Galactic calibration of the tip of the red giant branch

AbstractIndications from Gaia data release 2 are that the tip of the red giant branch (a population II standard candle related to the helium flash in low mass stars) is close to –4 in absolute I magnitude in the Cousins photometric system. Our sample is high-latitude southern stars from the thick disk and inner halo, and our result is consistent with longstanding findings from globular clusters, whose distances were calibrated with RR Lyrae stars. As the Gaia mission proceeds, there is every reason to think an accurate Galactic geometric calibration of tip of the red giant branch will be a significant outcome for the extragalactic distance scale.

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Low-Mass Evolution from He Ignition to Beyond the Horizontal Branch

International Astronomical Union Colloquium ◽

10.1017/s0252921100081951 ◽

1980 ◽

Vol 58 ◽

pp. 483-489

Author(s):

Keith Despain

Keyword(s):

Stellar Model ◽

Horizontal Branch ◽

Helium Burning ◽

Rr Lyrae Stars ◽

The Core ◽

Rr Lyrae ◽

Low Mass ◽

Red Giant ◽

Lyrae Stars

AbstractThe evolution of an 0.6 M⊙ stellar model during core helium burning is presented. Following the off-center ignition of helium in the “core” flash, the star remains on the red giant branch for > 106 years, undergoing twelve additional flashes. After leaving the giant branch, the star evolves on the horizontal branch for 8.15×107 years before returning to the giant branch and undergoing strong helium-shell flashes. The implications for horizontal branch and RR Lyrae stars are discussed.

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General Properties of the Two Groups of Globular Clusters and Their Variable Stars

Symposium - International Astronomical Union ◽

10.1017/s0074180900010743 ◽

1975 ◽

Vol 67 ◽

pp. 541-543

Author(s):

A. V. Mironov ◽

N. N. Samus'

Keyword(s):

Chemical Composition ◽

Globular Clusters ◽

Variable Stars ◽

Rr Lyrae Stars ◽

General Properties ◽

Rr Lyrae ◽

Lyrae Stars

The dependences of the numbers of variable stars in globular clusters on the chemical composition are studied. For given metallicity the numbers of RR Lyrae stars reduced to some definite total number of stars in the cluster are different for the two groups of globular clusters introduced by Mironov.

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Predicted properties of RR Lyrae stars in the Sloan Digital Sky Survey photometric system

Monthly Notices of the Royal Astronomical Society ◽

10.1111/j.1365-2966.2006.10787.x ◽

2006 ◽

Vol 371 (3) ◽

pp. 1503-1512 ◽

Cited By ~ 11

Author(s):

M. Marconi ◽

M. Cignoni ◽

M. Di Criscienzo ◽

V. Ripepi ◽

F. Castelli ◽

...

Keyword(s):

Sloan Digital Sky Survey ◽

Photometric System ◽

Rr Lyrae Stars ◽

Rr Lyrae ◽

Sky Survey ◽

Lyrae Stars

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On the Two Oosterhoff Groups of Globular Clusters

International Astronomical Union Colloquium ◽

10.1017/s0252921100033522 ◽

1973 ◽

Vol 21 ◽

pp. 196-196

Author(s):

T. S. Van Albada ◽

Norman Baker

Keyword(s):

Stellar Evolution ◽

Globular Clusters ◽

Transition Point ◽

Transition Period ◽

Observational Evidence ◽

Horizontal Branch ◽

Average Difference ◽

Rr Lyrae Stars ◽

Rr Lyrae ◽

Lyrae Stars

AbstractThe observational evidence leading to the classification, following Oosterhoff, of globular clusters containing RR Lyrae stars into two distinct groups, is summarized and discussed in the light of results of stellar evolution theory and pulsation theory. The dichotomy is caused, at least in part, by a dichotomy in the ‘transition period’ between the type-ab and type-c stars which reflects a difference in effective temperature at the transition point. When this difference is accounted for, there remains a smaller average difference between the groups, though no longer a clear dichotomy, that is probably a mass and luminosity effect. If this remaining difference is interpreted as a luminosity effect the average difference in luminosity between the two Oosterhoff groups is at most 0.1 mag. It is suggested that Christy’s theoretical relationship between transition period and luminosity cannot be valid, at least not for clusters of different Oosterhoff groups. It is conjectured that the transition-temperature dichotomy may be a reflection of different predominant directions of evolution along the horizontal branch, accompanied by a hysteresis effect in the pulsations.

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Light Curves and Metal Abundances of RR Lyrae Variables in the Bar of the Large Magellanic Cloud

International Astronomical Union Colloquium ◽

10.1017/s0252921100057481 ◽

2000 ◽

Vol 176 ◽

pp. 172-175 ◽

Cited By ~ 1

Author(s):

G. Clementini ◽

A. Bragaglia ◽

L. Di Fabrizio ◽

E. Carretta ◽

R. G. Gratton

Keyword(s):

Large Magellanic Cloud ◽

Magellanic Cloud ◽

Light Curves ◽

Photometric System ◽

Rr Lyrae Stars ◽

Rr Lyrae ◽

Visual Magnitude ◽

Metal Abundance ◽

Definition Of ◽

Lyrae Stars

AbstractThe Large Magellanic Cloud (LMC) is widely considered a corner-stone of the astronomical distance scale. However, a difference of 0.2−0.3 mag exists in its distance as predicted by the short and long distance scales. Distances to the LMC from Population II objects are founded on the RR Lyrae variables. We have undertaken an observational campaign devoted to the definition of the average apparent luminosity, and to the study of the mass–metallicity relation for RR Lyrae stars in the bar of the LMC. These are compared with analogous quantities for cluster RR Lyrae stars. The purpose is to see whether an intrinsic difference in luminosity, possibly due to a difference in mass, might exist between field and cluster RR Lyrae stars, which could be responsible for the well-known dichotomy between short and long distance scales. Preliminary results are presented on the V and B − V light curves, the average apparent visual magnitude, and the pulsational properties of 102 RR Lyrae stars in the bar of the LMC, observed at ESO in January 1999. The photometric data are accurately tied to the Johnson photometric system. Comparison is presented with the photometry of RR Lyrae stars in the bar of the LMC obtained by the MACHO collaboration (Alcock et al. 1996). Our sample includes 9 double-mode RR Lyrae stars selected from Alcock et al. (1997) for which an estimate of the metal abundance from the ΔS method is presented.

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Observations of low mass stars in clusters: Some constraints and puzzles for stellar evolution theory

Symposium - International Astronomical Union ◽

10.1017/s0074180900030709 ◽

1984 ◽

Vol 105 ◽

pp. 123-138

Author(s):

R.D. Cannon

Keyword(s):

Globular Clusters ◽

Main Sequence ◽

Star Clusters ◽

Variable Stars ◽

Open Clusters ◽

Low Mass Stars ◽

Theory Of Evolution ◽

Theoretical Predictions ◽

Low Mass ◽

Red Giant

This review will attempt to do two things: (i) discuss some of the data which are available for testing the theory of evolution of low mass stars, and (ii) point out some problem areas where observations and theory do not seem to agree very well. This is of course too vast a field of research to be covered in one brief review, so I shall concentrate on one particular aspect, namely the study of star clusters and especially their colour-magnitude (CM) diagrams. Star clusters provide large samples of stars at the same distance and with the same age, and the CM diagram gives the easiest way of comparing theoretical predictions with observations, although crucial evidence is also provided by spectroscopic abundance analyses and studies of variable stars. Since this is primarily a review of observational data it is natural to divide it into two parts: (i) galactic globular clusters, and (ii) old and intermediate-age open clusters. Some additional evidence comes from Local Group galaxies, especially now that CM diagrams which reach the old main sequence are becoming available. For each class of cluster I shall consider successive stages of evolution from the main sequence, up the hydrogen-burning red giant branch, and through the helium-burning giant phase.

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Search for Variables in the Galactic Globular Clusters NGC 6544 and NGC 6642

International Astronomical Union Colloquium ◽

10.1017/s0252921100117774 ◽

1993 ◽

Vol 139 ◽

pp. 337-337

Author(s):

Martha L. Hazen

Keyword(s):

Globular Clusters ◽

Slow Variable ◽

Variable Stars ◽

Horizontal Branch ◽

Rr Lyrae Stars ◽

Rr Lyrae ◽

A Value ◽

Short Period ◽

Period Variable ◽

Lyrae Stars

A search for variable stars in the globular cluster NGC 6544 has revealed only one possible short period variable within the tidal radius of the cluster. A search in NGC 6642 yielded 16 new RR Lyrae stars within the tidal radius and 5 new field RRs. The previously discovered (Hoffleit 1972) V1 is a slow variable, and V2 is an RR Lyrae star. Photometry of the variables within the tidal radius gives a mean B for the horizontal branch of < B > = 17.0 mag. With E(B – V) = 0.37 mag and (B – V) = 0.35 mag for RR Lyraes, a value for V(HB) = 16.3 mag is derived. This is about one mag fainter than previous estimates (Webbink 1985), and places NGC 6642 at a distance of approximately 7.9 kpc.

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