Stellar Atmospheres: Structure, Composition and Limb Darkening

H. Melvin Dyck (U.S. Naval Observatory)

Abstract:

In this talk, we explore the phenomenon of stellar limb darkening. A simple geometrical picture is shown, followed by elementary results from radiative transfer theory. The zeroth-order astrophysical data derived from limb darkening is the temperature structure of the photosphere.

Observations of the Sun, and their interpretation, are reviewed. The analysis of these observations at many wavelengths led to the discovery of H- in the Sun. We then move on to limb darkening in other stars, where interferometric techniques are required. It is argued that observations of stars hotter than about 4000-4500 K may be accounted for by current plane-parallel model atmospheres. For the cooler, more extended stars, the situation is more complex with a number of important details that need to be accounted for. In this latter case, observations in carefully chosen and restricted wavelength bands may lead to a better understanding of the molecular species in cool star atmospheres.

Realaudio of lecture.
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General Texts:

• Radiative Transfer
  Chandrasekhar, S. (Dover: New York, 1960). ·

• Fundamentals of Stellar Astrophysics
  Collings, G.W., (W.H. Freeman: New York, 1989).

• The Physics of Astrophysics. Volume I. Radiation
  Shu, F. H. (Univ. Science Books: Mill Valley, CA, 1991).

Selected Papers:

• Claret, A. 1998, A&AS, 131, 395.

• Hajian, A. R. et al. 1998, ApJ, 496, 484.

• Hanbury Brown, R. et al. 1974, MNRAS, 167, 475.

• Hestroffer, D. 1997, A&A, 327, 199.

• Hofmann, K.-H. & Scholz, M. 1998, A&A, 335, 637.

• Manduca, A. et al. 1977, A&A, 61, 809.

• Michelson, A. A. & Pease, F. G. 1921, ApJ, 53, 249.

• Petro, L. D. et al. 1984, ApJ, 283, 426.

• Pierce, A. K. & Waddell, J. H. 1961, MemRAS, 58, 89.

• Scholz, M. & Takeda, Y. 1987, A&A, 186, 200.

• van Hamme, W. 1993, AJ, 106, 2096.