The B[e] supergiant LHA 115-S 18

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

San Juan

Congreso; 54 Reunion Anual de la Asociación Argentina de Astronomía; 2011

AAA y Sochias

LHA 115-S 18 is a B[e] supergiant located in the Small Magellanic Cloud, whose spectrum shows features of an extremely wide range of excitation and ionization stages, extending from highly ionized atomic lines (Si IV, C IV and He II) in the UV and in the optical region to cool gas in form of molecular emission bands of CO and TiO. The He II 4686 emission line is variable, and it can even disappear. LHA 115-S 18 is the only B[e] supergiant for which this high variability in He II emission has been recorded. In this work, we present a spectroscopic study of LHA 115-S 18, based on optical high-resolution spectra obtained between 2000 and 2008 with FEROS at the ESO 1.52 m telescope in La Silla (Chile) and the echelle spectrograph at the du Pont 2.5 m telescope in Las Campanas Observatory (Chile). We measured equivalent widths of different lines and show the temporal evolution of these lines, e. g. He II 4686. The data reveal the appearance of two emission features corresponding to emission lines at 6825 and 7082. Up to now these two lines have only been observed in symbiotic stars and are attributed to Raman scattering of O VI UV photons by neutral hydrogen. We also present preliminar resuls of modelling of TiO emission bands which can be compared to the observed profiles. Observations of molecules in the disk of B[e] supergiants can provide strong constraints for disk models.