Abstract
We have used the B-V color difference (dB-v) between the horizontal branch (HB) and the red giant branch to explore the ages of globular clusters with red HB morphologies. Of these, 14 are Galactic, one belongs to the Large Magellanic Cloud (ESO 121-SC 03), and another to the Small Magellanic Cloud (Lindsay 1). Our observed values of dB-v for these clusters are compared with theoretical values derived by constructing synthetic red HB models with a range of metallicities and ages. Based on ages determined via this comparison and main-sequence turnoff photometry for a subset of our clusters, we conclude that the usefulness of dB-V as an age indicator seriously diminishes for clusters with [Fe/H] > -0.7. Furthermore, the Galactic globular clusters with [Fe/H] ≤ -0.7 and red HBs have a weighted mean age of 〈age〉 = 11.6 ± 0.3 Gyr, where the uncertainty is the standard error of the weighted mean. In contrast, from the work of Chaboyer, Sarajedini, and Demarque, clusters with HB morphologies bluer than those considered herein have 〈age〉 = 14.0 ± 0.3 Gyr, leading to the conclusion that the red HB clusters are younger than the remaining clusters by 2.4 ± 0.4 Gyr. This, and other evidence presented here, reinforces the conclusion of previous investigators that age is the second parameter, which, in addition to metal abundance, governs the morphology of the HB.
| Original language | English |
|---|---|
| Pages (from-to) | 712-721 |
| Number of pages | 10 |
| Journal | Astrophysical Journal |
| Volume | 450 |
| Issue number | 2 |
| DOIs | |
| Publication status | Published - 1995 Sep 10 |
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All Science Journal Classification (ASJC) codes
- Astronomy and Astrophysics
- Space and Planetary Science
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Ages for globular clusters with predominantly red horizontal branches. / Sarajedini, Ata; Lee, Young Wook; Lee, Dong Han.
In: Astrophysical Journal, Vol. 450, No. 2, 10.09.1995, p. 712-721.Research output: Contribution to journal › Article
TY - JOUR
T1 - Ages for globular clusters with predominantly red horizontal branches
AU - Sarajedini, Ata
AU - Lee, Young Wook
AU - Lee, Dong Han
PY - 1995/9/10
Y1 - 1995/9/10
N2 - We have used the B-V color difference (dB-v) between the horizontal branch (HB) and the red giant branch to explore the ages of globular clusters with red HB morphologies. Of these, 14 are Galactic, one belongs to the Large Magellanic Cloud (ESO 121-SC 03), and another to the Small Magellanic Cloud (Lindsay 1). Our observed values of dB-v for these clusters are compared with theoretical values derived by constructing synthetic red HB models with a range of metallicities and ages. Based on ages determined via this comparison and main-sequence turnoff photometry for a subset of our clusters, we conclude that the usefulness of dB-V as an age indicator seriously diminishes for clusters with [Fe/H] > -0.7. Furthermore, the Galactic globular clusters with [Fe/H] ≤ -0.7 and red HBs have a weighted mean age of 〈age〉 = 11.6 ± 0.3 Gyr, where the uncertainty is the standard error of the weighted mean. In contrast, from the work of Chaboyer, Sarajedini, and Demarque, clusters with HB morphologies bluer than those considered herein have 〈age〉 = 14.0 ± 0.3 Gyr, leading to the conclusion that the red HB clusters are younger than the remaining clusters by 2.4 ± 0.4 Gyr. This, and other evidence presented here, reinforces the conclusion of previous investigators that age is the second parameter, which, in addition to metal abundance, governs the morphology of the HB.
AB - We have used the B-V color difference (dB-v) between the horizontal branch (HB) and the red giant branch to explore the ages of globular clusters with red HB morphologies. Of these, 14 are Galactic, one belongs to the Large Magellanic Cloud (ESO 121-SC 03), and another to the Small Magellanic Cloud (Lindsay 1). Our observed values of dB-v for these clusters are compared with theoretical values derived by constructing synthetic red HB models with a range of metallicities and ages. Based on ages determined via this comparison and main-sequence turnoff photometry for a subset of our clusters, we conclude that the usefulness of dB-V as an age indicator seriously diminishes for clusters with [Fe/H] > -0.7. Furthermore, the Galactic globular clusters with [Fe/H] ≤ -0.7 and red HBs have a weighted mean age of 〈age〉 = 11.6 ± 0.3 Gyr, where the uncertainty is the standard error of the weighted mean. In contrast, from the work of Chaboyer, Sarajedini, and Demarque, clusters with HB morphologies bluer than those considered herein have 〈age〉 = 14.0 ± 0.3 Gyr, leading to the conclusion that the red HB clusters are younger than the remaining clusters by 2.4 ± 0.4 Gyr. This, and other evidence presented here, reinforces the conclusion of previous investigators that age is the second parameter, which, in addition to metal abundance, governs the morphology of the HB.
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U2 - 10.1086/176177
DO - 10.1086/176177
M3 - Article
AN - SCOPUS:0001458994
VL - 450
SP - 712
EP - 721
JO - Astrophysical Journal
JF - Astrophysical Journal
SN - 0004-637X
IS - 2
ER -