Context :

Aims : We have investigated the properties of the central star and dust in the bipolar nebula IRAS 19312+1950 , which is an unusual object showing characteristics of a supergiant , a young stellar object , and an asymptotic giant branch ( AGB ) star .

Methods : We obtained H -band polarimetric data of IRAS 19312+1950 using the near-infrared camera ( CIAO ) on the 8 m Subaru telescope .
In order to investigate the physical properties of the central star and the nebula , we performed dust radiative transfer modeling and compared the model results with the observed spectral energy distributions ( SEDs ) , the radial profiles of the total intensity image , and the fraction of linear polarization map .

Results : The total intensity image shows a nearly spherical core with \sim 3 \arcsec radius , an S -shaped arm extending \sim 10 \arcsec in the northwest to southeast direction , and an extended lobe towards the southwest .
The polarization map shows a centro-symmetric vector alignment in almost the entire nebula and low polarizations along the S -shaped arm .
These results suggest that the nebula is accompanied by a central star , and the S -shaped arm has a physically ring-like structure .
From our radiative transfer modeling , we estimated the stellar temperature , the bolometric luminosity , and the current mass-loss rate to be 2 800 K , 7 000 ~ { } L _ { \sun } , and 5.3 \times 10 ^ { -6 } ~ { } M _ { \sun } yr ^ { -1 } , respectively .

Conclusions : Taking into account previous observational results , such as the detection of SiO maser emissions and silicate absorption feature in the 10 \mu m spectrum , our dust radiative transfer analysis based on our near-infrared imaging polarimetry suggests that ( 1 ) the central star of IRAS 19312+1950 is likely to be an oxygen-rich , dust-enshrouded AGB star and ( 2 ) most of the circumstellar material originates from other sources ( e.g .
ambient dark clouds ) rather than as a result of mass loss from the central star .