Photometric study and preliminary elements of the low-mass ratio W UMa system ASAS 021209+2708.3

Abstract

We present CCD B and V light curves, obtained in the year 2006, and a photometric solution of the low-mass ratio contact binary ASAS 021209+2708.3. With our data we were able to determine six new times of minimum light and refine the orbital period of the system to 0.3181963 days. The light curves are analyzed using the 2003 version of the Wilson-Devinney program and the analysis was performed with and without adding a spot on the surface of one star because the light curves appear to exhibit a typical O'Connell effect, with Maximum I brighter than Maximum II. The results show that ASAS 021209+2708.3 may be classified as an A-subtype W Ursae Majoris system with a small mass ratio q = 0.1889, a large over-contact degree of f = 0.587, a very small difference between the component temperatures of ΔT = 53 K and an orbital inclination of i = 81 • . It is known that deep (f > 50%), low-mass ratio (q < 0.25) overcontact binary stars are a very important resource for understanding the phenomena of Blue Straggler/FK Com-type stars. The formations of Blue Straggler stars and FK Com-type stars are unsolved problems in stellar astrophysics. One of the possible explanations for their formation is from the coalescence of W UMa-type overcontact binary systems. The absolute dimensions of ASAS 021209+2708.3 are estimated and its dynamical evolution is inferred.

Period change investigation of the low mass ratio contact binary BO Ari

“…The orbital period of BO Ari in this study was shorter than the value obtained by Acerbi, Barani and Martignoni (2011). The (O − C) residuals were calculated by using the Eq.…”

“…1. The primary massive star was eclipsed by the less massive star at the primary minimum, indicating that this contact binary is an A-type system, same as identified by Acerbi, Barani and Martignoni (2011). For the A-type contact binary, the more massive component is assigned to be star 1 and the other component is assigned as star 2.…”

“…that the value assumed in previous study by Acerbi, Barani and Martignoni (2011). The Wilson-Devinney (W-D) method (Wilson and Devinney, 1971;Wilson, 1979Wilson, , 1990Wilson and van Hamme, 2003) was used to derive the photometric solution for BO Ari.…”

“…The photometric parameters were obtained for the minimum sum of the squared residuals, Σ(O −C) 2 = 0.0124, resulting in a mass ratio of q = 0.1754 Notes: † Acerbi, Barani and Martignoni (2011). * Parameters of a starspot on the primary star.…”

“…BO Ari (RA(2000) = 02 h 12 m 08 s .78, Dec.(2000) = 27 • 08 ′ 18 ′′ .2), was identified as EW type binary by Nicholson and Varley (2006) with the first measured light minimum of HJD = 2451479.6566 and the orbital period of 0.3182 d. The revised period was obtained to be 0.3181963 d by Acerbi, Barani and Martignoni (2011). BO Ari was classified as an A-type system.…”