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Astron. Astrophys. 324, 629-640 (1997)


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The infrared reflection nebula around the embedded sources in S 140

David Harker 1, 2, Jesse Bregman 2, AGGM Tielens 2, Pasquale Temi 1 and David Rank 1

1 University of California Observatories/Lick Observatory University of California, Santa Cruz, CA 95064, USA
2 NASA Ames Research Center, MS 245-6, Moffet Field, CA 94035-1000, USA

Received 6 October 1995 / Accepted 23 July 1996

Abstract

We have observed the protostellar system in S 140 at 2.2, 3.1 and 3.45 µm using a 128x128 InSb array camera with the Lick Observatory 3m telescope. We have developed a simple model of this region which has been used to derive the physical conditions of the dust and gas. IRS1 is surrounded by a dense dusty disk viewed almost edge-on. Photons leaking out through the poles of the disk illuminate the inner edge of a surrounding shell of molecular gas as seen at locations NW and VLA4. The optical depth at K through the poles of the disk is about 0.22, while [FORMULA] =30 towards IRS1. Analysis of the observed colors and intensities of the NIR light, using Mie scattering theory, reveals that the dust grains in the molecular cloud are somewhat larger than in the general diffuse interstellar medium. Moreover, the incident light has a "cool" color temperature, [FORMULA] K, and likely originates from a dust photosphere close to the protostar. There is little H2 O ice associated with the dusty disk around IRS1. Most of the 3.1 µm ice extinction arises instead from cool intervening molecular cloud material. We have also compared our infrared dust observations with millimeter and radio observations of molecular gas associated with this region. The large scale structure observable in the molecular gas is indicative of the interaction between the protostellar wind and the surrounding molecular cloud rather than the geometry of the protostellar disk. We conclude that S 140 is a young blister formed by this outflow on the side of a molecular cloud and viewed edge-on.

Key words: ISM: S 140 – stars: S 140 IRS 1 – reflection nebulae – dust – infrared: ISM: continuum; lines and bands

© European Southern Observatory (ESO) 1997

Online publication: May 26, 1998

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