BL Andromedae and GW Tauri: close binary stars in a key evolutionary stage |
| |
| Authors: | Liying Zhu Shengbang Qian |
| |
| Institution: | National Astronomical Observatories/Yunnan Observatory, Chinese Academy of Sciences, PO Box 110, 650011 Kunming, China;United Laboratory of Optical Astronomy, Chinese Academy of Sciences (ULOAC), 100012 Beijing, China;Graduate School of the Chinese Academy of Sciences 100012 Beijing, China |
| |
| Abstract: | 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. |
| |
| Keywords: | binaries: close binaries: eclipsing stars: evolution stars: individual: BL Andromedae stars: individual: GW Tauri |
|
|
