IRAS 12311−3509: a carbon star with SiC2 emission |
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Authors: | T Lloyd Evans M E Hurst P J Sarre |
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Institution: | South African Astronomical Observatory, PO Box 9, Observatory 7935, Cape Town, South Africa;School of Chemistry, The University of Nottingham, University Park, Nottingham NG7 2RD |
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Abstract: | The optical spectrum of the carbon star IRAS 12311?3509 is dominated by the Merrill–Sanford emission bands of SiC2, by absorption and emission in the Swan system of C2, and by resonance emission lines of neutral metals. The infrared energy distribution is flat from 1 to 60 μm. These observations are interpreted as arising from a star with a cool dusty disc which is edge-on to the observer and obscures direct starlight. The infrared continuum is caused predominantly by absorption of stellar light by dust in the disc and re-emission at longer wavelengths. The optical stellar spectrum is seen by reflection off dusty material which lies out of the plane of the disc, and the molecular and atomic emission arises in the same geometry through resonance fluorescence. The object has similarities to the J-silicate stars, but may have a carbon-rich rather than oxygen-rich disc. A full spectroscopic assignment and discussion of the SiC2 bands and their intensities are given. Modelling of the rotational contours of the band yields a rotational temperature of 250 K, indicating very cool gas. |
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Keywords: | stars: carbon circumstellar matter stars: individual: IRAS 12311?3509 ISM: molecules |
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