On the carbon abundance of subgiant stars in the globular cluster M 92

Langer, G. E.; Kraft, Robert P.; Carbon, D. F.; Friel, Eileen D.; Oke, J. B.

doi:10.1086/131781

Cited by 73 publications

(83 citation statements)

References 8 publications

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“…However, a close inspection of the data does suggest that there might be a slight peak on the subgiant branch, as indeed Fukuoka and Simoda make the comment that "the only meaningful deviation may be a bump at V ~ 18". Curiously, this is very close to where Langer et al (1986) find the depletion in the surface 12 C abundance in M 92 stars to begin. But, if there truly is a peak in the observed luminosity function at about this magnitude (M v ~ 3.3), it is a very subtle feature.…”

Section: A Abundance Changes In Standard Modelssupporting

confidence: 62%

“…Is it possible to construct partially-mixed main-sequence models which can explain the observed abundances without violating other constraints from the data? Second, the change in C abundance which is seen along the giant branch in systems like M 92 (Langer et al 1986) suggests that deep mixing in this case commences near the base of Post-ZAMS Models Within the mathematical framework of the stellar evolution code used for the present calculations, it is possible to arbitrarily homogenize any region of a model and to follow its evolution. This provides a means by which mixing at different evolutionary stages, and to different depths, can be experimented with in order to search for potential mixing histories that could produce the cluster abundance inhomogeneities.…”

Section: A Abundance Changes In Standard Modelsmentioning

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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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: A Abundance Changes In Standard Modelssupporting

confidence: 62%

Section: A Abundance Changes In Standard Modelsmentioning

confidence: 99%

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

VandenBerg¹,

Smith²

1988

PASP

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“…In giants it is possible that material from deep layers, where carbon is converted into nitrogen, has been brought to the surface during previous mixing episodes. This phenomenon is well known in globular cluster stars (e.g., Langer et al 1986;Kraft 1994). To check for this effect, Fig.…”

Section: Cs 22948-066mentioning

confidence: 78%

First stars V - Abundance patterns from C to Zn and supernova yields in the early Galaxy

Cayrel

Depagne

Spite

et al. 2004

A&A

1,106

246

1,891

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Abstract. In the framework of the ESO Large Programme "First Stars", very high-quality spectra of some 70 very metal-poor dwarfs and giants were obtained with the ESO VLT and UVES spectrograph. These stars are likely to have descended from the first generation(s) of stars formed after the Big Bang, and their detailed composition provides constraints on issues such as the nature of the first supernovae, the efficiency of mixing processes in the early Galaxy, the formation and evolution of the halo of the Galaxy, and the possible sources of reionization of the Universe. This paper presents the abundance analysis of an homogeneous sample of 35 giants selected from the HK survey of Beers et al. (1992Beers et al. ( , 1999, emphasizing stars of extremely low metallicity: 30 of our 35 stars are in the range −4.1 < [Fe/H] < −2.7, and 22 stars have [Fe/H] < −3.0. Our new VLT/UVES spectra, at a resolving power of R ∼ 45 000 and with signal-to-noise ratios of 100-200 per pixel over the wavelength range 330-1000 nm, are greatly superior to those of the classic studies of McWilliam et al. (1995) and Ryan et al. (1996). The immediate objective of the work is to determine precise, comprehensive, and homogeneous element abundances for this large sample of the most metal-poor giants presently known. In the analysis we combine the spectral line modeling code "Turbospectrum" with OSMARCS model atmospheres, which treat continuum scattering correctly and thus allow proper interpretation of the blue regions of the spectra, where scattering becomes important relative to continuous absorption (λ < 400 nm). We obtain detailed information on the trends of elemental abundance ratios and the star-to-star scatter around those trends, enabling us to separate the relative contributions of cosmic scatter and observational/analysis errors. Abundances of 17 elements from C to Zn have been measured in all stars, including K and Zn, which have not previously been detected in stars with [Fe/H] < −3.0. Among the key results, we discuss the oxygen abundance (from the forbidden [OI] line), the different and sometimes complex trends of the abundance ratios with metallicity, the very tight relationship between the abundances of certain elements (e.g., Fe and Cr), and the high [Zn/Fe] ratio in the most metal-poor stars. Within the error bars, the trends of the abundance ratios with metallicity are consistent with those found in earlier literature, but in many cases the scatter around the average trends is much smaller than found in earlier studies, which were limited to lower-quality spectra. We find that the cosmic scatter in several element ratios may be as low as 0.05 dex. The evolution of the abundance trends and scatter with declining metallicity provides strong constraints on the yields of the first supernovae and their mixing into the early ISM. The abundance ratios found in our sample do not match the predicted yields from pair-instability hypernovae, but are consistent with element production by supernovae with progenitor masses up to 100 M . Mo...

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“…We were able to estimate values of [C/Fe] and [N/Fe], and show that, in M92 at least, although wide variations in these abundances could be found at any given location in the HR diagram, on the average [C/Fe] fell by a factor of 10 as stars progressed from the main sequence to the tip of the giant branch , indicating that the external stellar layers had been processed by convective mixing to regions in or near the hydrogen-burning shell. Stars near the main sequence had to be observed using the Palomar 200-inch telescope, thanks to an observing run with Bev Oke (Langer et al 1986). 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.…”

Section: Globular Cluster Carbon and Nitrogen Abundances-syntheticmentioning

confidence: 99%

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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On the carbon abundance of subgiant stars in the globular cluster M 92

Cited by 73 publications

References 8 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

First stars V - Abundance patterns from C to Zn and supernova yields in the early Galaxy

An Astronomical Life Salted by Pure Chance

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