Astron. Astrophys. 358, L33-L36 (2000)

Letter to the Editor

Line formation in the Atmosphere of brown dwarf Gliese 229B : at 2.3 µ m

S. Sengupta and V. Krishan

Indian Institute of Astrophysics, Koramangala, Bangalore 560 034, India

Received 28 March 2000 / Accepted 12 May 2000

Abstract

We investigate the formation of methane line at 2.3 in Brown Dwarf Gliese 229B. Two sets of model parameters with (a) K and , (b) K and are adopted both of which provide excellent fit for the synthetic continuum spectra with the observed flux at a wide range of wavelengths. In the absence of observational data for individual molecular lines, we set the additional parameters that are needed in order to model the individual lines by fitting the calculated flux with the observed flux at the continuum. A significant difference in the amount of flux at the core of the line is found with the two different models although the flux at the continuum remains the same. Hence, we show that if spectroscopic observation at with a resolution as high as is possible then a much better constraint on the surface gravity and on the metallicity of the object could be obtained by fitting the theoretical model of individual molecular line with the observed data.

Key words: molecular processes line: formation radiative transfer stars: low-mass, brown dwarfs

Send offprint requests to: Sujan Sengupta (sujan@iiap.ernet.in)

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Contents

• 1. Introduction
• 2. The line transfer equations
• 3. The absorption coefficient
• 4. The synthetic continuum spectra in the infrared region
• 5. Results and discussion
• Acknowledgements
• References

© European Southern Observatory (ESO) 2000

Online publication: June 8, 2000
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