NDLI: Core collapse and horizontal-branch morphology in Galactic globular clusters

Content Provider	EDP Sciences
Author	M. Pasquato G. Raimondo E. Brocato C. Chung A. Moraghan Y.-W. Lee
Abstract	Context. Stellar collision rates in globular clusters (GCs) do not appear to correlate with horizontal branch (HB) morphology, suggesting that dynamics does not play a role in the second-parameter problem. However, core densities and collision rates derived from surface-brightness may be significantly underestimated as the surface-brightness profile of GCs is not necessarily a good indicator of the dynamical state of GC cores. Core-collapse may go unnoticed if high central densities of dark remnants are present.Aims. We test whether GC HB morphology data supports a dynamical contribution to the so-called second-parameter effect.Methods. To remove first-parameter dependence we fitted the maximum effective temperature along the HB as a function of metallicity in a sample of 54 Milky Way GCs. We plotted the residuals to the fit as a function of second-parameter candidates, namely dynamical age and total luminosity. We considered dynamical age (i.e. the ratio between age and half-light relaxation time) among possible second-parameters. We used a set of direct N-body simulations, including ones with dark remnants to illustrate how core density peaks, due to core collapse, in a dynamical-age range similar to that in which blue HBs are overabundant with respect to the metallicity expectation, especially for low-concentration initial conditions.Results. GC total luminosity shows nonlinear behavior compatible with the self-enrichment picture. However, the data are amenable to a different interpretation based on a dynamical origin of the second-parameter effect. Enhanced mass-stripping in the late red-giant-branch phase due to stellar interactions in collapsing cores is a viable candidate mechanism. In this picture, GCs with HBs bluer than expected based on metallicity are those undergoing core-collapse.
Page Count	6
File Format	HTM / HTML PDF
ISSN	00046361
Alternate Webpage(s)	https://www.aanda.org/articles/aa/abs/2013/06/aa21361-13/aa21361-13.html
e-ISSN	14320746
Journal	Astronomy & Astrophysics
Volume Number	554
DOI	10.1051/0004-6361/201321361
Language	English
Publisher	EDP Sciences
Publisher Date	2013-06-01
Access Restriction	Open
Rights Holder	© ESO, 2013
Subject Keyword	methods: statistical methods: numerical globular clusters: general stars: evolution stars: mass-loss methods: statistical / methods: numerical / globular clusters: general / stars: evolution / stars: mass-loss
Content Type	Text
Resource Type	Article
Subject	Astronomy and Astrophysics Space and Planetary Science

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