Optical outburst of a pre-main-sequence object

We present a study of CB34V, a pre-main-sequence object that has increased in brightness by similar to 3.7 mag in the red between 1951 November (1951.9) and 1996 February (1996.1). Our data consist of intermediate and high-resolution optical spectroscopy as well as optical and near-infrared photometry (BVRIJHK). We find that the color behavior of the CB34V brightness variation is peculiar, corresponding to a gray brightening. We demonstrate that CB34V is a pre-main-sequence object embedded in a small molecular cloud by 2.4 visual magnitudes. At optical wavelengths CB34V has a G5 (III-IV) spectral type and is rapidly rotating with a v sin i similar to 145+/-20 km s(-1). We estimate a current bolometric luminosity of 7 <L(CB34V) <39 (D/kpc)(2) L.. If the optical light is stellar in origin, the object's position on the HR diagram implies a stellar mass of similar to 2 M. and an age of similar to 1 X 10(6) years. We consider two possible explanations for the observed brightening: (1) a high accretion episode (FU Orionis type) and (2) time variable extinction due to motions of the non-uniform circumstellar environment. Although we favor the latter, CB34V seems difficult to classify into any of the known types of pre-main-sequence variability. (C) 1997 American Astronomical Society.