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Astron. Astrophys. 345, 965-976 (1999)

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Mapping of the extinction in giant molecular clouds using optical star counts

L. Cambrésy

Observatoire de Paris, Département de Recherche Spatiale, F-92195 Meudon Cedex, France

Received 2 December 1998 / Accepted 5 March 1999


This paper presents large scale extinction maps of most nearby Giant Molecular Clouds of the Galaxy (Lupus, [FORMULA] Ophiuchus, Scorpius, Coalsack, Taurus, Chamaeleon, Musca, Corona Australis, Serpens, IC 5146, Vela, Orion, Monoceros R1 and R2, Rosette, Carina) derived from a star count method using an adaptive grid and a wavelet decomposition applied to the optical data provided by the USNO-Precision Measuring Machine. The distribution of the extinction in the clouds leads to estimate their total individual masses M and their maximum of extinction. I show that the relation between the mass contained within an iso-extinction contour and the extinction is similar from cloud to cloud and allows the extrapolation of the maximum of extinction in the range 5.7 to 25.5 magnitudes. I found that about half of the mass is contained in regions where the visual extinction is smaller than 1 magnitude. The star count method used on large scale ([FORMULA] square degrees) is a powerful and relatively straightforward method to estimate the mass of molecular complexes. A systematic study of the all sky would lead to discover new clouds as I did in the Lupus complex for which I found a sixth cloud of about [FORMULA].

Key words: methods: data analysis – ISM: clouds – ISM: dust, extinction – ISM: structure

Send offprint requests to: Laurent Cambrés (Laurent.Cambresy@obspm.fr)

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© European Southern Observatory (ESO) 1999

Online publication: April 28, 1999