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Water vapor toward starless cores: The Herschel view
- Source :
- Astronomy & astrophysics, 521:29. EDP Sciences, Astronomy & Astrophysics, 521, L29, Astronomy and Astrophysics-A&A, Astronomy and Astrophysics-A&A, EDP Sciences, 2010, 521, pp.L29. ⟨10.1051/0004-6361/201015097⟩, Astronomy & Astrophysics, 521. EDP Sciences, Astronomy and Astrophysics-A&A, 2010, 521, pp.L29. ⟨10.1051/0004-6361/201015097⟩, Astronomy & Astrophysics, 521, pp. L29
- Publication Year :
- 2010
- Publisher :
- EDP Sciences, 2010.
-
Abstract
- SWAS and Odin provided stringent upper limits on the gas phase water abundance of dark clouds (x(H2O) < 7x10^-9). We investigate the chemistry of water vapor in starless cores beyond the previous upper limits using the highly improved angular resolution and sensitivity of Herschel and measure the abundance of water vapor during evolutionary stages just preceding star formation. High spectral resolution observations of the fundamental ortho water (o-H2O) transition (557 GHz) were carried out with Herschel HIFI toward two starless cores: B68, a Bok globule, and L1544, a prestellar core embedded in the Taurus molecular cloud complex. The rms in the brightness temperature measured for the B68 and L1544 spectra is 2.0 and 2.2 mK, respectively, in a velocity bin of 0.59 km s^-1. The continuum level is 3.5+/-0.2 mK in B68 and 11.4+/-0.4 mK in L1544. No significant feature is detected in B68 and the 3 sigma upper limit is consistent with a column density of o-H2O N(o-H2O) < 2.5x10^13 cm^-2, or a fractional abundance x(o-H2O) < 1.3x10^-9, more than an order of magnitude lower than the SWAS upper limit on this source. The L1544 spectrum shows an absorption feature at a 5 sigma level from which we obtain the first value of the o-H2O column density ever measured in dark clouds: N(o-H2O) = (8+/-4)x10^12 cm^-2. The corresponding fractional abundance is x(o-H2O) ~ 5x10^-9 at radii > 7000 AU and ~2x10^-10 toward the center. The radiative transfer analysis shows that this is consistent with a x(o-H2O) profile peaking at ~10^-8, 0.1 pc away from the core center, where both freeze-out and photodissociation are negligible. Herschel has provided the first measurement of water vapor in dark regions. Prestellar cores such as L1544 (with their high central densities, strong continuum, and large envelopes) are very promising tools to finally shed light on the solid/vapor balance of water in molecular clouds.<br />Accepted for publication in Astronomy and Astrophysics (HIFI first results issue)
- Subjects :
- Astronomy
FOS: Physical sciences
Astrophysics
INITIAL CONDITIONS
7. Clean energy
ISM: clouds
OXYGEN
Gas phase
PRESTELLAR CORES
Radiative transfer
TEMPERATURE
Physics
stars: formation
DENSE INTERSTELLAR CLOUDS
Research Programm of Institute for Mathematics, Astrophysics and Particle Physics
[SDU.ASTR.SR]Sciences of the Universe [physics]/Astrophysics [astro-ph]/Solar and Stellar Astrophysics [astro-ph.SR]
astrochemistry
Molecular cloud
Photodissociation
Astronomy and Astrophysics
[PHYS.ASTR.SR]Physics [physics]/Astrophysics [astro-ph]/Solar and Stellar Astrophysics [astro-ph.SR]
Astrophysics - Astrophysics of Galaxies
MOLECULAR-IONS
molecular processes
L1544
13. Climate action
Space and Planetary Science
radiative transfer
Astrophysics of Galaxies (astro-ph.GA)
ComputingMethodologies_DOCUMENTANDTEXTPROCESSING
PRE-STELLAR CORES
ABUNDANCE
line: formation
DEPLETION
Water vapor
Galaxy Astrophysics
Subjects
Details
- Language :
- English
- ISSN :
- 14320746 and 00046361
- Volume :
- 521
- Database :
- OpenAIRE
- Journal :
- Astronomy & Astrophysics
- Accession number :
- edsair.doi.dedup.....c689cdc91b70bf61693336fe1c4bb172