An Improved Orbital Ephemeris for Cygnus X-1

TL;DR

This paper refines the orbital ephemeris of Cygnus X-1 by combining historical and recent radial velocity data with photometric observations, achieving highly precise measurements of its orbital period.

Contribution

It provides a more accurate and consistent orbital period for Cygnus X-1 by integrating extensive spectroscopic and photometric data, improving previous estimates.

Findings

Refined orbital period of 5.599829±0.000016 days.

Photometric period of 5.599836±0.000024 days, closely matching spectroscopic results.

Enhanced ephemeris accuracy for Cygnus X-1.

Abstract

By accumulating all available radial velocity data and combining it with our own spectroscopy we present a new and improved ephemeris for Cygnus X-1 (V1357 Cygni/HDE226868). We initially calculate an orbital period of 5.599847+/-0.000018.days and then, by including the more recent radial velocities of LaSala et al. (1998) and Sowers et al.(1998) we refine this to 5.599829+/-0.000016 days. Using 27 years' worth of photometry, we also calculate a photometric period of 5.599836+/-0.000024 - remarkably similar to the spectroscopic one.