A multi-wavelenth study of sharpless 185
Creators: name: Blouin, Dominique
Publisher: name: University of British Columbia
Year: 2009

description: The HIT region S 185 (nebulosity around -y Cas) has been observed with the DRAO synthesis telescope in continuum and line emission at 21 cm, and in continuum emission at 74 cm. Continuum emission is clearly detected for IC 63 and is barely above the detection limit for IC 59. The emission of both clouds is thermal. A small amount ( ≈0.15 and 0.65 M for IC 63 and IC 59 respectively) of atomic hydrogen is found to be associated with the nebulae at velocity (LSR) near 0 km s⁻¹. Infrared emission from the clouds is also detected from the IRAS survey. The infrared and radio luminosities of the clouds are consistent with heating an dionization being produced by the B0.51V exciting star Cas. However, comparison of the amount of atomic material with the dissociation properties of Cas requires an age less than the main sequence life time by orders of magnitude. As a result, production of the extended atomic gas in the clouds by dissociation appears to have already ceased. The geometry of the region is inferred from the assumption that the clouds are bounded to the ionizing radiation coming from Cas. Accordingly, the weak radio continuum emission of IC 59 may be explained by one of the following hypothesis. The cloud is either farther away from the exciting star than the observed projected distance, or the Lyman continuum radiation from the exciting star is shielded by the postulated Be star envelope. In the former case, the line joining the cloud and the star would make an angle of 51° with the line of sight. The star-to-cloud distance would be about 3 pc. The strong infrared and weak continuum emissions would be due to the long extent (≈ 0.8 pc) of the cloud in the radial direction from the star. For the latter hypothesis, the envelope is shielding about 60% of the stellar ionizing luminosity. IC 63 appears to be composed of two main components: a series of dense filaments on the side of the exciting star which have been compressed by the stellar winds or radiation pressure from the star, and a mixture of lower density dust and dissociated hydrogen mostly located farther away from the exciting star. It is suggested that the density increase on the edges facing the exciting star would have allowed molecules to form in these tiny regions. IC 59, being farther away from the star, would only exhibit the low density component. Atomic hydrogen is also detected at VLSR —34kms⁻¹ near the infrared source IRAS 00556+6048. The emission is very fragmented and exhibits a shell-like structure that appears to surround the infrared source. The source which is probably not associated with S 185 would be located at a kinematic distance of ≈1.8kpc and may be a candidate for a dissociating star object. Another source with flux density 114 mJy, is detected in the 21cm Bonn continuum galactic plane survey. Surprisingly, the source is not detected in the NRAO survey performed at the same wavelength with a similar telescope. Moreover, it is not detected by the DRAO continuum observations while a coincident large ridge of HI emission at VLSR ≈ —29 km s⁻¹ is observed.