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Monthly Notices of the Royal Astronomical Society

Optical Spectroscopy of X-Mega targets in the Carina Nebula. V.
The spectroscopic binary HD93161A and its visual companion HD93161B(+)

Y. Nazé1, I.I. Antokhin2,**, H. Sana1,* and E. Gosset1,**,*** and G. Rauw1,**,***

1 Institut d'Astrophysique et de Géophysique - Université de Liège, Allée du 6 Août, Bât B5c, B-4000 Liège (Sart Tilman), Belgium
2 Sternberg Astronomical Institute, Moscow University, Universitetskij Prospect 13, Moscow 119899, Russia.

* Research Fellow FNRS, Belgium
** Research Associate FNRS, Belgium
*** Visiting Astronomer, CTIO, National Optical Astronomy Observatories (NOAO). NOAO is operated by the Association of Universities for Research in Astronomy, Inc. under contract with the National Science Foundation.

+ Based on observations collected at the European Southern Observatory (La Silla, Chile), at the Cerro Tololo Inter-American Observatory (CTIO), and with XMM-Newton, an ESA Science Mission with instruments and contributions directly funded by ESA Member States and the USA (NASA).


     We present the analysis of an extensive set of high-resolution spectroscopic observations of HD93161, a visual binary with a separation of 2 arcsec. HD93161A is a spectroscopic binary, with both components clearly detected throughout the orbit. The primary star is most probably of spectral type O8V, while the secondary is likely an O9V. We obtain the first orbital solution for this system, characterized by a period of 8.566±0.004 days. The minimum masses of the primary and secondary stars are 22.2±0.6 Msol. and 17.0±0.4 Msol. respectively. These values are quite large, suggesting a high inclination of the orbit. The second object, HD93161B, displays an O6.5V((f)) spectral type and is thus slightly hotter than its neighbour. This star is at first sight single but presents radial velocity variations.
We finally study HD93161 in the X-ray domain. No significant variability is detected. The X-ray spectrum is well described by a 2T model with kT1 ~ 0.3 keV and kT2 ~ 0.7 keV. The X-ray luminosity is rather moderate, without any large emission excess imputable to a wind interaction.

Key Words
stars: individual: HD93161 (A,B) -- stars: binaries: spectroscopic -- stars: early-type -- stars: fundamental parameters -- X-rays: stars -- X-rays: individual: HD93161

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