A long-term photometric study of the FU Orionis star V 733 Cephei

¹ Institute of Astronomy, Bulgarian Academy of Sciences, 72 Tsarigradsko Shose Blvd., 1784 Sofia, Bulgaria e-mail: [speneva;esemkov]@astro.bas.bg
² INAF Osservatorio Astronomico di Padova, Sede di Asiago, 36032 Asiago (VI), Italy
³ Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany

Received: 18 January 2010
Accepted: 17 February 2010

Abstract

Context. The FU Orionis candidate V733 Cep was discovered by Roger Persson in 2004. The star is located in the dark cloud L1216 close to the Cepheus OB3 association. Because only a small number of FU Orionis stars have been detected to date, photometric and spectral studies of V733 Cep are of great interest.

Aims. The studies of the photometrical variability of PMS stars are very important to the understanding of stellar evolution. The main purpose of our study is to construct a long-time light curve of V733 Cep. On the basis of BVRI monitoring we also study the photometric behavior of the star.

Methods. We gather data from CCD photometry and archival photographic plates. The photometric BVRI data (Johnson-Cousins system) that we present were collected from June 2008 to October 2009. To facilitate transformation from instrumental measurements to the standard system, fifteen comparison stars in the field of V733 Cep were calibrated in BVRI bands. To construct a historical light curve of V733 Cep, a search for archival photographic observations in the Wide-Field Plate Database was performed. As a result, 192 photographic plates containing the field of V733 Cep were found. Some plates were analyzed at our request to estimate the magnitude of V733 Cep.

Results. Our photometric study confirms the affiliation of V733 Cep to the group of FU Orionis objects. An outburst in the optical and a slow rise in brightness during the period 1971–1993 are well documented. During the period 1993–2004, V733 Cep exhibited its maximum brightness and the amplitude of the observed outburst exceeded 45 (R). The BVRI photometric data imply that from February 2007 to October 2009, a slow decrease in brightness of V733 Cep was observed. The observed color evolution of V–I index also suggest that V733 Cep is currently fading. The long-time light curve of V733 Cep is similar to the light curves of other FU Orionis objects.