Mikhail Kovalev

Yunnan observatories · Binary Population Synthesis Group

Whereas light element abundance variations are a hallmark of globular clusters, there is little evidence for variation in neutron-capture elements. A significant exception is M15, which shows a star-to-star dispersion in neutron-capture abundances of at least one order of magnitude. The literature contains evidence both for and against a neutron-ca...

We present the detection of false positive double-lined spectroscopic binaries candidates (SB2) using medium-resolution survey (MRS) spectra from the one time-domain field of LAMOST data release 10 (DR10). The secondary component in all these binaries has near zero radial velocity and solar-like spectral lines. Highly likely this is light from the...

We present the detection of false positive double-lined spectroscopic binaries candidates (SB2) using medium-resolution survey (MRS) spectra from the one time-domain field of LAMOST data release 10 (DR10). The secondary component in all these binaries has near zero radial velocity and solar-like spectral lines. Highly likely this is light from the...

In this paper we applied previously developed method of binary spectral model fitting to the high resolution spectra of HD 20784. Simultaneously analyzing all three available epochs we found spectroscopic parameters for both components of the system. These parameters are consistent with stellar evolution model’s predictions and analysis of the phot...

Launch of the Gaia space observatory started a new era in astrometry when the accuracy of star coordinates increased by thousands of times. Significant improvement of accuracy was also expected for the coordinates of the Solar system bodies. Gaia DR3 provided us with the data which could be used to test our expectations. In this work, we refine the...

We present a study of the detached eclipsing binary J064726.39+223431.6 using spectra from the LAMOST medium-resolution spectra and TESS photometry. We use full-spectrum fitting to derive radial velocities and spectral parameters: TeffA, B = 6177, 5820 K, Vsin iA, B = 59, 50 km s−1 and [Fe/H]A, B = −0.19 dex. The orbital solution and light curve an...

We present a new method for the detection of double-lined spectroscopic binaries (SB2s) using Vsin i values from spectral fits. The method is tested on synthetic and real spectra from the Large Sky Area Multi-Object fiber Spectroscopic Telescope Medium Resolution Survey. It can reliably detect SB2 candidates for double-lined binaries with $V \sin {...

We analyse spectra of 26 early-type stars, with suspected binarity, using a binary spectral model adapted for high-resolution FEROS spectra. We confirm seven SB2 candidates (AE Pic, $\epsilon$ Vol, HD 20784, HD 208433, HD 43519, HD 56024, CD-73~375A) and derive mass ratios and spectroscopic parameters for them. We find good agreement with theoretic...

We present a study of eclipsing binary J064726.39+223431.6 using spectra from the LAMOST-MRS and TESS photometry. We use full-spectrum fitting to derive radial velocities and spectral parameters: ${T_{\rm eff}}_{A,B}=6177,\,5820$ K, $v \sin{i}_{A,B}=59,\,50~\kms$ and ${\rm [Fe/H]}_{A,B}=-0.19$ dex. The orbital solution and light curve analysis sugg...

We present a new method for the detection of double-lined spectroscopic binaries (SB2) $v\sin{i}$ values from spectral fits. The method is tested on synthetic and real spectra from LAMOST-MRS. It can reliably detect SB2 candidates for double-lined binaries with $v\sin{i}_1+v\sin{i}_2<300\,km\,s^{-1}$ if the radial velocity separation is large enoug...

We present a study of the spectroscopic binary TYC 2990-127-1 from the LAMOST survey. We use full-spectrum fitting to derive radial velocities and spectral parameters. The high mass ratio indicates that the system underwent mass transfer in the past. We compute the orbital solution and find that it is a very close sub-giant/red giant pair on circul...

We present a study of the spectroscopic binary TYC 2990-127-1 from the LAMOST survey. We use full-spectrum fitting to derive radial velocities and spectral parameters. The high mass ratio indicates that the system underwent mass transfer in the past. We compute the orbital solution and find that it is a very close sub-giant/red giant pair on circul...

From Oct. 2019 to Apr. 2020, LAMOST performed a time-domain (TD) spectroscopic survey of four K2 plates with both low- and medium-resolution observations. The low-resolution spectroscopic survey acquired 282 exposures ( ≈ 46.6 h) over 25 nights, yielding a total of about 767 000 spectra, and the medium-resolution survey took 177 exposures ( ≈ 49.1...

We have developed a new method for spectral analysis of binaries. Our method successfully identifies SB2 candidates from high-resolution Gaia-ESO spectra. Compared to the commonly used cross-correlation function analysis, it works for binaries with rapidly rotating components. We test our method on synthetic and observational spectra of BAFG-stars...

{We introduce the SAPP (Stellar Abundances and atmospheric Parameters Pipeline), the prototype of the code that will be used to determine parameters of stars observed within the core program of the PLATO space mission. The pipeline is based on the Bayesian inference and provides effective temperature, surface gravity, metallicity, chemical abundanc...

From Oct. 2019 to Apr. 2020, LAMOST performs a time-domain spectroscopic survey of four $K$2 plates with both low- and med-resolution observations. The low-resolution spectroscopic survey gains 282 exposures ($\approx$46.6 hours) over 25 nights, yielding a total of about 767,000 spectra, and the med-resolution survey takes 177 exposures ($\approx$4...

We have developed a new method for spectral analysis of binaries. Our method successfully identifies SB2 candidates from high-resolution Gaia-ESO spectra. Compared to the commonly used cross-correlation function analysis, it works for binaries with rapidly rotating components. We test our method on synthetic and observational spectra of young hot s...

Recent surveys uncovered new young massive clusters (YMCs) that host dozens of red supergiants (RSGs) in the inner Milky Way. These clusters are ideal for studying the most recent and violent star formation events in the inner Galaxy. However, due to the high extinction that affects the Galactic plane, they need to be studied through infrared (IR)...

Recent surveys uncovered new Young Massive Clusters (YMCs) that host dozens of Red Supergiants (RSGs) in the inner Milky Way. These clusters are ideal for studying the most recent and violent star formation events in the inner Galaxy. However, due to the high extinction that affects the Galactic plane, they need to be studied through infrared (IR)...

There is no consensus on the progenitors of Type Ia supernovae (SNe Ia) despite their importance for cosmology and chemical evolution. We address this question by using our previously published catalogs of Mg, Si, Ca, Cr, Fe, Co, and Ni abundances in dwarf galaxy satellites of the Milky Way to constrain the mass at which the white dwarf explodes du...

Aims. We study the effects of non-local thermodynamic equilibrium (NLTE) on the determination of stellar parameters and abundances of Fe, Mg, and Ti from the medium-resolution spectra of FGK stars. Methods. We extended the Payne fitting approach to draw on NLTE and LTE spectral models. These were used to analyse the spectra of the Gaia -ESO benchma...

Aims We study the effects of non-local thermodynamic equilibrium (NLTE) on the determination of stellar parameters and abundances of Fe, Mg, and Ti from the medium-resolution spectra of FGK stars.} Methods We extend the Payne fitting approach to draw on NLTE and LTE spectral models. These are used to analyse the spectra of the Gaia-ESO benchmark st...

There is no consensus on the progenitors of Type Ia supernovae (SNe Ia) despite their importance for cosmology and chemical evolution. We address this question by using our previously published catalogs of Mg, Si, Ca, Cr, Fe, Co, and Ni abundances in dwarf galaxy satellites of the Milky Way to constrain the mass at which the white dwarf explodes du...

We present measurements of the abundances of chromium, cobalt, and nickel in 4113 red giants, including 2277 stars in globular clusters, 1820 stars in the Milky Way's dwarf satellite galaxies, and 16 field stars. We measured the abundances from mostly archival Keck/DEIMOS medium-resolution spectroscopy with a resolving power of R ~ 6500 and a wavel...

The signatures of the formation and evolution of a galaxy are imprinted in its stars. Their velocities, ages, and chemical compositions present major constraints on models of galaxy formation, and on various processes such as the gas inflows and outflows, the accretion of cold gas, radial migration, and the variability of star formation activity. U...

We will study the formation history of the Milky Way, and the earliest phases of its chemical enrichment, with a sample of more than 1.5 million stars at high galactic latitude. Elemental abundances of up to 20 elements with a precision of better than 0.2 dex will be derived for these stars. The sample will include members of kinematically coherent...

The mechanisms of the formation and evolution of the Milky Way are encoded in the orbits, chemistry and ages of its stars. With the 4MOST MIlky way Disk And BuLgE Low-Resolution Survey (4MIDABLE-LR) we aim to study kinematic and chemical substructures in the Milky Way disc and bulge region with samples of unprecedented size out to larger distances...

In this work, we develop the spectral analysis pipeline that combines the NLTE synthetic spectra withthe Payne spectral model (Ting et al.2018). We compute two spectral grids, one grid with all elements treated in LTE and a second grid with iron, magnesium, titanium and manganese modelled in NLTE, to study the NLTE effects on the determination of t...

We present measurements of the abundances of chromium, cobalt, and nickel in 4113 red giants, including 2277 stars in globular clusters (GCs), 1820 stars in the Milky Way's dwarf satellite galaxies, and 16 field stars. We measured the abundances from mostly archival Keck/DEIMOS medium-resolution spectroscopy with a resolving power of R ~ 6500 and a...

We have analysed high-resolution spectra of 328 stars and derived Mg abundances using non-local thermodynamic equilibrium (NLTE) spectral line formation calculations and plane-parallel model stellar atmospheres derived from the mean stratification of 3D hydrodynamical surface convection simulations of late-type stars. The distribution of Mg abundan...

We determine Mg abundances in 8 standard stars using 1D hydrostatic and averaged 3D model atmospheres. The stars cover a large range of Teff from 4286 to 6500 K, log g from 1.64 to 4.44, and metallicity from -3.0 to solar. Radiative transfer calculations are performed in local thermodynamic equilibrium (LTE) and in non-LTE (NLTE). The linelist incl...

Red giant stars are perhaps the most important type of stars for Galactic and extra-galactic archaeology: they are luminous, occur in all stellar populations, and their surface temperatures allow precise abundance determinations for many different chemical elements. Yet, the full star formation and enrichment history of a galaxy can be traced direc...