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

TORRES, A. F.; KRAUS, M.; CIDALE, L. S.; BARBA, R.; BORGES FERNANDES, M.; BRANDI, E.

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY

WILEY-BLACKWELL PUBLISHING, INC

Lugar: Londres; Año: 2012 vol. 427 p. 80 - 84

0035-8711

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 ultraviolet and optical regions to molecular emission bands of CO and TiO in the optical and infrared regions. The most distinguishing spectral characteristic of LHA 115-S 18 is the high variability detected in the He II 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 6825 and 7082 Å, which we have identified as Raman-scattered lines. This is the first time that 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.