MILLIMETER CONTINUUM OBSERVATIONS OF X-RAY SELECTED T-TAURI STARS IN OPHIUCHUS

We present the results of 1.3 mm dust continuum observations for a sam ple of 17 X-ray selected T Tauri stars in the Ophiuchus star forming r egion performed with the MPIfR 7-channel bolometer array mounted at th e IRAM 30 m Millimeter Radio Telescope. We have detected cold dust emi ssion from 3 of the objects and have derived 3 sigma upper limits (sim ilar to 21 mJy on average) for the remaining objects. These upper limi ts suggest that the disk masses (gas + dust) are less than 5 . 10(-3) M.. Combining our results with those obtained by Andre & Montmerle (19 94) for a sample of 21 X-ray selected T Tauri stars (3 additional dete ctions) we improve the statistical significance of our conclusions. As the frequency of circumstellar disks and the disk properties might de pend on the selection criteria as well as local conditions, comparison is made with 1.3 mm surveys of H alpha selected T Tauri stars in Cham aeleon, Lupus, Ophiuchus, and Taurus-Auriga. In order to study the mas s of cold dust in multiple systems we also observed a sample of 15 wel l known binaries, triples, and quadruples by 1.3 mm photometry. From t hese observations we report the 1.3 mm detection of 4 multiple systems . It seems that the measured 1.3 mm flux density increases slightly wi th increasing binary separation. In addition, we have mapped the hiera rchical triple SR 24 at lambda = 1.3 mm with the 7-channel bolometer a rray. We detected cold dust emission only from the southern component with a peak intensity of similar to 230 mJy and a corresponding circum stellar disk mass of similar to 0.035 M. (gas + dust), while for the n orthern component we derived an upper limit of 10 % of the SR 24S peak flux density. The non-detection of 1.3 mm emission from SR 24N sugges ts a lack of cold circumstellar dust in the outer part of the disk, wh ich might have been cleared by the close infrared companion 0.'' 2 awa y from SR 24N.