Barium stars are G to K class giants, whose spectra indicate an overabundance of s-process elements by the presence of singly ionized barium, Ba II, at λ 455.4nm. Barium stars also show enhanced spectral features of carbon, the bands of the molecules CH, CN and C₂. The class was originally recognized and defined by William Bidelman and Philip Keenan.^[1] Giant star is a star that has stopped fusing hydrogen in its core. ... In astronomy, stellar classification is a classification of stars based initially on photospheric temperature and its associated spectral characteristics, and subsequently refined in terms of other characteristics. ... This article or section does not cite its references or sources. ... General Name, Symbol, Number barium, Ba, 56 Chemical series alkaline earth metals Group, Period, Block 2, 6, s Appearance silvery white Atomic mass 137. ... The wavelength is the distance between repeating units of a wave pattern. ... General Name, Symbol, Number carbon, C, 6 Chemical series nonmetals Group, Period, Block 14, 2, p Appearance black (graphite) colorless (diamond) Standard atomic weight 12. ...

Observational studies of their radial velocity suggested that all barium stars are binary stars^[2][3][4] Observations in the ultraviolet using International Ultraviolet Explorer detected white dwarfs in some barium star systems. Radial velocity is the velocity of an object in the direction of the line of sight. ... A binary star system consists of two stars both orbiting around their barycenter. ... UV redirects here. ... International Ultraviolet Explorer (IUE) was an astronomical observatory satellite primarily designed to take ultraviolet spectra. ... A white dwarf is an astronomical object which is produced when a low to medium mass star dies. ...

Barium stars are believed to be the result of mass transfer in a binary star system. The mass transfer occurred when the presently-observed giant star was on the main sequence. Its companion, the donor star, was a carbon star on the asymptotic giant branch (AGB), and had produced carbon and s-process elements in its interior. These nuclear fusion products were mixed by convection to its surface. Some of that matter "polluted" the surface layers of the main sequence star as the donor star lost mass at the end of its AGB evolution, and it subsequently evolved to become a white dwarf. We are observing these systems an indeterminate amount of time after the mass transfer event, when the donor star has long been a white dwarf, and the "polluted" recipient star has evolved to become a red giant.^[5] Mass transfer is the phrase commonly used in engineering for physical processes that involve molecular and convective transport of atoms and molecules within physical systems. ... Artists impression of a binary system consisting of a black hole, with an accretion disc around it, and a main sequence star. ... Hertzsprung-Russell diagram The main sequence of the Hertzsprung-Russell diagram is the curve where the majority of stars are located in this diagram. ... A carbon star is a red giant (or occasionally red dwarf) star whose atmosphere contains more carbon than oxygen; the two elements combine in the upper layers of the star, forming carbon monoxide and other carbon compounds. ... A period of Stellar evolution undertaken by all low to intermediate mass stars (0. ... Convection in the most general terms refers to the internal movement of currents within fluids (i. ... Cross section of a red giant showing nucleosynthesis and elements formed According to the Hertzsprung-Russell diagram, a red giant is a large non-main sequence star of stellar classification K or M; so-named because of the reddish appearance of the cooler giant stars. ...

During its evolution, the barium star will at times be larger and cooler than the limits of the spectral types G or K. When this happens, ordinarily such a star is spectral type M, but the s-process excesses may cause it to show its altered composition as another spectral peculiarity. While the star's surface temperature is in the M-type regime, the star may show molecular features of the s-process element zirconium, zirconium oxide (ZrO) bands. When this happens, the star will appear as an "extrinsic" S star. General Name, Symbol, Number zirconium, Zr, 40 Chemical series transition metals Group, Period, Block 4, 5, d Appearance silvery white Standard atomic weight 91. ... In astronomy, stellar classification is a classification of stars based initially on photospheric temperature and its associated spectral characteristics, and subsequently refined in terms of other characteristics. ...

Historically, barium stars posed a puzzle, because in standard stellar evolution theory G and K giants are not far enough along in their evolution to have synthesized carbon and s-process elements and mix them to their surfaces. The discovery of the stars' binary nature resolved the puzzle, putting the source of their spectral peculiarities into a companion star which should have produced such material. The mass transfer episode is believed to be quite brief on an astronomical timescale. The mass transfer hypothesis predicts that there should be main sequence stars with barium star spectral peculiarities. At least one such star, HR 107, is known.^[6] In astronomy, stellar evolution is the sequence of radical changes that a star undergoes during its lifetime (the time in which it emits light and heat). ...

Prototypical barium stars include zeta Capricorni, HR 774, and HR 4474. Zeta Capricorni (abbr. ...

The CH stars are Population II stars with similar evolutionary state, spectral peculiarities, and orbital statistics, and are believed to be the older, metal-poor analogs of the barium stars.^[7] Stars can be grouped into two general types called Population I and Population II. The criteria for classification include space velocity, location in the galaxy, age, chemical composition, and differences in distribution on the Hertzsprung-Russell diagram. ...

References

1. ^ Bidelman, W.P., & Keenan, P.C. Astrophysical Journal, vol. 114, p. 473, 1951
2. ^ McClure, R.D., Fletcher, J.M., & Nemec, J.M. Astrophysical Journal Letters, vol. 238, p. L35
3. ^ McClure, R.D. & Woodsworth, A.W. Astrophysical Journal, vol. 352, pp. 709-723, April 1990.
4. ^ Jorissen, A. & Mayor, M. Astronomy & Astrophysics, vol. 198, pp. 187-199, June 1988
5. ^ McClure, R. Journal of the Royals Astronomical Society of Canada, vol 79, pp. 277-293, Dec. 1985
6. ^ Tomkin, J., Lambert, D.L., Edvardsson, B., Gustafsson, B., & Nissen, P.E., Astronomy & Astrophysics, vol 219, pp. L15-L18, July 1989
7. ^ McClure, R. Publications of the Astronomical Society of the Pacific, vol 96, p. 117, 1984