EDP Sciences
Free access
Volume 395, Number 2, November IV 2002
Page(s) 663 - 667
Section Diffuse matter in space
DOI http://dx.doi.org/10.1051/0004-6361:20021279

A&A 395, 663-667 (2002)
DOI: 10.1051/0004-6361:20021279

Extending the limits of globule detection

ISOPHOT Serendipity Survey observations of interstellar clouds II
L. V. Tóth1, 2, 3, Cs. Kiss4, M. Juvela1, M. Stickel3, U. Lisenfeld5 and S. Hotzel3

1  Helsinki University Observatory, PO Box 14, 00014 University of Helsinki, Finland
2  Department of Astronomy, Loránd Eötvös University, Pázmány Péter sétány 1/a, 1117 Budapest, Hungary
3  Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
4  Konkoly Observatory, Budapest, PO Box 67, 1525, Hungary
5  IRAM, Avenida Divina Pastora 7, N.C., 18012 Granada, Spain

(Received 1 March 2002 / Accepted 2 September 2002)

Small isolated clouds were discovered by the ISOPHOT 170  $\mu $m Serendipity Survey (ISOSS) as faint $I_{\rm 170}<13$ MJy sr -1 FIR sources. One of them is ISOSS J20246+6540, a cold ( $T_{\rm d}\approx 14.5$ K) pointlike ISOSS source without an IRAS pointsource counterpart. In the Digitized Sky Survey B band it is seen as a 3´size bipolar nebulosity with an average excess DSS blue band surface brightness of 8% of the background's photographical density. The CO column density distribution determined by multi-isotopic, multi-level CO measurements with the IRAM-30 m telescope agrees well with the optical appearance. An average hydrogen column density of $\approx$ 1021 cm -2 was derived from both the FIR and CO data. Using a kinematic distance estimate of 400 pc the NLTE modelling of the CO, HCO +, and CS measurements gives a peak density of $\approx$ 104 cm -3. The multiwavelength data characterise ISOSS 20246+6540 as a representative of a class of globules which has not been discovered so far due to their small angular size and low 100  $\mu $m brightness. A significant overabundance of 13CO is found X(13CO $) \ge 150\times X($C 18O ). This is likely due to isotope selective chemical processes.

Key words: ISM: clouds -- dust, extinction -- ISM: molecules -- Infrared: ISM: -- Surveys

Offprint request: L. V. Tóth, lvtoth@mpia-hd.mpg.de

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