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We present a mock catalog of Milky Way stars, matching in volume and depth the content of the Gaia data release 2 (GDR2). We generated our catalog using Galaxia, a tool to sample stars from a Besançon Galactic model, together with a realistic 3D dust extinction map. The catalog mimics the complete GDR2 data model and contains most of the entries in the Gaia source catalog: five-parameter astrometry, three-band photometry, radial velocities, stellar parameters, and associated scaled nominal uncertainty estimates. In addition, we supplemented the catalog with extinctions and photometry for non-Gaia bands. This catalog can be used to prepare GDR2 queries in a realistic runtime environment, and it can serve as a Galactic model against which to compare the actual GDR2 data in the space of observables. The catalog is hosted through the virtual observatory GAVO's Heidelberg data center (http://dc.g-vo.org/tableinfo/gdr2mock.main) service, and thus can be queried using ADQL as for GDR2 data.

We present results of our study of the long-period eclipsing binary star NN Delphini (hereafter NN Del). The results are based on spectral data obtained with the HRS échelle spectrograph of the Southern African Large Telescope (SALT). Our constructed velocity curve is based on 19 spectra obtained between 2017 and 2019 years and covers all phases of the binary’s orbit. The orbital period, P=99.252 days, was determined from our spectral data and coincides with the period determined in previous studies, as well as the system eccentricity of e=0.517. Calculated velocity amplitudes of both components allow us to determine the masses of both system components M1=1.320M⊙ and M2=1.433M⊙ with the accuracy about of one percent (0.8% and 1.1%), respectively. Luminosities of both components are presented as L1=4.164L⊙ and L2=6.221L⊙, and the effective temperatures of both components were directly evaluated (Teff1=6545 K and Teff2=6190 K) together with the metallicity of the system [Fe/H]=−0.19 dex and its color excess E(B-V) = 0.026 mag. Comparison with evolutionary tracks shows that the system age is 2.25±0.19 Gyr, and both components are on the main sequence and have not yet passed the turn point. Spectral type is F5V for the hotter component and F8V for another one.

We collected radial velocities of more than 50.000 individual stars in 156 Galactic globular clusters (GGC) and matched them with HST photometry and Gaia DR2 proper motions. This allowed us to derive the GGC’s mean proper motions and space velocities. By fitting a large set of N-body simulations to their velocity dispersion and surface density profiles, combined with new measurements of their internal radially dependent mass functions, we have determined their present-day masses and structural parameters, and for 144 GGCs their internal kinematics. We also derive the initial cluster masses by calculating the cluster orbits backwards in time applying suitable recipes to account for mass-loss and dynamical friction. The new fundamental parameters of GGCs are publicly available via an online database, which will regularly be updated.

Gaia DR2 catalog provides a unique possibility to study the three-dimensional structure and the three-dimensional velocity field of the nearby open clusters. We can either select stars with a maximum membership probability and the most accurate values for the proper motions, parallaxes, and the radial velocities, or study these clusters statistically using overwhelmingly large areas of sky of tens by tens degrees. The second approach allows us to reveal the extensive outer parts of the clusters - a corona and the tidal tails and to study the luminosity and mass functions of these clusters. We present the first results of the investigation of several nearby open clusters, including Pleiades, Alpha Persei, Ruprecht 147.

In this paper, we analyze the open cluster NGC 1039. This young open cluster is observed as a part of Beijing-Arizona-Taiwan-Connecticut Multicolor Sky Survey. Combining our observations with the Sloan Digital Sky Survey photometric data, we employ the Padova stellar model and the zero-age main-sequence curve to the data to derive a reddening, E ( B − V ) = 0.10 0.02 , and a distance modulus, ( m − M ) 0 = 8.4 0.2 , for NGC 1039. The photometric membership probabilities of stars in the region of NGC 1039 are derived using the spectral energy distribution-fitting method. According to the membership probabilities ( P SED ) obtained here, 582 stars are cluster members with P SED larger than 60%. In addition, we determine the structural parameters of NGC 1039 by fitting its radial density profile with the King model. These parameters are a core radius, R c = 4.44 1.31 pc ; a tidal radius, R t = 13.57 4.85 pc ; and a concentration parameter of C 0 = log ( R t R c ) = 0.49 0.20 . We also fit the observed mass function of NGC 1039 with masses from 0.3 M to 1.65 M with a power-law function Φ ( m ) ∝ m to derive its slopes of mass functions of different spatial regions. The results obtained here show that the slope of the mass function of NGC 1039 is flatter in the central regions ( = 0.117), becomes steeper at larger radii ( = −2.878), and breaks at m break 0.80 M . In particular, for the first time, our results show that the mass segregation appears in NGC 1039.

The rate of star formation (SFR) is one of the important quantities that helps to study galaxies’ evolutionary path. In fact, measuring the SFR during the life of the Universe shows us how galaxies have acquired their metallicity and star mass. In this regard, the galaxies of the Local Group give us a great opportunity to study the connection between different stellar populations and galaxy evolution. In this paper, we use the Long-Period variable stars to estimate the radial star formation in the disc of the M31 galaxy. These stars are powerful instruments to achieve this goal. They reach their peak luminosity and coldest state at the final point of their evolution. Also, there is a directly related between their mass and luminosity, so using stellar evolution theoretical models, we construct the mass function and hence the star formation history (SFH). In the disc of M31, we see an increase in the rate of star formation and a decrease in the age of stars in the outer parts. These results predict the inside-out growth well.

One of the ways to understand the genesis and evolution of the universe is to know how galaxies have formed and evolved. In this regard, the study of star formation history (SFH) plays an important role in the accurate understanding of galaxies. In this paper, we used long-period variable stars (LPVs) for estimating the SFH in the Andromeda galaxy (M31). These cool stars reach their peak luminosity in the final stage of their evolution also their birth mass is directly related to their luminosity. Therefore, using stellar evolution models, we construct the mass function and hence the star formation history.

From data collection to photometric fitting and analysis of white dwarfs, to generating a white dwarf luminosity function requires numerous astrophysical, mathematical, and computational domain knowledge. The steep learning curve makes it difficult to enter the field, and often individuals have to reinvent the wheel to perform identical data reduction and analysis tasks. We have gathered a wide range of publicly available white dwarf cooling models and synthetic photometry to provide a toolkit that allows (i) visualization of various models, (ii) photometric fitting of a white dwarf with or without distance and reddening, and (iii) the computing of white dwarf luminosity functions with a choice of initial mass function, main-sequence evolution model, star-formation history, initial–final mass relation, and white dwarf cooling model. We have recomputed and compared the effective temperature of the white dwarfs from the Gaia EDR3 white dwarf catalogue. The two independent works show excellent agreement in the temperature solutions.

Many intermediate polars are hard X-ray sources. The theory of their hard X-ray radiation is well developed and allows us to determine white dwarf masse in this kind of cataclysmic variables. Here we present the results of determination the masses of 35 white dwarfs in the intermediate polars observed by observatories NuSTAR (10 sources) and Swift/BAT (25 sources). The corresponding mass accrerion rates and the luminosity function were also derived due to accurate distance to the sources well known now after Gaia DR2.

We theoretically investigate the impact of feedback and its metallicity dependence in massive star formation from prestellar cores at all metallicity range. We include the feedback by MHD disk winds, radiation pressure, and photoevaporation solving the evolution of protostars and accretion flows self-consistently. Interestingly, we find that the feedback does not set the upper mass limit of stellar birth mass at any metallicity. At the solar metallicity, the MHD disk wind is the dominant feedback to set the star formation efficiencies (SFEs) from the prestellar cores similar to low-mass star formation. The SFE is found to be lower at lower surface density environment. The photoevaporation becomes significant at the low metallicity of Z < 10 −2 Z ⊙ . Considering this efficient photoevaporation, we conclude that the IMF slope is steeper, i.e., massive stars are rarer at the extremely metal-poor environment of 10 −5 − 10 −3 Z ⊙ . Our study raises a question on the common assumption of the universal IMF with a truncated at 100 M ⊙ . Since the total feedback strength in the cluster/galaxy scale is sensitive to the number fraction of massive stars, the re-evaluations of IMF at various environments are necessary.