CCD photometry of YY Orionis stars^*

¹ Laboratoire d'Astrophysique, Observatoire de Grenoble, Université Joseph Fourier, BP. 53, 38041 Grenoble Cedex 9, France
² Institut d'Astrophysique de Paris, 98 bis boulevard Arago, 75014 Paris, France

Send offprint request to: S. Harder

Received: 12 June 1997
Accepted: 29 September 1997

Abstract

Photometric UBVRI observations of the YY Orionis stars YY Ori, SY Ori, CE Ori, NS Ori and XX Ori are presented. The luminosity of all stars is variable on a timescale of a few days. This variation is rather irregular and no periodic variability was observed in the present data sets. The and colors become redder when the stars become fainter, suggesting that inhomogeneous surface temperature distributions are responsible for the observed irregular variability. Two stars located in the vicinity of our program stars and observed in the same frames turned out to be variable. They were identified as V481 Ori and AO Ori. We report a periodic modulation of the V481 Ori light curve with a period of 4.9 days.