Barium star | Wikipedia audio article | Wikipedia audio article
Channel: wikipedia tts
Date: 2018-11-18

This is an audio version of the Wikipedia Article:
Barium star | Wikipedia audio article

Listening is a more natural way of learning, when compared to reading. Written language only began at around 3200 BC, but spoken language has existed long ago.

Learning by listening is a great way to:
- increases imagination and understanding
- improves your listening skills
- improves your own spoken accent
- learn while on the move
- reduce eye strain

Now learn the vast amount of general knowledge available on Wikipedia through audio (audio article). You could even learn subconsciously by playing the audio while you are sleeping! If you are planning to listen a lot, you could try using a bone conduction headphone, or a standard speaker instead of an earphone.

You can find other Wikipedia audio articles too at:
https://www.youtube.com/channel/UCuKfABj2eGyjH3ntPxp4YeQ

You can upload your own Wikipedia articles through:
https://github.com/nodef/wikipedia-tts



"The only true wisdom is in knowing you know nothing."
- Socrates



SUMMARY
=======
Barium stars are spectral class G to K giants, whose spectra indicate an overabundance of s-process elements by the presence of singly ionized barium, Ba II, at λ 455.4 nm.  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 P. Bidelman and Philip Keenan.Observational studies of their radial velocity suggested that all barium stars are binary stars  Observations in the ultraviolet using International Ultraviolet Explorer detected white dwarfs in some barium star systems.
Barium stars are believed to be the result of mass transfer in a binary star system.  The mass transfer occurred when the now-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.  These systems are being observed at 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.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 its 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.
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.Prototypical barium stars include zeta Capricorni, HR 774, and HR 4474.
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.