Sofya Alexeeva

Sofya Alexeeva
Chinese Academy of Sciences | CAS · Optical Astronomy Research Department

PhD

About

33
Publications
1,824
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354
Citations
Additional affiliations
September 2019 - present
Chinese Academy of Sciences
Position
  • Fellow
September 2017 - September 2019
Shandong University
Position
  • PostDoc Position
Education
September 2012 - August 2017
September 2010 - June 2012
Ural Federal University
Field of study
  • Astrophysics

Publications

Publications (33)
Article
Blazar PG 1553+113 is thought to be a host of supermassive black hole binary system. A 2.2 yr quasi-periodicity in the γ -ray light curve was detected, possibly a result of jet precession. Motivated by the previous studies based on the γ -ray data, we analyzed the X-ray light curve and spectra observed during 2012–2020. The 2.2 yr quasi-periodicity...
Preprint
Full-text available
Blazar PG 1553+113 is thought to be a host of supermassive black hole binary (SMBHB) system. A 2.2-year quasi-periodicity in the $\gamma$-ray light curve was detected, possibly result of jet precession. Motivated by the previous studies based on the $\gamma$-ray data, we analyzed the X-ray light curve and spectra observed during 2012--2020. The 2.2...
Preprint
Full-text available
During October 2019 and March 2020, the luminous red supergiant Betelgeuse demonstrated an unusually deep minimum of its brightness. It became fainter by more than one magnitude and this is the most significant dimming observed in the recent decades. While the reason for the dimming is debated, pre-phase of supernova explosion, obscuring dust, or c...
Article
Full-text available
During October 2019 and March 2020, the luminous red supergiant Betelgeuse demonstrated an unusually deep minimum of its brightness. It became fainter by more than one magnitude and this is the most significant dimming observed in the recent decades. While the reason for the dimming is debated, pre-phase of supernova explosion, obscuring dust, or c...
Preprint
The BL Lacertae OJ 287 is a supermassive black holes binary (SMBHB) system with complex physics of its irregular flares. During 2016 October -- 2017 April period, a surprising outburst in X-ray, UV and optical bands was detected, while no variability was seen in $\gamma$-ray light curve. During the outburst, the X-ray light curves are dominated wit...
Article
Full-text available
We present accurate element abundance patterns based on the non-local thermodynamic equilibrium (non-LTE, NLTE) line formation for 14 chemical elements from He to Nd for a sample of nine A9 to B3-type stars with well-determined atmospheric parameters and low rotational velocities. We constructed new model atom of Zr ii–iii and updated model atoms f...
Preprint
Full-text available
We present accurate element abundance patterns based on the non-local thermodynamic equilibrium (non-LTE, NLTE) line formation for 14 chemical elements from He to Nd for a sample of nine A9 to B3 type stars with well determined atmospheric parameters and low rotational velocities. We constructed new model atom of Zr II-III and updated model atoms f...
Preprint
Full-text available
We constructed a comprehensive model atom for NeI -- NeII using the most up-to-date atomic data available and evaluated the non-local thermodynamic equilibrium (NLTE) line formation for NeI and NeII in classical 1D models representing the atmospheres of B-type stars. We find that the large NLTE strengthening of the NeI lines corresponding to the 2p...
Article
Full-text available
One-dimensional (1D) model atmospheres are still the most commonly used tool for the determination of stellar chemical composition. Convection in the model is usually treated by mixing-length theory (MLT). The mixing-length parameter α is generally calibrated from the Sun and applied to all other stars. The metal-poor giant, HD 122563, is an import...
Article
Full-text available
Context. Mixing-length theory is used to treat stellar convection. As a simulation in one-dimensional stellar atmospheres models, the mixing-length parameter α is calibrated from the Sun and then applied to other stars. However, there is no strong evidence to suggest that α should be the same for stars of different evolutionary stages. Aims. We eva...
Preprint
Full-text available
We present a model atom for C I - C II - C III - C IV using the most up-to-date atomic data and evaluated the non-local thermodynamic equilibrium (NLTE) line formation in classical 1D atmospheric models of O-B-type stars. Our models predict the emission lines of C II 9903~\AA\ and 18535~\AA\ to appear at effective temperature \Teff~$\geq$~17\,500~K...
Preprint
Full-text available
The typical blazar S5 0716$+$714 is very interesting due to its rapid and large amplitude variability and high duty cycle of micro-variability in optical band. We analyze the observations in I, R and V bands obtained with the $1.0m$ telescope at Weihai observatory of Shandong University from 2011 to 2018. The model of synchrotron radiation from tur...
Preprint
Full-text available
We report on the discovery of five carbon-enhanced metal-poor (CEMP) stars in the metallicity range of $-3.3<$ [Fe/H] $<-2.4$. These stars were selected from the LAMOST DR3 low-resolution (R$ \sim$ 2,000) spectroscopic database as metal-poor candidates and followed-up with high-resolution spectroscopy (R$ \sim$110,000) with the LICK/APF. Stellar pa...
Article
Full-text available
Non-local thermodynamical equilibrium (NLTE) line formation for Mg i and Mg ii lines is considered in classical 1D LTE model atmospheres of the Sun and 17 stars with reliable atmospheric parameters and in a broad range of spectral types: 3900 K ≤ ≤ 17,500 K, 1.1 ≤ log g ≤ 4.7, and −2.6 ≤ [Fe/H] ≤ +0.4. We find that, for each star, NLTE leads to sma...
Preprint
Full-text available
Non-local thermodynamical equilibrium (NLTE) line formation for Mg I and Mg II lines is considered in classical 1D-LTE model atmospheres of the Sun and 17 stars with reliable atmospheric parameters and in a broad range of spectral types: 3900 $\le$ \Teff\ $\le$ 17500~K, 1.1 $\le$ log$g$ $\le$ 4.7, and $-$2.6 $\le$ [Fe/H] $\le$ +0.4. We find that, f...
Article
The program package SME (Spectroscopy Made Easy), designed to perform an analysis of stellar spectra using spectral fitting techniques, was updated due to adding new functions (isotopic and hyperfine splittins) in VALD and including grids of NLTE calculations for energy levels of few chemical elements. SME allows to derive automatically stellar atm...
Article
We present accurate methods of abundance determination based on the non-local thermodynamic equilibrium (NLTE) line formation for carbon, oxygen, calcium, titanium, and iron in the atmospheres of BAF-type stars. For C I-II, O I, Ca I-II, and Ti I-II, their comprehensive model atoms were described in our previous papers. A fairly complete model atom...
Article
Full-text available
For the first time, we present an extensive study of stars with individual non-local thermodynamic equilibrium (NLTE) abundances for 17 chemical elements from Li to Eu in a sample of stars uniformly distributed over the $-2.62 \le$ [Fe/H] $\le +0.24$ metallicity range that is suitable for the Galactic chemical evolution research. The star sample ha...
Article
Full-text available
We constructed a comprehensive model atom for C\ione\ -- C\ii\ using the most up-to-date atomic data available and evaluated the non-local thermodynamic equilibrium (NLTE) line formation for C\ione\ and C\ii\ in classical 1D models representing the atmospheres of A and late B-type stars. Our NLTE calculations predict the emission that appears at ef...
Article
Full-text available
We performed extensive tests of the accuracy of atmospheric parameter determination for FGK stars based on the spectrum fitting procedure Spectroscopy Made Easy (sme). Our stellar sample consists of 13 objects, including the Sun, in the temperature range 5000–6600 K and metallicity range −1.4–+0.4. The analysed stars have the advantage of having pa...
Article
Full-text available
A comprehensive model atom was constructed for C i using the most up-to-date atomic data. We evaluated non-local thermodynamical equilibrium (NLTE) line formation for neutral carbon in classical one-dimensional (1D) models representing atmospheres of late-type stars, where carbon abundance varies from the solar value down to [C/H] = −3. NLTE leads...
Article
Full-text available
The main objective of this paper is to study the possibility of triggered star formation on the border of the H ii region S233, which is formed by a B-star. Using high-resolution spectra, we determine the spectral class of the ionizing star as B0.5 V and the radial velocity of the star to be −17.5 ± 1.4 km s−1. This value is consistent with the vel...
Article
Full-text available
We present atmospheric parameters for 51 nearby FG dwarfs uniformly distributed over the -2.60 < [Fe/H] < +0.20 metallicity range that is suitable for the Galactic chemical evolution research. Lines of iron, Fe I and Fe II, were used to derive a homogeneous set of effective temperatures, surface gravities, iron abundances, and microturbulence veloc...
Article
Full-text available
Context. Synthetic model atmosphere calculations are still the most commonly used tool when determining precise stellar parameters and stellar chemical compositions. Besides three-dimensional models that consistently solve for hydrodynamic processes, one-dimensional models that use an approximation for convective energy transport play the major rol...
Article
Full-text available
We evaluate non-local thermodynamical equilibrium (non-LTE) line formation for neutral sodium in model atmospheres of the 79 red giants using the model atom that incorporates the best available atomic data. The non-LTE abundances of Na were determined from Na I 6154, 6161 \AA\ for the 38 stars of the thin disk (15 of them the BaII stars), 15 stars...
Article
We determined NLTE abundances of Na in the atmospheres of 80 red giants including the 33 stars of the thin disk, 35 stars of the thick disk and 12 stars of Hercules stream.
Article
We present the results of special tests of the automatic procedure for atmospheric parameters determination based on spectroscopy.
Article
Full-text available
We report the physical and orbital parameters of the visible component of the spectroscopic binary HD37737 (m V = 8.03). The observations were performed with the 1.2-m telescope of the Kourovka Astronomical Observatory of the Ural Federal University in 2012 and the 6-m BTA telescope of the SAO RAS in 2007 and 2009. Radial velocities were measured s...

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