Open AccessObservations and modelling of spectral energy distributions of carbon stars with optically thin envelopes
Author(s) -
Bagnulo S.,
Doyle J. G.,
Andretta V.
Publication year - 1998
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1046/j.1365-8711.1998.01394.x
Subject(s) - physics , carbon star , photometry (optics) , stars , astrophysics , infrared , astronomy , carbon fibers , near infrared spectroscopy , optics , materials science , composite number , composite material
We present broad‐band photometry in the optical, near‐infrared and submillimetre, and mid‐infrared spectrophotometry of a selection of carbon stars with optically thin envelopes. Most of the observations were carried out simultaneously. Beside the emission feature at 11.3 μ m due to silicon carbide grains in the circumstellar environment, many of our mid‐infrared spectra show an emission feature at 8.6 μ m. All the observed spectral energy distributions exhibit a very large far‐infrared flux excess. Both these features are indeed common to many carbon stars surrounded by optically thin envelopes. We have modelled the observed spectral energy distributions by means of a full radiative transfer treatment, paying particular attention to the features quoted above. The peak at 8.6 μ m is usually ascribed to the presence of hydrogenated amorphous carbon grains. We find also that the feature at 8.6 μ m might be reproduced by assuming that the stars have a circumstellar environment formed of both carbon‐ and oxygen‐rich dust grains, although this is in contrast with what one should expect in a carbon‐rich environment. The far‐infrared flux excess is usually explained by the presence of a cool detached dust shell. Following this hypothesis, our models suggest a time‐scale for the modulation of the mass‐loss rate of the order of some 10 3 yr.