UBV Photometry of the Shortest Period Contact Binary CC COM

Abstract

Red colours: B–V=+1.23, U-B = + 1.03 and short period: P=0.2207 days place CC Com at the lower temperature end of the period-colour relation for the W UMa-type binaries. Contrary to the typical behaviour of (B–V) which shows reddening during both minima, the (U–B) index reveals rather large scatter, especially when different nights are intercompared. In addition (U–B) seems to decrease abnormally during some of primary minima when the colours change to B–V = + 1.29 and U–B = +0.99; it is unclear whether the ultraviolet excess δ(U–B) of about +0.11 is not related to these changes. Small night-to-night changes seem to be present in the V-light curve as well.

The large amplitudes of light variations (0.86 and 0.74 mag) and the presence of total eclipses with semi-duration of about 7 deg in phase permit to determine the geometrical elements with rather high accuracy in spite of larger than normal observational errors due to the faintness of the system (V= 11.3-12.2). CC Com belongs to the W-type systems with the relative temperature excess of secondary component X= +0.058 ± 0.002. Other elements are: i = 88⁰6 ± 0.⁰9, q = 0.511 ± 0.009, f = 0.78 ± 0.03 for the assumed T_e⁰ = 4300 K. To obtain a perfect fit to the light curve, the gravity darkening exponent was also varied with the resulting value β = 0.09 ± 0.02.

There are indications that CC Com might belong to the Coma cluster.