The incidence of binaries in globular cluster stellar populations
Journal
Date Issued
2015
Description
This research was partially supported by the Munich Institute for Astro- and Particle Physics (MIAPP) of the DFG cluster of excellence “Origin and Structure of the Universe”. S.L., A.S., E.C., A.B. acknowledge partial support from PRIN-MIUR 2010-2011 PI Francesca Matteucci Evoluzione chimica e dinamica della nostra galassia e delle galassie del gruppo locale. E.V. acknowledges support by grants NASA-NNX13AF45G and HST-12830.01-A.
Abstract
Binary fraction and orbital characteristics provide indications on the conditions of star formation, as they shed light on the environment they were born in. Multiple systems are more common in low density environments than in higher density environments. In the current debate about the formation of globular clusters and their multiple populations, studying the binary incidence in the populations they host offers a crucial piece of information on the environment of their birth and their subsequent dynamical evolution. Through a multiyear observational campaign using FLAMES at VLT, we monitored the radial velocity of 968 red-giant-branch stars located around the half-light radii in a sample of ten Galactic globular clusters. We found a total of 21 radial velocity variables identified as bona fide binary stars, for a binary fraction of 2.2% ± 0.5%. When separating the sample into first generation and second generation stars, we find a binary fraction of 4.9% ± 1.3% and 1.2% ± 0.4%, respectively. Through simulations that take possible sources of bias into account in detecting radial velocity variations in the two populations, we show that the difference is significant and only marginally affected by these effects. This kind of different binary fraction strongly suggests different conditions in the environment of formation and evolution of first and second generations stars, with the latter being born in a much denser environment. Our result hence strongly supports the idea that the second generation forms in a dense subsystem at the center of the loosely distributed first generation, where (loose) binaries are efficiently destroyed.
Based on data obtained with the Very Large Telescope at the European Southern Observatory, programs: 073.D-0100, 073.D-0211 and 083.D-0208.Full Tables 1, 3, and table of the individual radial velocities are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/584/A52
Volume
584
Start page
A52
Issn Identifier
0004-6361
Ads BibCode
2015A&A...584A..52L
Rights
open.access
File(s)![Thumbnail Image]()
Loading...
Name
165_lucatello_bin_inGCs_2015.pdf
Size
227.66 KB
Format
Adobe PDF
Checksum (MD5)
d707dc15f2bf71c2939657ba8c5a69dc