Barium star
Barium stars are giant stars of the spectral G or K, the spectra of an over frequency of s-process - elements show primarily from basic ionized barium , Ba II, at a wavelength λ = 455.4 n m . They also show stronger spectral lines of carbon , bands of the molecules of CH , CN and C 2 .
This star class of peculiar stars was first recognized and defined by William Bidelman and Philip C. Keenan .
Emergence
Double stars
Studies of their radial velocities show that all barium stars binary stars are. Investigations by the International Ultraviolet Explorer in the ultraviolet spectral range also found white dwarfs in many barium star systems .
Cataclysm
It is therefore assumed that barium stars are formed by mass transfer in a binary star system.
The mass of its partner was transferred to the current giant barium star when the barium star was still in the development phase of its main sequence stage . Its companion, the donor star, was a carbon star on the asymptotic giant branch (AGB: A symptotic G iant B ranch), which produced carbon and s-process elements inside . These nuclear fusion products then passed by convection into the companion's upper stellar atmosphere . Some of this matter was then transferred to the main sequence star, as the donor star at the end of its AGB development grows above its Roche limit and therefore becomes unstable.
We observe these binary star systems at a time when the donor star has long been a white dwarf and the barium star has evolved into a red giant .
The episode of mass transfer is considered to be relatively short on astronomical timescales. This hypothesis also predicts barium stars on the main sequence. HR 107 is an example in the literature .
development
During its development phase, the barium star can become significantly larger and cooler than typical stars of the spectral classes G or K; it or its photosphere then typically develops into the spectral type M.
However, the abundance of s-process elements such as Zr and molecular bands of zirconium oxide (ZrO) show its changed composition and thus its spectral / molecular peculiarities. During this time, the star appears as an extrinsic ( Latin disturbed, strange ) S star .
history
Historically, the barium stars were initially a mystery, since stars of the spectral classes G and K have not evolved long enough to have carbon and other s-process elements accumulated in their photosphere.
The discovery of the binary star nature solved the riddle by shifting the source of these elements and thus the cause of the spectral peculiarities of the barium stars to the much more developed binary star partner.
Examples
The prototypes of the barium stars are ζ Capricorni , HR 774 and HR 4474.
CH stars are Population II stars with a comparable level of development, spectral features and orbital features and are believed to be the older, less metal counterparts of the barium stars.
See also
Individual evidence
- ↑ Bidelman, WP, & Keenan, PC Astrophysical Journal , vol. 114, p. 473, 1951
- ↑ McClure, RD, Fletcher, JM, & Nemec, JM Astrophysical Journal Letters, vol. 238, p. L35
- ↑ McClure, RD & Woodsworth, AW Astrophysical Journal, vol. 352, pp. 709-723, April 1990.
- ↑ Jorissen, A. & Mayor, M. Astronomy & Astrophysics , vol. 198, pp. 187-199, June 1988
- ↑ McClure, R. Journal of the Royal Astronomical Society of Canada , vol 79, pp. 277-293, Dec. 1985
- ↑ Boffin, HMJ & Jorissen, A., Astronomy & Astrophysics, vol. 205, pp. 155-163, October 1988
- ↑ Tomkin, J., Lambert, DL, Edvardsson, B., Gustafsson, B., & Nissen, PE, Astronomy & Astrophysics, vol 219, pp. L15-L18, July 1989
- ↑ McClure, R. Publications of the Astronomical Society of the Pacific, vol 96, p. 117, 1984