Stars/CHs

"CH stars are particular type of carbon stars which are characterized by the presence of exceedingly strong CH (methylidyne) absorption bands in their spectra. They belong to the star population II, meaning they're metal poor and generally pretty middle-aged stars, and are underluminous compared to the classical C–N carbon stars. Many CH stars are known to be binaries, and it's reasonable to believe this is the case for all CH stars. Like Barium stars, they are probably the result of a mass transfer from a former classical carbon star, now a white dwarf, to the current CH-classed star."

The mass transfer hypothesis may be needed to explain elemental occurrences on their surfaces such as carbon and s-process elements otherwise due to surface fusion.

Stars

Main article: Stars

"CH stars are characterized by the strong G band of CH in their spectra. These stars are not a homogeneous group of stars. They consist of two populations: the more metal-poor one has a spherical distribution, and the one slightly richer in metals is characterized by a flattened ellipsoidal distribution (Zinn 1985). These stars form a group of warm stars of spectral types equivalent to G and K giants, but show weak metallic lines. The ratio of the local density of CH stars is as high as 30 per cent of metal-poor giants (Hartwick & Cowley 1985). Being the most populous type of halo carbon starsknown, CH stars are important objects for our understanding of Galactic chemical evolution, the evolution of low-mass stars and nucleosynthesis in metal-poor stars."

"Most of the CH stars are known to be high-velocity objects. ‘CH- like’ stars, where CH are less dominant, have low space velocities (Yamashita 1975). At low resolution, to make a distinction between CH and C-R stars is difficult, as many C-R stars also show quite a strong CH band. In such cases, the secondary P-branch head near 4342 Å is used as a more useful indicator. Another important feature is the strength of Ca I at 4226 Å, which in the case of CH stars is weakened by the overlying faint bands of the CH band systems. In C-R stars, this feature is quite strong. These spectral characteristics allow for an identification of CH and C-R stars even at low resolution. Enhanced lines of s-process elements, weaker Fe-group elements as well as various strengths of C2 bands are some of the other distinguishing spectral features of CH stars. However, at low dispersion the narrow lines are difficult to estimate and essentially do not provide a strong clue to distinguish C-R stars from CH stars. Although CH and C-R stars have similar ranges of temperatures, the distribution of CH stars places most of them in the Galactic halo: their large radial velocities, typically ∼200 km s⁻¹, are indicative of their being halo objects (McClure 1983, 1984)."

See also

• Stars/Nova-likes