Volume 395, Number 2, November IV 2002
|Page(s)||663 - 667|
|Published online||14 November 2002|
Extending the limits of globule detection *
ISOPHOT Serendipity Survey observations of interstellar clouds II
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
Corresponding author: L. V. Tóth, email@example.com
Accepted: 2 September 2002
Small isolated clouds were discovered by the ISOPHOT 170 μm Serendipity Survey (ISOSS) as faint MJy sr-1 FIR sources. One of them is ISOSS J20246+6540, a cold ( 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 ≈ 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 ≈ 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 μm brightness. A significant overabundance of 13CO is found COC18O. This is likely due to isotope selective chemical processes.
Key words: ISM: clouds / dust, extinction / ISM: molecules / Infrared: ISM: / Surveys
© ESO, 2002
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