An Optical Study of Two VY Sculptoris-Type Cataclysmic Binary Stars: V704 And and RX J2338+431

TL;DR

This study characterizes two VY Scl-type cataclysmic variables, V704 And and RX J2338+431, through optical observations, revealing their orbital periods, photometric states, and secondary star features, and introduces a novel spectral state classification method.

Contribution

It provides detailed observational data on two VY Scl-type CVs and introduces a new method to classify spectral states based on emission-line properties.

Findings

V704 And has an orbital period of 3.63 hours.

RX J2338+431 has an orbital period of 3.13 hours.

A novel method links emission-line properties to photometric states.

Abstract

We report observations of the known cataclysmic variable star (CV) V704 And, and also confirm that the optical counterpart of the ROSAT Galactic Plane Survey source RX J2338+431 is a heretofore-neglected CV. Photometric and spectroscopic observations from MDM Observatory show both systems to be novalike variables that exhibit dips of 4-5 magnitudes from their mean brightnesses, establishing them as members of the VY~Scl subclass. From high-state emission-line radial velocities, we determine orbital periods of 0.151424(3) d (3.63 hr) for V704 And and 0.130400(1) d (3.13 hr) for RX J2338+431. In V704 And, we find that the H-alpha emission-line measures cluster into distinct regions on a plot of equivalent width versus full width at half-maximum, which evidently correspond to high, intermediate, and low photometric states. This allows us to assign spectra to photometric states when contemporaneous photometry is not available, an apparently novel method that may be useful in studies of other novalikes. Our low-state spectra of RX J2338+431 show features of an M-type secondary star, from which we estimate a distance of 890 +- 200 pc, in good agreement with the Gaia DR2 parallax.