Photometric Studies of Twelve Deep, Low-mass Ratio Overcontact Binary Systems

Details Photometric Studies of Twelve Deep, Low-mass Ratio Overcontact Binary Systems Photometric Studies of Twelve Deep, Low-mass Ratio Overcontact Binary Systems

Aug 2006

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006ap%26ss.304...25q&link_type=abstract

Astrophysics and Space Science, Volume 304, Issue 1-4, pp. 25-28

Astronomy and Astrophysics

Astrophysics

6

Stars: Binaries : Close{, Stars: Binaries : Eclipsing &Ndash, Stars: Individuals (Fg Hya, Gr Vir&Rsquo, Ik Per, Tv Mus, Cu Tau, V857 Her, V410 Aur, Xy Boo, Sx Crv, Qx And. Gsc 619-232, And Ah Cnc), Stars: Evolution

Scientific paper

The formations of the blue straggler stars and the FK Com-type stars are unsolved problems in stellar astrophysics. One of the possibilities for their formations is from the coalescence of W UMa-type overcontact binary systems. Therefore, deep (f > 50%), low-mass ratio (q < 0.25) overcontact binary stars are a very important source to understand the phenomena of Blue Straggler/FK Com-type stars. Recently, 12 W UMa-type binary stars, FG Hya, GR Vir, IK Per, TV Mus, CU Tau, V857 Her, V410 Aur, XY Boo, SX CrV, QX And, GSC 619-232, and AH Cnc, were investigated photometrically. Apart from TV Mus, XY boo, and GSC 619-232, new observations of the other 9 binaries were obtained. Complete light curves of the 10 systems, FG Hya, GR Vir, IK Per, TV Mus, CU Tau, V857 Her, GSC 619-232, V410 Aur, XY Boo, and AH Cnc, were analyzed with the 2003 version of the W-D code. It is shown that all of those systems are deep (f > 50%), low-mass ratio (q < 0.25) overcontact binary stars. We found that the system GSC 619-232 has the highest degree of overcontact (f = 93.4%). The derived photometric mass ratio of V857 Her, q = 0.0653, indicates that it is the lowest-mass ratio system among W UMa-type binaries. Of the 12 sample stars, long-term period changes of 11 systems were found. About 58% (seven) of the sample binaries show cyclic period oscillation. No cyclic period changes were discovered for the other 5 systems, which may be caused by the short observational time interval or by insufficient observations. Therefore, we think that all W UMa-type binary stars may contain cyclic period variations. By considering the long-term period changes (both increase and decrease) of those binary stars, we proposed two evolutionary scenarios evolving from deep, low-mass ratio overcontact binaries into Blue Straggler/FK Com-type stars.

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