Dynamical Modeling of CXOGBS J175553.2-281633: A 10 Hour Long Orbital Period Cataclysmic Variable

TL;DR

This study models the long-term optical and radial velocity data of CXOGBS J175553.2-281633, revealing it as a long-period cataclysmic variable with detailed orbital and stellar parameters.

Contribution

The paper provides the first detailed dynamical model of CXOGBS J175553.2-281633, including refined orbital period, inclination, and component masses, based on extensive photometric and spectroscopic data.

Findings

Refined orbital period of 10.34488 hours.

Identification of an evolved K7 secondary star.

Derived stellar masses consistent with a white dwarf primary.

Abstract

We present modeling of the long-term optical light curve and radial velocity curve of the binary stellar system CXOGBS J175553.2-281633, first detected in X-rays in the \textit{Chandra} Galactic Bulge Survey. We analyzed 7 years of optical I-band photometry from OGLE and found long-term variations from year to year. These long-term variations can most likely be explained with by either variations in the luminosity of the accretion disk or a spotted secondary star. The phased light curve has a sinusoidal shape, which we interpret as being due to ellipsoidal modulations. We improve the orbital period to be $P = 10.34488 \pm 0.00006$ h with a time of inferior conjunction of the secondary star $T_0 = {\rm HJD\ } 2455260.8204 \pm 0.0008$. Moreover, we collected 37 spectra over 6 non-consecutive nights. The spectra show evidence for an evolved K7 secondary donor star, from which we obtain a semi-amplitude for the radial velocity curve of $K_2 = 161 \pm 6 $ km s$^{-1}$. Using the light curve synthesis code {\tt XRbinary}, we derive the most likely orbital inclination for the binary of $i = 63.0\pm0.7$ deg, a primary mass of $M_1 = 0.83 \pm 0.06$ M$_\odot$, consistent with a white dwarf accretor, and a secondary donor mass of $M_2 = 0.65 \pm 0.07$ M$_\odot$, consistent with the spectral classification. Therefore, we identify the source as a long orbital period cataclysmic variable star.