Color and population gradients in the core of the postcollapse globular cluster M30

Piotto, G.; King, Ivan R.; Djorgovski, S. G.

doi:10.1086/114937

Cited by 21 publications

(29 citation statements)

References 3 publications

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“…These measurements are in keeping with earlier observations of M30's central blueing trend (cf. Cordoni & Aurière 1984;Peterson 1986;Piotto et al 1988;Burgarella & Buat 1996). Note, the revised WFPC2 background flux estimates ( § 2.1) result in a color profile that is somewhat different from that published by GWYSB using the same data set, especially for r ∼ > 40 ′′ .…”

Section: Color Profile Of the Cluster Starlightmentioning

confidence: 99%

“…Though several authors have shown that central depletion of bright red giant branch (RGB) stars is an important contributor to the color gradient in these clusters (cf. Piotto, King, & Djorgovski 1988;Burgarella & Buat 1996;Guhathakurta et al 1998, hereafter GWYSB), a satisfactory explanation of the underlying physical cause of this RGB depletion has proven elusive (Djorgovski et al 1991). Most globular clusters are well fit by King models (KMs;King 1962) and very few of these show any such color gradient.…”

Section: Introductionmentioning

confidence: 99%

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Radial Color Gradient and Main-Sequence Mass Segregation in M30 (NGC 7099)

Howell

Guhathakurta

Tan

2000

The Astronomical Journal

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It has long been known that the post-core-collapse globular cluster M30 (NGC 7099) has a bluer-inward color gradient, and recent work suggests that the central deficiency of bright red giant stars does not fully account for this gradient. This study uses Hubble Space Telescope Wide Field Planetary Camera 2 images in the F439W and F555W bands, along with ground-based CCD images with a wider field of view for normalization of the non-cluster background contribution, and finds ∆(B − V ) ∼ +0.3 mag for the overall cluster starlight over the range 2 ′′ to ∼ > 1 ′ in radius. The slope of the color profile in this radial range is: ∆(B − V )/∆ log(r) = 0.20 ± 0.07 mag dex −1 , where the quoted uncertainty accounts for Poisson fluctuations in the small number of bright evolved stars that dominate the cluster light. We explore various algorithms for artificially redistributing the light of bright red giants and horizontal branch stars uniformly across the cluster. The traditional method of redistribution in proportion to the cluster brightness profile is shown to be inaccurate. There is no significant residual color gradient in M30 after proper uniform redistribution of all bright evolved stars; thus the color gradient in M30's central region appears to be due entirely to post-main-sequence stars. Two classes of plausible

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Section: Color Profile Of the Cluster Starlightmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Radial Color Gradient and Main-Sequence Mass Segregation in M30 (NGC 7099)

Howell

Guhathakurta

Tan

2000

The Astronomical Journal

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“…Because M30 has a core of high stellar density, we consider the possibility that this environment has influenced the populations of evolved stars in the cluster. M30 has one of the most robustly determined color gradients (approximately linear in log r: ∼ +0.20 mag dex −1 ; Piotto, King, & Djorgovski 1988) of all the globular clusters in the Galaxy. The sense of the color gradient is such that the integrated colors become bluer towards the cluster center.…”

Section: Environmental Effectsmentioning

confidence: 99%

Wide‐Field CCD Photometry of the Globular Cluster M30

Sandquist¹,

Bolte²,

Langer³

et al. 1999

ApJ

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We present new V I photometry for the halo globular cluster M30 (NGC 7099 = C2137-174), and compute luminosity functions (LFs) in both bands for samples of about 15,000 hydrogen-burning stars from near the tip of the red giant branch (RGB) to over four magnitudes below the main-sequence (MS) turnoff. We confirm previously observed features of the LF that are at odds with canonical theoretical predictions: an excess of stars on subgiant branch (SGB) approximately 0.4 mag above the turnoff and an excess number of RGB stars relative to MS stars.Based on subdwarfs with Hipparcos-measured parallaxes, we compute apparent distance moduli of (m − M) V = 14.87 ± 0.12 and 14.65 ± 0.12 for reddenings of E(V − I) = 0.06 and 0.02 respectively. The implied luminosity for the horizontal branch (HB) at these distances is M HB V = 0.11 and 0.37 mag. The two helium indicators we have been able to measure (R and ∆) both indicate that M30's helium content is high relative to other clusters of similar metallicity. M30 has a larger value for the parameter ∆V HB T O than any of the other similarly metal-poor clusters for which this quantity can be reliably measured. This suggests that M30 has either a larger age or higher helium content than all of the other metal-poor clusters examined. The color-difference method for measuring relative ages indicates that M30 is coeval with the metal-poor clusters M68 and M92.

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“…Color gradients near the'centers of post core collapse-globular clusters have long been thought to be due to the depletion of the brightest red giants in these very dense environments (Piotto et al 1988). This is quantified by Webster et al (1998) in their detailed investigation of M30's color gradient.…”

Section: Deficiency Of the Brightest Red Giants Near Dense Cluster Cementioning

confidence: 99%

Mass Functions & Stellar Populations of Globular Clusters

Guhathakurta¹,

Piotto²,

Vesperini³

1998

Highlights astron.

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I present a summary of results from various HST photometric studies of the dense central regions of Galactic globular clusters that my collaborators and I have carried out over the last 6 years. The dataset includes short exposures of 47 Tuc, M15, M3 and M13 obtained with the aberrated Planetary Camera-I (PC-I) and F555W (“V”) and F785LP (“I”) filters, as well as post-refurbishment Wide Field Planetary Camera 2 (WFPC2) snapshots of the post core collapse clusters M15, M30, and NGC 6624 in F336W (“U”), F439W (“B”), and V. Recently, a very deep, doubly oversampled PC-I U image of the core of 47 Tuc, and accompanying B and V images, have also been analyzed. In addition, we have carried out extensive checks of incompleteness and photometric error with the help of multiband image simulations that mimic the relevant characteristics of the HST PC-I and WFPC2 images: empirical point spread function, crowding effects based on a realistic density profile and stellar luminosity function (LF), noise, undersampling, A/D saturation, etc..

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Color and population gradients in the core of the postcollapse globular cluster M30

Cited by 21 publications

References 3 publications

Radial Color Gradient and Main-Sequence Mass Segregation in M30 (NGC 7099)

Radial Color Gradient and Main-Sequence Mass Segregation in M30 (NGC 7099)

Wide‐Field CCD Photometry of the Globular Cluster M30

Mass Functions & Stellar Populations of Globular Clusters

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