On the Masses, Luminosities, and Compositions of Horizontal-Branch Stars

Albada, T. S. van; Baker, N. H.

doi:10.1086/151144

Cited by 129 publications

(67 citation statements)

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“…Moreover, empirical evidence suggests that the morphological structure of the horizontal branches is related to the mean period of RR Lyrae variables in metal-poor clusters (vanAlbada & Baker 1972). We investigate the detailed data for RR Lyrae in globular clusters from Clement et al (2001), and show that the redder the horizontal branch, the lower the mean period with a height correlation coefficient r = 0.8 ± 0.1.…”

Section: Criteria To Select the Subsystemsmentioning

confidence: 86%

Two populations among the metal-poor field RR Lyrae stars

Borkova¹,

Марсаков²

2003

A&A

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Abstract. We compute the spatial velocity components and the galactic orbital elements for 209 metal-poor ([Fe/H] < −1.0) RRLyrae (ab) variable stars in the solar neighborhood using proper motions, radial velocities, and photometric distances available in the literature. The computed orbital elements and published heavy element abundances are used to study relationships between the chemical, spatial, and kinematical characteristics of nearby field RR Lyrae variables. We observe abrupt changes in the stellar spatial and kinematical characteristics when the peculiar velocities relative to the local standard of rest cross the threshold value, V pec ≈ 280 km s −1 . This provides evidence that the general population of metal-poor RRLyrae stars is not uniform, and includes two spherical subsystems occupying different volumes in the Galaxy. Based on the agreement between typical parameters of corresponding subsystems of field RRLyrae stars and of the globular clusters, studied by us earlier, we conclude that metal-poor stars and globular clusters can be subdivided into two populations, but using different criteria for stars and clusters. We suppose that field stars with velocities below the threshold value and clusters with extremely blue horizontal branches form the spherical, slowly rotating subsystem of the proto-disk halo (related by its origin to the Galactic thick disk). It has a negligible, but non-zero, vertical metallicity gradient. Field stars with fast motion and clusters with redder horizontal branches constitute the spheroidal subsystem of the accreted outer halo, which is approximately two times larger in size than the first subsystem. It has absolutely no metallicity gradients, most of its stars have eccentric orbits, many stars display retrograde motion in the Galaxy, and their ages are comparatively low, supporting the hypothesis that the objects in this subsystem have an extragalactic origin.

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Section: Criteria To Select the Subsystemsmentioning

confidence: 86%

Two populations among the metal-poor field RR Lyrae stars

Borkova¹,

Марсаков²

2003

A&A

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“…Qualitatively, at a Ðxed temperature and mass, a lower density star has a larger radius and hence a greater luminosity. More precisely, we adopt the relations given by van Albada & Baker (1971). For the fundamental mode, the period of an RR Lyrae variable is…”

Section: Period Shift Analysismentioning

confidence: 99%

RR Lyrae Luminosity Differences between Oosterhoff Group I and II Cluster Systems and the Origin of the Oosterhoff Dichotomy

Lee

Carney

1999

The Astronomical Journal

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We present a comparative study of the Oosterho † II cluster M2 and the Oosterho † I cluster M3. Both have similar metallicities, [Fe/H] \ [1.62 for M2 and [1.66 for M3, but very di †erent horizontal-branch (HB) morphologies (B[R)/(B ] V ] R) \ 0.92 for M2 and 0.08 for M3. A period shift analysis and main-sequence Ðtting show that RRab variables in M2 are about 0.2 mag brighter than those in M3. Comparisons of the M2 period shift with Oosterho † I clusters NGC 3201 and NGC 7006 also yield similar results, while a comparison between M2 and the Oosterho † II cluster NGC 5986 reveals that the RR Lyrae luminosities are very similar. The luminosity di †erence is thought to be due to the evolutionary e †ect described in 1990 by Lee, Demarque, & Zinn : the M2 RRab variables have evolved away from the zero-age horizontal branch (ZAHB), while most M3 RRab variables lie near the ZAHB. A comparison of the mean period change rates of two clusters supports this hypothesis. Our relative age estimation using the di †erence in color between the base of giant branch and turn-o † point shows that M2 is about 2 Gyr older than M3. Our result strongly suggests that the Oosterho † dichotomy is due to age di †erences between Oosterho † group I and II. This is consistent with the idea that the global second parameter is age.We discuss the kinematic di †erences between Oosterho † group I and II clusters. Our result shows that the Oosterho † group I clusters have zero or retrograde rotation with km s~1 and Sv rot T \ [68^56 km s~1, while the Oosterho † group II clusters have prograde rotation with p los \ 131^28 Sv rot T \ ]94^47 km s~1 and km s~1, conÐrming a similar conclusion of van den Bergh. The p los \ 115^29 di †erence in kinematics and ages between Oosterho † group I and II clusters suggests that they may have di †erent origins : The Oosterho † II clusters were formed very early in the proto-Galaxy while the Oosterho † I clusters were formed at di †erent locations and at a later time, and were probably merger events. The period distributions of an unbiased sample of Ðeld RRab variables with kpc and Â Z Â ¹ 3 ÂZ Â º 5 kpc indicate that they may belong to di †erent populations, with peak periods of 0.65 and 0.55 days, respectively. If the hypothesis that the Oosterho † dichotomy is due to evolution is correct, then this period shift among the Ðeld RR Lyrae variables suggests that the RRab population with kpc is Â Z Â ¹ 3 somewhat older than the RRab population with kpc. This also suggests di †erent formation his-Â Z Â º 5 tories.In an appendix, we discuss that the frequently used Gaussian HB mass-dispersion rate (i.e., the massloss rate at the red giant branch [RGB] tip) in synthetic HB model calculations cannot fully explain the extended blue HB population and the pulsational properties of RR Lyrae variables in M2. Comparisons with synthetic HB models strongly suggests that an enhanced mass loss is required that extends the HB toward lower HB masses. We also discuss statistical e †ects on the metallicity estimate using for ...

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“…Iben & Huchra 1971), whereas the convective ones were able to predict also an approximate evaluation of the effective temperature of the red edge (Tuggle & Iben 1973;Xiong et al 1998) because it is the quenching effect of convection on pulsation that determines the occurrence of the red edge. A very important result of linear non adiabatic convective models was obtained by van Albada & Baker (1971), who predicted linear relations (logarithmic scale) between the pulsation period and the stellar mass, luminosity and effective temperature for both the fundamental and the first overtone mode. These relations establish an important link between pulsational and evolutionary parameters and represented the milestone of any study aimed at investigating the evolutionary behaviour of RR Lyrae through the analysis of their pulsation characteristics.…”

Section: Linear Non-adiabatic Modelsmentioning

confidence: 96%

RR Lyrae Pulsation Theory

Marconi¹,

Guzik²,

Bradley³

2009

AIP Conference Proceedings

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Abstract. RR Lyrae stars play an important role as distance indicators and stellar population tracers. In this context the construction of accurate pulsation models is crucial to understand the observed properties and to constrain the intrinsic stellar parameters of these pulsators. The physical mechanism driving pulsation in RR Lyrae stars has been known since the middle of the 20th century and many efforts have been performed during the last few decades in the construction of more and more refined pulsation models. In particular, nonlinear pulsation models including a nonlocal time-dependent treatment of convection, such as the ones originally developed in Los Alamos in the seventies, allow us to reproduce all the relevant observables of stellar radial pulsation and to establish accurate relations and methods to contrain the intrinsic stellar properties and the distances of these variables. The most recent results on RR Lyrae pulsation obtained through these kinds of models will be presented and a few still debated problems will be discussed.

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On the Masses, Luminosities, and Compositions of Horizontal-Branch Stars

Cited by 129 publications

References 0 publications

Two populations among the metal-poor field RR Lyrae stars

Two populations among the metal-poor field RR Lyrae stars

RR Lyrae Luminosity Differences between Oosterhoff Group I and II Cluster Systems and the Origin of the Oosterhoff Dichotomy

RR Lyrae Pulsation Theory

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