Astronomy and Astrophysics – Astrophysics
Scientific paper
Feb 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994ap%26ss.212..221f&link_type=abstract
Astrophysics and Space Science, vol. 212, nos. 1-2, p. 221-229
Astronomy and Astrophysics
Astrophysics
7
Cosmic Dust, Early Stars, Stellar Envelopes, Variable Stars, Astronomical Photometry, Infrared Radiation, Light Curve, Pre-Main Sequence Stars, Thermal Radiation
Scientific paper
A number of variable stars of the Orion population has been identified with Infrared Astronomy Satellite (IRAS) point sources by us. This finding supports the conclusion that the prominent Algol-like minima in the lightcurves of these stars originate from obscurations by dust clouds in a circumstellar shell. The discussion of the existing UBVR data leads to the remarkable conclusion that the extinction properties of the grain populations contained in individual dust clouds moving in one and the same circumstellar shell are quite different. From the multicolour photometric data of the different Algol-like minima we derived individual values of the reddening parameter R = Av/E(B - V). It covers a remarkable wide range of values from that one typical of the interstellar extinction law up to 7. In the case of SV Cep one of the grain populations produces a virtually neutral extinction. The large values of R speak in favor of larger than normal (interstellar) dust grains, which may have grown by coagulation processes. The cloudy circumstellar dust shell provides a natural explanation for the observed infrared excess. The properties derived from the optical light variations are fully compatible with the properties deduced from the infrared radiation. The irregularity of the light variations indicates that many clouds are involved and may sometimes superimpose themselves.
Friedemann Ch.
Guertler J.
Reimann Hans-Georg
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