Search

The Spitzer instability leads to the formation of a black hole subsystem (BHSub) at the centre of a star cluster providing energy to luminous stars (LSs) and increasing their rate of evaporation. When the self-depletion time of the BHSub exceeds the evaporation time of the LSs, a dark star cluster (DSC) will appear. Using the nbody7 code, we performed a comprehensive set of direct N -body simulations over a wide range of initial conditions to study the pure effect of the top-heaviness of the initial mass function (IMF) on the formation of the DSC phase. In the Galactic tidal field, top-heavy IMFs lead to the fast evaporation of LSs and the formation of DSCs. Therefore, DSCs can be present even in the outer region of the Milky Way (MW). To successfully transition to the DSC phase, the MW Globular Clusters (GCs) must possess an initial black hole (BH) mass fraction of |$\widetilde {\mathit {M}}_\mathrm{BH}(0)\gt 0.05$|⁠. For star clusters with |$\widetilde {\mathit {M}}_\mathrm{BH}(0)\gt 0.08$|⁠ , the DSC phase will be created for any given initial density of the cluster and Galactocentric distance. The duration of the cluster's lifetime spent in the DSC phase shows a negative (positive) correlation with the initial density, and Galactocentric distance of the star cluster if |$\widetilde {\mathit {M}}_\mathrm{BH}(0)\le 0.12$| (⁠|$\widetilde {\mathit {M}}_\mathrm{BH}(0)\ge 0.15$|⁠). Considering the canonical IMF, it is unlikely for any MW GCs to enter the DSC phase. We discuss the BH retention fraction in view of the observed properties of the GCs of the MW. [ABSTRACT FROM AUTHOR]

The given text appears to be a correction to a previous paper that examined the relationship between neutron star mass and dark matter accumulation within dark matter clumps. The authors identified an error in their code that resulted in distance measurements being given with respect to the Sun instead of the Galactic center. They corrected the distance values and found that the resulting plots changed, but the results and conclusions remained qualitatively similar. The document includes figures and graphs that illustrate the corrected analysis. [Extracted from the article]

We searched for OB-runaway stars inside supernova remnants (SNRs) as a pre-supernova binary companion. As the majority of massive stars are found in close binary systems, a runaway star ejected by the orbital energy after the supernova (SN) is expected to be found. Considering a binary mass fraction, q = 0.25−1.0, the runaway star is likely to have an OB spectral type. We selected 12 SNRs at Galactic longitudes 109°−189°. Using Gaia astrometry, we selected stars having consistent distances with those of the SNRs and showing a peculiar proper motion directed away from the central region of the SNRs. We also determined the radial distribution of the extinction towards the SNRs and estimated the spectral types of the OB-runaway candidates through Gaia and Two Micron All Sky Survey photometry. We found two candidates among 12 SNRs. By spectroscopic observations, Gaia DR3 195632152560621440 inside SNR G166.0 + 4.3 was found to be an evolved A3 type star that cannot be the pre-SN binary companion to the progenitor. Gaia DR3 513927750767375872 inside SNR HB 3 is the only OB-runaway candidate (2D space velocity of 33.3 ± 3.3 km s−1). Based on photometric study, the star can be an early B-type main-sequence star with a slightly higher extinction relative to the SNR; however, it might instead be an evolved A-type star at the same distance. The other 11 SNRs do not host an OB-runaway star within their central regions. Although the runaway search was performed in a large interval of distance and extinction, we also estimated distances to the SNRs. [ABSTRACT FROM AUTHOR]

Stellar mergers and accretion events have been crucial in shaping the evolution of the Milky Way (MW). These events have been dynamically identified and chemically characterized using red giants and main-sequence stars. RR Lyrae (RRL) variables can play a crucial role in tracing the early formation of the MW since they are ubiquitous, old (t ≥ 10 Gyr) low-mass stars and accurate distance indicators. We exploited Data Release 3 of the GALAH survey to identify 78 field RRLs suitable for chemical analysis. Using synthetic spectra calculations, we determined atmospheric parameters and abundances of Fe, Mg, Ca, Y, and Ba. Most of our stars exhibit halo-like chemical compositions, with an iron peak around [Fe/H] ≈ −1.40, and enhanced Ca and Mg content. Notably, we discovered a metal-rich tail, with [Fe/H] values ranging from −1 to approximately solar metallicity. This sub-group includes almost 1/4 of the sample, it is characterized by thin disc kinematics and displays sub-solar α-element abundances, marginally consistent with the majority of the MW stars. Surprisingly, they differ distinctly from typical MW disc stars in terms of the s-process elements Y and Ba. We took advantage of similar data available in the literature and built a total sample of 535 field RRLs for which we estimated kinematical and dynamical properties. We found that metal-rich RRLs (1/3 of the sample) likely represent an old component of the MW thin disc. We also detected RRLs with retrograde orbits and provided preliminary associations with the Gaia–Sausage–Enceladus, Helmi, Sequoia, Sagittarius, and Thamnos stellar streams. [ABSTRACT FROM AUTHOR]

We present the results of a search for Miras and long-period variables (LPVs) in M33 using griJHKS archival observations from the Canada–France–Hawaii Telescope. We use multiband information and machine learning techniques to identify and characterize these variables. We recover ∼1300 previously discovered Mira candidates and identify ∼13 000 new Miras and LPVs. We detect for the first time a clear first-overtone pulsation sequence among Mira candidates in this galaxy. We use O-rich, fundamental-mode Miras in the LMC and M33 to derive a distance modulus for the latter of μ = 24.629 ± 0.046 mag. [ABSTRACT FROM AUTHOR]

We present the results of a search for Miras and long-period variables (LPVs) in M33 using griJHKS archival observations from the Canada–France–Hawaii Telescope. We use multiband information and machine learning techniques to identify and characterize these variables. We recover ∼1300 previously discovered Mira candidates and identify ∼13 000 new Miras and LPVs. We detect for the first time a clear first-overtone pulsation sequence among Mira candidates in this galaxy. We use O-rich, fundamental-mode Miras in the LMC and M33 to derive a distance modulus for the latter of μ = 24.629 ± 0.046 mag. [ABSTRACT FROM AUTHOR]

Black hole low-mass X-ray binaries (BH-LMXBs) are excellent observational laboratories for studying many open questions in accretion physics. However, determining the physical properties of BH-LMXBs necessitates knowing their distances. With the increased discovery rate of BH-LMXBs, many canonical methods cannot produce accurate distance estimates at the desired pace. In this study, we develop a versatile statistical framework to obtain robust distance estimates soon after discovery. Our framework builds on previous methods where the soft spectral state and the soft-to-hard spectral state transitions, typically present in an outbursting BH-LMXB, are used to place constraints on mass and distance. We further develop the traditional framework by incorporating general relativistic corrections, accounting for spectral/physical parameter uncertainties, and employing assumptions grounded in current theoretical and observational knowledge. We tested our framework by analysing a sample of 50 BH-LMXB sources using X-ray spectral data from the Swift /XRT, MAXI /GSC, and RXTE /PCA missions. By modelling their spectra, we applied our framework to 26 sources from the 50. Comparison of our estimated distances to previous distance estimates indicates that our findings are dependable and in agreement with the accurate estimates obtained through parallax and H  i absorption methods. Investigating the accuracy of our constraints, we have found that estimates obtained using both the soft and transition spectral information have a median uncertainty (1σ) of 20 per cent, while estimates obtained using only the soft spectral state spectrum have a median uncertainty (1σ) of around 50 per cent. Furthermore, we have found no instrument-specific biases. [ABSTRACT FROM AUTHOR]

A new fine grid of non-linear convective pulsation models for the so-called 'bump Cepheids' is presented to investigate the Hertzprung progression (HP) phenomenon shown by their light and radial pulsation velocity curves. The period corresponding to the centre of the HP is investigated as a function of various model assumptions, such as the efficiency of superadiabatic convection, the mass–luminosity relation, and the metal and helium abundances. The assumed mass–luminosity relation is found to significantly affect the phenomenon but variations in the chemical composition as well as in the stellar mass (at fixed mass–luminosity relation) also play a key role in determining the value of the HP centre period. Finally, the predictive capability of the presented theoretical scenario is tested against observed light curves of bump Cepheids in the ESA Gaia data base, also considering the variation of the pulsation amplitudes and of the Fourier parameters R 21 and Φ21 with the pulsation period. A qualitative agreement between theory and observations is found for what concerns the evolution of the light curve morphology as the period moves across the HP centre, as well for the pattern in period–amplitude, period– R 21, and period–Φ21 planes. A larger sample of observed Cepheids with accurate light curves and metallicities is required in order to derive more quantitative conclusions. [ABSTRACT FROM AUTHOR]

The Magellanic Cloud system represents a unique laboratory for study of both interacting dwarf galaxies and the ongoing process of the formation of the Milky Way and its halo. We focus on one aspect of this complex, three-body interaction – the dynamical perturbation of the Small Magellanic Cloud (SMC) by the Large Magellanic Cloud (LMC), and specifically potential tidal effects on the SMC's eastern side. Using Gaia astrometry and the precise radial velocities (RVs) and multielement chemical abundances from Apache Point Observatory Galactic Evolution Experiment (APOGEE-2) Data Release 17, we explore the well-known distance bimodality on the eastern side of the SMC. Through estimated stellar distances, proper motions, and RVs, we characterize the kinematics of the two populations in the bimodality and compare their properties with those of SMC populations elsewhere. Moreover, while all regions explored by APOGEE seem to show a single chemical enrichment history, the metallicity distribution function (MDF), of the 'far' stars on the eastern periphery of the SMC is found to resemble that for the more metal-poor fields of the western periphery, whereas the MDF for the 'near' stars on the eastern periphery resembles that for stars in the SMC Centre. The closer eastern periphery stars also show RVs (corrected for SMC rotation and bulk motion) that are, on average, approaching us relative to all other SMC populations sampled. We interpret these trends as evidence that the near stars on the eastern side of the SMC represent material pulled out of the central SMC as part of its tidal interaction with the LMC. [ABSTRACT FROM AUTHOR]

The magnetic dipole moment μ of an accretion-powered pulsar in magnetocentrifugal equilibrium cannot be inferred uniquely from time-averaged pulse period and aperiodic X-ray flux data, because the radiative efficiency η 0 of the accretion is unknown, as are the mass, radius, and distance of the star. The degeneracy associated with the radiative efficiency is circumvented if fluctuations of the pulse period and aperiodic X-ray flux are tracked with a Kalman filter, whereupon μ can be measured uniquely up to the uncertainties in the mass, radius, and distance. Here, the Kalman filter analysis is demonstrated successfully in practice for the first time on Rossi X-ray Timing Explorer observations of the X-ray transient SXP 18.3 in the Small Magellanic Cloud (SMC), which is monitored regularly. The analysis yields μ = 8.0 − 1.2 + 1.3 × 10 30 G cm 3 and η 0 = 0.04 − 0.01 + 0.02 , compared to μ = 5.0 − 1.0 + 1.0 × 10 30 G cm 3 as inferred traditionally from time-averaged data assuming η 0 = 1. The analysis also yields time-resolved estimates of two hidden state variables, the mass accretion rate and the Maxwell stress at the disk–magnetosphere boundary. The success of the demonstration confirms that the Kalman filter analysis can be applied in the future to study the magnetic moments and disk–magnetosphere physics of accretion-powered pulsar populations in the SMC and elsewhere. [ABSTRACT FROM AUTHOR]

4U 1702−429, an atoll-type neutron star low-mass X-ray binary, was observed twice by the AstroSat /Soft X-ray Telescope (SXT) and Large Area X-ray Proportional Counters (LAXPC-20) on 2018 April 27 and 2019 August 8. Persistent emission spectra of the source were well fitted with the model combination - constant × tbabs (thcomp × diskbb+powerlaw). The parameters obtained from the spectral analysis revealed the source to be in a hard spectral state during the observations. Time-resolved spectral analyses were performed on the three type I X-ray bursts detected from the source. Burst analysis showed that the source underwent a photospheric radius expansion. Consequently, the radius of the neutron star and distance to the source (with isotropic and anisotropic burst emission) were obtained as 12.65 |$\substack{+0.90\\-0.86}$| km and 6.92 |$\substack{+0.16\\-0.09}$| and 8.43 |$\substack{+0.20\\-0.10}$| kpc, respectively. [ABSTRACT FROM AUTHOR]

Homogeneous multiwavelength observations of classical Cepheids from the forthcoming Rubin-LSST have the potential to significantly contribute to our understanding of the evolutionary and pulsation properties of these pulsating stars. Updated pulsation models for classical Cepheid stars have been computed under various assumptions about chemical compositions, including relatively low metallicity (Z = 0.004 with Y = 0.25 and Z  = 0.008 with Y = 0.25), solar metallicity (Z  = 0.02 with Y  = 0.28), and supersolar metallicity environments (Z = 0.03 with Y = 0.28). From the predicted periods, intensity-weighted mean magnitudes, and colours, we have derived the first theoretical pulsation relations in the Rubin-LSST filters (ugrizy), including period–luminosity–colour, period–Wesenheit, and period–age–colour relations. We find that the coefficients of these relations are almost insensitive to the efficiency of superadiabatic convection but are significantly affected by the assumption of the mass–luminosity relation and the adopted chemical composition. Metal-dependent versions of these relations are also derived, representing valuable tools for individual distance determinations and correction for metallicity effects on the cosmic distance scale. [ABSTRACT FROM AUTHOR]

We present the results of a sensitive search for high-velocity gas in interstellar absorption lines associated with the Cygnus Loop supernova remnant (SNR). We examine high-resolution high signal-to-noise ratio optical spectra of six stars in the Cygnus Loop region with distances greater than ∼700 pc. All stars show low-velocity Na  i and Ca  ii absorption. However, only one star, HD 198301, exhibits high-velocity Ca  ii absorption components, at velocities of +62, +82, and  +96 km s−1. The distance to this star of ∼870 pc helps to constrain the distance to the receding edge of the Cygnus Loop's expanding shock front. One of our targets, HD 335334, was previously thought to exhibit high positive and high negative velocity interstellar Na  i and Ca  ii absorption. This was one factor leading Fesen et al. to derive a distance to the Cygnus Loop of 725 ± 15 pc. However, we find that HD 335334 is in fact a double-line spectroscopic binary and shows no evidence of high-velocity interstellar absorption. As such, the distance to HD 335334 cannot be used to constrain the distance to the Cygnus Loop. Our detection of Ca  ii absorption approaching 100 km s−1 toward HD 198301 is the first conclusive detection of high-velocity absorption from a low-ionization species associated with the Cygnus Loop SNR. A large jump in the Na  i column density toward BD+31 4218, a star located beyond the northwestern boundary of the Cygnus Loop, helps to constrain the distance to a large molecular cloud complex with which the Cygnus Loop is evidently interacting. [ABSTRACT FROM AUTHOR]

Magnetic fields are a defining yet enigmatic aspect of the interstellar medium, with their three-dimensional (3D) mapping posing a substantial challenge. In this study, we harness the innovative velocity gradient technique (VGT), underpinned by magnetohydrodynamic turbulence theories, to map the magnetic field structure by applying it to the atomic neutral hydrogen (H  i) emission line and the molecular tracer 12CO. We construct the tomography of the magnetic field in the low-mass star-forming region L1688, utilizing two approaches: (1) VGT-H  i combined with the Galactic rotational curve, and (2) stellar polarization paired with precise star parallax measurements. Our analysis reveals that the magnetic field orientations deduced from stellar polarization undergo a distinct directional change in the vicinity of L1688, providing evidence that the misalignment between VGT-H  i and stellar polarization stems from the influence of the molecular cloud's magnetic field on the polarization of starlight. When comparing VGT-12CO to stellar polarization and Planck polarization data, we observe that VGT-12CO effectively reconciles the misalignment noted with VGT-H  i , showing statistical alignment with Planck polarization measurements. This indicates that VGT-12CO could be integrated with VGT-H  i , offering vital insights into the magnetic fields of molecular clouds, thereby enhancing the accuracy of our 3D magnetic field reconstructions. [ABSTRACT FROM AUTHOR]

This article is a review of the book "De Mundi Recentioribus Phænomenis: Cosmologie et Science dans l’Europe des Temps Modernes, XVe – XVIIIe Siècles, Essais en l’Honneur de Miguel Ángel Granada." The book contains a bibliography of Miguel Ángel Granada's works and 19 essays on astronomy and science during the modern period. It is written in multiple languages, which may be challenging for readers. The review highlights essays on topics such as the relationship between astronomical events and Martin Luther's ideas, and Copernicus' debt to Islamic astronomy. The book is considered an important contribution to the understanding of the history of astronomy, but it is primarily intended for specialists. [Extracted from the article]

This paper investigates a hypothesis proposed in previous research relating neutron star (NS) mass and its dark matter (DM) accumulation. As DM accumulates, NS mass decreases, predicting lower NS masses toward the Galactic centre. Due to limited NSs data near the Galactic centre, we examine NSs located within DM clumps. Using the CLUMPY code simulations, we determine the DM clumps distribution, with masses from 10 to 108 M⊙ and scales from 10−3 to 10 kpc. These clumps' DM exhibit a peak at the centre, tapering toward the outskirts, resembling our Galaxy's DM distribution. We analyse these DM clumps' NS mass variations, considering diverse DM particle masses and galaxy types. We find relatively stable NS mass within 0.01 – 5 kpc from the clump centre. This stability supports the initial hypothesis, particularly for NSs located beyond 0.01 kpc from the clump centre, where NS mass reaches a plateau around 0.1 kpc. Nevertheless, NS mass near the clump's periphery reveals spatial dependence: NS position within DM clumps influences its mass in Milky Way-type galaxies. Moreover, this dependence varies with the DM model considered. In summary, our study investigates the proposed link between NS mass and DM accumulation by examining NSs within DM clumps. While NS mass remains stable at certain distances from the clump centre, spatial dependencies arise near the clump's outer regions, contingent on the specific DM model. [ABSTRACT FROM AUTHOR]

Currently, astrometric microlensing is the only tool that can directly measure the mass of a single star; it can also help us to detect compact objects such as isolated neutron stars and black holes. The number of microlensing events that are being predicted and reported is increasing. In this paper, potential lens stars are selected from three types of stars: high-proper-motion stars, nearby stars, and high-mass stars. For each potential lens star, we select a larger search scope to find possible matching sources and to avoid missing events as much as possible. Using data from Gaia Data Release 3, we predict 4500 astrometric microlensing events with δθ+ > 0.1 mas, which occur between J2010.0 and J2070.0, where 1664 events are different from those found previously. There are 293 lens stars that can cause two or more events, where five lens stars can cause more than 50 events. We find that 116 events have the distance of background stars from the proper motion path of lens stars more than 8 arcsec in the reference epoch, where the maximum distance is 16 |${_{.}^{\prime\prime}}$| 6. Thus, the cone search method of expanding the search range of sources for each potential lens star can reduce the possibility of missing events. [ABSTRACT FROM AUTHOR]

We identify 71 distant stars in James Webb Space Telescope/NIRCam early release observations (ERO) images of the field of galaxy cluster SMACS J0723.3-7327 (SMACS 0723). Given the relatively small (∼10°) angular separation between SMACS 0723 and the Large Magellanic Cloud (LMC), it is likely that these stars are associated with the LMC outskirts or the Leading Arm. This is further bolstered by a spectral energy distribution (SED) analysis, which suggests an excess of stars at a physical distance of 40–100 kpc, consistent with being associated with or located behind the Magellanic system. In particular, we find that the overall surface density of stars brighter than 27.0 mag in the field of SMACS 0723 is ∼2.3 times that of stars in a blank field with similar Galactic latitude (the North Ecliptic Pole Time Domain Field), and that the density of stars in the SMACS 0723 field with SED-derived distances consistent with the Magellanic system is ∼6.1 times larger than that of the blank field. The candidate stars at these distances are consistent with a stellar population at the same distance modulus with [Fe/H] = −1.0 and an age of ∼5.0 Gyr. On the assumption that all of the 71 stars are associated with the LMC, then the stellar density of the LMC at the location of the SMACS 0723 field is ∼740 stars kpc−3, which helps trace the density of stars in the LMC outskirts. [ABSTRACT FROM AUTHOR]

We investigate the question whether or not the orbitals of exoplanets follow the symmetry-governed sequence found by Barut from the dynamical group of the Kepler problem. In particular, we consider their star distances, periods, and velocities. Previous studies have shown the validity of this regularity for our solar system, and for some selected exoplanet systems. Here, we study all the systems which are known with four or more planets. A remarkable result is found: 63 out of 100 systems show a better agreement between the theory and observation than our solar system. We discuss the relation between the symmetry-inspired transformations and the generalized Titius–Bode (gTB) rule. It turns out that the gTB rule, which has been considered purely empirical, can be obtained from the transformations corresponding to the dynamical group of the Kepler problem. [ABSTRACT FROM AUTHOR]

The goal of this study is tracking of possible changes in the spectrum of the interstellar cloud seen along the sightline towards a runaway star AE Aur. The study considers variations in the radial velocities of the interstellar molecules and atoms, dwelling in the cloud, for the period ≈17 yr. The most recent results of 6 yr monitoring of equivalent widths variability for the CH and CH+ absorption lines are also presented. The study was done using the CH B-X(0,0) 3886 Å, A-X (0,0) 4300 Å and the CH+ A-X (1-0) 3958 Å, A-X (0,0) 4232 Å lines as well as the interstellar potassium K  i 7699 Å line. Moreover, a short discussion concerning the distance to the star is included. The present study is a continuation of our previous works and works of other researchers dedicated to the problem of small-scale structure in diffuse interstellar clouds. High resolution optical spectra from different spectrographs have been used in this work. The results of the study do not demonstrate significant changes in the radial velocities of the spectral features mentioned. The intensities of the CH and CH+ lines show slight tendency to vary at 1–3  per cent level. [ABSTRACT FROM AUTHOR]

We present precise photometric estimates of stellar parameters, including effective temperature, metallicity, luminosity classification, distance, and stellar age, for nearly 26 million stars using the methodology developed in the first paper of this series, based on the stellar colors from the Stellar Abundances and Galactic Evolution Survey (SAGES) Data Release 1 and Gaia Early Data Release 3. The optimal design of stellar-parameter sensitive uv filters by SAGES has enabled us to determine photometric-metallicity estimates down to −3.5, similar to our previous results with the SkyMapper Southern Survey (SMSS), yielding a large sample of over five million metal-poor ([Fe/H] ≤ −1.0) stars and nearly one million very metal-poor ([Fe/H] ≤ −2.0) stars. The typical precision is around 0.1 dex for both dwarf and giant stars with [Fe/H] > −1.0, and 0.15–0.25/0.3–0.4 dex for dwarf/giant stars with [Fe/H] < −1.0. Using the precise parallax measurements and stellar colors from Gaia, effective temperature, luminosity classification, distance, and stellar age are further derived for our sample stars. This huge data set in the Northern sky from SAGES, together with similar data in the Southern sky from SMSS, will greatly advance our understanding of the Milky Way, in particular its formation and evolution. [ABSTRACT FROM AUTHOR]

Accurately quantifying the rates d M /d t at which massive stars lose mass is essential to any understanding of their evolution. All d M /d t estimates to date assume wind clumping factors; not allowing for clumping leads to overestimates of d M /d t and underestimates of lifetimes and masses when these stars explode as supernovae. Mid-infrared spectroscopy suggested that the wind of the nearest Wolf–Rayet (WR) star, γ2 Vel, is resolved with a full width at 10 per cent intensity of 0.5 arcsec, or 171 au at the 342 pc distance of the star. As the Zorro speckle imager on Gemini South is capable of ∼0.02 arcsec resolution, we have used it to image γ2 Vel at two orbital phases (0.30 and 0.44) with two narrow-band and two intermediate-band filters in an attempt to resolve its wind. Our observations demonstrate that γ2 Vel's wind may be resolved as a ∼0.07 arcsec westward elongation through an 832 nm filter at orbital phase 0.3. If confirmed, this is the smallest scale (∼24 au) at which a WR star wind asymmetry has been directly imaged. Similar imaging at multiple phases is needed to determine if the asymmetry is due to stochastic wind clumping, co-rotating interaction regions or colliding-wind, cone-shaped shocks. [ABSTRACT FROM AUTHOR]

We propose a new method for measuring the spatial density distribution of the stellar halo of the Milky Way. Our method is based on a pairwise statistic of the distribution of stars in the sky, the angular two-point correlation function (ATPCF). The ATPCF utilizes two-dimensional data of stars only and is therefore immune to the large uncertainties in the determination of distances to stars. We test our method using mock stellar data coming from various models including the single power-law (SPL) and the broken power-law (BPL) density profiles. We also test the influence of axisymmetric flattening factors using both constant and varying values. We find that the ATPCF is a powerful tool for recovering the spatial distributions of the stellar haloes in our models. We apply our method to observational data from the type ab RR Lyrae catalogue in the Catalina Survey Data Release 1. In the 3-parameter BPL model, we find that |$s_{1}=2.46_{-0.20}^{+0.18}, s_{2}=3.99_{-1.33}^{+0.75}$|⁠ , and |$r_{0}=31.11_{-5.88}^{+7.61}$|⁠ , which are in good agreement with previous results. We also find that introducing an extra parameter, the radially varying flattening factor, greatly improves our ability to model accurately the observed data distribution. This implies perhaps that the stellar halo of the Milky Way should be regarded as oblate. [ABSTRACT FROM AUTHOR]

The projection stellar target simulator is a stellar target simulator in which star points are projected to be imaged on a fixed plane at a fixed distance. Compared with conventional stellar target simulators, the projection stellar target simulator makes star points visible and provides the necessary condition for a semi-physical simulation test of the star camera. In this paper, the projection stellar target simulator optical system with high-quality imaging is designed by combining the projection technology, which breaks the collimated imaging of the conventional stellar target simulator optical system, and offers a new thought to solve the problem of decreasing the calibration accuracy caused by the influence of the coaxiality and other factors in the stellar target simulator calibrating the star camera. Based on the imaging behavior of the star map, this paper proposes a method to realize the automatic detection of a projection stellar target simulator by using CCD and introduces the composition and working principle of the detection system in detail. According to the imaging characteristics of star points, denoising and threshold segmentation of the star map are carried out, and an improved centroid algorithm is proposed to achieve high-precision positioning of the centroid coordinates of the star points. The measurement model and measuring formulas for the angular distance between stars are established. The error sources of the detection system are analyzed and obtain the theoretical error of 9.22″ for this detection system. The result of an actual test experiment shows that the position error of single star is less than 11″, in line with the theoretical analysis of the error, indicating the detection system has high detection precision and meets the requirement for the detection accuracy of the projection stellar target simulator. [ABSTRACT FROM AUTHOR]

This work presents the magnetic field geometry in a complex of three cometary (with head–tail morphology) globules, namely LDN 323, LDN 328, and LDN 331, using R -band polarization measurements of background stars. These observations were combined with a Planck sky survey to study the large-scale morphology of the magnetic fields in the region. The distances of the target stars were adopted from the Gaia catalogue. The variation of the degree of polarization and polarization position angle with distances of stars is analysed. The field geometry is mostly found to follow the cometary shape of the cloud, with some randomness at certain locations. For studying the correlation between cloud morphology and magnetic field orientations, a modified version of the histogram of relative orientation (HRO) analysis was employed. [ABSTRACT FROM AUTHOR]

We present the results from our deep optical photometric observations of Bochum 2 (Boc2) star cluster obtained using the 1.3-m Devasthal Fast Optical Telescope along with archival photometric data from Pan-STARRS2/2MASS/UKIDSS surveys. We also used high-quality parallax and proper motion data from the Gaia Data Release 3. We found that the Boc2 cluster has a small size (∼ 1.1 pc) and circular morphology. Using Gaia parallax of member stars and isochrone fitting method, the distance of this cluster is estimated as 3.8 ± 0.4 kpc. We have found that this cluster holds young ( ∼ 5 Myr) and massive (O7–O9) stars as well as an older population of low mass stars. We found that the massive stars were formed in the inner region of the Boc2 cluster in a recent epoch of star formation. We have derived mass function slope (Γ ) in the cluster region as - 2.42 ± 0.13 in the mass range of ∼ 0.72 < M / M ⊙ < 2.8 . The tidal radius of the Boc2 cluster (∼ 7–9) is much more than its observed radius ( ∼ 1.1 pc). This suggests that most of the low-mass stars in this cluster are the remains of an older population of stars formed via an earlier epoch of star formation. [ABSTRACT FROM AUTHOR]

We investigate the underlying distribution of orbital eccentricities for planets around early-to-mid M dwarf host stars. We employ a sample of 163 planets around early-to mid-M dwarfs across 101 systems detected by NASA's Kepler Mission. We constrain the orbital eccentricity for each planet by leveraging the Kepler lightcurve together with a stellar density prior, constructed using metallicity from spectroscopy, Ks magnitude from 2MASS, and stellar parallax from Gaia. Within a Bayesian hierarchical framework, we extract the underlying eccentricity distribution, assuming alternately Rayleigh, half-Gaussian, and Beta functions for both single- and multi-transit systems. We described the eccentricity distribution for apparently single-transiting planetary systems with a Rayleigh distribution with σ = 0:19+0:04-0:03, and for multitransit systems with σ = 0:03+0:02-0:01. The data suggest the possibility of distinct dynamically warmer and cooler subpopulations within the single-transit distribution: The single-transit data prefer a mixture model composed of two distinct Rayleigh distributions with σ1 = 0:02+0:11-0:00 and σ2 = 0:24+0:20-0:03 over a single Rayleigh distribution, with 7:1 odds. We contextualize our findings within a planet formation framework, by comparing them to analogous results in the literature for planets orbiting FGK stars. By combining our derived eccentricity distribution with other M dwarf demographic constraints, we estimate the underlying eccentricity distribution for the population of early- to mid-M dwarf planets in the local neighborhood. [ABSTRACT FROM AUTHOR]

The Be stars display variable optical emission lines originating in the circumstellar disc. Here we analyze high resolution spectroscopic observations of Be stars and the distance between the peaks of Hα$$ \mathrm{H}\alpha $$, Hβ$$ \mathrm{H}\beta $$, and Hγ$$ \mathrm{H}\gamma $$ emission lines (ΔVα$$ \Delta {V}_{\alpha } $$,ΔVβ$$ \Delta {V}_{\beta } $$, and ΔVγ$$ \Delta {V}_{\gamma } $$ respectively). Combining published data, spectra from the ELODIE archive (obtained in the period 1998–2003) and Rozhen spectra (obtained 2015–2023) of 93 Be stars, we find a set of relations connecting ΔVα$$ \Delta {V}_{\alpha } $$, ΔVβ$$ \Delta {V}_{\beta } $$ and ΔVγ$$ \Delta {V}_{\gamma } $$. They are effective for 30≤ΔVα≤500kms−1$$ 30\le \Delta {V}_{\alpha}\le 500\kern0.3em \mathrm{km}\kern0.3em {\mathrm{s}}^{-1} $$, 80≤ΔVβ≤600kms−1$$ 80\le \Delta {V}_{\beta}\le 600\kern0.3em \mathrm{km}\kern0.3em {\mathrm{s}}^{-1} $$, and 40≤ΔVγ≤300kms−1$$ 40\le \Delta {V}_{\gamma}\le 300\kern0.3em \mathrm{km}\kern0.3em {\mathrm{s}}^{-1} $$. The new equations are in the form y=ax+b$$ y= ax+b $$ and are valid for a wider velocity range than in previous studies. [ABSTRACT FROM AUTHOR]

The document titled "Exoplanet Division Meeting, 2023 September 30: Variations on an exoplanet theme" provides an update on the Asteroids & Remote Planets Section Exoplanet Division Meeting held on September 30, 2023. The meeting aimed to review the variations in exoplanet transits and demonstrate how these variations can be measured to infer possible causes. Presentations were given on topics such as the effects of stellar activity on transit timings, the causes of transit-timing variations, and the potential habitability of transiting exoplanets. Various software packages for analyzing exoplanet data were also discussed. The document concludes with a list of new members welcomed by the British Astronomical Association. [Extracted from the article]

Gravitational-wave astronomy allows us to study objects and events invisible to electromagnetic waves. So far, only signals triggered by coalescing binaries have been detected. However, as the interferometers' sensitivities improve over time, we expect to observe weaker signals in the future, e.g. emission of continuous gravitational waves from spinning, isolated neutron stars. Parallax is a well-known method, widely used in electromagnetic astronomical observations, to estimate the distance to a source. In this work, we consider the application of the parallax method to gravitational-wave searches and explore possible distance estimation errors. We show that detection of parallax in the signal from a spinning down source can constrain the neutron star moment of inertia. For instance, we found that the relative error of the moment of inertia estimation is smaller than 10 per cent for all sources closer than 300 pc, for the assumed birth frequency of 700 Hz, ellipticity ≥10−7, and for 2 yr of observations by the Einstein Telescope, assuming spin-down due purely to quadrupolar gravitational radiation. [ABSTRACT FROM AUTHOR]

Detection of continuous gravitational waves from rapidly spinning neutron stars opens up the possibility of examining their internal physics. We develop a framework that leverages a future continuous gravitational wave detection to infer a neutron star's moment of inertia, equatorial ellipticity, and the component of the magnetic dipole moment perpendicular to its rotation axis. We assume that the neutron star loses rotational kinetic energy through both gravitational wave and electromagnetic radiation, and that the distance to the neutron star can be measured, but do not assume electromagnetic pulsations are observable or a particular neutron star equation of state. We use the Fisher information matrix and Monte Carlo simulations to estimate errors in the inferred parameters, assuming a population of gravitational-wave-emitting neutron stars consistent with the typical parameter domains of continuous gravitational wave searches. After an observation time of 1 yr, the inferred errors for many neutron stars are limited chiefly by the error in the distance to the star. The techniques developed here will be useful if continuous gravitational waves are detected from a radio, X-ray, or gamma-ray pulsar, or else from a compact object with known distance, such as a supernova remnant. [ABSTRACT FROM AUTHOR]

The Milky Way halo is one of the few galactic haloes that provides a unique insight into galaxy formation by resolved stellar populations. Here, we present a catalogue of ∼47 million halo stars selected independent of parallax and line-of-sight velocities, using a combination of Gaia DR3 proper motion and photometry by means of their reduced proper motion. We select high tangential velocity (halo) main sequence stars and fit distances to them using their simple colour-absolute-magnitude relation. This sample reaches out to ∼21 kpc with a median distance of 6.6 kpc thereby probing much further out than would be possible using reliable Gaia parallaxes. The typical uncertainty in their distances is |$0.57_{-0.26}^{+0.56}$|  kpc. Using the colour range 0.45 < (G 0 − G RP, 0) < 0.715, where the main sequence is narrower, gives an even better accuracy down to |$0.39_{-0.12}^{+0.18}$| kpc in distance. The median velocity uncertainty for stars within this colour range is 15.5 km s−1. The distribution of these sources in the sky, together with their tangential component velocities, are very well-suited to study retrograde substructures. We explore the selection of two complex retrograde streams: GD-1 and Jhelum. For these streams, we resolve the gaps, wiggles and density breaks reported in the literature more clearly. We also illustrate the effect of the kinematic selection bias towards high proper motion stars and incompleteness at larger distances due to Gaia 's scanning law. These examples showcase how the full RPM catalogue made available here can help us paint a more detailed picture of the build-up of the Milky Way halo. [ABSTRACT FROM AUTHOR]

Machine learning can play a powerful role in inferring missing line-of-sight velocities from astrometry in surveys such as Gaia. In this paper, we apply a neural network to Gaia Early Data Release 3 (EDR3) and obtain line-of-sight velocities and associated uncertainties for ∼92 million stars. The network, which takes as input a star's parallax, angular coordinates, and proper motions, is trained and validated on ∼6.4 million stars in Gaia with complete phase-space information. The network's uncertainty on its velocity prediction is a key aspect of its design; by properly convolving these uncertainties with the inferred velocities, we obtain accurate stellar kinematic distributions. As a first science application, we use the new network-completed catalogue to identify candidate stars that belong to the Milky Way's most recent major merger, Gaia -Sausage-Enceladus (GSE). We present the kinematic, energy, angular momentum, and spatial distributions of the ∼450 000 GSE candidates in this sample, and also study the chemical abundances of those with cross matches to GALAH and APOGEE. The network's predictive power will only continue to improve with future Gaia data releases as the training set of stars with complete phase-space information grows. This work provides a first demonstration of how to use machine learning to exploit high-dimensional correlations on data to infer line-of-sight velocities, and offers a template for how to train, validate, and apply such a neural network when complete observational data is not available. [ABSTRACT FROM AUTHOR]

Actively accreting young stellar objects show H α emission line in their spectra. We present the results of survey for H α emission-line stars in the star-forming region IC 5070 taken with 2-m Himalyan Chandra Telescope. Based on the H α slitless spectroscopy data, we identified 131 emission-line stars in ∼ 0.29 square degrees area of the IC 5070 region. Using Gaia early data release 3, we estimated the mean proper motion and parallax of the emission-line stars. We also estimated the mean distance and reddening toward the region using the emission-line stars, which are ∼ 833 pc and ∼ 2 mag, respectively. By examining the locations of these stars in the color–magnitude diagrams constructed using Gaia and PanSTARRS1 data, we found that a majority of the H α emitters are young low-mass ( < 1.5 M ⊙ ) stars. We also compared our catalog of emission-line stars with the available young stellar catalogs and found that most of them are class ii/flat spectrum sources with the spectral type ranging from K to M. Based on the proper motion/parallax values and locations on the color–magnitude diagrams, about 20 emission-line stars are flagged as non-members. The relative proper motion of the emission-line stars with respect to the ionizing source suggest the possibility of the 'rocket effect' scenario in the remnant cloud (BRC 31). [ABSTRACT FROM AUTHOR]

Serpens molecular cloud is one of the most active sites of ongoing star formation at a distance of about 300 pc, and hence, is very well-suited for studies of young low-mass stars and sub-stellar objects. In this paper, for the Serpens star-forming region, we found potential members of the Young Stellar Objects (YSOs) population from the Gaia DR3 data and study their kinematics and distribution. We compiled a catalog of 656 YSOs from available catalogs ranging from X-ray to the infrared. We use this as a reference set and cross-match it to find 87 Gaia DR3 member stars to produce a control sample with revised parameters. We queried the DR3 catalog with these parameters and found 1196 stars. We then applied three different density-based machine learning algorithms (DBSCAN, OPTICS and HDBSCAN) to this sample and found potential YSOs. The three clustering algorithms identified a common set of 822 YSO members from Gaia DR3 in this region. We also classified these objects using 2MASS and WISE data to study their distribution and the progress of star-formation in Serpens. [ABSTRACT FROM AUTHOR]

We present a sample of 254,882 luminous red giant branch (LRGB) stars selected from the APOGEE and LAMOST surveys. By combining photometric and astrometric information from the Two Micron All Sky Survey and Gaia survey, the precise distances of the sample stars are determined by a supervised machine-learning algorithm: the gradient-boosted decision trees. To test the accuracy of the derived distances, member stars of globular clusters (GCs) and open clusters are used. The tests by cluster member stars show a precision of about 10% with negligible zero-point offsets, for the derived distances of our sample stars. The final sample covers a large volume of the Galactic disk(s) and halo of 0 < R < 30 kpc and ∣ Z ∣ ≤ 15 kpc. The rotation curve (RC) of the Milky Way across the radius of 5 ≲ R ≲ 25 kpc has been accurately measured with ∼54,000 stars of the thin disk population selected from the LRGB sample. The derived RC shows a weak decline along R with a gradient of −1.83 ± 0.02 (stat.) ± 0.07 (sys.) km s−1 kpc−1, in excellent agreement with the results measured by previous studies. The circular velocity at the solar position, yielded by our RC is 234.04 ± 0.08 (stat.) ± 1.36 (sys.) km s−1, again in great consistency with other independent determinations. From the newly constructed RC, as well as constraints from other data, we have constructed a mass model for our Galaxy, yielding a mass of the dark matter halo of M 200 = (8.05 ± 1.15) × 1011 M ⊙ with a corresponding radius of R 200 = 192.37 ± 9.24 kpc and a local dark matter density of 0.39 ± 0.03 GeV cm−3. [ABSTRACT FROM AUTHOR]

The first James Webb Space Telescope (JWST) data on the massive colliding cluster El Gordo allow for 23 known families of multiply lensed images to be confirmed and for eight new members of these families to be identified. Based on these families, which have been confirmed spectroscopically by MUSE, we derived an initial lens model. This model guided the identification of 37 additional families of multiply lensed galaxies, among which 28 are entirely new systems, and nine were previously known. The initial lens model determined geometric redshifts for the 37 new systems. The geometric redshifts agree reasonably well with spectroscopic or photometric redshifts when those are available. The geometric redshifts enable two additional models that include all 60 families of multiply lensed galaxies spanning a redshift range 2 < z < 6. The derived dark-matter distribution confirms the double-peak configuration of mass found by earlier work with the southern and northern clumps having similar masses. We confirm that El Gordo is the most massive known cluster at z > 0:8 and has an estimated virial mass close the maximum mass allowed by standard cosmological models. The JWST images also reveal the presence of small-mass perturbers that produce small lensing distortions. The smallest of these is consistent with being a dwarf galaxy at z = 0:87 and has an estimated mass of 3:8 109 M, making it the smallest substructure found at z > 0:5. The JWST images also show several candidate caustic-crossing events. One of them is detected at high significance at the expected position of the critical curve and is likely a red supergiant star at z = 2:1878. This would be the first red supergiant found at cosmological distances. The cluster lensing should magnify background objects at z > 6, making more of them visible than in blank fields of a similar size, but there appears to be a deficiency of such objects. [ABSTRACT FROM AUTHOR]

HD 172555 is a young (~20 Myr) A7V star surrounded by a 10 au wide debris disk suspected to be replenished partly by collisions between large planetesimals. Small evaporating transiting bodies, that is exocomets, have also been detected in this system by spectroscopy. After β Pictoris, this is another example of a system possibly witnessing a phase of the heavy bombardment of planetesimals. In such a system, small bodies trace dynamical evolution processes. We aim to constrain their dust content by using transit photometry. We performed a 2-day-long photometric monitoring of HD 172555 with the CHEOPS space telescope in order to detect shallow transits of exocomets with a typical expected duration of a few hours. The large oscillations in the light curve indicate that HD 172555 is a δ Scuti pulsating star. After removing those dominating oscillations, we found a hint of a transient absorption. If fitted with an exocomet transit model, it would correspond to an evaporating body passing near the star at a distance of 6.8±1.4R★ (or 0.05±0.01 au) with a radius of 2.5 km. These properties are comparable to those of the exocomets already found in this system using spectroscopy, as well as those found in the β Pic system. The nuclei of the Solar System's Jupiter family comets, with radii of 2-6 km, are also comparable in size. This is the first piece of evidence of an exocomet photometric transit detection in the young system of HD 172555. [ABSTRACT FROM AUTHOR]

We report the spectroscopic analysis of 20 halo ab-type RR Lyrae stars with heliocentric distances between 15 and 165 kpc, conducted using medium-resolution spectra from the Magellan Inamori Kyocera Echelle (MIKE) spectrograph. We obtain the systemic line-of-sight velocities of our targets with typical uncertainties of 5–10 km s−1 and compute orbital parameters for a subsample out to 50 kpc from the Galactic centre, including proper motion data from Gaia DR3. The orientation of our stars' orbits, determined for an isolated Milky Way and for a model perturbed by the Large Magellanic Cloud, appears to suggest an accreted origin for at least half of the sample. In addition, we derive atmospheric parameters and chemical abundance ratios for seven stars beyond 20 kpc. The derived α-abundances of five of these stars follow a Milky Way halo-like trend, while the other two display an underabundance of α-elements for their [Fe/H], indicating an association with accretion events. Furthermore, based on the [Sr/Ba] ratio, we can speculate about the conditions for the formation of a potential chemically peculiar carbon-enhanced metal-poor (CEMP) RR Lyrae star. By analysing the stars' orbital parameters and abundance ratios, we find hints of association of two of our stars with two massive satellites, namely the Large Magellanic Cloud and Sagittarius. Overall, our results are in line with the suggestion that the accretion of sub-haloes largely contributes to the outer halo stellar populations. [ABSTRACT FROM AUTHOR]

The distance to the Galactic centre R 0 is a fundamental parameter for understanding the Milky Way, because all observations of our Galaxy are made from our heliocentric reference point. The uncertainty in R 0 limits our knowledge of many aspects of the Milky Way, including its total mass and the relative mass of its major components, and any orbital parameters of stars employed in chemo-dynamical analyses. While measurements of R 0 have been improving over a century, measurements in the past few years from a variety of methods still find a wide range of R 0 being somewhere within 8.0 to |$8.5\, \mathrm{kpc}$|⁠. The most precise measurements to date have to assume that Sgr A* is at rest at the Galactic centre, which may not be the case. In this paper, we use maps of the kinematics of stars in the Galactic bar derived from APOGEE DR17 and Gaia EDR3 data augmented with spectrophotometric distances from the astroNN neural-network method. These maps clearly display the minimum in the rotational velocity vT and the quadrupolar signature in radial velocity vR expected for stars orbiting in a bar. From the minimum in vT , we measure |$R_0 = 8.23\pm 0.12\, \mathrm{kpc}$|⁠. We validate our measurement using realistic N -body simulations of the Milky Way. We further measure the pattern speed of the bar to be |$\Omega _\mathrm{bar} = 40.08\pm 1.78\, \mathrm{km\, s}^{-1}\,\mathrm{kpc}^{-1}$|⁠. Because the bar forms out of the disc, its centre is manifestly the barycentre of the bar+disc system and our measurement is therefore one of the most robust and accurate measurements of R 0 to date. [ABSTRACT FROM AUTHOR]

Knowledge of the three-dimensional structure of Galactic molecular clouds is important for understanding how clouds are affected by processes such as turbulence and magnetic fields and how this structure affects star formation within them. Great progress has been made in this field with the arrival of the Gaia mission, which provides accurate distances to ∼109 stars. Combining these distances with extinctions inferred from optical–infrared, we recover the three-dimensional structure of 16 Galactic molecular cloud complexes at ∼1 pc resolution using our novel three-dimensional dust mapping algorithm dustribution. Using astrodendro , we derive a catalogue of physical parameters for each complex. We recover structures with aspect ratios between 1 and 11, i.e. everything from near-spherical to very elongated shapes. We find a large variation in cloud environments that is not apparent when studying them in two dimensions. For example, the nearby California and Orion A clouds look similar on sky, but we find California to be more sheet-like, and massive, which could explain their different star formation rates. By calculating the total mass of these individual clouds, we demonstrate that it is necessary to define cloud boundaries in three dimensions in order to obtain an accurate mass; simply integrating the extinction overestimates masses. We find that Larson's relationship on mass versus radius holds true whether you assume a spherical shape for the cloud or take their true extents. [ABSTRACT FROM AUTHOR]

For solar-like oscillators, the asteroseismic relations connect the stellar mean density and surface gravity to observable properties of the oscillations. Since the space missions CoRoT and Kepler, the asteroseismic relations have been massively employed out of their theoretical domain of validity, that is the main-sequence solar-type stars, in particular for red giant stars. However, despite a surprisingly good performance of the asteroseismic relation with red giant stars, they are biased and attempts to parametrize the departure of the relations for evolved stars have been the subject of many recent efforts. In this study, we propose a new parametrization of the asteroseismic relations for red giants of radii up to |${\sim } 50\, \mathrm{R}_\odot$|⁠ , based on a calibration performed with Gaia parallax data. We find that the asteroseismic scaling relations depend on metallicity and effective temperature. For this solution, we obtain a parallax offset of about −0.026 ± 0.001 mas, and radius ranges from 3.8 to 53.2 R⊙. Most stars have masses that range from 0.9 to 1.7 M⊙, with the star count peaking around 1.2 M⊙. We also use data of the eclipsing binaries with solar-like oscillating components for calibration and discuss the diagnostic potential of the mass–metallicity diagram for our understanding of the evolution of red giants and the chemodynamics of the Galactic disc. Using this diagram, we identify stars that lost and gained mass and estimate the minimum change in mass. [ABSTRACT FROM AUTHOR]

Up to now and probably for still a long time, the only support of information used to detect exoplanets has been the analysis of light, either visible or infrared. In the vast majority of cases it is the light from a star and not the light from the planet itself which is used, because the huge contrast in brightness between the star and a planet orbiting it as well as the extremely short angular distance between them makes direct imaging a real challenge. It is then a subtle effect detected on the starlight that in general indicates the planet's presence and provides information on some of its characteristics: mass, radius, distance to the star, temperature, etc. As an introduction to the different contributions appearing in this volume, this article proposes a kind of brief review of the various methods imagined by astronomers to exploit one of the properties of the light to succeed in detecting and characterizing exoplanets. We'll show that even direct detection became a reality and contributes to the more than 5000 exoplanets detected today. [ABSTRACT FROM AUTHOR]

In addition to the complete set of fundamental parameters of its individual components, we present the solution for the discrepancy between the two main astrometric space telescopes Gaia and Hipparcos, in their measurements of the trigonometric parallax for the stellar binary system Hip 84976. In our analysis of the system, we followed Al-Wardat's method for analyzing binary and multiple stellar systems along with Tokovinin's dynamical method. Using these two methods, we estimated the system's atmospheric, dynamical, and geometrical parameters including the individual masses. The estimated masses and the modified orbital elements were used to give a new dynamical parallax for the system as ( π Dyn = 11.48 ± 0.45 mas), which lies between the measurements given by the old (9.01 ± 1.22 mas) and the new (11.80 ± 1.23 mas) Hipparcos catalogs. It also shows that Hipparcos 2's (2007) parallax measurement is more accurate than that given by Gaia DR3 (12.5899 ± 0.3496 mas) for this system, while that given by Gaia DR2 (24.1841 ± 1.8560 mas) is far from accurate. The results were used to put the two components of the system on the right positions on the H-R diagram, evolutionary tracks, and isochrones, and proposed that the system was formed by fragmentation 1.99 Gyr ago. [ABSTRACT FROM AUTHOR]

The next generation of detectors will detect gravitational waves from binary neutron stars at cosmological distances, for which around a 1000 electromagnetic follow-ups may be observed per year. So far, most work devoted to the expected cosmological impact of these standard sirens employed them only as distance indicators. Only recently their use as tracers of clustering, similar to what already proposed for supernovae, has been studied. Focusing on the expected specifications of the Einstein Telescope (ET), we forecast here the performance on cosmological parameters of future standard sirens as both distance and density indicators, with emphasis on the linear perturbation growth index and on spatial curvature. We improve upon previous studies in a number of ways: a more detailed analysis of available telescope time, the inclusion of more cosmological and nuisance parameters, the Alcock–Paczynski correction, the use of sirens also as both velocity and density tracers, and a more accurate estimation of the distance posterior. We find that the analysis of the clustering of sirens improves the constraints on H 0 by 30 per cent and on Ω k 0 by over an order of magnitude, with respect to their use merely as distance indicators. With 5 yr of joint ET and Rubin Observatory follow-ups we could reach precision of 0.1 km s−1 Mpc−1 in H 0 and 0.02 in Ω k 0 using only data in the range 0 < z < 0.5. We also find that the use of sirens as tracers of density, and not only velocity, yields good improvements on the growth of structure constraints. [ABSTRACT FROM AUTHOR]

Westerlund 1 (Wd 1) is one of the most relevant star clusters in the Milky Way to study massive star formation, although it is still poorly known. Here, we used photometric and spectroscopic data to model the eclipsing binary W36, showing that its spectral type is O6.5 III  +  O9.5 IV, hotter and more luminous than thought before. Its distance d W36 = 4.03 ± 0.25 kpc agrees, within the errors, with three recent Gaia-EDR3-based distances reported in Paper I, Beasor & Davies, and by Negueruela's group. However, they follow different approaches to fix the zero-points for red sources such as those in Wd 1, and to select the best approach, we used an accurate modelling of W36. The weighted mean distance of our parallax (Paper I) and binary distances results in d wd1 = 4.05 ± 0.20 kpc, with an unprecedented accuracy of 5 per cent. We adopted isochrones based on the Geneva code with supersolar abundances to infer the age of W36B as 6.4 ± 0.7 Myr. This object seems to be part of the prolific star formation burst represented by OB giants and supergiants that occurred at 7.1 ± 0.5 Myr ago, which coincides with the recently published PMS isochrone with age 7.2 Myr. Other BA-type luminous evolved stars and yellow hypergiants spread in the age range of 8–11 Myr. The four red supergiants discussed in paper I represent the oldest population of the cluster with an age of 10.7 ± 1 Myr. The multiple episodes of star formation in Wd 1 are reminiscent of that reported for the R136/30 Dor LMC cluster. [ABSTRACT FROM AUTHOR]