High-Resolution Optical Spectroscopy of the Post-AGB Supergiant V340 Ser (=IRAS 17279-1119)

Evidence of wind variability and velocity stratification in the extended atmosphere has been found in the spectra of the supergiant V340 Ser (=IRAS 17279-1119) taken at the 6-m BTA telescope with a resolution R >= 60 000. The H alpha line has a P Cyg profile whose absorption component (V-circle dot = +34 km s(-1)) is formed in the upper layers of the expanding atmosphere close the circumstellar medium. For four dates the mean velocity has been derived from the positions of 300-550 symmetric metal absorptions with an accuracy better than +/- 0.1 km s(-1): V-circle dot = 59.30, 60.09, 58.46, and 55.78 km s(-1). A lot of low-excitation metal lines have an inverse P Cyg profile. The mean positions of their emission components, V-circle dot = 46.3 +/- 0.4 km s(-1), differ systematically from the velocity inferred from symmetric absorptions, suggesting the presence of a velocity gradient in the supergiant's extended atmosphere. The multicomponent profile of the Na I D lines contains the interstellar, V-circle dot = -11.2 km s(-1), and circumstellar, V-circle dot = +10 km s(-1), components and the component forming in the upper atmospheric layers, V-circle dot = +34.0 km s(-1). Themean velocity from20-30 diffuse interstellar bands (DIBs) identified in the spectra, V-circle dot(DIBs) = - 11.6 +/- 0.2 km s(-1), agrees with the velocity from interstellar Na I and KI components. The equivalent width of the oxygen tripletW(O I 7774) = 1.25 angstrom corresponds to an absolute magnitude of the star Mv approximate to -4.6(m), which, given the total (interstellar + circumstellar) extinction, leads to a distance to the star d approximate to 2.3 kpc.