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Astrophysics Luncheon Seminar

Water Absorption in Galactic Translucent Clouds: Conditions and History of the Gas Derived from Herschel/HIFI PRISMAS Observations
Presented by Nicolas Flagey
Jet Propulsion Laboratory, California Institute of Technology

Monday, January 28, 2013
12:00 noon in 169-336

Water is a molecule of great astrophysical interest: (1) it is an important reservoir of oxygen, the most abundant element in the universe after hydrogen and helium, (2) it plays a critical role in cooling the dense gas, which affects the star formation process, and (3) it has two forms (ortho and para) whose relative amount can be used as a thermometer. I will present Herschel/HIFI observations of water vapor detected in our Galaxy as part of the PRISMAS (PRobing InterStellar Molecules with Absorption line Studies) Guaranteed Time Key Program. Water vapor associated with the interstellar clouds in Galactic arms is detected in absorption. I will then present how to infer the optical depth of each interstellar cloud and derive the amount of water in these clouds. In the observed interstellar clouds, we find that: (1) the water abundance relative to hydrogen is remarkably constant, (2) the excitation temperature is below 5 K, and the density is below 104 cm3 , and (3) the water ortho-to-para ratio is consistent with high temperature (above 40 K), except in two clouds where the ratio indicates that the water has been in a cold phase at some point in its recent history.

SVCP Astrophysics

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