The near-ultraviolet continuum of late-type stars.
ALLENDE PRIETO C. and LAMBERT D.L.
Abstract (from CDS):
Analyses of the near-ultraviolet continuum of late-type stars have led to controversial results regarding the performance of state-of-the-art model atmospheres. The release of the homogeneous International Ultraviolet Explorer (IUE) final archive and the availability of the high-accuracy Hipparcos parallaxes provide an opportunity to revisit this issue, as accurate stellar distances make it possible to compare observed absolute fluxes with the predictions of model atmospheres. The near-UV continuum is highly sensitive to Teff and [Fe/H], and once the gravity is constrained from the parallax, these parameters may be derived from the analysis of low-dispersion, long-wavelength (2000-3000 Å) IUE spectra for stars previously studied by Alonso, Arribas, & Martínez-Roger using the Infrared Flux Method (IRFM). A second comparison is carried out against the stars spectroscopically investigated by Gratton, Carretta, & Castelli. It is shown that there is a good agreement between Teff values obtained from the IRFM and those from the near-UV continuum, and a remarkable correspondence between observed and synthetic fluxes for stars with 4000 K≤Teff≤6000 K of any metallicity and gravity. These facts suggest that model atmospheres provide an adequate description of the near-UV continuum forming region and that the opacities involved are essentially understood.