Proton Capture Chains in Globular Cluster Stars.II.Oxygen, Sodium, Magnesium, and Aluminum Abundances in M13 Giants Brighter Than the Horizontal Branch

Kraft, Robert P.; Sneden, Christopher; Smith, Graeme H.; Shetrone, Matthew; Langer, G. E.; Pilachowski, Catherine A.

doi:10.1086/118251

Cited by 177 publications

(223 citation statements)

References 0 publications

Supporting

Mentioning

204

Contrasting

Order By: Relevance

“…In some clusters the peculiarities are particularly wide spread and strong, as in M 13 and NGC 6752 (Da Costa & Cottrell 1980;Norris et al 1981;Smith & Norris 1993;Pilachowski et al 1996;Kraft et al 1997;Sneden 2000;Gratton et al 2001). The fact that these clusters present also the "anomaly" of an extended and exclusively blue horizontal branch has been noticed by Catelan & de Freitas Pacheco (1995), who observe that clusters with super oxygen-poor giants have all very blue HBs.…”

Section: Introductionmentioning

confidence: 80%

Helium variation due to self–pollution among Globular Cluster stars

D’Antona

Caloi²,

Montalbán

et al. 2002

A&A

293

243

View full text Add to dashboard Cite

Abstract. It is becoming clear that "self-pollution" by the ejecta of massive asymptotic giant branch stars has an important role in the early chemical evolution of globular cluster stars, producing CNO abundance spreads which are observed also at the surface of unevolved stars. Observing that the ejecta which are CNO processed must also be helium enriched, we have modelled stellar evolution of globular cluster stars by taking into account this possible helium enhancement with respect to the primordial value. We show that the differences between the main evolutionary phases (main sequence, turn-off and red giants) are small enough that it would be very difficult to detect them observationally. However, the difference in the evolving mass may play a role in the morphology of the horizontal branch, and in particular in the formation of blue tails, in those globular clusters which show strong CNO abundance variations, such as M13 and NGC 6752.

show abstract

Section: Introductionmentioning

confidence: 80%

Helium variation due to self–pollution among Globular Cluster stars

D’Antona

Caloi²,

Montalbán

et al. 2002

A&A

293

243

View full text Add to dashboard Cite

show abstract

“…The cluster stars appear to suffer from some sort of evolutionary effect. It has been proposed that these objects experience differing degrees of internal, '' deep '' mixing as they evolve (Pilachowski et al 1996b;Kraft et al 1997). Such mixing can alter the composition of the stellar envelope as it encounters regions affected by CNO burning (Wallerstein et al 1997).…”

Section: Sodiummentioning

confidence: 99%

Abundances from High-Resolution Spectra of Kinematically Interesting Halo Stars

Stephens

Boesgaard

2002

The Astronomical Journal

146

182

View full text Add to dashboard Cite

There are stars in the halo of the Galaxy whose orbital properties are distinctly different from the majority of the halo population. One suggestion to account for these kinematically peculiar stars is that they have been gravitationally subsumed by the Milky Way through the breakup of nearby dwarf galaxies. One test of this hypothesis lies in determining the chemical composition of the deviant halo stars relative to that of normal ('' native '') halo field stars. The possibly accreted stars are predicted to have different chemical enrichments due to a slower rate of star formation in nearby low-mass spheroidal or irregular galaxies. We have obtained echelle spectra of metal-poor halo dwarfs with unusual orbital properties: from the outer halo, from the '' high '' halo, and on retrograde orbits. Our spectra are at high spectral resolution (35,000-48,000) and high signal-to-noise ratios (median value 140), primarily from the Keck I 10 m telescope with HIRES (53 stars), but also from the echelle spectrometer of the KPNO Mayall 4 m Telescope (three stars). The spectra cover a large spectral range: $4000-6800 Å . The strengths of approximately 9000 lines have been measured to determine the stellar parameters (T eff , log g, [Fe/H], and ) and the abundances of 10 elements, including Na, -fusion products (Mg, Si, Ca, Ti), iron peak elements (Cr, Fe, Ni), and neutron capture elements (Y, Ba). A model atmosphere was computed for each star, which was used to determine the composition under the assumption of LTE. The comparison of the abundances with the kinematic properties revealed no special trends, except that the ratio of the mean of the -fusion elements to Fe is weakly correlated with stellar apogalactica in the sense that the outermost stars have lower ratios of [ /Fe] than those with smaller apogalactica. The hallmark of an accreted halo star is presumed to be a deficiency (compared with normal stars) of the -elements (e.g., O, Mg, Si, Ca, Ti) with respect to Fe, a consequence of sporadic bursts of star formation within the dwarf galaxies. However [Fe/H]. The kinematically peculiar stars in our sample must have had their origins in localized star-forming regions far removed from the Galactic center. They do not carry the chemical signature of an accreted population. It seems clear that the chemical enrichment in our sample comes primarily from Type II supernovae with only a small component from Type Ia supernovae. Our stars would have formed at most $1 Gyr after the beginning of a star formation episode in the remote halo. The general conclusion extracted from these data is that the formation of the nascent Milky Way was not dominated by the late accretion of dwarf galaxies like the ones that currently orbit the Galaxy. However, the assimilation of fragments early in the evolution of the Galaxy is a natural by-product of hierarchical models of structure formation and can explain many properties of the halo population.

show abstract

“…However, if deeper mixing occurs, the products of the Ne-Na and Mg-Al cycles (which occur at much hotter temperatures) may also be brought up to the stellar surface. This results in sodium and aluminium enhancements and the dilution of oxygen and magnesium in the photospheres of these stars (see, for example, Pagel 1997; Kraft et al 1997). Hence, given the absence of massive star evolution for ∼6 Gyr within the LMC, the evolution of low to intermediate mass stars and the Mg-Al cycle may have become significant in modifying the relative amounts of O, Mg, Si replenished to the ISM.…”

Section: α-Elements (O Mg Si)mentioning

confidence: 99%

The present-day chemical composition of the LMC

Rolleston

Trundle

Dufton

2002

A&A

121

113

View full text Add to dashboard Cite

Abstract. High-resolution observations of five OB-type main-sequence stars in the Large Magellanic Cloud (LMC) have been obtained with the UCLéchelle spectrograph on the 3.9-m Anglo-Australian Telescope. These spectra have been analysed using LTE model-atmosphere techniques, to derive stellar atmospheric parameters and chemical compositions. As these stars are located within the hydrogen burning main-sequence band, their surface abundances should reflect those of the present-day interstellar medium. Detailed line-by-line differential analyses have been undertaken relative to Galactic comparison stars. We conclude that there exists a general metal deficiency of −0.31 ± 0.04 dex within the LMC, and find no significant abundance variations between cluster and field stars. There is also tentative evidence to suggest a lower oxygen to iron abundance ratio, and an over-deficiency of magnesium relative to the other α-elements. These are discussed in terms of previous abundance analyses and models of discontinuous (or bursting) star formation within the LMC. Finally, there is some evidence to suggest a greater chemical enrichment of material within the H  region LH 104.

show abstract

Proton Capture Chains in Globular Cluster Stars.II.Oxygen, Sodium, Magnesium, and Aluminum Abundances in M13 Giants Brighter Than the Horizontal Branch

Cited by 177 publications

References 0 publications

Helium variation due to self–pollution among Globular Cluster stars

Helium variation due to self–pollution among Globular Cluster stars

Abundances from High-Resolution Spectra of Kinematically Interesting Halo Stars

The present-day chemical composition of the LMC

Contact Info

Product

Resources

About