Near-IR Spectra of Red Supergiants and Giants. I- Models with Solar and with Mixing-Induced Surface Abundance Ratios

摘要

We provide a grid of PHOENIX spectra of red giant and supergiant stars, thatextend through optical and near-IR wavelengths. For the first time, models arealso provided with modified surface abundances of C, N and O, as a step towardsaccounting for the changes known to occur due to convective dredge-up (and tobe enhanced in the case of rotation). The aims are (i) to assess how wellcurrent models reproduce observed spectra, (ii) to quantify the effects of theabundance changes on the spectra, and (iii) to determine how these changesaffect estimates of fundamental stellar parameters. Observed giant star spectra can be fitted very well at solar metallicity downto about 3400K. Modified surface abundances are preferred in only a minority ofcases for luminosity class II, possibly indicating mixing in excess of standardfirst dredge-up. Supergiant stars show a larger variety of near-IR spectra, and good fits arecurrently obtained for about one third of the observations only. Modifiedsurface abundances help reproducing strong CN bands, but do not suffice toresolve all the difficulties. The effect of the abundance changes on theestimated Teff depends on the wavelength range of observation and can amountseveral 100K. Reasons for the remaining discrepancies are discussed.