A new observational tracer for high-density disc-like structures around B[e] supergiants

Authors

  • A. Aret,

    Corresponding author
    1. Astronomickýústav, Akademie věd České republiky, Fričova 298, 251 65 Ondřejov, Czech Republic
    2. Tartu Observatory, 61602, Tõravere, Tartumaa, Estonia
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  • M. Kraus,

    Corresponding author
    1. Astronomickýústav, Akademie věd České republiky, Fričova 298, 251 65 Ondřejov, Czech Republic
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  • M. F. Muratore,

    Corresponding author
    1. Departamento de Espectroscopía Estelar, Facultad de Ciencias Astronómicas y Geofísicas, Universidad Nacional de La Plata, Paseo del Bosque s/n, B1900FWA, La Plata, Argentina
    2. Instituto de Astrofísica de La Plata, CCT La Plata, CONICET-UNLP, Paseo del Bosque s/n, B1900FWA, La Plata, Argentina
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  • M. Borges Fernandes

    Corresponding author
    1. Observatório Nacional, Rua General José Cristino 77, 20921-400 São Cristovão, Rio de Janeiro, Brazil
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  • Based on observations collected with the ESO 2.2 m telescope in La Silla, Chile, under programme 076.D-0609(A).

E-mail: aret@aai.ee (AA); kraus@sunstel.asu.cas.cz (MK); fmuratore@carina.fcaglp.unlp.edu.ar (MFM); borges@on.br (MBF)

ABSTRACT

The disc formation mechanism of B[e] supergiants is one of the puzzling phenomena in massive star evolution. Rapid stellar rotation seems to play an important role for the non-spherically symmetric mass-loss leading to a high-density disc- or ring-like structure of neutral material around these massive and luminous objects. The radial density and temperature structure as well as the kinematics within this high-density material are, however, not well studied. Based on the high-resolution optical spectra of a sample of B[e] supergiants in the Magellanic Clouds we especially searched for tracers of the kinematics within their discs. Besides the well-known [O i] lines, we discovered the [Ca ii] λλ7291, 7324 lines which can be used as a complementary set of disc tracers. We find that these lines originate from very high density regions, located closer to the star than the [O i] λ5577 line-forming region. The line profiles of both the [O i] and the [Ca ii] lines indicate that the discs or rings of high-density material are in Keplerian rotation. We estimate plausible ranges of disc inclination angles for the sample of B[e] supergiants and suggest that the star LHA 120-S 22 might have a spiral arm rather than a disc.

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