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Tim Kendall's Extreme Astrophysics

Onset of ice formation in the Pipe nebula

15 Dec 2017, 15:33 UTC
Onset of ice formation in the Pipe nebula ESO
(200 words excerpt, click title or image to see full post)

In a recent paper, Goto et al., (preprint) have used infrared absorption spectroscopy of background stars to probe ice formation on grains in the Pipe nebula (APOD image and credits), detecting water ice absorption in seven out of 21 lines of sight investigated. The peak optical depths of the water ice are about half as large as those on the sources in Taurus with similar visual extinctions. One possible explanation (among others) is that the formation of the ice mantle has just started, that is, the Pipe Nebula is in an earlier phase of ice evolution than Taurus is. Alternatively the interstellar radiation field impinging on the Pipe nebula is larger than that on the Taurus molecular cloud, or the visual extinction through the Pipe nebula may have been overestimated. From the abstract:

Spectroscopic studies of ices in nearby star-forming regions indicate that ice mantles form on dust grains in two distinct steps, starting with polar ice formation (water rich) and switching to apolar ice (CO rich). We test how well the picture applies to more diffuse and quiescent clouds where the formation of the first layers of ice mantles can be witnessed. Medium-resolution near-infrared spectra are obtained toward background ...

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