BIMA Array Observations of the Highly Unusual SiO Maser Source with a Bipolar Nebulosity, IRAS 19312+1950

Abstract

We report the results of mapping observations of the bipolar nebula with SiO maser emission, IRAS 19312+1950, in the CO (J=1-0 and J=2-1), 13CO (J=1-0 and J=2-1), C18O (J=1-0), CS (J=2-1), SO (J_K=3_2-2_1) and HCO+ (J=3-2) lines with the Berkeley-Illinois-Maryland Association array. Evolutional status of this source has been evoking a controversy since its discovery, though SiO maser sources are usually identified as late-type stars with active mass loss. In line profiles, two kinematical components are found as reported in previous single-dish observations: a broad pedestal component and a narrow component. Spatio-kinetic properties of a broad component region traced by 12CO lines are roughly explained by a simple spherical outflow model with a typical expanding velocity of an AGB star, though some properties of the broad component region still conflict with properties of a typical AGB spherical outflow. A narrow component region apparently exhibits a bipolar flow. The angular size of the narrow component region is spatially larger than that of a broad component region. Intensity distribution of the CS emission avoids the central region of the source, and that of an SO broad component emission exhibits a small feature peaked exactly at the mapping center. According to the present results, if a broad component really originates in a spherical outflow, an oxygen-rich evolved stellar object seems to be a natural interpretation for the central star of IRAS 19312+1950.

27 pages, 11 figures; accepted for publication in ApJ

References in corpus (9)

• Multiple Molecular Winds in Evolved Stars I. A Survey of CO(2-1) and CO(3-2) Emission from 45 Nearby AGB Stars
• SiO Maser Survey of Cold IRAS Sources
• HST/NICMOS Imaging Polarimetry of Proto-Planetary Nebulae: Probing of the Dust Shell Structure via Polarized Light
• Detections of SiO and H${}_2$O Masers in the Bipolar Nebula IRAS 19312+1950
• Period Measurement of AGB Stars in the Outer Galactic Disk
• Disk-Like Structure in the Semi-Regular Pulsating Star, X Her
• Study of the Bipolar Nebula IRAS 19312+1950. I. Mapping Observations
• Study of the Bipolar Nebula IRAS 19312+1950. II. Circumstellar Chemistry
• Detection of Bipolar Flow toward an Unusual SiO Maser Source IRAS 19312+1950

Cited by in corpus (11)

• Correlation between Infrared Colors and Intensity Ratios of SiO Maser Lines
• Submillimeter Array Observation of the Proto-Planetary Nebula CRL 618 in the CO J=6-5 Line
• Maser Properties of the Enigmatic IRAS Source 19312+1950
• Extremely Strong ^{13}CO J=3-2 Line in the "Water Fountain" IRAS 16342-3814: Evidence for the Hot-Bottom Burning
• 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
• BIMA CO Observation of EP Aqr the Semiregular Pulsating Star with a Double Component Line Profile
• Molecules in the peculiar age-defying source IRAS 19312+1950
• Molecular Line Observations of the SiO Maser Source IRAS 19312+1950