Astron. Astrophys. Suppl. Ser. 147, 243-249

Period changes in W UMa-type eclipsing binaries: DK Cygni, V401 Cygni, AD Phoenicis and Y Sextantis

M. Wolf¹ - P. Molík¹ - K. Hornoch¹ - L. Sarounová ²

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1 - Astronomical Institute, Charles University Prague, CZ-180 00 Praha 8, V Holesovickách 2, Czech Republic
e-mail: wolf@mbox.cesnet.cz
2 - Astronomical Institute, Academy of Sciences of Czech Republic, CZ-251 65 Ondrejov, Czech Republic

Received July 21; accepted September 11, 2000

Abstract:

We present a period analysis of the four well-known W UMa-type eclipsing binaries DK Cyg ( $P = 0\hbox{$.\!\!^{\rm d}$ }47$), V401 Cyg ( $0\hbox{$.\!\!^{\rm d}$ }58$), AD Phe ( $0\hbox{$.\!\!^{\rm d}$ }38$) and Y Sex ( $0\hbox{$.\!\!^{\rm d}$ }42$). Several new times of minimum light, recorded photoelectrically, have been gathered. Analysis of all available eclipse timings of the DK Cygni and V401 Cygni has confirmed a significant increase in period of $1.15 \ 10^{-10}$ and $1.48 \ 10^{-10}$ day cycle^-1, respectively. A simultaneous solution of the B, V and R light curves was computed for V401 Cyg using the Binary Maker 2.0 synthetic lightcurve software. This solution indicates that V401 Cyg is in contact with a filing factor of 46%.

The period of AD Phe seems to be constant. Period changes of Y Sex could be explain by a light-time effect caused by a third body in an eccentric orbit with a period of 58 years.

Key words: stars: binaries: eclipsing -- stars: individual: DK Cyg -- stars: individual: V401 Cyg -- stars: individual: AD Phe -- stars: individual: Y Sex -- stars: fundamental parameters