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http://hdl.handle.net/20.500.12386/32912
Title: | Core collapse and horizontal-branch morphology in Galactic globular clusters | Authors: | PASQUATO, MARIO RAIMONDO, Gabriella BROCATO, Enzo Chung, C. Moraghan, A. Lee, Y. -W. |
Issue Date: | 2013 | Journal: | ASTRONOMY & ASTROPHYSICS | Number: | 554 | First Page: | A129 | 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. <BR /> Aims: We test whether GC HB morphology data supports a dynamical contribution to the so-called second-parameter effect. <BR /> 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. <BR /> 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. | URI: | http://hdl.handle.net/20.500.12386/32912 | URL: | https://www.aanda.org/articles/aa/full_html/2013/06/aa21361-13/aa21361-13.html | ISSN: | 0004-6361 | DOI: | 10.1051/0004-6361/201321361 | Bibcode ADS: | 2013A&A...554A.129P | Fulltext: | open |
Appears in Collections: | 1.01 Articoli in rivista |
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