Results of CYG~X-1 = V1357~CYG investigation based on high-resolution optical spectra observed at Terskol Observatory

Details Results of CYG~X-1 = V1357~CYG investigation based on high-resolution optical spectra observed at Terskol Observatory Results of CYG~X-1 = V1357~CYG investigation based on high-resolution optical spectra observed at Terskol Observatory

Oct 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007smma.conf...67k&link_type=abstract

Spectroscopic methods in modern astrophysics. Proceedings of the conference held 13-15 September 2006, Moscow, Russia. Eds. L. M

Astronomy and Astrophysics

Astrophysics

2

Scientific paper

70 echelle spectra for the "soft" and "hard" states of Cyg X-1 were obtained in 2002-2004 during 28 nights (spectral resolution R = 45000 and 13000) at the Peak Terskol Observatory. We use also 5 spectra from BOAO (Korea, R = 30000, 44000), and 20 spectra got in 1997 at Crimean Astrophysical Observatory. The sequence of line profile variations with the orbital phases is clearly observable. Some spectral line profile dependencies of X-ray 2-12 keV flux wereanalyzed by comparing the profiles with RXTE/ASM X-ray data. X-ray flare of 13.06.2003 leaded to strong changes in H_α and He II λ4686 Å emission profiles over several hours. We relate such behavior to changes of gas ionization in Cyg X-1 system. Comparison of the observed and non-LTE profiles for H I, He I and Mg II is given. The tidal distortion of Cyg X-1 optical component and its illumination by X-ray emission from the second one are taken into account. We used the 2003-2004 spectra to determine the optical component main characteristics (T_{eff} = 30400 ± 500 K, log g = 3.31± 0.07) and chemical composition, which points to a metallicity ([M/H] = 0.34 dex) typical for young stars. The chemical composition is assumed to be affected by matter transformation in the CNO cycle reactions at the main sequence stage ([N/C] = [N/O] = 0.7 dex) and by light elements burning ([Ne/H] = [Si/H] = 0.7 dex). The Doppler images constructed by means of an improved Doppler tomography method on the base of 9 He II λ4686 A profiles of 2003 ("soft" X-ray state) and 6 profiles of 2004 ("hard" X-ray state) allow to set a limit of the black hole to supergiant mass ratio 1/4≤ M_X/M_O≤ 1/3. The photometric and spectral variations make evident that the supergiant (Cyg X-1 optical component) parameters are changing on a time scale of tens of years. It is followed from Lyuty's 35-year long Cyg X-1 photometric set and spectra of 1997 and 2003-2004. Comparison of observations with the model simulated dependencies of U, B, V fluxes and He I λ4713 A line profile on the star physical parameters leads to the conclusion that from 1997 to 2003-2004 the star radius has grown about 1 - 4% and the temperature decreased by 1300 - 2400 K.

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