Luminosity Functions for Post-Turnoff Stars in Globular Clusters. II. NGC 7099

Bergbusch, Peter A.

doi:10.1086/118078

Cited by 19 publications

(23 citation statements)

References 1 publication

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“…We do this partly because it involves the same filter bands, and partly because the residuals are the lowest on average (although the scatter in star-to-star residuals is large). As a note, comparisons with the most recent study (Bergbusch 1996) show no signs of color trends in the residuals except within about a magnitude of the tip of the giant branch. 10, 12, 14, and 16 Gyr, and they have been shifted so that the theoretical and observational TO magnitudes match, and then normalized to the observed LF in a 0.5 mag bin 2 magnitudes below the turnoff.…”

Section: A32 Calibrationmentioning

confidence: 52%

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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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Section: A32 Calibrationmentioning

confidence: 52%

“…The magnitude of this change was used as the error estimate. We have improved this, following a suggestion by Bergbusch (1996), by estimating the error by varying F, σ, and δ individually and adding the resulting error estimates in quadrature.…”

Section: The Lfs and Incompletenessmentioning

confidence: 99%

Wide‐Field CCD Photometry of the Globular Cluster M30

Sandquist¹,

Bolte²,

Langer³

et al. 1999

ApJ

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“…[of NGC 1261] does not show any marked gap or clump," so we do not classify this object as a gap cluster. With regard to M30, neither the Hubble Space Telescope (HST) ultraviolet and visual CMDs published by Yanni et al (1994) and Mould et al (1996), nor the ground-based photometry by Montgomery (1995), Bergbusch (1996), or Burgarella & Buat (1996, seem to show HB gaps either. M3 is also included in the Fusi Pecci et al list of gap clusters.…”

Section: Discussionmentioning

confidence: 98%

Bimodality and Gaps on Globular Cluster Horizontal Branches. II. The Cases of NGC 6229, NGC 1851, and NGC 2808

Catelan

Borissova

Sweigart

et al. 1998

ApJ

147

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The outer halo globular cluster NGC 6229 has a peculiar horizontal-branch (HB) morphology, with clear indications of a bimodal HB and a "" gap ÏÏ on the blue HB. In this paper, we present extensive synthetic HB simulations to determine whether peculiar distributions in the underlying physical parameters are needed to explain the observed HB morphology. We Ðnd that a unimodal mass distribution along the HB can satisfactorily account for the observed HB bimodality, provided the mass dispersion is substantially larger than usually inferred for the Galactic globular clusters. In this case, NGC 6229 should have a well-populated, extended blue tail. A truly bimodal distribution in HB masses can also satisfactorily account for the observed HB morphology, although in this case the existence of an extended blue tail is not necessarily implied. The other two well-known bimodal-HB clusters, NGC 1851 and NGC 2808, are brieÑy analyzed. While the HB morphology of NGC 1851 can also be reproduced with a unimodal mass distribution assuming a large mass dispersion, the same is not true of NGC 2808, for which a bimodal, and possibly multimodal, mass distribution seems deÐnitely required.The problem of gaps on the blue HB is also discussed. Applying the standard Hawarden and Newell s2 test, we Ðnd that the NGC 6229 gap is signiÐcant at the 99.7% level. However, in a set of 1000 simulations, blue-HB gaps comparable to the observed one are present in D6%È9% of all cases. We employ a new and simple formalism, based on the binomial distribution, to explain the origin of this discrepancy, and conclude that HawardenÏs method, in general, substantially overestimates the statistical signiÐcance of gaps. Paper I). showed that the horizontal-branch (HB) morphology of this cluster is characterized by two peculiar properties : (1) A distinctly bimodal distribution in B[V colors, consistent with the relatively small number of RR Lyrae variables, compared to the blue HB and red HB populations ; and (2) at least one "" gap ÏÏ on the blue HB, as previously noted by Fullton, & Trammell Carney, (1991). Bimodal-HB clusters are relatively rare, as are clusters with gaps on the blue HB. NGC 6229 is one of only four known casesÈthe others being NGC 2808, NGC 6388, and NGC 6441Èwhere these two anomalies are simultaneously present. As argued by many authors, an understanding of the nature of the detected peculiarities in "" bimodal ÏÏ and "" gap ÏÏ clusters would be of paramount importance for understanding the nature of the second parameter phenomenon (see, e. for producing HB bimodality in the speciÐc cases of NGC 6229, NGC 1851, and NGC 2808 ? (3) Are gaps on the blue HB a natural consequence of stellar evolution, as claimed by some authors ? (4) What is the statistical signiÐcance of gaps ?In this paper, we present extensive synthetic HB simulations for NGC 6229. We begin in the next section by laying out a proposed nomenclature for both deÐning and di †er-entiating "" bimodal ÏÏ and "" gap ÏÏ clusters. In we describe°3, the theoretical proc...

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“…Counts of post-main-sequence stars in star clusters contain information on evolutionary timescales (Renzini & Fusi Pecci 1988) and, through them, the physical processes occurring in and near regions of nuclear fusion. Star counts in the globular cluster M30 previously revealed a discrepancy between theoretical predictions and observations of the relative numbers of red giant branch (RGB) and main-sequence (MS) stars (Bolte 1994;Bergbusch 1996;Guhathakurta et al 1998;Sandquist et al 1999). Similar studies of other globular clusters (M5, Sandquist et al 1996;M3, Rood et al 1999) have not found such discrepancies.…”

Section: Introductionmentioning

confidence: 93%

The Unusual Luminosity Function of the Globular Cluster M10

Pollard

Sandquist

Hargis

et al. 2005

ApJ

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We present the I-band luminosity function of the differentially reddened globular cluster M10. We combine photometric analysis derived from wide-field (23' x 23') images that include the outer regions of the cluster and high-resolution images of the cluster core. After making corrections for incompleteness and field star contamination, we find that the relative numbers of stars on the lower giant branch and near the main-sequence turnoff are in good agreement with theoretical predictions. However, we detect significant (> 6 \sigma) excesses of red giant branch stars above and below the red giant branch bump using a new statistic (a population ratio) for testing relative evolutionary timescales of main-sequence and red giant stars. The statistic is insensitive to assumed cluster chemical composition, age, and main-sequence mass function. The excess number of red giants cannot be explained by reasonable systematic errors in our assumed cluster chemical composition, age, or main-sequence mass function. Moreover, M10 shows excesses when compared to the cluster M12, which has nearly identical metallicity, age, and color-magnitude diagram morphology. We discuss possible reasons for this anomaly, finding that the most likely cause is a mass function slope that shows significant variations as a function of mass.Comment: 31 pages, 12 figures, accepted for Ap

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Luminosity Functions for Post-Turnoff Stars in Globular Clusters. II. NGC 7099

Cited by 19 publications

References 1 publication

Wide‐Field CCD Photometry of the Globular Cluster M30

Wide‐Field CCD Photometry of the Globular Cluster M30

Bimodality and Gaps on Globular Cluster Horizontal Branches. II. The Cases of NGC 6229, NGC 1851, and NGC 2808

The Unusual Luminosity Function of the Globular Cluster M10

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