carbon stars


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carbon stars

(C stars) Red giant stars of low temperature that have an over-abundance of carbon relative to oxygen in their surface layers. In cool stars carbon and oxygen atoms combine to form stable carbon monoxide, and in carbon stars the excess carbon can then form other molecules. Their spectra therefore show strong bands of carbon compounds, including C2, CN, and CH. All carbon stars undergo mass loss, enriching the interstellar medium with considerable carbon, some nitrogen and oxygen, and also s-process elements. In the earlier Harvard classification (see spectral types) carbon stars were divided into R stars and N stars : N stars are the ‘classical’ carbon stars, discovered spectroscopically by Angelo Secchi (1868). They are very cool and very luminous and many have been discovered in the Magellanic Clouds and other galaxies. They are observed to be losing mass rapidly and are much further evolved than the hotter less luminous R stars. The R stars are enriched in the isotopes 13C and 14N, but unlike most N stars, show no enhancement in s-process elements. See also R Coronae Borealis stars; S stars.
References in periodicals archive ?
A spectroscopic study of RV Tauri stars in the Large Magellanic Cloud showed that they have the same range of spectra as their galactic counterparts but that at least one is a carbon star with s-process elements as might be expected if they are post-AGB objects.
With Peter Sarre he carried out the first complete study of the silicon dicarbide molecule in stellar spectra, following his discovery of a carbon star (IRAS 12311-3509) with [C.
And finally, carbon stars are notoriously variable, not just in magnitude but in colour too, and it is probably no more than fortuitous that WZ Cas should happen to have one of the largest numerical values of (B-V) in the database consulted by Mr Ahad.
Decin and her colleagues now plan to extend the observations to other carbon stars.
Based on an analysis of 110 carbon stars dotted across the sky brighter than magnitude 8.
The primary in this pair is a deep red variable carbon star of 7th magnitude average brightness, with a colour index, B-V, of +3.
Of all the stars recorded by 2MASS, the astronomers chose to analyze carbon stars first because of three remarkable properties.
By comparing the luminosity of a carbon star to how bright it appears in the sky, Skrutskie, Weinberg, and their colleagues determined the distance to each of the 30,000 carbon stars in 2MASS.
Otherwise, the orbits of the carbon stars would spread out rather than remain in a circle, Ibata says.
The carbon stars we discovered were almost certainly dumped into the halo from the Sagittarius dwarf galaxy," he says.
What this tells us is that carbon stars could have been pumping dust soon after the first galaxies were born," Sloan said.
While everyone is focused on the questions of how much and what kind of dust supernovae make, they may not have appreciated that carbon stars can make at least some of the dust we are seeing," Sloan said.