SS 433: C II emission from the disk photosphere

TL;DR

This study tracks C II emission lines in SS 433 over two orbital cycles to measure the compact object's velocity, revealing lines formed in the disk photosphere and suggesting potential for improved measurements with advanced instruments.

Contribution

First measurement of the orbital velocity of SS 433's compact object using C II emission lines, demonstrating lines are eclipsed by the companion and formed in the disk photosphere.

Findings

Orbital velocity of the compact object is 176 ± 13 km/s.

C II emission lines are eclipsed by the companion star.

Spectroscopic data supports lines forming in the disk photosphere.

Abstract

The Galactic microquasar SS 433 is a member of a binary system but there is a lack of data on the orbital velocities of the components. The emission lines of the C II doublet at 7231 and 7236 Angstrom have been tracked nightly over two orbital cycles. The spectra are adequate to establish that these lines are eclipsed by the companion and hence to extract a measure of the orbital velocity of the compact object; the lines are formed in the disk photosphere. This velocity is 176 plus/minus 13 km/s. Could XSHOOTER do better?