Tuesday, 21 August 2012

Water and Hydroxides in the Circumstellar Disk around HD 163296.

HD 163296 is a young Herbig Ae star (a star producing heat by gravitational collapse, which is expected will fuse Hydrogen in the future, but which has not reached this stage yet) slightly under 400 light years from Earth. It is surrounded by a fairly well documented circumstellar disk, which reaches slightly over 900 AU from the star (i.e. over 900 times as far from the star as Earth is from the Sun). Such disks around young stars are thought to provide the reserve of material from which planets form, making understanding the processes that go on within them important for understanding the formation of planets.

Hubble Space Telescope image of the disk around HD 163296. Grady et al. (2000).

In a paper published on the online arXiv database at Cornell University Library on 17 July 2012, and in the journal Astronomy & Astrophysics on 18 July 2012, a team of scientists led by Davide Fedele of the Max Planck Institut für Extraterrestrische Physik describe the discovery of a band of warm, gaseous, Water (H₂O) and Hydroxide (HO) molecules within the HD 163296 Circumstellar Disk, using the Spitzer Space Telescope.

The H₂O producing region was found to be 15-20 AU from the star, and to have a temperature of 200-300 K (-73.15 to 26.85 ℃). This would be to cold for gaseous water on Earth, but in space water sublimates directly from a solid to a gas, so this is less surprising. It is not clear if the molecules were being produced by the disk, or were being ejected from the star, which is known to produce microjets of material from its polar regions.


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