Optical spectrum of distant OH/IR star V1648 Aql (IRAS 19386+0155)
Abstract
An optical spectrum of the star V1648 Aql (=IRAS 19386+0155) was obtained at the 6-meter telescope with a spectral resolution of R60\,000. Heliocentric radial velocity measured from numerous metallic absorptions is equal to Vr=10.180.05 km s-1 (V LSR=18.1 km s-1). We determined the atmospheric, circumstellar, and interstellar components in the profile of the NaI D~lines at Vr=9.2, -3.4, and -12.8 km s-1 respectively. The averaged over twenty identified DIBs velocity Vr(DIBs)=-12.50.2 km~s-1 coincides with the interstellar NaI component. Weak emissions with an intensity of about 10% of the local continuum level were detected in the spectrum; they are identified as low-excitation metal lines. Their averaged position, Vr=8.440.28 km s-1, may point to the presence of a weak velocity gradient in the upper layers of the stellar atmosphere. Based on the spectroscopic data and taking into account the interstellar and circumstellar reddening, we estimated the star's luminosity MV≈-5 m and also obtained the lower estimate of distance d1.8 kpc. Using the model atmosphere method, we determined the fundamental parameters and chemical abundances in the atmosphere approving the status of a post-AGB star for V1648 Aql.