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

Authors

  • A. F. Torres,

    Corresponding author
    1. Departamento de Espectroscopía, Facultad de Ciencias Astronómicas y Geofísicas, Universidad Nacional de La Plata, Paseo del Bosque S/N, La Plata, B1900FWA, Buenos Aires, Argentina
    2. Instituto de Astrofísica de La Plata (CCT La Plata – CONICET, UNLP), Paseo del Bosque S/N, La Plata, B1900FWA, Buenos Aires, Argentina
      E-mail: andy@carina.fcaglp.unlp.edu.ar
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  • M. Kraus,

    1. Astronomickýústav, Akademie věd České republiky, Fričova 298, 251 65 Ondřejov, Czech Republic
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  • L. S. Cidale,

    1. Departamento de Espectroscopía, Facultad de Ciencias Astronómicas y Geofísicas, Universidad Nacional de La Plata, Paseo del Bosque S/N, La Plata, B1900FWA, Buenos Aires, Argentina
    2. Instituto de Astrofísica de La Plata (CCT La Plata – CONICET, UNLP), Paseo del Bosque S/N, La Plata, B1900FWA, Buenos Aires, Argentina
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  • R. Barbá,

    1. Instituto de Ciencias Astronómicas, de la Tierra y del Espacio (ICATE – CONICET), Casilla 467, 5400 San Juan, Argentina
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  • M. Borges Fernandes,

    1. Observatório Nacional, Rua General José Cristino 77, 20921-400 São Cristovão, Rio de Janeiro, Brazil
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  • E. Brandi

    1. Departamento de Espectroscopía, Facultad de Ciencias Astronómicas y Geofísicas, Universidad Nacional de La Plata, Paseo del Bosque S/N, La Plata, B1900FWA, Buenos Aires, Argentina
    2. Comisión de Investigaciones Científicas de la Provincia de Buenos Aires (CIC), Calle 526 entre 10 y 11, Buenos Aires, Argentina
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E-mail: andy@carina.fcaglp.unlp.edu.ar

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 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 iiλ4686 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 λλ6825 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.

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