Investigating the properties of the near contact binary system TW CrB

TL;DR

This study analyzes the binary system TW CrB, revealing its period, starspot activity, and potential mass transfer, suggesting it is near Roche lobe filling and possibly an X-ray source.

Contribution

The paper provides a new ephemeris, revised period change rate, and detailed light curve modeling including starspots and hotspots for TW CrB.

Findings

Period is 0.58887492 days with a revised rate of change.

Stars are close to filling their Roche lobes, possibly with one filling.

Evidence of cyclical period variation and starspot activity.

Abstract

TW Coronae Borealis (TW CrB) is a binary system likely to be active showing evidence of starspots and a hotspot. We calculated a new ephemeris based on all available timings from 1946 and find the period to be 0.58887492(2) days. We have revised the average rate of change of period down from 1.54(16) x 10-7 days yr-1 to 6.66(14) x10-8 days yr-1. Based on light curve simulation analysis we conclude that the two stars are close to filling their Roche lobes, or possibly that one of the stars' Roche lobe has been filled. The modelling also led to a hotspot and two starspots being identified. Conservative mass transfer is one of a number of possible mechanisms considered that could explain the change in period, but the mass transfer rate would be significantly lower than previous estimates. We found evidence that suggests the period was changing in a cyclical manner, but we do not have sufficient data to make a judgement on the mechanism causing this variation. The existence of a hotspot suggests mass transfer with a corresponding increase in the amplitude in the B band as compared with the R and V bands. The chromospheric activity implied by the starspots make this binary a very likely X-ray source.