The Frequency of Binaries among A-Type Stars.
Abstract
Previously it was reported that an investigation of a random sample of 25 metallic-line (Am) stars showed that 88% gave evidence of binary motion. After a reasonable allowance for undetected binaries we concluded that all Am stars are members of spectroscopic binaries. This is a preliminary report on the binary frequency among the normal field stars in the same region of the color-magnitude diagram as the Am stars. A sample of 57 such stars (A4-F2 V, IV) was observed repeatedly with the McDonald 82-inch coude' and Mount Wilson 60-inch Cassegrain spectrographs. Complete measurements on 24 stars yielded nine spectroscopic binaries, indicating a frequency of at least 35%. However, surprisingly all nine binaries have periods greater than too days; also none of the remaining 33 incompletely measured stars have large velocity variations. Therefore it appears that all stars in this region of the color- magnitude diagram that are members of binaries with periods less than too days have abnormal spectra while the single stars have normal spectra. The way in which duplicity affects the spectral appearance is probably through its effect on the rotational velocity. There are no rapidly rotating Am stars or slowly rotating normal ones. Perhaps rapid rotation inhibits the magnetic fields which, in turn, may (according to Uns&ld and Bo~hmVitense) account for their peculiar spectra. % gave evidence of binary motion. After a reasonable allowance for undetected binaries we concluded that all Am stars are members of spectroscopic binaries. This is a preliminary report on the binary frequency among the normal field stars in the same region of the color-magnitude diagram as the Am stars. A sample of 57 such stars (A4-F2 V, IV) was observed repeatedly with the McDonald 82-inch coude' and Mount Wilson 60-inch Cassegrain spectrographs. Complete measurements on 24 stars yielded nine spectroscopic binaries, indicating a frequency of at least 35%. However, surprisingly all nine binaries have periods greater than too days; also none of the remaining 33 incompletely measured stars have large velocity variations. Therefore it appears that all stars in this region of the color- magnitude diagram that are members of binaries with periods less than too days have abnormal spectra while the single stars have normal spectra. The way in which duplicity affects the spectral appearance is probably through its effect on the rotational velocity. There are no rapidly rotating Am stars or slowly rotating normal ones. Perhaps rapid rotation inhibits the magnetic fields which, in turn, may (according to Uns&ld and Bo~hmVitense) account for their peculiar spectra. % gave evidence of binary motion. After a reasonable allowance for undetected binaries we concluded that all Am stars are members of spectroscopic binaries. This is a preliminary report on the binary frequency among the normal field stars in the same region of the color-magnitude diagram as the Am stars. A sample of 57 such stars (A4-F2 V, IV) was observed repeatedly with the McDonald 82-inch coude' and Mount Wilson 60-inch Cassegrain spectrographs. Complete measurements on 24 stars yielded nine spectroscopic binaries, indicating a frequency of at least 35%. However, surprisingly all nine binaries have periods greater than too days; also none of the remaining 33 incompletely measured stars have large velocity variations. Therefore it appears that all stars in this region of the color- magnitude diagram that are members of binaries with periods less than too days have abnormal spectra while the single stars have normal spectra. The way in which duplicity affects the spectral appearance is probably through its effect on the rotational velocity. There are no rapidly rotating Am stars or slowly rotating normal ones. Perhaps rapid rotation inhibits the magnetic fields which, in turn, may (according to Uns&ld and Bo~hmVitense) account for their peculiar spectra.
- Publication:
-
The Astronomical Journal
- Pub Date:
- March 1961
- DOI:
- 10.1086/108502
- Bibcode:
- 1961AJ.....66Q.277A