Millimeter continuum observations of X-ray selected T Tauri stars in Ophiuchus

Dieter Nürnberger , Wolfgang Brandner , Harold W. Yorke , and Hans Zinnecker
Astronomisches Institut der Universität Würzburg, Am Hubland, D-97074 Würzburg, Germany
Department of Astronomy, University of Illinois at Urbana-Champaign, 1002 West Green Street, Urbana, IL 61801, USA
Astrophysikalisches Institut Potsdam, An der Sternwarte 16, D-14482 Potsdam, Germany
Abstract: We present the results of 1.3 mm dust continuum observations for a sample of 17 X-ray selected T Tauri stars in the Ophiuchus star forming region performed with the MPIfR 7-channel bolometer array mounted at the IRAM 30 m Millimeter Radio Telescope. We have detected cold dust emission from 3 of the objects and have derived 3 upper limits (  21 mJy on average) for the remaining objects. These upper limits suggest that the disk masses (gas + dust) are less than  M .

Combining our results with those obtained by André & Montmerle (1994) for a sample of 21 X-ray selected T Tauri 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 1.3 mm surveys of H selected T Tauri 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 1.3 mm photometry. From these observations we report the 1.3 mm detection of 4 multiple systems. It seems that the measured 1.3 mm flux density increases slightly with increasing binary separation.

In addition, we have mapped the hierarchical triple SR 24 at  = 1.3 mm with the 7-channel bolometer array (Figure ). We detected cold dust emission only from the southern component with a peak intensity of  230 mJy and a corresponding circumstellar disk mass of  0.035 M (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 1.3 mm emission from SR 24N suggests a lack of cold circumstellar dust in the outer part of the disk, which might have been cleared by the close infrared companion away from SR 24N.

Astronomy & Astrophysics 330, 549 (1998)
Preprints are available at http://www.astro.uni-wuerzburg.de/~nurnberg/publications.html or from nurnberg@iram.fr upon request.

  
Figure: SR 24N/S mapped at  = 1.3 mm with the MPIfR 7-channel bolometer array mounted at the IRAM 30 m MRT. Contour lines correspond to 10, 20, 30, , 90 percent of peak intensity (  230 mJy) before (top) and after (center) deconvolution with a Gaussian maximum likelihood algorithm using maps of Uranus and Mars as point spread functions. Crosses mark the positions of the optical counterparts (  = 16.0,  = 15.9, ang. sep. = 52, pos. ang. = 348 ). For comparison, the mid infrared (N-band) image of SR 24N/S obtained with TIMMI mounted at the ESO 3.6 m telescope on La Silla, Chile (pixel scaling 034/pix; Stanke & Zinnecker 1998) is given in the bottom panel. Both the northern and the southern component show roughly equal emission (F  = 1.3 Jy and F  = 1.6 Jy at 10  m).