Spectroscopic Observations of the Mass Donor Star in SS 433

TL;DR

This study confirms the spectral features of the mass donor star in SS 433, leading to revised mass estimates of approximately 12.3 solar masses for the donor and 4.3 for the compact object, improving understanding of this binary system.

Contribution

The paper provides new spectroscopic observations that reliably identify the mass donor star's spectrum and refine the mass estimates of both components in SS 433.

Findings

Confirmed the spectral features of the mass donor star.

Revised the mass estimates to 12.3 and 4.3 solar masses.

Supported the identification of the donor star's spectrum.

Abstract

The microquasar SS 433 is an interacting massive binary consisting of an evolved mass donor and a compact companion that ejects relativistic jets. The mass donor was previously identified through spectroscopic observations of absorption lines in the blue part of the spectrum that showed Doppler shifts associated with orbital motion and strength variations related to the orbital modulation of the star-to-disk flux ratio and to disk obscuration. However, subsequent observations revealed other absorption features that lacked these properties and that were probably formed in the disk gas outflow. We present here follow-up observations of SS 433 at orbital and precession phases identical to those from several previous studies with the goals of confirming the detection of the mass donor spectrum and providing more reliable masses for the two system components. We show that the absorption features present as well as those previously observed almost certainly belong to the mass donor star, and we find revised masses of 12.3 +/- 3.3 and 4.3 +/- 0.8 M(sun) for the mass donor and compact object, respectively.