CCD photometry of globular clusters. IV - NGC 7006

Buonanno, R.; Pecci, F. Fusi; Capellaro, E.; Ortolani, S.; Richtler, T.; Geyer, E. H.

doi:10.1086/115928

Cited by 25 publications

(22 citation statements)

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“…This test results in a 0.6% probability that CN-strong and CN-weak stars follow the same radial distribution. It is worth mentioning here that Buonanno et al (1991) found the radial gradient in HB morphologies on a scale of order of 70 , while we find a lack of CN-strong stars on radial scales of order 4 . A detailed study of CN -especially in the central parts -appears desirable.…”

Section: Radial Distribution Of Cn Strengthssupporting

confidence: 43%

“…In the scenario of deep mixing one would expect, with metallicity as a fixed parameter, a correlation between the HB morphology of a globular cluster and the star-to-star CN abundance variations within a cluster. Besides the strong "global" second parameter at work in NGC 7006, Buonanno et al (1991) found evidence for an "internal" second parameter effect within it: The morphology of the HB becomes bluer with decreasing radial distance. Unless one accepts the unlikely scenario of an age-spread of order of a few billion years within a globular cluster, such an internal second parameter effect provides evidence of additional third parameters other than age, such as environment.…”

Section: Morphology Of the Horizontal Branchmentioning

confidence: 88%

“…The morphology of the HB changes with the radial distance to the cluster's center (Buonanno et al 1991): The HB morphology appears bluer in the central parts than in the outskirts. It appears therefore interesting to see if a similar trend can be found for the distribution of CN absorption strength.…”

Section: Radial Distribution Of Cn Strengthsmentioning

confidence: 99%

“…For instance, age differences measured with differential age-dating techniques from the main-sequence turn-off (MSTO) might be able to reproduce the differences in the HB morphologies of the pair NGC 288/NGC 362 at a metallicity of [Fe/H] = −1.2 dex, where NGC 288 would be 2 ± 1 Gyr older than NGC 362 (Catelan et al 2001) or for the pair M 3/M 13 at a metallicity of [Fe/H] = −1.6 dex, where M 13 would be 1.7±0.7 Gyr older (Rey et al 2001). Buonanno et al (1991) found a "normal" age for NGC 7006 from the difference in luminosity of the HB and the main sequence turn-over. Van den Bergh (1998) and Stetson et al (1999) found a general trend of outer halo GCs being one to two Gyr younger than the inner halo GCs.…”

Section: Morphology Of the Horizontal Branchmentioning

confidence: 99%

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CN variations in NGC 7006

Harbeck

Smith

Grebel

2003

A&A

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Abstract. Rotationally induced mixing with subsequent dredge-up of nucleosynthesized material is discussed as a second parameter of the horizontal branch morphology in globular clusters. CNO abundances have been proposed as tracers of the dredge up of processed material. NGC 7006 is a prominent example of a second parameter GC: Its HB morphology is too red for its metallicity. We present spectroscopic measurements of CN molecular band strengths S(3839) and CH band CH(4300) strengths for 12 giants in NGC 7006 to test rotationally-driven mixing as a second parameter in this cluster. Our observations reveal (i) a scatter in star-to-star CN absorption strengths with the same amplitude as seen in other GCs of the same metallicity, but different HB morphologies; (ii) a possible continuous distribution of CN absorption strength with a preference for CN-enriched stars, and (iii) a possible weak radial gradient in the number ratio of CN-strong and CN-weak stars. We argue against the hypothesis that CN-variations are directly correlated with the second parameter effect of the HB morphology. However, the small sample of stars measured in NGC 7006 prevents us from drawing firm conclusions. Finally, we identify one star of our sample as a foreground dwarf carbon star.

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Section: Radial Distribution Of Cn Strengthssupporting

confidence: 43%

Section: Morphology Of the Horizontal Branchmentioning

confidence: 88%

Section: Radial Distribution Of Cn Strengthsmentioning

confidence: 99%

Section: Morphology Of the Horizontal Branchmentioning

confidence: 99%

See 2 more Smart Citations

CN variations in NGC 7006

Harbeck

Smith

Grebel

2003

A&A

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“…Instead, one finds 3.50 ± 0.10 mag for both M13 (see Fig. 6 ) and NGC 7006 (Buonanno et al 1991). So it appears difficult to accomodate a difference in HB level of 0.5 mag, without considering an age difference of more than 5 Gyr in the sense of a younger M13 (since its turn-off would appear more luminous than in NGC 7006).…”

Section: T Omentioning

confidence: 94%

Mixing, enhanced helium and blue tails in globular clusters

Caloi¹

2001

A&A

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Abstract. We investigate the consequences of an increase in the envelope helium abundance of pre-helium flash red giants in globular clusters, an occurrence suggested by chemical peculiarities in many red giant atmospheres. Comparing predictions with the CM diagrams of a few crucial globular clusters, one finds no evidence for a substantial increase in the surface helium content of horizontal branch members of these clusters, at least for objects in the RR Lyrae region or close to it. The possibility that the most peculiar giants belong to the asymptotic giant branch is discussed. The consequences of a delay in the helium flash are briefly examined.

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Integrated colours of Milky Way globular clusters and horizontal branch morphology

Smith

Strader

2007

Astron Nachr

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Broadband colours are often used as metallicity proxies in the study of extragalactic globular clusters. A common concern is the effect of variations in horizontal branch (HB) morphology -the second-parameter effect -on such colours. We have used UBVI, Washington, and DDO photometry for a compilation of over 80 Milky Way globular clusters to address this question. Our method is to fit linear relations between colour and [Fe/H], and study the correlations between the residuals about these fits and two quantitative measures of HB morphology. While there is a significant HB effect seen in U − B, for the commonly used colours B − V , V − I, and C − T1, the deviations from the baseline colour-[Fe/H] relations are less strongly related to HB morphology. There may be weak signatures in B − V and C − T1, but these are at the limit of observational uncertainties. The results may favour the use of B − I in studies of extragalactic globular clusters, especially when its high [Fe/H]-sensitivity is considered.

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CCD photometry of globular clusters. IV - NGC 7006

Cited by 25 publications

References 0 publications

CN variations in NGC 7006

CN variations in NGC 7006

Mixing, enhanced helium and blue tails in globular clusters

Integrated colours of Milky Way globular clusters and horizontal branch morphology

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