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Register a new userStellar and accretion disk parameters of the close binary HD 50526
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Added by
Jaime Andr\\'es Rosales Guzm\\'an
Publication date
2021
fields
Physics
and research's language is
English
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We present a photometric and spectroscopic study of HD 50526, an ellipsoidal binary member of the group Double Periodic Variable stars. Performing data-mining in photometric surveys and conducting new spectroscopic observations with several spectrographs during 2008 to 2015, we obtained orbital and stellar parameters of the system. The radial velocities were analyzed with the genetic PIKAIA algorithm, whereas Doppler tomography maps for the H$alpha$ and H$beta$ lines were constructed with the Total Variation Minimization code. An optimized simplex-algorithm was used to solve the inverse-problem adjusting the light curve with the best stellar parameters for the system. We find an orbital period of $6.701 pm 0.001 ~mathrm{d}$ and a long photometric cycle of $191 pm 2 ~mathrm{d}$. We detected the spectral features of the coldest star, and modeled it with a $log{g} = 2.79 pm 0.02 ~mathrm{dex}$ giant of mass $1.13 pm 0.02 ~mathrm{M_{odot}}$ and effective temperature $10500 pm 125 ~mathrm{K}$. In addition, we determine a mass ratio $q= 0.206 pm 0.033$ and that the hot star is a B-type dwarf of mass $5.48 pm 0.02 ~mathrm{M_{odot}}$. The $V$-band orbital light curve can be modeled including the presence of an accretion disk around the hotter star. This fills the Roche lobe of the hotter star, and has a radius $14.74 pm 0.02 ~mathrm{R_{odot}}$ and temperature at the outer edge $9400 ~mathrm{K}$. Two bright spots located in the disk account for the global morphology of the light curve. The Doppler tomography maps of H$alpha$ and H$beta$, reveal complex structures of mass fluxes in the system.
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Prompted by peculiar spectroscopic variability observed in SDSS/APOGEE $H$-band spectra, we monitored the Be star HD 55606 using optical spectroscopy and found that it is an exotic double-lined spectroscopic binary (SB2) consisting of a Be star and a hot, compact companion that is probably an OB subdwarf (sdOB) star. Motion of the sdOB star is traced by its impact on the strong He~I lines, observed as radial velocity ($V_{r}$) variable, double-peaked emission profiles with narrow central absorption cores. Weak He II 4686 {AA} absorption associated with the companion star is detected in most spectra. Use of the emission peaks of low-ionization emission lines to trace the Be star $V_{r}$ and the He I lines to trace the companion star $V_{r}$ yields a circular orbital solution with a 93.8-day period and masses of $M_{rm Be}=6.2$ $M_{rm odot}$ and $M_{rm sdOB}=0.9$ $M_{rm odot}$ in the case of $i=80^{circ}$. HD 55606 exhibits a variety of phase-locked variability, including the development of shell lines twice per orbit. The shell phases coincide with variation in the double emission peak separations, and both forms of variability are likely caused by a two-armed spiral density perturbation in the Be disk. The intensity ratios of the double emission peaks are also phase-locked, possibly indicating heating by the sdOB star of the side of the Be disk facing it. HD 55606 is a new member of the growing sample of Be+sdOB binaries, in which the Be stars rapid rotation and ability to form a disk can be attributed to past mass transfer.
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