An optical spectroscopic and polarimetric study of the microquasar binary system SS 433

TL;DR

This study provides a detailed optical spectroscopic and polarimetric analysis of SS 433, revealing properties of its accretion disk, wind outflows, and system masses, with implications for understanding microquasar behavior.

Contribution

It offers new insights into the mass transfer, wind structure, and polarization characteristics of SS 433, including revised system parameters and evidence for a stratified outflow.

Findings

Derived system masses: Mx=4.2±0.4 M☉, Ma=11.3±0.6 M☉

Detected a strong, variable disk wind with specific velocity structure

Confirmed polarization consistent with electron scattering and no change during flares

Abstract

We present a study of the mass transfer and wind outflows of SS433, focusing on the so-called stationary lines based on archival high and low resolution optical spectra, and new optical multifilter polarimetry and low resolution optical spectra spanning an interval of a decade and a broad range of precessional and orbital phases. We derive $\text{E(B-V)}=0.86\pm0.10$ and revised UV and U band polarizations and polarization angles that yield the same position angle 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 polarization changes were observed during a flare event. Using profile orbital and precessional modulation of multiple lines we derive properties for the accretion disk, present evidence for a strong disk wind, determine its velocity structure, and demonstrate its variability on timescales unrelated to the orbit. We derive a mass ratio $q=0.37\pm0.04$, and masses $\text{M}_X=4.2\pm0.4\ \text{M}_\odot$, $\text{M}_A=11.3\pm 0.6\ \text{M}_\odot$, and show that the A star fills its Roche surface. The O I 7772 \r{A} and 8446 \r{A} lines show different but related orbital modulation and no evidence for a circumbinary disk component. Instead, the spectral line profile variability can be understood with an ionization stratified outflow predicted by thermal wind modeling, which also accounts for an extended equatorial structure detected at long wavelength.