The little-studied cluster Berkeley 90. I. LS III +46 11: a very massive O3.5 If* + O3.5 If* binary

Lorenzo, J.; Sanchez Bermudez, J.; Gamen, R. C.; Alonso-Santiago, J.; Marco, A.; Sota, A.; Simón-Díaz, S.; Walborn, N. R.; Pellerin, A.; Barbá, R. H.; Negueruela, I.; Maíz Apellániz, J.
Bibliographical reference

Astronomy and Astrophysics, Volume 579, id.A108, 12 pp.

Advertised on:
Number of authors
IAC number of authors
Refereed citations
Context. It appears that most (if not all) massive stars are born in multiple systems. At the same time, the most massive binaries are hard to find owing to their low numbers throughout the Galaxy and the implied large distances and extinctions. Aims: We want to study LS III +46 11, identified in this paper as a very massive binary; another nearby massive system, LS III +46 12; and the surrounding stellar cluster, Berkeley 90. Methods: Most of the data used in this paper are multi-epoch high S/N optical spectra, although we also use Lucky Imaging and archival photometry. The spectra are reduced with dedicated pipelines and processed with our own software, such as a spectroscopic-orbit code, CHORIZOS, and MGB. Results: LS III +46 11 is identified as a new very early O-type spectroscopic binary [O3.5 If* + O3.5 If*] and LS III +46 12 as another early O-type system [O4.5 V((f))]. We measure a 97.2-day period for LS III +46 11 and derive minimum masses of 38.80 ± 0.83 M⊙ and 35.60 ± 0.77 M⊙ for its two stars. We measure the extinction to both stars, estimate the distance, search for optical companions, and study the surrounding cluster. In doing so, a variable extinction is found as well as discrepant results for the distance. We discuss possible explanations and suggest that LS III +46 12 may be a hidden binary system where the companion is currently undetected.
Related projects
The IACOB project: A new Era in the Study of Galactic OB Stars

IACOB is an ambitious long-term project whose main scientific goal is to provide an unprecedented empirical overview of the main physical properties of Galactic massive O- and B-type stars which can be used as definitive anchor point for our theories of stellar atmospheres, winds, interiors and evolution of massive stars

Simón Díaz