Globular cluster photometry with the Hubble space telescope. VII. Color gradients and blue, stragglers in the central region of M30 from wide field planetary camera 2 observations

Puragra Guhathakurta, Zodiac T. Webster, Brian Yanny, Donald P. Schneider, John N. Bahcall

Research output: Contribution to journalArticle

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Abstract

We present F555W (V), F439W (B), and F336W (17) photometry of 9507 stars in the central 2′ of the dense, post-core-collapse cluster M30 (NGC 7099) derived from Hubble Space Telescope Wide Field Planetary Camera 2 images. These data are used to study the mix of stellar populations in the central region of the cluster. Forty-eight blue straggler stars are identified; they are found to be strongly concentrated toward the cluster center. The specific frequency of blue stragglers, FBSS = N(BSS)/N(V < VHB + 2), is 0.25 ± 0.05 in the inner region of M30 (r < 20″), significantly higher than the frequency found in other clusters: FBSS = 0.05-0.15. The shape of M30's blue straggler luminosity function resembles the prediction of the collisional formation model, and is inconsistent with the binary merger model of Bailyn & Pinsonneault. An unusually blue star (B = 18.6, B-V = -0.97), possibly a cataclysmic variable based on its color, is found about 1″.2 from the crowded cluster center; the photometric uncertainty for this star is large, however, because of the presence of a very close neighbor. Bright red giant stars (B < 16.6) appear to be depleted by a factor of 2-3 in the inner r < 10″ relative to fainter giants, subgiants, and main-sequence turnoff stars (95% significance). We confirm that there is a radial gradient in the color of the overall cluster light, going from B-V ∼ 0.82 at r ∼ 1′ to B - V ∼ 0.45 in the central 10″. The central depletion of the bright red giants is responsible for about half of the observed color gradient ; the rest of the gradient is caused by the relative underabundance of faint red main-sequence stars near the cluster center (presumably a result of mass segregation). The luminosity function of M30's evolved stars does not match the luminosity function shape derived from standard stellar evolutionary models: the ratio of the number of bright giants to the number of turnoff stars in the cluster is 30% higher than predicted by the model (3.8 σ effect), roughly independent of red giant brightness over the range MV = -2 to +2.

Original languageEnglish (US)
Pages (from-to)1757-1774
Number of pages18
JournalAstronomical Journal
Volume116
Issue number4
DOIs
StatePublished - Oct 1998

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globular clusters
Hubble Space Telescope
photometry
cameras
color
gradients
blue stars
stars
main sequence stars
luminosity
merger
red giant stars
stellar models
shape functions
cataclysmic variables
prediction
brightness
depletion
predictions

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

Cite this

@article{c92cc2c1d4eb444ebfdb6d80e2657ab0,
title = "Globular cluster photometry with the Hubble space telescope. VII. Color gradients and blue, stragglers in the central region of M30 from wide field planetary camera 2 observations",
abstract = "We present F555W (V), F439W (B), and F336W (17) photometry of 9507 stars in the central 2′ of the dense, post-core-collapse cluster M30 (NGC 7099) derived from Hubble Space Telescope Wide Field Planetary Camera 2 images. These data are used to study the mix of stellar populations in the central region of the cluster. Forty-eight blue straggler stars are identified; they are found to be strongly concentrated toward the cluster center. The specific frequency of blue stragglers, FBSS = N(BSS)/N(V < VHB + 2), is 0.25 ± 0.05 in the inner region of M30 (r < 20″), significantly higher than the frequency found in other clusters: FBSS = 0.05-0.15. The shape of M30's blue straggler luminosity function resembles the prediction of the collisional formation model, and is inconsistent with the binary merger model of Bailyn & Pinsonneault. An unusually blue star (B = 18.6, B-V = -0.97), possibly a cataclysmic variable based on its color, is found about 1″.2 from the crowded cluster center; the photometric uncertainty for this star is large, however, because of the presence of a very close neighbor. Bright red giant stars (B < 16.6) appear to be depleted by a factor of 2-3 in the inner r < 10″ relative to fainter giants, subgiants, and main-sequence turnoff stars (95{\%} significance). We confirm that there is a radial gradient in the color of the overall cluster light, going from B-V ∼ 0.82 at r ∼ 1′ to B - V ∼ 0.45 in the central 10″. The central depletion of the bright red giants is responsible for about half of the observed color gradient ; the rest of the gradient is caused by the relative underabundance of faint red main-sequence stars near the cluster center (presumably a result of mass segregation). The luminosity function of M30's evolved stars does not match the luminosity function shape derived from standard stellar evolutionary models: the ratio of the number of bright giants to the number of turnoff stars in the cluster is 30{\%} higher than predicted by the model (3.8 σ effect), roughly independent of red giant brightness over the range MV = -2 to +2.",
author = "Puragra Guhathakurta and Webster, {Zodiac T.} and Brian Yanny and Schneider, {Donald P.} and Bahcall, {John N.}",
year = "1998",
month = "10",
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Globular cluster photometry with the Hubble space telescope. VII. Color gradients and blue, stragglers in the central region of M30 from wide field planetary camera 2 observations. / Guhathakurta, Puragra; Webster, Zodiac T.; Yanny, Brian; Schneider, Donald P.; Bahcall, John N.

In: Astronomical Journal, Vol. 116, No. 4, 10.1998, p. 1757-1774.

Research output: Contribution to journalArticle

TY - JOUR

T1 - Globular cluster photometry with the Hubble space telescope. VII. Color gradients and blue, stragglers in the central region of M30 from wide field planetary camera 2 observations

AU - Guhathakurta, Puragra

AU - Webster, Zodiac T.

AU - Yanny, Brian

AU - Schneider, Donald P.

AU - Bahcall, John N.

PY - 1998/10

Y1 - 1998/10

N2 - We present F555W (V), F439W (B), and F336W (17) photometry of 9507 stars in the central 2′ of the dense, post-core-collapse cluster M30 (NGC 7099) derived from Hubble Space Telescope Wide Field Planetary Camera 2 images. These data are used to study the mix of stellar populations in the central region of the cluster. Forty-eight blue straggler stars are identified; they are found to be strongly concentrated toward the cluster center. The specific frequency of blue stragglers, FBSS = N(BSS)/N(V < VHB + 2), is 0.25 ± 0.05 in the inner region of M30 (r < 20″), significantly higher than the frequency found in other clusters: FBSS = 0.05-0.15. The shape of M30's blue straggler luminosity function resembles the prediction of the collisional formation model, and is inconsistent with the binary merger model of Bailyn & Pinsonneault. An unusually blue star (B = 18.6, B-V = -0.97), possibly a cataclysmic variable based on its color, is found about 1″.2 from the crowded cluster center; the photometric uncertainty for this star is large, however, because of the presence of a very close neighbor. Bright red giant stars (B < 16.6) appear to be depleted by a factor of 2-3 in the inner r < 10″ relative to fainter giants, subgiants, and main-sequence turnoff stars (95% significance). We confirm that there is a radial gradient in the color of the overall cluster light, going from B-V ∼ 0.82 at r ∼ 1′ to B - V ∼ 0.45 in the central 10″. The central depletion of the bright red giants is responsible for about half of the observed color gradient ; the rest of the gradient is caused by the relative underabundance of faint red main-sequence stars near the cluster center (presumably a result of mass segregation). The luminosity function of M30's evolved stars does not match the luminosity function shape derived from standard stellar evolutionary models: the ratio of the number of bright giants to the number of turnoff stars in the cluster is 30% higher than predicted by the model (3.8 σ effect), roughly independent of red giant brightness over the range MV = -2 to +2.

AB - We present F555W (V), F439W (B), and F336W (17) photometry of 9507 stars in the central 2′ of the dense, post-core-collapse cluster M30 (NGC 7099) derived from Hubble Space Telescope Wide Field Planetary Camera 2 images. These data are used to study the mix of stellar populations in the central region of the cluster. Forty-eight blue straggler stars are identified; they are found to be strongly concentrated toward the cluster center. The specific frequency of blue stragglers, FBSS = N(BSS)/N(V < VHB + 2), is 0.25 ± 0.05 in the inner region of M30 (r < 20″), significantly higher than the frequency found in other clusters: FBSS = 0.05-0.15. The shape of M30's blue straggler luminosity function resembles the prediction of the collisional formation model, and is inconsistent with the binary merger model of Bailyn & Pinsonneault. An unusually blue star (B = 18.6, B-V = -0.97), possibly a cataclysmic variable based on its color, is found about 1″.2 from the crowded cluster center; the photometric uncertainty for this star is large, however, because of the presence of a very close neighbor. Bright red giant stars (B < 16.6) appear to be depleted by a factor of 2-3 in the inner r < 10″ relative to fainter giants, subgiants, and main-sequence turnoff stars (95% significance). We confirm that there is a radial gradient in the color of the overall cluster light, going from B-V ∼ 0.82 at r ∼ 1′ to B - V ∼ 0.45 in the central 10″. The central depletion of the bright red giants is responsible for about half of the observed color gradient ; the rest of the gradient is caused by the relative underabundance of faint red main-sequence stars near the cluster center (presumably a result of mass segregation). The luminosity function of M30's evolved stars does not match the luminosity function shape derived from standard stellar evolutionary models: the ratio of the number of bright giants to the number of turnoff stars in the cluster is 30% higher than predicted by the model (3.8 σ effect), roughly independent of red giant brightness over the range MV = -2 to +2.

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