Millimeter continuum observations of X-ray selected TTauri stars in Ophiuchus

We present the results of 1.3mm dust continuum observations for a sample of 17 X-ray selected TTauri stars in the Ophiuchus star forming region performed with the MPIfR 7-channel bolometer arraymounted at the IRAM30mMillimeter Radio Telescope. We have detected cold dust emission from 3 of the objects and have derived 3σ upper limits (∼ 21mJy on average) for the remaining objects. These upper limits suggest that the disk masses (gas + dust) are less than 5 · 10−3 M . Combining our results with those obtained by André & Montmerle (1994) for a sample of 21 X-ray selected TTauri stars (3 additional detections) we improve the statistical significance of our conclusions. As the frequency of circumstellar disks and the disk properties might depend on the selection criteria as well as local conditions, comparison is made with 1.3mm surveys of Hα selected TTauri stars in Chamaeleon, Lupus, Ophiuchus, and Taurus-Auriga. In order to study the mass of cold dust in multiple systems we also observed a sample of 15 well known binaries, triples, and quadruples by 1.3mmphotometry. From these observations we report the 1.3mm detection of 4 multiple systems. It seems that the measured 1.3mm flux density increases slightly with increasing binary separation. In addition, we have mapped the hierarchical triple SR 24 at λ= 1.3mm with the 7-channel bolometer array. We detected cold dust emission only from the southern component with a peak intensity of ∼ 230mJy and a corresponding circumstellar disk mass of ∼ 0.035M (gas + dust), while for the northern component we derived an upper limit of 10% of the SR 24S peak flux density. The non-detection of 1.3mm emission from SR24N suggests a lack of cold circumstellar dust in the outer part of the disk, which might have been cleared by the close infrared companion 0. ′′2 away from SR24N. Send offprint requests to: Dieter Nürnberger ? Based on observations obtained with the IRAM 30mMRT on Pico Veleta, Spain