The massive multiple system HD 64315

Lorenzo, J., Simón Diaz, S., Negueruela, I., Vilardell, F., García, M., Evans, C. J., Montes, D. 2017. The massive multiple system HD 64315. Astronomy and Astrophysics 606, DOI: 10.1051/0004-6361/201731352

The O6 Vn star HD64315 is believed to belong to the star-forming region known as NGC 2467, but previous distance estimates do not support this association. Moreover, it has been identified as a spectroscopic binary, but existing data support contradictory values for its orbital period.

Aims. We explore the multiple nature of this star with the aim of determining its distance, and understanding its connection to NGC 2467.

Methods. A total of 52 high-resolution spectra have been gathered over a decade. We use their analysis, in combination with the photometric data from All Sky Automated Survey and HIPPARCOS catalogues, to conclude that HD64315 is composed of at least two spectroscopic binaries, one of which is an eclipsing binary. We have developed our own program to fit four components to the combined line shapes. Once the four radial velocities were derived, we obtained a model to fit the radial-velocity curves using the Spectroscopic Binary Orbit Program (SBOP). We then implemented the radial velocities of the eclipsing binary and the light curves in the Wilson-Devinney code iteratively to derive stellar parameters for its components. We were also able to analyse the non-eclipsing binary, and to derive minimum masses for its components which dominate the system flux.

Results. HD64315 contains two binary systems, one of which is an eclipsing binary. The two binaries are separated by similar to 0.09 arcsec (or similar to 500 AU) if the most likely distance to the system, similar to 5 kpc, is considered. The presence of fainter companions is not excluded by current observations. The non-eclipsing binary (HD 64315AaAb) has a period of 2.70962901 +/- 0.00000021 d. Its components are hotter than those of the eclipsing binary, and dominate the appearance of the system. The eclipsing binary (HD 64315 BaBb) has a shorter period of 1.0189569 +/- 0.0000008 d. We derive masses of 14.6 +/- 2.3 M-circle dot for both components of the BaBb system. They are almost identical; both stars are overfilling their respective Roche lobes, and share a common envelope in an overcontact configuration. The non-eclipsing binary is a detached system composed of two stars with spectral types around O6V with minimum masses of 10.8 M-circle dot and 10.2 M-circle dot, and likely masses approximate to 30 M-circle dot.

Conclusions. HD64315 provides a cautionary tale about high-mass star isolation and multiplicity. Its total mass is likely above 90 M-circle dot, but it seems to have formed without an accompanying cluster. It contains one the most massive overcontact binaries known, a likely merger progenitor in a very wide multiple system.

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