SIMBAD references

1997A&A...318..841C - Astronomy and Astrophysics, volume 318, 841-869 (1997/2-3)

Notes on the convection in the ATLAS9 model atmospheres.

CASTELLI F., GRATTON R.G. and KURUCZ R.L.

Abstract (from CDS):

The mixing-length theory for the convection, as it is used in the ATLAS9 code (Kurucz, 1993a), is summarized and discussed. We investigated the effect of the modification called ``approximate overshooting'' on the model structure of the Sun and of stars with Teff included between 4000K and 8500K, logg included between 2.5 and 4.5, and metallicities [M/H]=0.0 and [M/H]=-3.0. We found that the Kurucz solar model (SUNK94) with the ``overshooting'' option switched on reproduces more observations than that without ``overshooting''. In the Hγ and Hβ regions no solar model is able to reproduce the level of the true continuum deduced from high-resolution observations absolutely calibrated. At 486 nm the computed continuum is about 6.6% higher than that inferred from the observed spectrum. We found that the largest effect of the ``approximate overshooting'' on the model structure occurs for models with Teff>6250K and it decreases with decreasing gravity. The differences in (b-y), (B-V), and (V-K) indices computed from models with the ``overshooting'' option switched on and off, correspond to Teff differences which may amount up to 180K, 100K, 60K respectively. The differences in Teff from Balmer profiles may amount up to 340K and they occur also for Teff<6250K down to about 5000K. The c1 index yields gravity differences {DELTA}logg as a function of logg which, for each Teff, grow to a maximum value. The maximum {DELTA}logg decreases with increasing temperatures and ranges, for solar metallicity, from 0.7 dex at logg=0.5 and Teff=5500K to 0.2dex at logg=4.5 and Teff=8000K. This behaviour does not change for [M/H]=-3.0. Comparisons with the observations indicate that model parameters derived with different methods are more consistent when the ``overshooting'' option is switched off (NOVER models), except for the Sun. In particular for Procyon, Teff and logg from NOVER models are closer to the parameters derived from model independent methods than are Teff and logg derived from the Kurucz (1995) grids. However, no model is able to explain the whole observed spectrum of either the Sun or Procyon with a unique Teff, regardless of whether the ``overshooting'' option is switched on or off. Independently of the convection option, the largest differences in Teff derived with different methods are of the order of 200K for Procyon and 150K for the Sun.

Abstract Copyright:

Journal keyword(s): stars: atmospheres - stars: fundamental parameters - stars: individual: Procyon - Sun: general - convection

Errata: vol. 324, p. 432

Simbad objects: 73

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