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

MAÍZ APELLÁNIZ, J.; NEGUERUELA, I.; BARBÁ, R.; WALBORN, N. R.; PELLERIN, A.; SIMÓN-DÍAZ, S.; SOTA, A.; MARCO, A.; ALONSO-SANTIAGO, J.; SANCHEZ BERMUDEZ, J.; GAMEN, R. C.; LORENZO, J.

ASTRONOMY AND ASTROPHYSICS

EDP SCIENCES S A

Lugar: Paris; Año: 2015 vol. 579 p. 108 - 120

0004-6361

Context. It appears that most (if not all) massive stars are born inmultiple systems. At the same time, the most massive binaries are hardto find owing to their low numbers throughout the Galaxy and the impliedlarge distances and extinctions. Aims: We want to study LS III+46 11, identified in this paper as a very massive binary; anothernearby massive system, LS III +46 12; and the surrounding stellarcluster, Berkeley 90. Methods: Most of the data used in thispaper are multi-epoch high S/N optical spectra, although we also useLucky Imaging and archival photometry. The spectra are reduced withdedicated pipelines and processed with our own software, such as aspectroscopic-orbit code, CHORIZOS, and MGB. Results: LS III +4611 is identified as a new very early O-type spectroscopic binary [O3.5If* + O3.5 If*] and LS III +46 12 as another early O-type system [O4.5V((f))]. We measure a 97.2-day period for LS III +46 11 and deriveminimum masses of 38.80 ± 0.83 M&sun; and 35.60± 0.77 M&sun; for its two stars. We measure theextinction to both stars, estimate the distance, search for opticalcompanions, and study the surrounding cluster. In doing so, a variableextinction is found as well as discrepant results for the distance. Wediscuss possible explanations and suggest that LS III +46 12 may be ahidden binary system where the companion is currently undetected.