the quasar sample, our filament reconstruction covers redshifts up to $z=2.2$, making it one of the deepest filament reconstructions to our knowledge. We follow a tomographic approach and slice the galaxy data in 269 shells at different redshift. The reconstruction algorithm is applied to 2D spherical maps. The catalogue provides the position and uncertainty of each detection for each redshift slice. We assess the quality of the detections with several metrics, which show improvement with respect to previous public catalogues obtained with similar methods. We also detect a highly significant correlation between our filament catalogue and galaxy cluster catalogues built from microwave observations of the Planck Satellite and the Atacama Cosmology Telescope.

We present a Bayesian parameter-estimation pipeline to measure the properties of inspiralling stellar-mass black hole binaries with LISA. Our strategy (i) is based on the coherent analysis of the three noise-orthogonal LISA data streams, (ii) employs accurate and computationally efficient post-Newtonian waveforms accounting for both spin-precession and orbital eccentricity, and (iii) relies on a nested sampling algorithm for the computation of model evidences and posterior probability density functions of the full 17 parameters describing a binary. We demonstrate the performance of this approach by analyzing the LISA Data Challenge (LDC-1) dataset, consisting of 66 quasi-circular, spin-aligned binaries with signal-to-noise ratios ranging from 3 to 14 and times to merger ranging from 3000 to 2 years. We recover 22 binaries with signal-to-noise ratio higher than 8. Their chirp masses are typically measured to better than $0.02 M_\odot$ at $90\%$ confidence, while the sky-location accuracy ranges from 1 to 100 square degrees. The mass ratio and the spin parameters can only be constrained for sources that merge during the mission lifetime. In addition, we report on the successful recovery of an eccentric, spin-precessing source at signal-to-noise ratio 15 for which we can measure an eccentricity of $3\times 10^{-3}$.

The cross-correlation between the cosmic microwave background (CMB) fields and matter tracers carries important cosmological information. In this paper, we forecast by a signal-to-noise ratio analysis the information contained in the cross-correlation of the CMB anisotropy fields with source counts for future cosmological observations and its impact on cosmological parameters uncertainties, using a joint tomographic analysis. We include temperature, polarization and lensing for the CMB fields and galaxy number counts for the matter tracers. By restricting ourselves to quasi-linear scales, we forecast by a Fisher matrix formalism the relative importance of the cross-correlation of source counts with the CMB in the constraints on the parameters for several cosmological models. We obtain that the CMB-number counts cross-correlation can improve the dark energy Figure of Merit (FoM) at most up to a factor $\sim 2$ for LiteBIRD+CMB-S4 $\times$ SKA1 compared to the uncorrelated combination of both probes and will enable the Euclid-like photometric survey to reach the highest FoM among those considered here. We also forecast how CMB-galaxy clustering cross-correlation could increase the FoM of the neutrino sector, also enabling a statistically significant ($\gtrsim$ 3$\sigma$ for LiteBIRD+CMB-S4 $\times$ SPHEREx) detection of the minimal neutrino mass allowed in a normal hierarchy by using quasi-linear scales only. Analogously, we find that the uncertainty in the local primordial non-Gaussianity could be as low as $\sigma (f_{\rm NL}) \sim 1.5-2$ by using two-point statistics only with the combination of CMB and radio surveys such as EMU and SKA1. Our results highlight the additional constraining power of the cross-correlation between CMB and galaxy clustering from future surveys which is mainly based on quasi-linear scales and therefore sufficiently robust to non-linear effects.

Atom-interferometer gravitational-wave (GW) observatory, as a new design of ground-based GW detector for the near future, is sensitive at a relatively low frequency for GW observations. Taking the proposed atom interferometer Zhaoshan Long-baseline Atom Interferometer Gravitation Antenna (ZAIGA), and its illustrative upgrade (Z+) as examples, we investigate how the atom interferometer will complement ground-based laser interferometers in testing the gravitational dipole radiation from binary neutron star (BNS) mergers. A test of such kind is important for a better understanding of the strong equivalence principle laying at the heart of Einstein's general relativity. To obtain a statistically sound result, we sample BNS systems according to their merger rate and population, from which we study the expected bounds on the parameterized dipole radiation parameter $B$. Extracting BNS parameters and the dipole radiation from the combination of ground-based laser interferometers and the atom-interferometer ZAIGA/Z+, we are entitled to obtain tighter bounds on $B$ by a few times to a few orders of magnitude, compared to ground-based laser interferometers alone, ultimately reaching the levels of $|B| \lesssim 10^{-9}$ (with ZAIGA) and $|B| \lesssim 10^{-10}$ (with Z+).

We consider the solutions of the Guderley problem, consisting of an imploding strong shock wave in an ideal gas with a power law initial density profile. The self-similar solutions, and specifically the similarity exponent which determines the behavior of the accelerating shock, are studied in detail, for cylindrical and spherical symmetries and for a wide range of the adiabatic index and the spatial density exponent. We then demonstrate how the analytic solutions can be reproduced in Lagrangian hydrodynamic codes, thus demonstrating their usefulness as a code validation and verification test problem.

Primordial black holes (PBHs) are a potential dark matter candidate whose masses can span over many orders of magnitude. If they have masses in the $10^{15}-10^{17}$ g range, they can emit sizeable fluxes of MeV neutrinos through evaporation via Hawking radiation. We explore the possibility of detecting light (non-)rotating PBHs with future neutrino experiments. We focus on two next generation facilities: the Deep Underground Neutrino Experiment (DUNE) and THEIA. We simulate the expected event spectra at both experiments assuming different PBH mass distributions and spins, and we extract the expected 95% C.L. sensitivities to these scenarios. Our analysis shows that future neutrino experiments like DUNE and THEIA will be able to set competitive constraints on PBH dark matter, thus providing complementary probes in a part of the PBH parameter space currently constrained mainly by photon data.

We present a set of idealised numerical experiments of a solstitial aquaplanet ocean and examine the thermodynamic and dynamic implications of surface gravity waves (SGWs) upon its mean state. The aquaplanet's oceanic circulation is dominated by an equatorial zonal jet and four Ekman driven meridional overturning circulation (MOC) cells aligned with the westerly atmospheric jet streams and easterly trade winds in both hemispheres. Including SGW parameterization (representing modulations of air-sea momentum fluxes, Langmuir circulation and Stokes-Coriolis force) increases mixed layer vertical momentum diffusivity by approx. 40% and dampens surface momentum fluxes by approx. 4%. The correspondingly dampened MOC impacts the oceanic density structure to 1 km depth by lessening the large-scale advective transports of heat and salt, freshening the equatorial latitudes (where evaporation minus precipitation [E-P] is negative) and increasing salinity in the subtropics (where E-P is positive) by approx. 1%. The midlatitude pycnocline in both hemispheres is deepened by the inclusion of SGWs. Including SGWs into the aquaplanet ocean model acts to increase mixed layer depth by approx. 10% (up to 20% in the wintertime in midlatitudes), decrease vertical shear in the upper 200 m and alter local midlatitude buoyancy frequency. Generally, the impacts of SGWs upon the aquaplanet ocean are found to be consistent across cooler and warmer climates. We suggest that the implications of these simulations could be relevant to understanding future projections of SGW climate, exoplanetary oceans, and the dynamics of the Southern Ocean mixed layer.

In [J. Blazquez-Salcedo, C. Knoll, E. Radu, Phys. Rev. Lett. 126 (2021) no.10, 101102] asymptotically flat traversable wormhole solutions were obtained in the Einstein-Dirac-Maxwell theory without using exotic matter. The normalizable numerical solutions found in \cite{Blazquez-Salcedo:2020czn} require a peculiar behavior at the throat: the mirror symmetry relatively the throat leads to the nonsmoothness of gravitational and matter fields. In particular, one must postulate the changing of the sign of the fermionic charge density at the throat requiring coexistence of particle and antiparticles without annihilation and posing a membrane of matter at the throat with specific properties. Apparently this kind of configurations could not exist in nature. We show that there are wormhole solutions, which are asymmetric relatively the throat and endowed by smooth gravitational and matter fields, being, thereby, free from all the above problems. This indicates that such wormhole configurations could also be supported in a realistic scenario.

As compact binary star systems move inside the halo of our Galaxies, they interact with dark matter particles. The interaction between dark matter particles and baryonic matter causes dark matter particles to lose some part of their kinetic energy. After dark matter particles have lost part of their kinetic energy, they gravitationally bound to stars and stars start to accrete dark matter particles from the halo. The accretion of dark matter particles inside compact binary systems increases the mass of the binary components and then, the total mass of the binary systems increases too. According to Kepler's third law, increased mass by this way can affect other physical parameters (e.g. semi-major axes and orbital periods) of these systems too. In this work, we estimated the period change of some known compact binary systems due to the accretion of dark matter particles into them. We investigated the effects of different dark matter particle candidates with masses in the range $\simeq 10^{-15} - 10^{5} GeV.c^{-2}$ and dark matter density as high as the dark matter density near the Galactic central regions. Our overall result is that the estimated period change due to the accretion of dark matter particles into compact binary systems can be as high as the measured values for these systems.

In this paper Modified gravity is studied over the linearized metric perturbation in post-Minkowskian theory. This is a different aspect for two body dynamics without taking usual self force originated from the radiative backscattering of gravitational waves. The new multiplicative approach to determine the background metric of curved space-time for two different massive sources is computed in post-Newtonian theory. The theoretical result is checked for galactic flat rotation curve and is very good agreement with solar rotational speed.

GAIA (originally the acronym for Global Astrometric Interferometer for Astrophysics) is a mission of the European Space Agency (ESA) which will make the largest, most precise three dimensional map of our Galaxy by an unparalleled survey of one per cent of the galaxy's population of 100 billion stars to the precision of micro arcseconds. This article will briefly review Gaia, the data releases and the possible implications of this mission. The reader will be introduced to the DR1 and DR2 data releases and the scientific outcomes of DR1 as a forerunner to the much awaited DR2 of this one-of-a-kind mission.