The little-studied cluster Berkeley 90. III. Cluster parameters

Abstract

The open cluster Berkeley 90 is the home to one of the most massive binary systems in the Galaxy, LS III +46${}^{\circ }$11, formed by two identical, very massive stars (O3.5 If* + O3.5 If*), and a second early-O system (LS III +46${}^{\circ }$12 with an O4.5 IV((f)) component at least). Stars with spectral types earlier than O4 are very scarce in the Milky Way, with no more than 20 examples. The formation of such massive stars is still an open question today, and thus the study of the environments where the most massive stars are found can shed some light on this topic. To this aim, we determine the properties and characterize the population of Berkeley 90 using optical, near-infrared and WISE photometry and optical spectroscopy. This is the first determination of these parameters with accuracy. We find a distance of $3.5_{-0.5}^{+0.5}$ kpc and a maximum age of 3 Ma. The cluster mass is around $1000$ $M_{\odot }$ (perhaps reaching $1500$ $M_{\odot }$ if the surrounding population is added), and we do not detect candidate runaway stars in the area. There is a second population of young stars to the Southeast of the cluster that may have formed at the same time or slightly later, with some evidence for low-activity ongoing star formation.

15 pages, 8 figures and 9 tables. Accepted for publication in MNRAS

References in corpus (11)

• The UKIRT Infrared Deep Sky Survey (UKIDSS)
• The WFCAM Science Archive
• The UKIRT Wide Field Camera ZYJHK Photometric System: Calibration from 2MASS
• Star formation through gravitational collapse and competitive accretion
• A Classification Scheme for Young Stellar Objects Using the WIDE-FIELD INFRARED SURVEY EXPLORER AllWISE Catalog: Revealing Low-Density Star Formation in the Outer Galaxy
• Trigonometric Parallaxes of Star Forming Regions in the Perseus Spiral Arm
• A Spectroscopic Survey of WNL Stars in the LMC: General Properties and Binary Status
• The Massive Star Content of NGC 3603
• A search for counterparts to massive X-ray binaries using photometric catalogues
• Young open clusters in the galactic star forming region NGC 6357
• The little-studied cluster Berkeley 90. I. LS III +46 11: a very massive O3.5 If* + O3.5 If* binary