A1 Refereed original research article in a scientific journal
An optical spectroscopic and polarimetric study of the microquasar binary system SS 433
Authors: Paolo Picchi, Steven N. Shore, Eamonn J. Harvey, Andrei Berdyugin
Publisher: EDP SCIENCES S A
Publication year: 2020
Journal: Astronomy and Astrophysics
Journal name in source: ASTRONOMY & ASTROPHYSICS
Journal acronym: ASTRON ASTROPHYS
Article number: ARTN A96
Volume: 640
Number of pages: 19
ISSN: 0004-6361
eISSN: 1432-0746
DOI: https://doi.org/10.1051/0004-6361/202037960
Self-archived copy’s web address: https://research.utu.fi/converis/portal/detail/Publication/50373867
Aims. Our aim is to study the mass transfer, accretion environment, and wind outflows in the SS 433 system, concentrating on the so-called stationary lines.
Methods. We used archival high-resolution (X-shooter) and low-resolution (EMMI) optical spectra, new optical multi-filter polarimetry, and low-resolution optical spectra (Liverpool Telescope), spanning an interval of a decade and a broad range of precessional and orbital phases, to derive the dynamical properties of the system.
Results. Using optical interstellar absorption lines and H I 21 cm profiles, we derive E(B-V) = 0.86 +/- 0.10, with an upper limit of E(B-V) = 1.8 +/- 0.1 based on optical Diffuse Interstellar Bands. We obtain revised values for the ultraviolet and U band polarizations and polarization angles (PA), based on a new calibrator star at nearly the same distance as SS 433 that corrects the published measurement and yields the same PA as the optical. The polarization wavelength dependence is consistent with optical-dominating electron scattering with a Rayleigh component in U and the UV filters. No significant phase modulation was found for PA while there is significant variability in the polarization level. We fortuitously caught a flare event; no polarization changes were observed but we confirm the previously reported associated emission line variations. Studying profile modulation of multiple lines of H I, He I, O I, Na I, Si II, Ca II, Fe II with precessional and orbital phase, we derive properties for the accretion disk and present evidence for a strong disk wind, extending published results. Using transition-dependent systemic velocities, we probe the velocity gradient of the wind, and demonstrate that it is also variable on timescales unrelated to the orbit. Using the rotational velocity, around 140 +/- 20 km s(-1), a redetermined mass ratio q=0.37 +/- 0.04, and masses M-X=4.2 +/- 0.4 M-circle dot, M-A=11.3 +/- 0.6 M-circle dot, the radius of the A star fills - or slightly overfills - its Roche surface. We devote particular attention to the O I 7772 angstrom and 8446 angstrom lines, finding that they show different but related orbital and precessional modulation and there is no evidence for a circumbinary component. The spectral line profile variability can, in general, be understood with an ionization stratified outflow predicted by thermal wind modeling, modulated by different lines of sight through the disk produced by its precession. The wind can also account for an extended equatorial structure detected at long wavelength.
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