X-ray and UV emission of the ultrashort-period, low-mass eclipsing binary system BX Tri

TL;DR

This study analyzes X-ray and UV emissions of the low-mass eclipsing binary BX Tri, revealing orbital modulation in UV and suggesting photospheric origin, while X-ray variability hints at magnetic activity.

Contribution

It extends low-mass binary system studies by analyzing X-ray and UV data of BX Tri, demonstrating the capability of PHOEBE for UV modeling and exploring emission origins.

Findings

Orbital modulation detected in UV light curve.

UV emission primarily photospheric in origin.

X-ray variability observed with no clear orbital modulation.

Abstract

Close binary systems provide an excellent tool to determine stellar parameters such as radii and masses with a high degree of precision. Due to the high rotational velocities, most of these systems exhibit strong signs of magnetic activity, which has been postulated to be the underlying reason for radius inflation in many of the components. We aim to extend the sample of low-mass binary systems with well-known X-ray properties. For this, we analyze data from a singular XMM-Newton pointing of the close, low-mass eclipsing binary system BX Tri. The UV light curve is modeled with the eclipsing binary modeling tool PHOEBE and data acquired with the EPIC cameras is analyzed to search for hints of orbital modulation. We find clear evidence of orbital modulation in the UV light curve and show that PHOEBE is fully capable of modeling data within this wavelength range. Comparison to a theoretical flux prediction based on PHOENIX models shows that the majority of UV emission is of photospheric origin. While the X-ray light curve does exhibit strong variations, the signal-to-noise ratio of the observation is insufficient for a clear detection of signs of orbital modulation. There is evidence of a Neupert-like correlation between UV and X-ray data.