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 ) , ^ { 13 } CO ( J = 1 –0 and J = 2 –1 ) , C ^ { 18 } O ( 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 ^ { 12 } CO 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 .