OPTICAL OUTBURST OF A PRE-MAIN-SEQUENCE OBJECT

We present a study of CB34V, a pre-main-sequence object that has incre ased in brightness by similar to 3.7 mag in the red between 1951 Novem ber (1951.9) and 1996 February (1996.1). Our data consist of intermedi ate and high-resolution optical spectroscopy as well as optical and ne ar-infrared photometry (BVRIJHK). We find that the color behavior of t he CB34V brightness variation is peculiar, corresponding to a gray bri ghtening. We demonstrate that CB34V is a pre-main-sequence object embe dded in a small molecular cloud by 2.4 visual magnitudes. At optical w avelengths CB34V has a G5 (III-IV) spectral type and is rapidly rotati ng 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 i mplies 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 br ightening: (1) a high accretion episode (FU Orionis type) and (2) time variable extinction due to motions of the non-uniform circumstellar e nvironment. Although we favor the latter, CB34V seems difficult to cla ssify into any of the known types of pre-main-sequence variability. (C ) 1997 American Astronomical Society.