Astronomy and Astrophysics – Astrophysics
Scientific paper
Jul 1997
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997a%26a...323l..25c&link_type=abstract
Astronomy and Astrophysics, v.323, p.L25-L28
Astronomy and Astrophysics
Astrophysics
49
Line: Identification, Molecular Processes, Ism: Individual Objects: Sgr B2, Ism: Molecules
Scientific paper
We report the discovery of widespread water vapour absorption in the 2_12_-1_01_ 179.5μm transition toward the SgrB2 molecular cloud. The data were obtained with the Long Wavelength Spectrometer (LWS) on board the ISO satellite. A raster map centered on SgrB2 made with the LWS grating clearly shows the 179.5μm H_2_O line in absorption against the far-infrared continuum at all observed positions with a line absorption depth of ~15%. The grating data are complemented with Fabry-Perot observations of the H_2_O 179.5 and 174.6μm lines, and the H_2_^18^O 181.05μm. The transitions connecting the ground level show a broad absorption profile between -150 and 100km/s proving that water vapour is present in the molecular gas along the line of sight toward SgrB2. The H_2_O absorption lines probably arise in the tenuous and extended envelope of SgrB2 where collisional excitation is negligible and the excitation is mainly due to absorption of photons emitted by the dust. We derive a lower limit to the H_2_O abundance in SgrB2 of 10^-5^.
Baluteau Jean-Paul
Caux Emmanuel
Cernicharo Jose
Clegg Peter
Cox Pierre
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