arXiv subjects

Y. Solovyeva

Publications and source records attributed to Y. Solovyeva.

15 recordsLinked to original sources

arXiv2026

Quasars behind the disk of M31 galaxy

We aim to increase the limited number of quasars behind M31, necessary for probing the chemical content of the gas and for proper motion reference, with reliable and homogeneous redshift measurements from emission lines. We carried out spectroscopic follow up of 32 quasar candidates. We confirm 23 quasars: two are new discoveries (J004029.727+403705.68 and J004215.489+412031.52) and the rest were reported elsewhere, but with somewhat deficient analysis; 16 spectra are published for the first time. We report new homogeneous redshifts for 34 quasars (from 40 spectra, adding 17 from archives) and summarize all available information about bona-fide quasars with reliable redshift, bringing their number to 124 within the mu_B=26 mag/arcsec^2 isophote. We carried out a comparison of redshifts from different sources and excluded some objects with redshifts derived from low-resolution spectra. We derive the reddening for them from the color excess with respect to dereddened counterparts with similar redshifts in the field. Comparisons of our reddenings with M31 reddening maps found no significant correlations. Most QSOs behind M31 show low reddening and do not probe high-extinctions underlining the need to identify fainter quasars behind nearby galaxies, especially behind higher extinction regions -- probably due to a bias towards following up brighter and less extinct candidates. Finally, the redshifts derived from low-resolution spectra must be treated with caution, because they can contain significant errors.

astro-ph.GA↗

arXiv2025

Probing the wind and evolutionary state of the quiescent luminous blue variable Var$\,$2 in the Galaxy M33: constraints from self-consistent non-LTE modeling

Luminous Blue Variables (LBVs) are massive stars with extreme luminosities, exhibiting significant irregular photometric and spectroscopic variability. This paper is dedicated to the study of dormant LBV Var$\,$2 in the galaxy M33, which has not shown significant brightness changes for almost century and currently observed as Ofpe/WN9 star. In order to obtain reliable estimates of the fundamental parameters of Var$\,$2, we had calculated self-consistent hydrodynamic models of the extended atmosphere, assuming non-local thermodynamic equilibrium (non-LTE) and taking into account the balance of radial forces in the wind of the star. Spectral modeling yields luminosity $L=6.5\times10^{5}\,L_\odot$, current mass $M_* \approx23\,M_\odot$ and hydrogen abundance on the surface ${\rm X}_{\rm H}\approx43\%$. Comparison with evolutionary tracks indicates that these parameters correspond to a star with the initial mass $M_{\rm init}\approx50\,M_\odot$ and age $t_{\rm age}\approx4.4\,$Myr that is evolving from lower temperatures towards the Wolf-Rayet stars. A study of dynamic properties of the wind showed that the shape of the wind velocity profile of Var$\,$2 is close to the one of O- and early B-supergiants rather than Wolf-Rayet stars. In contrast, for the obtained mass-loss rate $\dot{M}=2.1\times10^{-5}\,M_{\odot}\,\text{yr}^{-1}$, the ratio of the wind momentum to the luminosity of Var$\,$2 is in good agreement with the values found for WNL stars. Given the obtained age estimates, Var$\,$2 could potentially have been ejected from the cluster associated with the nearest large star-forming region located at a distance of $\sim100\,$pc. However, statistical analysis of the projected distribution of stars in the vicinity of Var$\,$2 suggests that this LBV could have formed in a local low-populated group.

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arXiv2025

On the spatial distribution of luminous blue variables in the M33 galaxy

In the current paper, we present a study of the spatial distribution of luminous blue variables (LBVs) and various LBV candidates (cLBVs) with respect to OB associations in the M33 galaxy. The identification of blue star groups was based on the LGGS data and was carried out by two clustering algorithms with initial parameters determined during simulations of random stellar fields. We have found that the distribution of distances to the nearest OB association obtained for the LBV/cLBV sample is close to that for massive stars with $M_{\rm init}>20\,M_\odot$ and Wolf-Rayet stars. This result is in good agreement with the standard assumption that luminous blue variables represent an intermediate stage in the evolution of the most massive stars. However, some objects from the LBV/cLBV sample, particularly Fe$\,$II-emission stars, demonstrated severe isolation compared to other massive stars, which, together with certain features of their spectra, implicitly indicates that the nature of these objects and other LBVs/cLBVs may differ radically.

astro-ph.GA↗

arXiv2022

Wind parameters of the new LBV in NGC1156

In this work we present the spectrum modeling results for the newly discovered luminous blue variable (LBV) in the NGC 1156 galaxy. Extended atmosphere models were calculated using the non-LTE code CMFGEN. We have obtained the luminosity of the discovered LBV $L\simeq (1.6\pm0.2) \times 10^{6} L_{\odot}$, effective temperature $T_{\text{eff}}=7.9\pm0.4$ kK and mass-loss rate $\dot{M}f^{-0.5}= (8.2\pm1.0) \times 10^{-4} M_{\odot}\text{yr}^{-1}$. The hydrogen abundance in the wind is $\approx20\,$% for the metallicity $Z=0.5 Z_{\odot}$ of the host galaxy.

astro-ph.SR↗

arXiv2022

Search for LBVs in the Local Volume galaxies: study of four stars in NGC 4449

We continue to search for LBV stars in galaxies outside the Local Group. In this work, we have investigated four luminous stars in NGC 4449. Multiple spectral observations carried out for J122810.94+440540.6, J122811.70+440550.9, and J122809.72+440514.8 revealed the emission features in their spectra that are characteristic of LBVs. Photometry showed noticeable brightness changes of J122809.72+440514.8 ($\Delta I=0.69\pm0.13^m$) and J122817.83+440630.8 ($\Delta R=2.15\pm0.13^m$), while the variability of J122810.94+440540.6 and J122811.70+440550.9 does not exceed $0.3^m$ regardless of the filter. We have obtained estimates of the interstellar reddening, photosphere temperatures, and bolometric luminosities $\log(\text{L}_\text{Bol}/\text{L}_{\odot}) \approx 5.24-6.42$. Using the CMFGEN code, we have modelled the spectrum of the cold state of J122809.72+440514.8 ($T_{\text{eff}}=9300\,$K) and have obtained possible value of the mass loss rate $\dot{M} = 5.2\times10^{-3}\,M_{\odot}\,yr^{-1}$. Based on the observational properties, J122809.72+440514.8 and J122817.83+440630.8 were classified as LBVs, while the other two stars were classified as LBV candidates or B[e]-supergiants candidates

astro-ph.SR↗

arXiv2022

Search for LBVs in the Local Volume galaxies: study of two stars in NGC 1156

We continue the search for luminous blue variables (LBVs) in Local Volume galaxies in order to study their fundamental parameters. In this paper, we report the discovery of two new LBVs in the dwarf irregular galaxy NGC 1156. Both stars exhibit spectral variability simultaneously with strong brightness variations: $\Delta \text{R}_c = 0.84 \pm 0.23^m$ for J025941.21+251412.2 and $\Delta \text{R}_c = 2.59 \pm 0.10^m$ for J025941.54+251421.8. The bolometric luminosities of the stars are in the range of L$_\text{Bol} \approx (0.8 - 1.6) \times 10^6$ L$_\odot$. These values are corrected for reddening A$_\text{V} \approx 0.9$ and are given for the distance to the galaxy D=7.0$\pm$0.4 Mpc, which we have measured by the TRGB method. Both stars are above the Humphreys-Davidson limit in the region of relatively low temperatures, T$_\text{eff} \lesssim 10$ kK on the temperature-luminosity diagram. J025941.54+251421.8 had a temperature below the hydrogen ionisation threshold at maximum brightness, exhibiting behaviour very similar to that of the known LBV R71 during its 2012 outburst. We have estimated the masses of the detected LBVs and studied the properties of their stellar environment. We discuss our results within the framework of both a single star and a binary system evolution scenario for LBVs.

astro-ph.GA↗

arXiv2022

Simultaneous X-ray/UV observations of ultraluminous X-ray source Holmberg II X-1 with Indian space mission AstroSat

We present the results of 8 epochs of simultaneous UV and X-ray observations of the highly variable ultraluminous X-ray source (ULX) Holmberg II X-1 with AstroSat -- Indian multiwavelength space satellite. During the entire observation period from late 2016 to early 2020, Holmberg II X-1 showed a moderate X-ray luminosity of $8\times10^{39}$ erg/s and a hard power-law spectrum with $\Gamma \lesssim 1.9$. Due to low variability of the object in X-rays (by a factor 1.5) and insignificant variability in the UV range (upper limit $\approx25$%) we could not find reliable correlation between flux changes in these ranges. Inside each particular observation, the X-ray variability amplitude is higher, it reaches a factor of 2-3 respect to the mean level at the time scales of $\sim10$ ks or even shorter. We discussed our results in terms of three models of a heated donor star, a heated disk and a heated wind, and estimated the lower limit to the variability which would allow to reject at least part of them.

astro-ph.HE↗

arXiv2021

New data for the LBV in NGC 4736

We present new spectral and photometric data of confirmed LBV star from the NGC4736 galaxy. The star NGC4736_1 (Mbol = -11.5 mag) showed noticeable spectral variability from 2015 to 2018, which was accompanied by a significant change in the brightness. We also have estimated possible initial mass of the object NGC4736_1 as ~130 Msun.

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arXiv2021

Optical Counterparts of ULXs in Two Dwarf Galaxies: NGC 4861 and NGC 4449

We present the results of a search for optical candidates of Ultraluminous X-ray sources (ULXs) in two dwarf galaxies: NGC 4861 and NGC 4449 using Hubble Space Telescope {\it HST} archival data. With a precise astrometry, we confirm that NGC 4861 X1 associated with an HII complex as reported by \cite{2014MNRAS.441.1841T} and we conclude that NGC 4861 X2 resides in a young star group with 400$\pm$80 M$\odot$. We also find that NGC 4449 X7 is associated with three optical candidates within an error radius of 0$\farcs$2 at the 90$\%$ confidence level. Absolute magnitudes (M$_{v}$) of these candidates are determined as $-$5.0 and $-$4.1. The age and mass values for the three candidates by using stellar evolutionary tracks are estimated as 40-50 Myr and $\sim$8 M$\odot$, respectively. The locations of optical candidates suggest possible association with a nearby group of stars. In addition, we analyzed the previously unused archival data of {\it XMM-Newton}, {\it Chandra} and {\it Swift} where the sources detected. Although the X-ray spectral data do not allow us to discriminate between physical models, long-term data at hand are consistent with the sources being in luminous hard states.

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arXiv2020

Determining parameters of ULXs with model grids of extended atmospheres

In current work we continued study of wind parameters of ultraluminous X-ray sources (ULXs) using model grids of extended atmospheres. We present sets of models with temperatures from 18000 up to 56000K as a line equivalent widths (EWs) and their ratios diagrams. The fundamental wind parameters for some spectrally studied ULXs were estimated using EW diagrams. Also, influence of the wind velocity law on the equivalent widths of observed emission lines was investigated. This study was funded by RFBR according to the research project 18-32-20214.

astro-ph.HE↗

arXiv2020

Observations of ultraluminous X-ray sources with the 6-m telescope of the SAO RAS

The nature of ultraluminous X-ray sources (ULXs) is not yet fully understood but it can be done in the most efficient way by analyzing its optical emission and environment. We present preliminary results of photometric and spectral studies of some newly identified ULX optical counterparts. Based on the X-ray catalog of ULX candidates by Liu 2011 we have unequivocally identified in the optical range more than 100 sources, for 49 of them we carried out a long slit spectroscopy. According to these results, the majority of the most brightest candidates (m$_V < 22^m$) turned out to be background objects of different types, but the observed parameters of other sources of the sample allow us to classify them as real ULX. Here we present results for ten selected sources.

astro-ph.HE↗

arXiv2020

Luminous Blue Variable candidates in M31

We study five Luminous Blue Variable (LBV) candidates in the Andromeda galaxy and one more (MN112) in the Milky Way. We obtain the same-epoch near-infrared (NIR) and optical spectra on the 3.5-meter telescope at the Apache Point Observatory and on the 6-meter telescope of the SAO RAS. The candidates show typical LBV features in their spectra: broad and strong hydrogen lines, HeI, FeII, and [FeII] lines. We estimate the temperatures, reddening, radii and luminosities of the stars using their spectral energy distributions. Bolometric luminosities of the candidates are similar to those of known LBV stars in the Andromeda galaxy. One candidate, J004341.84+411112.0, demonstrates photometric variability (about 0.27 mag in V band), which allows us to classify it as a LBV. The star J004415.04+420156.2 shows characteristics typical for B[e]-supergiants. The star J004411.36+413257.2 is classified as FeII star. We confirm that the stars J004621.08+421308.2 and J004507.65+413740.8 are warm hypergiants. We for the first time obtain NIR spectrum of the Galactic LBV candidate MN112. We use both optical and NIR spectra of MN112 for comparison with similar stars in M31 and notice identical spectra and the same temperature in the J004341.84+411112.0. This allows us to confirm that MN112 is a LBV, which should show its brightness variability in longer time span observations.

astro-ph.SR↗

arXiv2020

New luminous blue variable candidates in the NGC 247 galaxy

We search for LBV stars in galaxies outside the Local Group. Here we present a study of two bright $H\alpha$ sources in the NGC 247 galaxy. Object j004703.27-204708.4 ($M_V=-9.08 \pm 0.15^m$) shows the spectral lines typical for well-studied LBV stars: broad and bright emission lines of hydrogen and helium He I with P Cyg profiles, emission lines of iron Fe II, silicon Si II, nitrogen N II and carbon C II, forbidden iron [Fe II] and nitrogen [N II] lines. The variability of the object is $\Delta B = 0.74\pm0.09^m$ and $\Delta V = 0.88\pm0.09^m$, which makes it reliable LBV candidate. The star j004702.18-204739.93 ($M_V=-9.66 \pm 0.23^m$) shows many emission lines of iron Fe II, forbidden iron lines [Fe II], bright hydrogen lines with broad wings, and also forbidden lines of oxygen [O I] and calcium [Ca II] formed in the circumstellar matter. The study of the light curve of this star also did not reveal significant variations in brightness ($\Delta V = 0.29\pm0.09^m$). We obtained estimates of interstellar absorption, the photosphere temperature, as well as bolometric magnitudes $M_\text{bol}=-10.5^{+0.5}_{-0.4}$ and $M_\text{bol}=-10.8^{+0.5}_{-0.6}$, which corresponds to bolometric luminosities $\log(L_\text{bol}/L_{\odot})=6.11^{+0.20}_{-0.16}$ and $6.24^{+0.20}_{-0.25}$ for j004703.27-204708.4 and j004702.18-204739.93 respectively. Thus, the object j004703.27-204708.4 remains a reliable LBV candidate, while the object j004702.18-204739.93 can be classified as B[e]-supergiant.

astro-ph.SR↗

arXiv2020

Modeling of extended atmospheres with temperatures below 40000K

We calculate models of extended stellar atmospheres with a temperature in the range of 12000-40000K and a mass loss rate of $10^{-6}-10^{-4} M_{\odot}$ yr$^{-1}$. A large number of objects with emission spectra, such as luminous blue variables (LBV), FeII - emission line stars, Of/late-WN stars, and even ultraluminous X-ray sources (ULXs) often have effective temperatures in this range. The paper presents the results of model grids calculating in the form of equivalent width diagrams for the selected lines of hydrogen, He, Si, and Fe, as well as the results of studies of some emission objects using the calculated models.

astro-ph.HE↗

arXiv2019

New Luminous Blue Variable Candidates in NGC 4736

We have found three new LBV candidates in the star-forming galaxy NGC 4736. They show typical well-known LBV spectra, broad and strong hydrogen lines, He I lines, many Fe II lines, and forbidden [Fe II] and [Fe III]. Using archival Hubble Space Telescope and ground-based telescope data, we have estimated the bolometric magnitudes of these objects from -8.4 to -11.5, temperatures, and reddening. Source NGC 4736_1 (Mv = -10.2 +/- 0.1 mag) demonstrated variability between 2005 and 2018 as Delta V = 1.1 mag and Delta B = 0.82 mag, the object belongs to LBV stars. NGC 4736_2 (Mv < -8.6 mag) shows P Cyg profiles and its spectrum has changed from 2015 to 2018. The brightness variability of NGC 4736_2 is Delta V = 0.5 mag and Delta B = 0.4 mag. In NGC 4736_3 (Mv = -8.2 +/- 0.2 mag), we found strong nebular lines, broad wings of hydrogen; the brightness variation is only 0.2 mag. Therefore, the last two objects may reside to LBV candidates.

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