Astron. Astrophys. 326, 257-262 (1997)
4. Conclusions
The gravity-brightening law, Eq. (1), is valid to a high degree for
all models generated in this work with a modified version of the UMA
code (plane-parallel atmosphere model in both hydrodynamic and local
thermodynamic equilibrium). The exponents for
convective atmospheres were calculated theoretically by forcing the
entropy at the bottom of the atmosphere to be equal in models that
should represent the same star. Our model reproduces the mean result
of Lucy (1967) for the convective regime.
We extended the result of Lucy (1967, for three values of
) to the range
and found that
practically only depends on , being rather
insensitive to the value of the mixing length parameter, to the use of
grey or non-grey atmospheres, and to the model total mass. A third
order polynomial, , was given as a convenient
way to use the results in the analysis of EBLC.
The influence of the "reflection effect" on the gravity-brightening
exponent for convective atmospheres is evidenced for the first time:
the external illumination increases the values of
significantly, indicating that in close systems,
where the reflection effect is prominent, the standard
values might be too low. A detailed analysis
including illuminated models and an extension of the present work to
higher effective temperatures are in progress.
© European Southern Observatory (ESO) 1997
Online publication: April 20, 1998
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