LS II +34 deg 26 is a low-mass post-asymptotic giant branch B supergiant and not a massive Population I B star located near the outer edge of the galaxy

Abstract

LS II +34 deg 26 is an 11th magnitude low-gravity, high-velocity and high Galactic latitude B1.5 Ia-Iabe supergiant star. It is found to be an IRAS source with far IR colors, flux distribution, and dust shell parameters similar to those of planetary nebulae. Based on these observations it is concluded that LS II + 34 deg 26 is a low-mass post-AGB B1.5 Ia-Iabe supergiant with a detached cold circumstellar dust shell and not a young massive B star of Population I located at 17.8 kpc near the outer edge of the Galaxy. It is the hottest post-AGB supergiant discovered so far. With this detection the sequence of post-AGB supergiants were found to extend from K to B type which indicates the evolution sequence of these objects from the tip of the AGB toward the left in the H-R diagram. LS II +34 deg 26 may be rapidly evolving toward hotter spectral type and into the region of planetary nebulae. These results demonstrate that some of the high-Galactic latitude and/or high-velocity, low-gravity, OB stars are not massive Population I stars; instead they are low-mass post-AGB stars. These stars may hence be closer than presumed and may not be suitable for the study of Galactic rotation law at large galactocentric distances.