AAS 207th Meeting, 8-12 January 2006
Session 81 ISM: From Dark to Blinded
Poster, Tuesday, 9:20am-6:30pm, January 10, 2006, Exhibit Hall

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[81.14] Emission from the Photon Dominated Regions in Cepheus B

B. Mookerjea (University of Maryland, College Park), C. Kramer, M. Roellig (KOSMA, University of Cologne, Germany)

We have observed largescale (10'\times10') maps (at 1' resolution) of [CI] (3P1--3P0 at 492 GHz) and CO (and its isotopomers) (upto J=4--3) with KOSMA (Gornergrat) and IRAM 30m, Spain, to study the PDR emission characteristics of the Cepheus~B molecular cloud. The observed [CI] emission is ubiquitous, and is strongly correlated with the C18O J=1--0 emission, tracing completely the east-west extending ridge of molecular gas having a high column density. The CO J=4--3 emission in contrast is strongly dominated by the warmer and higher density hotspot located to the north-western edge of the molecular cloud. The [CI] emission is uncorrelated with the observed far-infrared emission, (hence presumably the far ultraviolet radiation field) which is primarily dominated by the deeply embedded B1 star.

Cepheus~B is potentially an edge-on PDR in which the molecular cloud is illuminated by the radiation from the OB3 association to the north-west. However, the [CI] and low and mid-J CO datasets do not show any stratification of species. The abundance of C0 relative to CO ranges between 0.1 and 0.3. The large extent of the [CI] emission, far from any exciting source suggest that the emission stems from a clumpy medium allowing the FUV radiation to penetrate deeper into the cloud. Comparison of observed intensity ratios with spherically symmetric PDR models (KOSMA-\tau) suggest clumps with densities ~105~cm-3 and masses between 0.01--0.1~M\odot mainly contribute to the emission.

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