Detection of two totally eclipsing B-type binaries with extremely low mass ratios

TL;DR

This study reports the discovery and analysis of two B-type eclipsing binaries with extremely low mass ratios, providing insights into binary star formation and evolution through TESS data and photometric modeling.

Contribution

It presents the first detailed analysis of two short-period B-type binaries with extremely low mass ratios, including their photometric solutions and implications for stellar evolution.

Findings

Both systems are detached binaries with total eclipses.

One system has an exceptionally low mass ratio of 0.067.

Secondary components are over-luminous and over-sized compared to normal low-mass stars.

Abstract

The detection of O- and B-type stars with extremely low-mass companions is very important for understanding the formation and evolution of binary stars. However, their finding remains a challenge because the low-mass components in such systems contribute such small flux to the total. During the searching for pulsations among O- and B-type stars by using the TESS data, we found two short-period and B-type (B9) eclipsing binaries with orbital periods of 1.61613 and 2.37857 days. Photometric solutions of the two close binaries were derived by analyzing the TESS light curves with the W-D method. It is discovered that both of them are detached binaries with extremely low mass ratios of 0.067(2) for TIC 260342097 and 0.140(3) for TIC 209148631, respectively. The determined mass ratio indicates that TIC 260342097 is one of the lowest mass ratios among known B-type binary systems. We showed that the two systems have total eclipses with a broad and flat secondary minimum, suggesting that the photometric parameters could be derived reliably. The absolute parameters of the two binaries are estimated and it is found that the secondary components in the two systems are over-luminous and over-size when compared with the normal low-mass and cool main-sequence (MS) stars. These findings may imply that the two systems are composed of a B-type MS primary and a cool pre-MS secondary with orbital periods shorter than 2.5 days. They are valuable targets to test theories of binary star formation and evolution.