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

Dieter Nürnberger tex2html_wrap_inline1968 , Wolfgang Brandner tex2html_wrap_inline1970 , Harold W. Yorke tex2html_wrap_inline1968 , and Hans Zinnecker tex2html_wrap_inline1974
tex2html_wrap_inline1968 Astronomisches Institut der Universität Würzburg, Am Hubland, D-97074 Würzburg, Germany
tex2html_wrap_inline1978 Department of Astronomy, University of Illinois at Urbana-Champaign, 1002 West Green Street, Urbana, IL 61801, USA
tex2html_wrap_inline1974 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 tex2html_wrap_inline1982 upper limits ( tex2html_wrap_inline1984  21 mJy on average) for the remaining objects. These upper limits suggest that the disk masses (gas + dust) are less than tex2html_wrap_inline1988  M tex2html_wrap_inline1990 .

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 tex2html_wrap_inline1796 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 tex2html_wrap_inline1768  = 1.3 mm with the 7-channel bolometer array (Figure gif). We detected cold dust emission only from the southern component with a peak intensity of tex2html_wrap_inline1984  230 mJy and a corresponding circumstellar disk mass of tex2html_wrap_inline1984  0.035 M tex2html_wrap_inline1990 (gas + dust), while for the northern component we derived an upper limit of 10  tex2html_wrap_inline2004 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 tex2html_wrap_inline2006 away from SR 24N.

Astronomy & Astrophysics 330, 549 (1998)
Preprints are available at or from upon request.

Figure: SR 24N/S mapped at tex2html_wrap_inline1768  = 1.3 mm with the MPIfR 7-channel bolometer array mounted at the IRAM 30 m MRT. Contour lines correspond to 10, 20, 30, tex2html_wrap_inline2013 , 90 percent of peak intensity ( tex2html_wrap_inline1772  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 ( tex2html_wrap_inline1774  = 16.0, tex2html_wrap_inline1776  = 15.9, ang. sep. = 52, pos. ang. = 348 tex2html_wrap_inline1780 ). 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 tex2html_wrap_inline1784  = 1.3 Jy and F tex2html_wrap_inline1784  = 1.6 Jy at 10  tex2html_wrap_inline1792 m).

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