Super-helium-rich stars in globular clusters: The origin of extreme horizontal branch

S. J. Joo, Y. W. Lee, S. J. Yoon, S. I. Han, C. Chung, C. H. Ree, Y. C. Kim, Y. J. Sohn, S. K. Yi

Research output: Contribution to journalArticle

Abstract

Recent observations of the globular cluster ω Centauri have shown that it has a double main sequence (MS), with a minority population of bluer and fainter MS well separated from a majority population of MS stars. Here we confirm that this special feature can only be reproduced by assuming a large range of helium abundance among several distinct populations in this cluster. We further show that the same helium enhancement required to reproduce this special feature on the MS can by itself reproduce the extreme horizontal-branch (EHB) stars observed in ω Cen, which are hotter than and separated from the majority population of normal HB stars. We also discuss the possibility that similar phenomena observed in the HB of other globular clusters are also due to the helium enhancement. If confirmed by further observations, this would establish that the third parameter that influences globular cluster color-magnitude diagram (CMD) morphology, in addition to metallicity and age, is indeed helium abundance.

Original languageEnglish
Pages (from-to)33-39
Number of pages7
JournalBaltic Astronomy
Volume15
Issue number1
Publication statusPublished - 2006 May 18

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B stars
globular clusters
helium
horizontal branch stars
augmentation
color-magnitude diagram
main sequence stars
minorities
metallicity
diagram
stars

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

Cite this

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title = "Super-helium-rich stars in globular clusters: The origin of extreme horizontal branch",
abstract = "Recent observations of the globular cluster ω Centauri have shown that it has a double main sequence (MS), with a minority population of bluer and fainter MS well separated from a majority population of MS stars. Here we confirm that this special feature can only be reproduced by assuming a large range of helium abundance among several distinct populations in this cluster. We further show that the same helium enhancement required to reproduce this special feature on the MS can by itself reproduce the extreme horizontal-branch (EHB) stars observed in ω Cen, which are hotter than and separated from the majority population of normal HB stars. We also discuss the possibility that similar phenomena observed in the HB of other globular clusters are also due to the helium enhancement. If confirmed by further observations, this would establish that the third parameter that influences globular cluster color-magnitude diagram (CMD) morphology, in addition to metallicity and age, is indeed helium abundance.",
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Super-helium-rich stars in globular clusters : The origin of extreme horizontal branch. / Joo, S. J.; Lee, Y. W.; Yoon, S. J.; Han, S. I.; Chung, C.; Ree, C. H.; Kim, Y. C.; Sohn, Y. J.; Yi, S. K.

In: Baltic Astronomy, Vol. 15, No. 1, 18.05.2006, p. 33-39.

Research output: Contribution to journalArticle

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T1 - Super-helium-rich stars in globular clusters

T2 - The origin of extreme horizontal branch

AU - Joo, S. J.

AU - Lee, Y. W.

AU - Yoon, S. J.

AU - Han, S. I.

AU - Chung, C.

AU - Ree, C. H.

AU - Kim, Y. C.

AU - Sohn, Y. J.

AU - Yi, S. K.

PY - 2006/5/18

Y1 - 2006/5/18

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AB - Recent observations of the globular cluster ω Centauri have shown that it has a double main sequence (MS), with a minority population of bluer and fainter MS well separated from a majority population of MS stars. Here we confirm that this special feature can only be reproduced by assuming a large range of helium abundance among several distinct populations in this cluster. We further show that the same helium enhancement required to reproduce this special feature on the MS can by itself reproduce the extreme horizontal-branch (EHB) stars observed in ω Cen, which are hotter than and separated from the majority population of normal HB stars. We also discuss the possibility that similar phenomena observed in the HB of other globular clusters are also due to the helium enhancement. If confirmed by further observations, this would establish that the third parameter that influences globular cluster color-magnitude diagram (CMD) morphology, in addition to metallicity and age, is indeed helium abundance.

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