The Radial Velocities of Long-Period Variable Stars. Second Paper.
Abstract
Measurements of radial velocity-These were taken from 6i8 Mount Wilson spectrograms of 206 long- period variables of spectral classes Me and Se and are recorded in Table i. For 152 of these objects no previous measurements have been reported. The velocities of 305 variables in Table 3 summarize all known measurements. It is recommended that velocities derived from the absorption lines (which differ appreciably from those derived from the emission lines) be used in studies of galactic motions. For 72 stars of Table 3, direct measurements of the absorption lines are available; for the other stars the meas- ured emission-line displacements were corrected in the manner described in Mt. W. Contr., No. 6~. A brief statistical study is given of the types, periods, and galactic latitudes of the stars in Table ~. Discussion of galactic motions-The residual radial velocities computed by applying the corrections for ordinary solar motion are decidedly high, the arithmetic mean being 36 km/sec. The higher velocities are associated with the earlier spectral types and the shorter periods (Tables 6 and 7 and Figs. 3 and 4). The relationship with period is partiularly well marked. Among 152 stars with periods shorter than 300 days, i6 have residual velocities greater than 100 km/sec, io have velocities between 80 and 100 km/sec; while among 153 stars with periods of 300 days or longer not one has a velocity exceeding 100 km/sec, and oniy 2 have velocities between 8o and 100 km/sec. The average velocity decreases steadily from 8o km/sec for a group of 27 stars with periods from i~o to 199 days to 17 km/sec for 35 stars with periods greater than 399 days. The evolutionary significance of these results is important but obscure. After correction for solar motion, the 305 variables have a group motion, V0, of 31 km/sec toward the apex a 3 i6°, ~ = + 5Q0 (see Table 8). When the stars are divided according to the absolute values of the residual velocity, V0 is only 4 km/sec for the group with velocities less than 25 km/sec, while for the remaining stars Vo is 6o km/sec. A somewhat similar result is obtained when the stars are divided ac- cording to period of light-variation. On the other hand, when the stars are divided according to distance from the sun, V0 is nearly the same for both groups. The well-marked relationship of group motion to random stellar velocity (Fig. 5) is an excellent example of the asymmetry of high stellar velocities. The apex for the high-speed stars is near that point of the sky toward which stars near the sun are moving in their huge galactic orbits. This fact confirms the view that the velocity asymmetry is an effect exhibited by stars having unusually small circular velocities in their galactic orbits. The radial components may be exceptionally large
- Publication:
-
The Astrophysical Journal
- Pub Date:
- September 1941
- DOI:
- 10.1086/144325
- Bibcode:
- 1941ApJ....94..171M