Infrared Spectra of Massive Stars in Transition: WNL, Of, Of/WN, Be, B[e], and Luminous Blue Variable Stars

Details Infrared Spectra of Massive Stars in Transition: WNL, Of, Of/WN, Be, B[e], and Luminous Blue Variable Stars Infrared Spectra of Massive Stars in Transition: WNL, Of, Of/WN, Be, B[e], and Luminous Blue Variable Stars

Oct 1996

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996apj...470..597m&link_type=abstract

Astrophysical Journal v.470, p.597

Astronomy and Astrophysics

Astronomy

104

Infrared: Stars, Stars: Early-Type, Stars: Emission-Line, Be, Stars: Wolf-Rayet, Stars: Supergiants

Scientific paper

We present an overview of the spectroscopic properties of several luminous stars belonging to Of supergiant, Ofpe/WN9, late-type nitrogen sequence Wolf-Rayet (WNL), B[e], Be supergiant, and luminous blue variable (LBV) classes at 2 μm and 1.6 μm, using recently published and new spectra of moderate to high resolution (500-1600). These objects are "transitional" in their optical classification and may be related in their evolution.
The 2 μm spectrum of the LBV AG Car has changed from its 1984-1985 appearance as an Of/WN star, now appearing as a Be or B[e] star by comparison to new spectra of HD 72754 (B2Iape) and GG Car (B[e], whose spectrum has varied since 1984-1985). Further support for a link between B[e] stars and LBVs is seen in the case of the SMC B[e] star S18, which has changed its 1987-1989 spectrum from one of Brγ emission only to one in which emission lines of Fe II, Mg II, Na I, 12CO overtone, He I 2.112-3 μm, and He I 2.058 μm (strong) are present. As the earlier observations were not of a high signal-to-noise ratio, we confirm only the He I and 12CO as new emission, where the latter was previously expected on the basis of TiO emission but was undetected. The overall morphology of the atomic spectrum of S18, including the He I 2.112-3 μm emission, are shared by only one other B star, namely, the quiescent LBV P Cyg (B1 Ia+), but is shared also by the LBV and Ofpe/WN9 star HDE 269582. Only AG Car is observed to have also varied in the 2.112-3 μm line. We thus consider S18 a strong candidate LBV.
Our new high-resolution 2 μm spectra also include HD 5980, a WN binary recently observed to undergo an LBV-like outburst in short-term brightness and spectroscopic variations. We provide a detailed K-band line identification of the probable LBV He 3-591 (WRA 751), which is rich in lines of permitted and forbidden iron (mainly Fe II) and includes new identification of [Ni II] at 2.308 μm and 2.369 μm.
A significant degree of overlap in spectral morphology exists between the groups, where at least one example from each group may be classified as a member of another from its 2 μm spectrum. This has serious consequences for observations of hot, luminous objects in visually obscured regions. The overlapping infrared spectral morphology reinforces the notion that the objects in this study are interrelated in their evolution. We propose that "transitional" massive stars with hydrogen present at their surfaces (including the least extreme WN types) may not yet be in the stage of core-helium burning but rather are in a previous phase in which the stellar atmosphere/wind is sometimes dynamically unstable.

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