Details

Autor(en) / Beteiligte

• Smith, R. G.
• Blum, R. D.
• Quinn, D. E.
• Sellgren, K.
• Whittet, D. C. B.

Titel

Ice in the Southern Coalsack

Ist Teil von

• Monthly notices of the Royal Astronomical Society, 2002-03, Vol.330 (4), p.837-843

Ort / Verlag

Oxford, UK: Blackwell Science Ltd

Erscheinungsjahr

2002

Quelle

Wiley-Blackwell Journals

Beschreibungen/Notizen

• To better understand the conditions under which ice mantles form on grains in molecular clouds, three globules in the Southern Coalsack have been searched for the presence of H2O ice. Given the total lack of star formation in the Coalsack, it is an ideal site for studying unprocessed icy molecular mantles. In our sample of eight field stars lying behind the Coalsack we detect strong H2O ice absorption in the lines of sight to two stars and possible weak absorption in four others. We estimate H2O ice column densities or upper limits for these lines of sight. Compared to dark clouds such as Taurus, the Coalsack H2O ice column densities are lower than expected given the quiescent nature of the Coalsack region. It is possible that the chemical evolution of the Coalsack may simply be at too early a stage for significant ice mantles to appear on the grains, except perhaps in the densest parts of some of the globules. Alternatively, the presence or absence of ice absorption may be related to the distribution of dust along each line of sight, specifically, the relative contributions of dense globules and a more extended diffuse component. For example, our observations are consistent with an ice threshold extinction similar to that observed in the Taurus dark cloud if extinction amounting to Av ∼ 5 towards Globules 2 and 3 arises in the extended component. Globule 1 appears to have no extended component.