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The Role of Thermohaline Mixing in Intermediate- and Low-Metallicity Globular Clusters

Angelou, George C.; Stancliffe, Richard J.; Church, Ross LU ; Lattanzio, John C. and Smith, Graeme H. (2012) In Astrophysical Journal 749(2).
Abstract
It is now widely accepted that globular cluster red giant branch (RGB) stars owe their strange abundance patterns to a combination of pollution from progenitor stars and in situ extra mixing. In this hybrid theory a first generation of stars imprints abundance patterns into the gas from which a second generation forms. The hybrid theory suggests that extra mixing is operating in both populations and we use the variation of [C/Fe] with luminosity to examine how efficient this mixing is. We investigate the observed RGBs ofM3, M13, M92, M15, and NGC 5466 as a means to test a theory of thermohaline mixing. The second parameter pair M3 and M13 are of intermediate metallicity and our models are able to account for the evolution of carbon along... (More)
It is now widely accepted that globular cluster red giant branch (RGB) stars owe their strange abundance patterns to a combination of pollution from progenitor stars and in situ extra mixing. In this hybrid theory a first generation of stars imprints abundance patterns into the gas from which a second generation forms. The hybrid theory suggests that extra mixing is operating in both populations and we use the variation of [C/Fe] with luminosity to examine how efficient this mixing is. We investigate the observed RGBs ofM3, M13, M92, M15, and NGC 5466 as a means to test a theory of thermohaline mixing. The second parameter pair M3 and M13 are of intermediate metallicity and our models are able to account for the evolution of carbon along the RGB in both clusters, although in order to fit the most carbon-depleted main-sequence stars in M13 we require a model whose initial [C/Fe] abundance leads to a carbon abundance lower than is observed. Furthermore, our results suggest that stars in M13 formed with some primary nitrogen (higher C+N+O than stars in M3). In the metal-poor regime only NGC 5466 can be tentatively explained by thermohaline mixing operating in multiple populations. We find thermohaline mixing unable to model the depletion of [C/Fe] with magnitude in M92 and M15. It appears as if extra mixing is occurring before the luminosity function bump in these clusters. To reconcile the data with the models would require first dredge-up to be deeper than found in extant models. (Less)
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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
M15, M92, M13, globular clusters: individual (M3, stars:, NGC 5466), abundances, stars: evolution, stars: Population II
in
Astrophysical Journal
volume
749
issue
2
publisher
University of Chicago Press
external identifiers
  • wos:000302785700032
  • scopus:84859339543
ISSN
0004-637X
DOI
10.1088/0004-637X/749/2/128
language
English
LU publication?
yes
id
f8df3f5d-5a9b-4992-8470-6ed764b7cfa2 (old id 2571068)
date added to LUP
2012-06-04 10:54:46
date last changed
2017-07-30 04:02:13
@article{f8df3f5d-5a9b-4992-8470-6ed764b7cfa2,
  abstract     = {It is now widely accepted that globular cluster red giant branch (RGB) stars owe their strange abundance patterns to a combination of pollution from progenitor stars and in situ extra mixing. In this hybrid theory a first generation of stars imprints abundance patterns into the gas from which a second generation forms. The hybrid theory suggests that extra mixing is operating in both populations and we use the variation of [C/Fe] with luminosity to examine how efficient this mixing is. We investigate the observed RGBs ofM3, M13, M92, M15, and NGC 5466 as a means to test a theory of thermohaline mixing. The second parameter pair M3 and M13 are of intermediate metallicity and our models are able to account for the evolution of carbon along the RGB in both clusters, although in order to fit the most carbon-depleted main-sequence stars in M13 we require a model whose initial [C/Fe] abundance leads to a carbon abundance lower than is observed. Furthermore, our results suggest that stars in M13 formed with some primary nitrogen (higher C+N+O than stars in M3). In the metal-poor regime only NGC 5466 can be tentatively explained by thermohaline mixing operating in multiple populations. We find thermohaline mixing unable to model the depletion of [C/Fe] with magnitude in M92 and M15. It appears as if extra mixing is occurring before the luminosity function bump in these clusters. To reconcile the data with the models would require first dredge-up to be deeper than found in extant models.},
  author       = {Angelou, George C. and Stancliffe, Richard J. and Church, Ross and Lattanzio, John C. and Smith, Graeme H.},
  issn         = {0004-637X},
  keyword      = {M15,M92,M13,globular clusters: individual (M3,stars:,NGC 5466),abundances,stars: evolution,stars: Population II},
  language     = {eng},
  number       = {2},
  publisher    = {University of Chicago Press},
  series       = {Astrophysical Journal},
  title        = {The Role of Thermohaline Mixing in Intermediate- and Low-Metallicity Globular Clusters},
  url          = {http://dx.doi.org/10.1088/0004-637X/749/2/128},
  volume       = {749},
  year         = {2012},
}