Photometric variability of WC9 stars |
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Authors: | Rémi Fahed Anthony F J Moffat Alceste Z Bonanos |
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Institution: | Département de physique, Universitéde Montréal, C.P. 6128, Succ. C.-V., Montréal, QC, H3C 3J7, Canada;Centre de recherche en astrophysique du Québec, Canada;Carnegie Institution of Washington, Department of Terrestrial Magnetism, 5241 Broad Branch Road, NW, Washington DC 20015, USA |
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Abstract: | Do some Wolf–Rayet stars owe their strong winds to something else besides radiation pressure? The answer to this question is still not entirely obvious, especially in certain Wolf–Rayet subclasses, mainly WN8 and WC9. Both of these types of Wolf–Rayet stars are thought to be highly variable, as suggested by observations, possibly due to pulsations. However, only the WN8 stars have so far been vigorously and systematically investigated for variability. We present here the results of a systematic survey during three consecutive weeks of 19 Galactic WC9 stars and one WC8 star for photometric variability in two optical bands, V and I . Of particular interest are the correlated variations in brightness and colour index in the context of carbon dust formation, which occurs frequently in WC9 and some WC8 stars. In the most variable case, WR76, we used this information to derive a typical dust grain size of ∼ 0.1 μm . However, most photometric variations occur at surprisingly low levels, and in fact almost half of our sample shows no significant variability at all above the instrumental level ( σ∼ 0.005– 0.01 mag). |
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Keywords: | stars: carbon circumstellar matter stars: individual: WR76 stars: variables: other stars: Wolf–Rayet |
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