Astronomy and Astrophysics – Astronomy
Scientific paper
May 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995a%26a...297..237s&link_type=abstract
Astronomy and Astrophysics (ISSN 0004-6361), vol. 297, no. 1, p, 237-245
Astronomy and Astrophysics
Astronomy
14
Atmospheric Stratification, Line Spectra, Manganese, Mercury (Metal), Spectrum Analysis, Stellar Atmospheres, Stellar Spectra, Ultraviolet Astronomy, Ultraviolet Spectra, Abundance, Atmospheric Models, Gallium, Iue, Resonance Lines, Stellar Models
Scientific paper
An analysis of co-added high-resolution IUE spectra is presented for three mercury-manganese stars (mu Lep, HR 2844, and HR 7143) which exhibit anomalous Ga III lambda 495 resonance line profiles. This line appears to have unusually weak wings in these stars when compared with synthetic profiles computed under the conventional assumptions of atmospheric chemical homogeneity and local thermodynamic equilibrium. It is shown that these anomalous line profiles can be reproduced by calculations in which gallium is stratified in the upper atmosphere. A detailed analysis of each star indicates that schematic stratified models can yield consistent fits to the anomalous lambda 1495 profiles simultaneously with the (apparently unaffected) Ga III lambda 1534 and Ga II lambda 1414 resonance lines. Moreover, the best-fit gallium abundance derived from these three lines is, in each base, in excellent agreement with the predicted maximum which can be supported in the photosphere by radiation pressure. Although other explanatory mechanism for the anomalous lambda 1495 profiles - for example non-LTE effects - cannot be excluded, this preliminary study provides tentative evidence for the presence of chemically stratified atmospheres in HgMn stars.
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