Systematic Displacements of Lines in the Spectra of Certain Bright Stars
Abstract
Measurements of high-dispersion spectrograms taken with the coudé spectrograph of the 100-inch reflector show that the sodium lines D1 and D2 in the spectra of ~3 Orionis, a Cygni, a Orionis, a Scorpil, a' Herculis, ~ Pegasi, and Pegasi give systematically larger negative radial velocities than the normal stellar lines. The D lines in the spectra of several of the stars are unsymmetrical and evidently consist of two components, one of which is a normal stellar line. The measured radial velocities are in full accord with this conclusion. Results agreeing with those found for the D lines are given by the H and K lines, and, in the case of the M-type stars, by the pair of Al i lines between H and K. The average deviation of these lines, most of which are blends, from the normal stellar lines is of the order of -5 km/sec. Less accurate observations of several Si ii lines in the spectrum of ~9 Orionis indicate differences in the same direction but less in amount. All these stars are relatively near, and it seems improbable that interstellar absorp- tion can account for the observed results. For the M stars at least, the hypothesis of a gradually expanding envelope appears more satisfactory. Interstellar absorption may perhaps be more effective in the cases of ~3 Orionis and a Cygni. In the spectrum of -y Cygni the lines of neutral iron give larger negative velocities than those of ionized iron and titanium, and lines of Cen stifi larger negative values. Similar but larger differences between neutral and enhanced lines are found in the spectra of a Canis Majoris and a Cygni. The hypothesis of radial convection currents affecting lines of different levels differently seems to be adequate to account for these results
- Publication:
-
The Astrophysical Journal
- Pub Date:
- March 1935
- DOI:
- 10.1086/143620
- Bibcode:
- 1935ApJ....81..119A