The massive multiple system HD 64315

Abstract

Context. The O6 Vn star HD 64315 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 HD 64315 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. HD 64315 contains two binary systems, one of which is an eclipsing binary. The two binaries are separated by ∼ 0.09 arcsec (or ∼ 500 AU) if the most likely distance to the system, ∼ 5 kpc, is considered. The presence of fainter companions is not excluded by current observations. The non-eclipsing binary (HD 64315 AaAb) 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 ⊙ 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 O6 V with minimum masses of 10.8 M ⊙ and 10.2 M ⊙ , and likely masses ≈ 30 M ⊙ . Conclusions. HD 64315 provides a cautionary tale about high-mass star isolation and multiplicity. Its total mass is likely above 90 M ⊙ , 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.

The Villafranca catalog of Galactic OB groups

“…However, there is, indeed, a star earlier than O4 associated with the cluster: HD 64 568, an O3 V((f*))z (Sota et al 2014) that appears in the Gaia DR2 data as a likely runaway from Villafranca O-012, probably Haffner 18, with a flight time around 400 ka. In addition, there is another O star in the vicinity, HD 64 315 AB, classified by Maíz Apellániz et al (2016) as O5.5 V + O7 V. HD 64 315 AB has a RUWE of 1.8 and a negative parallax, possibly due to the presence of two unresolved visible components (each one of them a binary itself, see Lorenzo et al 2017) in the Gaia data, but its position in the CMD indicates that it is likely to be at a similar distance as HD 64 568 and Villafranca O-012. Interestingly, HD 64 315 AB is moving away from Haffner 18 in a direction nearly opposite to that of HD 64 568 and with a similar flight time, leading to the possibility that the two O-type systems were simultaneously ejected from the cluster.…”

The Villafranca catalog of Galactic OB groups

“…Both cases are similar in that one of the ejected systems contains a very-early-O star (hence, very massive) and the other one contains another O star earlier than O7. Another common characteristic is the complexity involved in the interactions that led to the ejections: in Villafranca O-014 NW both O-type systems are SB2s and were ejected in two different episodes that involved other stars and in Villafranca O-012 S HD 64 315 A,B is a SB2+SB2 (Lorenzo et al 2017) and HD 64 568 appears to be single, implying a minimum of five stars.…”

Clues on the Origin and Evolution of Massive Contact Binaries: Atmosphere Analysis of VFTS 352

“…Based on galactic studies, about 40% of all stars born as O-type are expected to interact with a companion before leaving the main sequence (Sana et al 2012). Ignoring particular evolutionary pathways such as those involving chemically homogeneous evolution or magnetic fields (though see below), more than half of these et al 2015 ;Popper 1978;Lorenzo et al 2017;Howarth et al 2015;Hilditch et al 2005;Penny et al 2008) Aside from binary interaction, stellar rotation can also have a dramatic influence on the evolution of massive stars. As a rapidly rotating massive star evolves, the core will shrink and the envelope will expand, leading to differential rotation (von Zeipel 1924;Eddington 1925Eddington , 1926Vogt 1924).…”