LINE-INTENSITIES FOR CB AND THEIR APPLICATION TO STELLAR ATMOSPHERES

We have performed a complete computation of the bound - bound transiti ons that can take place in the CH molecule among the four lowest elect ronic stales. The results of the computation is stored in the form of a line list of 112,821 lines (for each of the isotopes (CH)-C-12-H-1 a nd (CH)-C-13-H-1) of the infrared transition X(2) Pi - X(2) Pi and the three electronic transitions A(2) Delta-X(2) Pi, B-2 Sigma-X(2) Pi, a nd C-2 Sigma(+)-X(2) Pi. The dipole moment function and the electronic transition moments are assumed to be identical for the two isotopes, whereas the isotopic shift in the frequency is computed for each indiv idual line. For each transition is given the lower and the upper quant um numbers, the wavenumber of the transition the gf-value, the excitat ion energy, and the isotopic shift. The list contains a total of 22492 lines from the X-X transition between 905 cm(-1) and 24650 cm(-1) (40 60 Angstrom-11.0 mu m), 72702 lines from the A-X transition between 33 3 cm(-1) and 35110 cm(-1) (2850 Angstrom-30.0 mu m), 5928 lines from t he B-X transition between 1012 cm(-1) and 27628 cm(-1) (3610 Angstrom- 1.0 mu m), and 13445 lines from the C-X transition between 7103 cm(-1) and 40367 cm(-1) (2480 Angstrom-1.4 mu m). The corresponding partitio n function to be used in connection with our line list is calculated a s function of temperature. Finally, we have computed a small grid of m odel atmospheres for C/O is an element of[0.43; 1.35], T-eff is an ele ment of[2800; 5800], Z is an element of [3 10(-+); 1]Z(.), and log(g) is an element of [0.0; 4.5]. This covers most of the very wide range o f spectral types which are known to show spectral features due to CH, i.e, spectral class F to M, including various types of the chemically peculiar stars. We show that CH has a strong cooling effect (as strong as the well known cooling due to CO) on models of metal-poor stars, T he spectral features of CH is seen primarily in the regions 2800 Angst rom to 5000 Angstrom (due to the C-X, B-X, and the A-X systems) and fr om 3.3 mu m to 5.3 mu m (due to the vibrational-rotational transitions ). The most pronounced spectral feature due to CH is the so-called G-b and (lambda approximate to 4300 Angstrom; due to the 0-0 vibrational t ransition in the A-X system), We analyse the behaviour of the G-band i ntensity in our model atmospheres as function of T-eff, gravity, metal licity, and C/O ratio.