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From an analysis of VLBI observations of H2CO and OH maser emission in the direction of the ultra-conpact HII region NGC 7538-IRS 1, the following model is proposed: The HII region is surrounded by a thick dusty shell which breaks open at the two poles and there is a bipolar outflow. Around it is a rotating gas/dust ring and matter falls from the ring onto the surface of the HII region. The whole system, HII region and the ring, moves with a sight line velocity of −61.0 km/s inside a large cloud which moves with a sight line velocity of −57 km/s. The H2CO and OH masers occur near the poles of the HII region and within 0.2 RHII of the surface. The positions of the H2O maser and other line sources are discussed in term of this model. 相似文献
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Truong-Bach Nguyen-Q-Rieu R.J. Sylvester M.J. Barlow X.W. Liu T. Lim A. Omont P. Cox C.J. Skinner 《Astrophysics and Space Science》1997,255(1-2):325-328
We present an ISO LWS 43-197 μm grating spectrum of the oxygen-rich AGB star R Cas. The spectrum is rich of isolated and blended
H2O lines. For their identification and in order to determine the physical parameters of the circumstellar envelope, we have
constructed a model which treats radiative transfer, chemical exchange and photodissociation reactions, and various heating
and cooling processes in a consistent manner. By fitting the observed line fluxes and using stellar parameters based upon
the Hipparcos distance, we derived a mass-loss rate of M = 1 10-6 M⊙ yr-1 which is close to the value 6 10-7 M⊙ yr-1 previously
derived for W Hya, another oxygen-rich AGB star.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
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