WR 7a: a V Sagittae or a qWR star? |
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Authors: | A S Oliveira J E Steiner D Cieslinski |
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Affiliation: | Departamento de Astronomia –IAG, Universidade de São Paulo, São Paulo, Brasil;DiviSão de Astrofísica, Instituto Nacional de Pesquisas Espaciais, S. J. dos Campos, Brasil |
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Abstract: | The star WR 7a, also known as SPH 2, has a spectrum that resembles that of V Sagittae stars although no O vi emission has been reported. The Temporal Variance Spectrum – TVS – analysis of our data shows weak but strongly variable emission of O vi lines which is below the noise level in the intensity spectrum. Contrary to what is seen in V Sagittae stars, optical photometric monitoring shows very little, if any, flickering. We found evidence of periodic variability. The most likely photometric period is P phot= 0.227(±14) d , while radial velocities suggest a period of P spec= 0.204(±13) d . One-day aliases of these periods can not be ruled out. We call attention to similarities with HD 45166 and DI Cru (= WR 46), where multiple periods are present. They may be associated to the binary motion or to non-radial oscillations. In contrast to a previous conclusion by Pereira et al., we show that WR 7a contains hydrogen. The spectrum of the primary star seems to be detectable as the N v 4604 ? absorption line is visible. If so, it means that the wind is optically thin in the continuum and that it is likely to be a helium main sequence star. Given the similarity to HD 45166, we suggests that WR 7a may be a qWR – quasi Wolf–Rayet – star. Its classification is WN4h/CE in the Smith, Shara & Moffat three-dimensional classification system. |
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Keywords: | stars: emission-line Be stars: fundamental parameters stars: individual: WR 7a stars: Wolf–Rayet |
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