Precession and nutation in the η Carinae binary system: evidence from the X-ray light curve |
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| Authors: | Z Abraham D Falceta-Gonçalves |
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| Institution: | Instituto de Astronomia, Geofísica e Ciências Atmosféricas, Universidade de São Paulo, Rua do Matão 1226, Cidade Universitária 05508-090, São Paulo, Brazil;Núcleo de Astrofísica Teórica, CETEC, Universidade Cruzeiro do Sul, Rua Galvão Bueno 868, CEP 01506-000 São Paulo, Brazil |
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| Abstract: | It is believed that η Carinae is actually a massive binary system, with the wind–wind interaction responsible for the strong X-ray emission. Although the overall shape of the X-ray light curve can be explained by the high eccentricity of the binary orbit, other features like the asymmetry near periastron passage and the short quasi-periodic oscillations seen at those epochs have not yet been accounted for. In this paper we explain these features assuming that the rotation axis of η Carinae is not perpendicular to the orbital plane of the binary system. As a consequence, the companion star will face η Carinae on the orbital plane at different latitudes for different orbital phases and, since both the mass-loss rate and the wind velocity are latitude dependent, they would produce the observed asymmetries in the X-ray flux. We were able to reproduce the main features of the X-ray light curve assuming that the rotation axis of η Carinae forms an angle of 29°± 4° with the axis of the binary orbit. We also explained the short quasi-periodic oscillations by assuming nutation of the rotation axis, with an amplitude of about 5° and a period of about 22 days. The nutation parameters, as well as the precession of the apsis, with a period of about 274 years, are consistent with what is expected from the torques induced by the companion star. |
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| Keywords: | binaries: general stars: individual: η Carinae stars: winds outflows |
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