arXiv subjects

S. A. Khokhlov

Publications and source records attributed to S. A. Khokhlov.

5 recordsLinked to original sources

arXiv2026

Differential Luminosity Response of Balmer-Line Profiles in Galactic B/A Luminous Stars

We investigate the differential luminosity response of the optical Balmer series from H8 to H-alpha in Galactic B5-A5 luminous stars using homogeneous measurements of central depth, FWHM, and equivalent width at a resolving power of approximately 12,000. Direct line-to-line comparisons show a systematic change in the central-depth response toward the lower-order transitions. For the primary 72-star luminosity sample, the fitted luminosity coefficients show an overall positive trend with upper-level quantum number, with a point-estimate gradient of dq/dn = 0.0419. A joint Monte Carlo analysis with 10,000 realisations gives a median dq/dn = 0.0387 and a 95 percent interval from 0.0253 to 0.0532, with no non-positive gradients obtained. The higher-order H8-H-delta coefficients form a statistically unresolved plateau, followed by a well-supported increase in response magnitude from H-delta toward H-alpha. The result is robust to the adopted effective-temperature scale. The FWHM coefficients show no comparable Balmer-order progression, and the directly fitted profile-shape response is consistent with zero from H8 through H-beta. For H-alpha, the full logarithmic sample is not formally significant, whereas removal of the three remaining strongly filled-core profiles yields a significantly negative shape response. The observed behaviour is qualitatively compatible with the systematic variation of pressure broadening across the Balmer series, while the enhanced H-alpha response may additionally reflect non-LTE and wind-related effects.

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arXiv2026

An Empirical Effective-Temperature Calibrations for Galactic B/A Supergiants

We present empirical effective temperature Teff calibrations for Galactic supergiants of spectral types B5-A5 based on optical spectra. The relationships were derived from a reference sample with adopted literature temperatures and use equivalent widths, central line depths, and ratios of selected spectral features as temperature indicators. Quadratic relationships are established for individual diagnostics and their ratios. Collectively, the calibrations span a Teff interval from 8 400 K to 14 700K, while the validity range of each relationships is individually specified. Detailed quantitative atmospheric analyzes remain indispensable for deriving physically consistent stellar parameters. However, their application to extensive spectroscopic samples is observationally and computationally demanding. The empirical relationships presented here provide a homogeneous and readily applicable temperature scale for the characterization of Galactic BA supergiants. The complete calibration tables, including fitted coefficients and uncertainty information, together with an interactive Python tool to apply the relationships, are publicly available through Zenodo. The reduced continuum-normalized spectra and associated metadata are published through a VO--compliant service of the Kazakhstan National Virtual Observatory.

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arXiv2020

Properties of Galactic B[e] Supergiants: V. 3 Pup -- constraining the orbital parameters and modeling the circumstellar environments

We report the results of a long-term spectroscopic monitoring of the A-type supergiant with the B[e] phenomenon 3 Pup = HD 62623. We confirm earlier findings that it is a binary system. The orbital parameters were derived using cross-correlation of the spectra in a range of 4460-4632 A, which contains over 30 absorption lines. The orbit was found circular with a period of $137.4\pm0.1$ days, radial velocity semi-amplitude $K_{1} = 5.0\pm0.8$ km s$^{-1}$, systemic radial velocity $γ= +26.4\pm2.0$ km s$^{-1}$, and the mass function $f(m) = (1.81^{+0.97}_{-0.76})\times10^{-3}$ M$_{\odot}$. The object may have evolved from a pair with initial masses of $\sim$6.0 M$_{\odot}$ and $\sim$3.6 M$_{\odot}$ with an initial orbital period of $\sim$5 days. Based on the fundamental parameters of the A-supergiant (luminosity $\log$ L/L$_{\odot} = 4.1\pm$0.1 and effective temperature T$_{\rm eff} = 8500\pm$500 K) and evolutionary tracks of mass-transferring binaries, we found current masses of the gainer M$_{2} = 8.8\pm$0.5 M$_{\odot}$ and donor M$_{1} = 0.75\pm0.25$ M$_{\odot}$. We also modeled the object's IR-excess and derived a dust mass of $\sim 5\,\times10^{-5}$ M$_{\odot}$ in the optically-thin dusty disk. The orbital parameters and properties of the H$α$ line profile suggest that the circumstellar gaseous disk is predominantly circumbinary. The relatively low mass of the gainer led us to a suggestion that 3 Pup should be excluded from the B[e] supergiant group and moved to the FS CMa group. Overall these results further support our original suggestion that FS CMa objects are binary systems, where an earlier mass-transfer caused formation of the circumstellar envelope.

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arXiv2018

Toward Understanding the B[e] Phenomenon. VII. AS 386, a single-lined binary with a candidate black hole component

We report the results of spectroscopic and photometric observations of the emission-line object AS 386. For the first time, we found that it exhibits the B[e] phenomenon and fits the definition of an FS CMa type object. The optical spectrum shows the presence of a B-type star with the following properties: T_ eff = 11000+/-500 K, log L/L_sun = 3.7+/-0.3, a mass of 7+/-1 M_sun, and a distance D = 2.4+/-0.3 kpc from the Sun. We detected regular radial velocity variations of both absorption and emission lines with the following orbital parameters: P_orb = 131.27+/-0.09 days, semi-amplitude K_1 = 51.7+/-3.0 km/s, systemic radial velocity gamma = -31.8+/-2.6 km/s, and a mass function of f(m) = 1.9+/-0.3 M_sun. AS 386 exhibits irregular variations of the optical brightness (V=10.92+/-0.05 mag), while the near-IR brightness varies up to ~0.3 mag following the spectroscopic period. We explain this behavior by a variable illumination of the dusty disk inner rim by the B-type component. Doppler tomography based on the orbital variations of emission-line profiles shows that the material is distributed near the B-type component and in a circumbinary disk. We conclude that the system has undergone a strong mass transfer that created the circumstellar material and increased the B-type component mass. The absence of any traces of a secondary component, whose mass should be >= 7 M_sun, suggests that it is most likely a black hole.

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arXiv2016

Towards Understanding The B[e] Phenomenon: VI. Nature and Spectral Variations of HD 85567

We report the results of high-resolution ($R \sim 80,000$) spectroscopic observations of the emission-line object HD 85567, which has been classified as a FS CMa type object or a pre-main-sequence star. The main goal is to put more constraints on the object's fundamental parameters as well as on its nature and evolutionary state. Absorption lines in the spectrum of HD 85567 were found similar to those of mid B--type dwarfs and correspond to the following fundamental parameters: T$_{\rm eff} = 15000\pm500$ K, $v \sin i = 31\pm3$ km s$^{-1}$, $\log g \sim 4.0$. The interstellar extinction, A$_V$ $= 0.50\pm0.02$ mag, was measured using the strengths of some diffuse interstellar bands. We also obtained $UBV(RI)_{\rm c}$ images of a $10^{\prime} \times 10^{\prime}$ region around the object. Photometry of projectionally close stars was used to derive an interstellar extinction law in this direction and resulted in a distance of 1300$\pm$100 pc to the object and a luminosity of $\log$ (L/L$_\odot) = 3.3\pm0.2$. We found no significant radial velocity variations of the absorption lines in the spectra of HD 85567 obtained during two month-long periods of time in 2012 and 2015. Our analysis of the spectroscopic and photometric data available for the star led us to a conclusion that it cannot be a pre-main-sequence Herbig Ae/Be star. We argue that the circumstellar gas and dust were produced during the object's evolution as most likely a binary system, which contains an undetected secondary component and is unlikely to be a merger product.

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