Study of the Bipolar Nebula IRAS 19312+1950. II. Circumstellar Chemistry

Abstract

The bipolar nebula, IRAS 19312+1950, is a unique SiO maser source exhibiting both properties as young and evolved objects. To clarify the nature of this object, we made molecular line observations with the Nobeyama 45-m radio telescope. We detected emission from O-bearing (HCO^+, SiO, SO, and SO_2), C- and N-bearing molecules (CN, CS, HCN, HNC, NH_3, N_2H^+, HC_3N, H_2CS, and CH_3OH), and their isotopic species (C^17O, ^13C^18O, and C^34S). Line profiles consist of a weak broad (Dv 30 km/s) and/or a strong narrow (DV< 5 km/s) components, depending on molecular species. Strong time variations of H_2O and SiO masers were also observed. Numerical modeling of the envelope with the LVG-code results in a good fit of the model with a mass loss rate of 2.6 10^-4 M_sun/yr to the observed intensities for the broad-component lines. On the other hand, non-O-bearing molecules, which have only the narrow profiles, were found to have abundances typical to those in cool dust clouds. No isotopic enrichment was found, indicating little evidence of the narrow cool component being an ejecta of the central AGB star or a possible companion. These facts compelled us to conclude that IRAS 19312+1950 is an exotic mass-losing evolved star embedded in a low-mass (~20 M_sun) dark cloud.

13 pages, 7 figures, high res. figure available at http://www.nro.nao.ac.jp/library/report/list.html (No. 614). PASJ Dec. 25 issue in press

References in corpus (4)

• Molecular abundances in carbon-rich circumstellar envelopes
• Chemistry and clumpiness in planetary nebulae
• Study of the Bipolar Nebula IRAS 19312+1950. I. Mapping Observations
• Detection of Bipolar Flow toward an Unusual SiO Maser Source IRAS 19312+1950

Cited by in corpus (9)

• Identification of Very Red Counterparts of SiO Maser and OH/IR Objects in the GLIMPSE Survey
• Maser Properties of the Enigmatic IRAS Source 19312+1950
• BIMA Array Observations of the Highly Unusual SiO Maser Source with a Bipolar Nebulosity, IRAS 19312+1950
• On the nature of the enigmatic object IRAS 19312+1950: A rare phase of massive star formation?
• Near-infrared polarimetric study of the bipolar nebula IRAS 19312+1950
• Methanol Observation of IRAS 19312+1950: A Possible New Type of Class I Methanol Masers
• Wide Field CO Mapping in the Region of IRAS 19312+1950
• Molecules in the peculiar age-defying source IRAS 19312+1950
• Molecular Line Observations of the SiO Maser Source IRAS 19312+1950