Ages for globular clusters in the outer galactic halo: The second-parameter clusters Palomar 3, Palomar 4, and Eridanus

Peter B. Stetson, Michael Bolte, William E. Harris, James E. Hesser, Sidney Van Den Bergh, Don A. Vandenberg, Roger A. Bell, Jennifer A. Johnson, Howard E. Bond, Laura K. Fullton, Gregory G. Fahlman, Harvey B. Richer

Research output: Contribution to journalArticle

66 Citations (Scopus)

Abstract

We have used the Wide Field Planetary Camera 2 on the Hubble Space Telescope to obtain photometry of the outer halo globular clusters Palomar 3, Palomar 4, and Eridanus. These three are classic examples of the "second-parameter" anomaly because of their red horizontal-branch morphologies in combination with their low-to-intermediate metallicities. Our color-magnitude diagrams (CMDs) in V, V - I reach Vlim ≃ 27.0, clearly delineating the subgiant and turnoff regions and about 3 mag of the unevolved main sequences. The slopes and dereddened colors of the giant branches are consistent with published [Fe/H] estimates that rank the clusters (Pal 3, Eridanus, Pal 4) in order of increasing metallicity, with all three falling near or between the abundance values of the classic nearby halo clusters M3 and M5. Differential fits of their CMDs are made to each other and to M3 and M5 for relative age determinations. We find that the three outer halo cluster CMDs differ from the nearby clusters in a way that is consistent with their being younger by ∼ 1.5-2 Gyr, if we have correctly estimated the clusters' chemical abundance ratios. Conversely, the inferred age difference could be smaller (≲1 Gyr) if either [Fe/H] or [α/Fe] for the outer halo clusters is significantly lower than we have assumed. Possible age spreads of order 1 Gyr among both the nearby and outer halo clusters may also be present.

Original languageEnglish (US)
Pages (from-to)247-263
Number of pages17
JournalAstronomical Journal
Volume117
Issue number1
DOIs
StatePublished - Jan 1999

Fingerprint

galactic halos
globular clusters
halos
diagram
color-magnitude diagram
age determination
metallicity
chronology
anomaly
parameter
falling
Hubble Space Telescope
photometry
cameras
anomalies
slopes
color
estimates

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

Cite this

Stetson, P. B., Bolte, M., Harris, W. E., Hesser, J. E., Van Den Bergh, S., Vandenberg, D. A., ... Richer, H. B. (1999). Ages for globular clusters in the outer galactic halo: The second-parameter clusters Palomar 3, Palomar 4, and Eridanus. Astronomical Journal, 117(1), 247-263. https://doi.org/10.1086/300670
Stetson, Peter B. ; Bolte, Michael ; Harris, William E. ; Hesser, James E. ; Van Den Bergh, Sidney ; Vandenberg, Don A. ; Bell, Roger A. ; Johnson, Jennifer A. ; Bond, Howard E. ; Fullton, Laura K. ; Fahlman, Gregory G. ; Richer, Harvey B. / Ages for globular clusters in the outer galactic halo : The second-parameter clusters Palomar 3, Palomar 4, and Eridanus. In: Astronomical Journal. 1999 ; Vol. 117, No. 1. pp. 247-263.
@article{d2da7f7eb6e14366a03f9a24f80efde0,
title = "Ages for globular clusters in the outer galactic halo: The second-parameter clusters Palomar 3, Palomar 4, and Eridanus",
abstract = "We have used the Wide Field Planetary Camera 2 on the Hubble Space Telescope to obtain photometry of the outer halo globular clusters Palomar 3, Palomar 4, and Eridanus. These three are classic examples of the {"}second-parameter{"} anomaly because of their red horizontal-branch morphologies in combination with their low-to-intermediate metallicities. Our color-magnitude diagrams (CMDs) in V, V - I reach Vlim ≃ 27.0, clearly delineating the subgiant and turnoff regions and about 3 mag of the unevolved main sequences. The slopes and dereddened colors of the giant branches are consistent with published [Fe/H] estimates that rank the clusters (Pal 3, Eridanus, Pal 4) in order of increasing metallicity, with all three falling near or between the abundance values of the classic nearby halo clusters M3 and M5. Differential fits of their CMDs are made to each other and to M3 and M5 for relative age determinations. We find that the three outer halo cluster CMDs differ from the nearby clusters in a way that is consistent with their being younger by ∼ 1.5-2 Gyr, if we have correctly estimated the clusters' chemical abundance ratios. Conversely, the inferred age difference could be smaller (≲1 Gyr) if either [Fe/H] or [α/Fe] for the outer halo clusters is significantly lower than we have assumed. Possible age spreads of order 1 Gyr among both the nearby and outer halo clusters may also be present.",
author = "Stetson, {Peter B.} and Michael Bolte and Harris, {William E.} and Hesser, {James E.} and {Van Den Bergh}, Sidney and Vandenberg, {Don A.} and Bell, {Roger A.} and Johnson, {Jennifer A.} and Bond, {Howard E.} and Fullton, {Laura K.} and Fahlman, {Gregory G.} and Richer, {Harvey B.}",
year = "1999",
month = "1",
doi = "10.1086/300670",
language = "English (US)",
volume = "117",
pages = "247--263",
journal = "Astronomical Journal",
issn = "0004-6256",
publisher = "IOP Publishing Ltd.",
number = "1",

}

Stetson, PB, Bolte, M, Harris, WE, Hesser, JE, Van Den Bergh, S, Vandenberg, DA, Bell, RA, Johnson, JA, Bond, HE, Fullton, LK, Fahlman, GG & Richer, HB 1999, 'Ages for globular clusters in the outer galactic halo: The second-parameter clusters Palomar 3, Palomar 4, and Eridanus', Astronomical Journal, vol. 117, no. 1, pp. 247-263. https://doi.org/10.1086/300670

Ages for globular clusters in the outer galactic halo : The second-parameter clusters Palomar 3, Palomar 4, and Eridanus. / Stetson, Peter B.; Bolte, Michael; Harris, William E.; Hesser, James E.; Van Den Bergh, Sidney; Vandenberg, Don A.; Bell, Roger A.; Johnson, Jennifer A.; Bond, Howard E.; Fullton, Laura K.; Fahlman, Gregory G.; Richer, Harvey B.

In: Astronomical Journal, Vol. 117, No. 1, 01.1999, p. 247-263.

Research output: Contribution to journalArticle

TY - JOUR

T1 - Ages for globular clusters in the outer galactic halo

T2 - The second-parameter clusters Palomar 3, Palomar 4, and Eridanus

AU - Stetson, Peter B.

AU - Bolte, Michael

AU - Harris, William E.

AU - Hesser, James E.

AU - Van Den Bergh, Sidney

AU - Vandenberg, Don A.

AU - Bell, Roger A.

AU - Johnson, Jennifer A.

AU - Bond, Howard E.

AU - Fullton, Laura K.

AU - Fahlman, Gregory G.

AU - Richer, Harvey B.

PY - 1999/1

Y1 - 1999/1

N2 - We have used the Wide Field Planetary Camera 2 on the Hubble Space Telescope to obtain photometry of the outer halo globular clusters Palomar 3, Palomar 4, and Eridanus. These three are classic examples of the "second-parameter" anomaly because of their red horizontal-branch morphologies in combination with their low-to-intermediate metallicities. Our color-magnitude diagrams (CMDs) in V, V - I reach Vlim ≃ 27.0, clearly delineating the subgiant and turnoff regions and about 3 mag of the unevolved main sequences. The slopes and dereddened colors of the giant branches are consistent with published [Fe/H] estimates that rank the clusters (Pal 3, Eridanus, Pal 4) in order of increasing metallicity, with all three falling near or between the abundance values of the classic nearby halo clusters M3 and M5. Differential fits of their CMDs are made to each other and to M3 and M5 for relative age determinations. We find that the three outer halo cluster CMDs differ from the nearby clusters in a way that is consistent with their being younger by ∼ 1.5-2 Gyr, if we have correctly estimated the clusters' chemical abundance ratios. Conversely, the inferred age difference could be smaller (≲1 Gyr) if either [Fe/H] or [α/Fe] for the outer halo clusters is significantly lower than we have assumed. Possible age spreads of order 1 Gyr among both the nearby and outer halo clusters may also be present.

AB - We have used the Wide Field Planetary Camera 2 on the Hubble Space Telescope to obtain photometry of the outer halo globular clusters Palomar 3, Palomar 4, and Eridanus. These three are classic examples of the "second-parameter" anomaly because of their red horizontal-branch morphologies in combination with their low-to-intermediate metallicities. Our color-magnitude diagrams (CMDs) in V, V - I reach Vlim ≃ 27.0, clearly delineating the subgiant and turnoff regions and about 3 mag of the unevolved main sequences. The slopes and dereddened colors of the giant branches are consistent with published [Fe/H] estimates that rank the clusters (Pal 3, Eridanus, Pal 4) in order of increasing metallicity, with all three falling near or between the abundance values of the classic nearby halo clusters M3 and M5. Differential fits of their CMDs are made to each other and to M3 and M5 for relative age determinations. We find that the three outer halo cluster CMDs differ from the nearby clusters in a way that is consistent with their being younger by ∼ 1.5-2 Gyr, if we have correctly estimated the clusters' chemical abundance ratios. Conversely, the inferred age difference could be smaller (≲1 Gyr) if either [Fe/H] or [α/Fe] for the outer halo clusters is significantly lower than we have assumed. Possible age spreads of order 1 Gyr among both the nearby and outer halo clusters may also be present.

UR - http://www.scopus.com/inward/record.url?scp=0344923880&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=0344923880&partnerID=8YFLogxK

U2 - 10.1086/300670

DO - 10.1086/300670

M3 - Article

AN - SCOPUS:0344923880

VL - 117

SP - 247

EP - 263

JO - Astronomical Journal

JF - Astronomical Journal

SN - 0004-6256

IS - 1

ER -