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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
2 - Astronomical Institute, Academy of Sciences of Czech Republic, CZ-251 65 Ondrejov, Czech Republic

Received July 21; accepted September 11, 2000


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

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