Broadening of the Na and K Resonance Lines by H2 and He with Application to Brown Dwarf Spectra

Details Broadening of the Na and K Resonance Lines by H2 and He with Application to Brown Dwarf Spectra Broadening of the Na and K Resonance Lines by H2 and He with Application to Brown Dwarf Spectra

May 2008

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008aas...212.0312k&link_type=abstract

American Astronomical Society, AAS Meeting #212, #3.12; Bulletin of the American Astronomical Society, Vol. 40, p.186

Astronomy and Astrophysics

Astronomy

1

Scientific paper

The visible and near-infrared spectra of late L- and T-type brown dwarf stars are defined in large part by resonance lines of neutral Na and K. It is the collision broadening of these atomic lines by the molecular H and atomic He in the stellar atmosphere that determines the continuum in the spectrum from below 500 nm to above 900 nm. In our work, a unified line shape theory and a set of pseudo-potentials has been used to model the entire line profile from the impact-broadened line center to the far wing (N.F. Allard et al., Eur. Phys. J. D 44, 507 (2007) and A&A 465, 1085 (2007)), and a distinctive feature at 695 nm in the spectrum of the T-dwarf εIndi Ba was identified as due to collisions of molecular H with K (F. Allard et al., A&A 474, L21 (2007)). Laboratory experiments serve to test and refine the theoretical models, the weak point of which is the knowledge of the interaction potential for the perturbing He atom or H molecule with the alkali. Precision measurements of impact broadening and shift, satellites in the line wings due to binary collisions, broadening of higher members of the principal series, and emission line shapes are all sensitive to different details of the atomic and molecular interactions. In this work we compare results from on-going experiments in our laboratory with these models.

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