scholarly journals Do Halo Field Stars and Globular Clusters Belong to the Same Population?

1983 ◽  
Vol 6 ◽  
pp. 129-137 ◽  
Author(s):  
Robert P. Kraft
Keyword(s):  
Globular Cluster ◽  
Globular Clusters ◽  
Main Sequence ◽  
Helium Content ◽  
The Past ◽  
Solar Motion ◽  
Trigonometric Parallaxes ◽  
The Common ◽  
Existent Problem

Obviously such transcendental issues as the helium content and age of the oldest stars depend on whether we are correct in our belief that the answer to this question is “yes” I hardly need say that over the past 40 years compelling affirmative arguments have been developed. Thus, for example, the solar motion of the common subdwarfs can be shown (e.g., Carney 1979) to be essentially identical with that of globular clusters (Kinman 1959) (Table 1), and the Fe-peak metallicities of giants and RR Lyraes in the halo field have been shown to be the same as those in clusters [see, e.g., recent reviews by Kraft (1979) and Freeman and Norris (1981)]. It is hard to believe that we would be incorrect in identifying the main sequence of a globular cluster with the main sequence defined by the trigonometric parallaxes, magnitudes and colors of subdwarfs having the same [Fe/H]. It might seem, therefore, that raising such an issue at this late date is equivalent to discussing a non-existent problem.

scholarly journals The light elements in a helio- and asteroseismic perspective

2009 ◽  
Vol 5 (S268) ◽  
pp. 387-394
Author(s):  
Sylvie Vauclair
Keyword(s):  
Main Sequence ◽  
Light Element ◽  
Heavy Elements ◽  
Light Elements ◽  
Main Sequence Stars ◽  
General Introduction ◽  
Helium Content ◽  
Element Abundances ◽  
The Past

AbstractAsteroseismology is a powerful tool to derive stellar parameters, including the helium content and internal helium gradients, and the macroscopic motions which can lead to lithium, beryllium, and boron abundance variations. Precise determinations of these parameters need deep analyses for each individual stars. After a general introduction on helio and asteroseismology, I first discuss the solar case, the results which have been obtained in the past two decades, and the crisis induced by the new determination of the abundances of heavy elements. Then I discuss asteroseismology in relation with light element abundances, especially for the case of main sequence stars.

scholarly journals The Absolute Magnitudes of RR Lyrae Stars and the Age of the Galaxy

1989 ◽  
Vol 111 ◽  
pp. 121-140
Author(s):  
Allan Sandage
Keyword(s):  
Globular Cluster ◽  
Globular Clusters ◽  
Main Sequence ◽  
Absolute Magnitude ◽  
Cluster System ◽  
Apparent Magnitude ◽  
Rr Lyrae ◽  
Globular Cluster System ◽  
The Absolute ◽  
Absolute Magnitudes

AbstractIt is shown that the intrinsic spread in the absolute magnitudes of the RR Lyrae variables in a given globular cluster can reach 0.5 magnitudes at a given period or at a given color, due to luminosity evolution away from the zero age horizontal (ZAHB). The size of this intrinsic luminosity spread is largest in clusters of the highest metallicity.The absolute magnitude of the ZAHB itself also differs from cluster to cluster as a function of metallicity, being brightest in clusters of the lowest metallicity. Three independent methods of calibrating the ZAHB RR Lyrae luminosities each show a strong variation of MV(RR) with [Fe/H]. The pulsation equation of P<ρ>0.5 = Q(M,Te, L) used with the observed periods, temperatures, and masses of field and of cluster RR Lyraes gives the very steep luminosity-metallicity dependence of dMv(RR)/d[Fe/H] = 0.42. Main sequence fitting of the color-magnitude diagrams of clusters which have modern main-sequence photometry gives a confirming steep slope of 0.39. A summary of Baade-Wesselink MV(RR) values for field stars determined in four independent recent studies also shows a luminosity-metallicity dependence, but less steep with a slope of dMV(RR)/d[Fe/H] = 0.21.Observations show that the magnitude difference between the main sequence turn-off point and the ZAHB in a number of well observed globular clusters is independent of [Fe/H], and has a stable value of dV = 3.54 with a disperion of only 0.1 magnitudes. Using this fact, the absolute magnitude of the main sequence turn-off is determined in any given globular cluster from the observed apparent magnitude of the ZAHB by adopting any particular MV(RR) = f([Fe/H]) calibration.Ages of the clusters are shown to vary with [Fe/H] by amounts that depend upon the slopes of the MV(RR) = f([Fe/H]) calibrations. The calibrations show that there would be a steep dependence of the age on [Fe/H] if MV(RR) does not depend on [Fe/H]. No dependence of age on metallicity exists if the RR Lyrae luminosities depend on [Fe/H] as dMV(RR)/d[Fe/H] = 0.37. If Oxygen is not enhanced as [Fe/H] decreases, the absolute average age of the globular cluster system is 16 Gyr, independent of [Fe/H], using the steep MV(RR)/[Fe/H] calibration that is favored. If Oxygen is enhanced by [O/Fe] = – 0.14 [Fe/H] + 0.40 for [Fe/H] < –1.0, as suggested from the observations of field subdwarfs, then the age of the globular cluster system decreases to 13 Gyr, again independent of [Fe/H], if the RR Lyrae ZAHB luminosities have a metallicity dependence of dMV(RR)/d[Fe/H] = 0.37.

scholarly journals Globular cluster ages from main sequence fitting and detached, eclipsing binaries: The case of 47 Tuc

2008 ◽  
Vol 4 (S258) ◽  
pp. 171-176 ◽  
Author(s):  
Aaron Dotter ◽  
Janusz Kaluzny ◽  
Ian B. Thompson
Keyword(s):  
Stellar Evolution ◽  
Globular Cluster ◽  
Globular Clusters ◽  
Main Sequence ◽  
Eclipsing Binaries ◽  
Eclipsing Binary ◽  
Age Constraints

AbstractAge constraints are most often placed on globular clusters by comparing their CMDs with theoretical isochrones. The recent discoveries of detached, eclipsing binaries in such systems by the Cluster AgeS Experiment (CASE) provide new insights into their ages and, at the same time, provide much-needed tests of stellar evolution models. We describe efforts to model the properties of the detached, eclipsing binary V69 in 47 Tuc and compare age constraints derived from stellar evolution models of V69A and B with ages obtained from fitting isochrones to the cluster CMD. We determine whether or not, under reasonable assumptions of distance, reddening, and metallicity, it is possible to simultaneously constrain the age and He content of 47 Tuc.

scholarly journals Hipparcos and Primary Distance Scale Indicators

1998 ◽  
Vol 11 (1) ◽  
pp. 576-577
Author(s):  
C. Turon
Keyword(s):  
Globular Clusters ◽  
Main Sequence ◽  
Open Clusters ◽  
Distance Scale ◽  
Relative Accuracy ◽  
Distance Information ◽  
Rr Lyrae ◽  
Trigonometric Parallaxes ◽  
Nearby Stars ◽  
Better Than

The Hipparcos data are providing a dramatic increase, qualitatively and quantitatively, of the basic available distance information. For example, the numbers of stars for which a relative accuracy better than 10 % is available from Hipparcos data and from ground-based data are respectively 22 396and about 1000. Moreover, the range of spectral types and luminosity classes for which precise parallaxes are available is considerably enlarged, including many stars in open clusters and a small number of Cepheids and RR Lyrae. The bottom of the main sequence is populated down to absolute Hpmagnitude 14, including a number of subdwarf stars essential to derive globular clusters distances and ages (Pont et al, 1997a). Finally, the Hipparcos data show how difficult are the calibration of photometric distances and the transformation of relative trigonometric parallaxes to absolute parallaxes. This is illustrated by the comparison of distances given in the last edition of the Catalogue of Nearby Stars (CNS3, Gliese & Jahreiß 1991), which is the best available compilation of stars said to be closer than 25 pc from ground-based data. About a third of them are found by Hipparcos to be (much) further than this limit (Perryman et ai, 1995). A second example is given by the study of (Binney et al, 1997).

scholarly journals Observational signatures of lithium depletion in the metal-poor globular cluster NGC6397

2009 ◽  
Vol 5 (S268) ◽  
pp. 263-268 ◽  
Author(s):  
Karin Lind ◽  
Francesca Primas ◽  
Corinne Charbonnel ◽  
Frank Grundahl ◽  
Martin Asplund
Keyword(s):  
Globular Cluster ◽  
Globular Clusters ◽  
Main Sequence ◽  
Galactic Halo ◽  
Main Sequence Stars ◽  
Surface Evolution ◽  
Halo Stars ◽  
Systematic Uncertainties ◽  
Low Mass ◽  
Lithium Depletion

AbstractThe “stellar” solution to the cosmological lithium problem proposes that surface depletion of lithium in low-mass, metal-poor stars can reconcile the lower abundances found for Galactic halo stars with the primordial prediction. Globular clusters are ideal environments for studies of the surface evolution of lithium, with large number statistics possible to obtain for main sequence stars as well as giants. We discuss the Li abundances measured for >450 stars in the globular cluster NGC 6397, focusing on the evidence for lithium depletion and especially highlighting how the inferred abundances and interpretations are affected by early cluster self-enrichment and systematic uncertainties in the effective temperature determination.

scholarly journals Commission 37: Star Clusters and Associations

1982 ◽  
Vol 18 (1) ◽  
pp. 499-526
Keyword(s):  
Globular Cluster ◽  
Working Group ◽  
Globular Clusters ◽  
Star Clusters ◽  
Open Clusters ◽  
General Assembly ◽  
Active Period ◽  
Star Clusters And Associations ◽  
The Past ◽  
Good Number

The past triennium has been a very active period in most branches of cluster research. Some controversial subjects, notably globular cluster abundances and ages have received much attention. A good number of photometric papers on clusters as well as associations have been published. Observational effects of mass loss have been discussed by several astronomers.This report has been assembled by the president of the commission although several sections have been contributed by other members. The report will first list some highlights in the activities of our commission. Then follow the tables containing current investigations of OB associations, open clusters and globular clusters. These have been assembled by B. Balázs, G. Harris and R. White, respectively. After these tables comes a section by D. Heggie about dynamics of star clusters. A working group under the chairmanship of A. Moffat has made a proposal about the numbering of stars in clusters. The proposal, which is included here will be discussed by our commission at the IAU General Assembly.

scholarly journals Pal 13: its moderately extended low-density halo and its accretion history

2020 ◽  
Vol 635 ◽  
pp. A93 ◽  
Author(s):  
Andrés E. Piatti ◽  
José G. Fernández-Trincado
Keyword(s):  
Globular Cluster ◽  
Globular Clusters ◽  
Main Sequence ◽  
Milky Way ◽  
Orbital Motion ◽  
Data Sets ◽  
Recent Estimate ◽  
Magnitude Diagram ◽  
Density Map ◽  
Stellar Density

We present results based on Dark Energy Camera Legacy Survey (DECaLS) DR8 astrometric and photometric data sets of the Milky Way globular cluster Pal 13. Because of its relatively small size and mass, there is not yet a general consensus on the existence of extra-tidal structures surrounding it. While some previous results suggest the absence of such features, others show that the cluster is under the effects of tidal stripping. We have built a cluster stellar density map from DECaLS g, r magnitudes – previously corrected for interstellar reddening – of stars placed along the cluster main sequence in the color-magnitude diagram. The resulting density map shows nearly smooth contours around Pal 13 out to approximately 1.6 t the most recent estimate of its Jacobi radius, which was derived whilst taking into account the variation along its orbital motion. This outcome favors the presence of stars escaping the cluster, a phenomenon frequently seen in globular clusters that have crossed the Milky Way disk a comparably large number of times. Particularly, the orbital high eccentricity and large inclination angle of this accreted globular cluster could have been responsible for the relatively large amount of lost cluster mass.

scholarly journals Coulomb Corrections and Globular Cluster Stellar Evolution

1993 ◽  
Vol 137 ◽  
pp. 451-453 ◽  
Author(s):  
Charles R. Proffitt
Keyword(s):  
Equation Of State ◽  
Stellar Evolution ◽  
Globular Cluster ◽  
Globular Clusters ◽  
Main Sequence ◽  
Stellar Interior ◽  
Coulomb Effects

AbstractThe effects of Coulomb corrections on the evolution of globular clusters stars are discussed. Coulomb corrections alter the equation of state by about 1% in most of the stellar interior, and for stars of fixed initial parameters, this results in an 8% increase in the ZAMS luminosity and an 8% decrease in the age at the main sequence turnoff. Ages for globular clusters measured by comparing to the turnoff luminosity of theoretical isochrones are lowered by ≈ 4% when Coulomb effects are included.

scholarly journals Globular Cluster Luminosity Functions

1988 ◽  
Vol 126 ◽  
pp. 121-131
Author(s):  
Pierre Demarque
Keyword(s):  
Globular Cluster ◽  
Globular Clusters ◽  
Mass Function ◽  
Initial Mass Function ◽  
Stellar Structure ◽  
Structure Theory ◽  
Initial Mass ◽  
Helium Content ◽  
Luminosity Functions

The use of luminosity functions in the following areas is reviewed: (a) the determination of the helium content and ages of the globular clusters; (b) the testing of stellar structure theory; and (c) the determination of the initial mass function of globular clusters.

scholarly journals Chemical Properties of Individual Globular Clusters

1980 ◽  
Vol 85 ◽  
pp. 385-400 ◽  
Author(s):  
Judith G. Cohen
Keyword(s):  
Spectroscopic Study ◽  
Globular Cluster ◽  
Globular Clusters ◽  
Chemical Properties ◽  
High Dispersion ◽  
The Past ◽  
The Many

Rapid improvements in instrumentation over the past few years have made the spectroscopic study of individual globular cluster giants feasable. Three years ago I began a program of high dispersion abundance analyses of such stars to provide a calibration for the many photometric systems used to rank globular clusters in metallicity. The results for four clusters (M92, M15, M13, and M3) of low and intermediate metallicity have already appeared (Cohen, 1978, 1979), and additional detailed analyses of stars in M5 and M13 (Pilachowski, Wallerstein and Leep, 1979) will soon be available. Ignoring the elements C, N, and O, to which we shall return later, these detailed abundance analyses yielded few great surprises; perhaps the metallicity scale that had previously been used was too high by about 0.2 dex, and also it became clear that M3 was a very metal poor cluster. However, the calibration of the metal rich globulars beyond the simple ranking level of Mould, Struthman, and McElroy (1979) had not been attempted.

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