Carbon and nitrogen abundances in giant stars of the metal-poor globular cluster M92

Carbon, D. F.; Langer, G. E.; Butler, D.; Kraft, Robert P.; Suntzeff, Nicholas B.; Kemper, E.; Trefzger, C. F.; Romanishin, W.

doi:10.1086/190796

Cited by 140 publications

(199 citation statements)

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“…The calculations of Smith and Bell (1986) indicate that the CN abundance will have values close to its maximum only over a carbon depletion range of A [C/CJ ~0.3 to 0.4. Hence, if the CN-rich stars were to be undergoing the type of progressive deep mixing indicated by the M 92 and M15 observations (Carbon et al 1982;Trefzger et al 1983), where the carbon changes by A[C/C ¡] = 1.0 over a range of AM v -3 mag, then they ought only to be found over a range of 1-2 magnitudes above the luminosity at which the mixing first commences. This is clearly not the case, as is evident from the observations cited above.…”

Section: Observational Constraintsmentioning

confidence: 96%

“…In other bimodal-CN clusters, such as NGC 6752 (Norris et al 1981;Cannon 1984), NGC 362 (Smith 1983), and M3 (Suntzeffl981; Norris and Smith 1984), the CN variations have been traced to observational limits of M v = +1 to +2, without any indication of a disappearance. This suggests a fundamental difference in the behavior of the carbon abundance depletions found among the M 92 and M15 giants (Carbon et al 1982;Trefzger et al 1983), where the [C/Fe] abundance appears to have returned to a likely primordial value of close to solar among the main-sequence turnoff stars.…”

Section: Observational Constraintsmentioning

confidence: 99%

“…Carbon et al (1982), Trefzger et al (1983), and Langer étal. (1986) have found that, on average, the carbon abundance decreases with increasing stellar luminosity among the giants in these two clusters.…”

Section: Introductionmentioning

confidence: 97%

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Constraints from stellar models on mixing as a viable explanation of abundance anomalies in globular clusters

VandenBerg¹,

Smith²

1988

PASP

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A detailed examination is made of the surface abundance changes (particularly of the CNO nuclei) which are predicted and observed to occur in evolving globular cluster (GC) stars. Discussed first are the standard stellar evolutionary sequences which have been constructed for a mass of 0.8 an d a metallicity of Z = 1CT 4 ([Fe/H] = -2.25), for comparison with observations of extremely metal-deficient cluster stars, and for a mass of 0.9 3K 0 and a metal content of Z = 6 X 10 3 ([Fe/H] = -0.49), for comparison with data from relatively metal-rich systems. These calculations illustrate the well-known problem that canonical models are completely inadequate insofar as being able to explain either the observed steep decline of the carbon abundance as a function of luminosity along the giant branches of M15 and M 92 or the CN-bimodality which is seen among giant stars of similar magnitude and color in several intermediate-metallicity and metal-rich GCs (e.g., NCG 362, 47 Tue).Then, on the premise that enhanced mixing of the envelope into the stellar interior is responsible for the observed abundances, partially-mixed models have been constructed in which artificially deep mixing is initiated at a wide variety of evolutionary phases and maintained during the subsequent evolution. The purpose of these calculations was not only to attempt to reproduce theoretically the abundance data but also to try to determine when the mixing could occur without producing accompanying side effects that violated other observational constraints. The present work shows, for instance, that the onset of deep mixing, of a sufficient degree to alter the surface composition in the requisite way, at any time between the zero-age main sequence (ZAMS) and the turnoff will induce a significantly larger color spread on the C-M plane than is generally permitted by recent CCD photometry. Indeed, in the case of 47 Tue, it is argued that the tightness of its C-M diagram, the reported good agreement between its observed luminosity function with that derived from canonical models, and the inferred small spread in the star-to-star helium abundances among the cluster horizontal-branch stars all provide persuasive evidence that unusual mixing in postmain-sequence stars does not occur in this system. Worthy of note, however, is the suggestion from our analysis that a mixing explanation for the CN-bimodality in GCs may be least problematical if the abundance anomalies arise during the very early evolutionary history of a star. What would seem to be required is that stars which presently show strong CN must have remained fully mixed as they initially contracted toward the ZAMS and somewhat beyond, until n( 12 C) ~ n( 14 N), and then evolved normally. However, even if stars can remain fully mixed for the time required, this possibility is not without its difficulties. Consequently, it is highly probable that some explanation other than mixing is responsible for the abundance anomalies which are seen in the bimodal-CN clusters. In contrast, the observed tr...

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Section: Observational Constraintsmentioning

confidence: 96%

Section: Observational Constraintsmentioning

confidence: 99%

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Constraints from stellar models on mixing as a viable explanation of abundance anomalies in globular clusters

VandenBerg¹,

Smith²

1988

PASP

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“…These authors measured this break in a sample of 200 stars concluding that ∆ depended both on stellar metallicity and B − V color. Analogous discontinuity definitions, like C(38 − 41) (McClure & van den Bergh 1968), and Γ(38 − 41) (Carbon et al 1982), have been also employed in the spectroscopic analysis of stars, star clusters and galaxies.…”

Section: Previous Work: Understanding the D 4000mentioning

confidence: 99%

Empirical calibration of the λ4000 Å break

Gorgas

Cardiel

Pedraz

et al. 1999

Astron. Astrophys. Suppl. Ser.

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Abstract. Empirical fitting functions, describing the behaviour of the λ4000Å break, D 4000 , in terms of effective temperature, metallicity and surface gravity, are presented. For this purpose, the break has been measured in 392 stars from the Lick/IDS Library. We have followed a very detailed error treatment in the reduction and fitting procedures, allowing for a reliable estimation of the break uncertainties. This calibration can be easily incorporated into stellar population models to provide accurate predictions of the break amplitude for, relatively old, composite systems.

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“…Suntzeff's thesis (1981) dealt with M3 and M13, for which similar variations were found at a given luminosity, but in which the systematic decline with luminosity in mean carbon abundance was not so clearly indicated. A similar study of halo field dwarfs was carried out with visiting Brazilian astronomer Beatriz Barbuy (Carbon et al 1984), with the result that [C/Fe] did not appear to depend on [Fe/H] and [N/Fe] did not follow the expected secondary origin of N.…”

Section: Globular Cluster Carbon and Nitrogen Abundances-syntheticmentioning

confidence: 81%

An Astronomical Life Salted by Pure Chance

Kraft

2009

Annu. Rev. Astron. Astrophys.

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My childhood upbringing in no way suggested that I would become an astronomer, but accidents of fate pushed me in the direction of science, and I have benefited greatly from being in the right place at the right time. I grew up in Seattle, earned B.S. and M.S. degrees in mathematics at the University of Washington, and eventually a Ph.D. in astronomy from the University of California, Berkeley. I was a postdoc at the Mt. Wilson Observatory, an assistant professor at Indiana University, later the Yerkes Observatory (University of Chicago), and still later I became a staff member of the Mt. Wilson and Palomar Observatories. After several years, I returned to the University of California, this time with the Lick Observatory staff at its new academic home on the Santa Cruz campus, where I have been ever since. My research has focused on the relation of Cepheids and RR Lyrae stars to problems of Galactic structure, the binary nature of cataclysmic variables, the decay of angular momentum of solar type stars, and the chemical history of the Galaxy as revealed by the abundances of very old stars in globular clusters and the Galactic halo field. None of this work would have been possible without the help of excellent teachers and mentors, great colleagues, and superb postdocs and graduate students. Most of all, I am grateful for the educational opportunities afforded me by state-supported public Universities.

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Carbon and nitrogen abundances in giant stars of the metal-poor globular cluster M92

Cited by 140 publications

References 0 publications

Constraints from stellar models on mixing as a viable explanation of abundance anomalies in globular clusters

Constraints from stellar models on mixing as a viable explanation of abundance anomalies in globular clusters

Empirical calibration of the λ4000 Å break

An Astronomical Life Salted by Pure Chance

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