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arXiv · 1209.2397

Discovery of Raman-scattered lines in the massive luminous emission-line star LHA 115-S 18

A. F. Torres·M. Kraus·L. S. Cidale·R. Barbá·M. Borges Fernandes·E. Brandi
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Abstract

LHA 115-S 18 is a very peculiar emission-line star exhibiting the B[e] phenomenon. Located in the Small Magellanic Cloud, its spectrum shows features of an extremely wide range of excitation and ionization stages, extending from highly ionized atomic lines (Si IV, C IV, He II) in the UV and optical regions to molecular emission bands of CO and TiO in the optical and IR regions. The most distinguishing spectral characteristic of LHA 115-S 18 is the high variability detected in the He II {\lambda}4686 emission line, which can be a very conspicuous or completely invisible feature. In this work, we report on another peculiarity of LHA 115-S 18. From high-resolution optical spectra taken between 2000 and 2008, we discovered the appearance and strengthening of two emission features at {\lambda}6825 \AA, and {\lambda}7082 \AA,, which we identified as Raman-scattered lines. This is the first time these lines have been detected in the spectrum of a massive luminous B[e] star. As the classification of LHA 115-S 18 is highly controversial, we discuss how the discovery of the appearance of Raman-scattered lines in this peculiar star might help us to solve this puzzle.

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A. F. Torres, M. Kraus, L. S. Cidale, R. Barbá, M. Borges Fernandes, E. Brandi. 2012-09-11. Discovery of Raman-scattered lines in the massive luminous emission-line star LHA 115-S 18. https://doi.org/10.1111/j.1745-3933.2012.01349.x

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