Ultrashort-period MS eclipsing systems. New observations and light curve solutions of six NSVS binaries

TL;DR

This study presents new observations and light curve analyses of six ultrashort-period eclipsing binary systems with MS components, revealing their overcontact nature, empirical relations, and notable activity in some targets.

Contribution

It provides the first detailed light curve solutions for these six binaries and establishes an empirical period–semi-major axis relation for short-period systems.

Findings

All targets are overcontact systems.

NSVS 925605 shows high magnetic activity and potential merging signs.

NSVS 2700153 exhibits significant long-term variability.

Abstract

We carried out photometric and low-resolution spectral observations of six eclipsing ultrashort-period binaries with MS components. The light curve solutions of the Rozhen observations show that all targets are overcontact systems. We found well-defined empirical relation "period -- semi-major axis" for the short-period binaries and used it for estimation of the global parameters of the targets. Our results revealed that NSVS 925605 is quite interesting target: (a) it is one of a few contact binaries with M components; (b) it exhibits high activity (emission in H$\alpha$ line, X-ray emission, large cool spots, non-Planck energy distribution); (c) its components differ in temperature by 700 K. All appearances of high magnetic activity and huge fillout factor (0.7) of NSVS 925605 might be assumed as a precursor of the predicted merging of close magnetic binaries. Another unusual binary is NSVS 2700153 which reveals considerable long-term variability.