Open AccessBL Andromedae and GW Tauri: close binary stars in a key evolutionary stage
Author(s) -
Zhu Liying,
Qian Shengbang
Publication year - 2006
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1111/j.1365-2966.2005.09963.x
Subject(s) - physics , light curve , contact binary , astrophysics , stars , roche lobe , orbital period , binary star , asymmetry , binary number , mass ratio , arithmetic , mathematics , quantum mechanics
A photoelectric light curve of BL And is presented along with the first CCD light curve of GW Tau. Both objects are short‐period eclipsing binaries and were observed in 2003 or 2004. Photometric elements were computed using the latest version of the Wilson–Van Hamme code. The results reveal that BL And is a semidetached system with the primary component filling its Roche lobe and the secondary one almost filling but still detached, while GW Tau is a marginal‐contact binary system with a small degree of contact ( f = 10.9 per cent) and a large temperature difference of about 3100 K. All available eclipse times, including new ones, were analysed for each system. It was found that the orbital period of BL And is decreasing at the rate of d P /d t =−2.36 × 10 −8 (±0.09) d yr −1 while that of GW Tau may be decreasing or oscillating. We think period decrease is more probable. The derived configuration and secular period decrease for BL And combined with the asymmetry of the light curve indicate that this system may evolve from the present semidetached phase into a contact stage, with mass transfer from the primary component to the secondary one through the L 1 point, or that it might just undergo the broken stage predicted by the theory of thermal relaxation oscillations. In contrast, GW Tau is a marginal‐contact binary in poor thermal contact and may be at the beginning of the contact phase.