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

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.

scholarly journals Galactic calibration of the tip of the red giant branch

2019 ◽  
Vol 36 ◽  
Author(s):  
Jeremy Mould ◽  
Gisella Clementini ◽  
Gary Da Costa
Keyword(s):  
Globular Clusters ◽  
Photometric System ◽  
Low Mass Stars ◽  
Rr Lyrae Stars ◽  
Geometric Calibration ◽  
Rr Lyrae ◽  
Low Mass ◽  
Red Giant ◽  
Extragalactic Distance Scale ◽  
Lyrae Stars

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.

scholarly journals Mass-Loss During the RR Lyrae Phase of the HB: Mass Dispersion on the HB and RR Lyrae Period Changes

1993 ◽  
Vol 139 ◽  
pp. 312-312
Author(s):  
Rebecca A. Koopmann ◽  
Young-Wook Lee ◽  
Pierre Demarque ◽  
Jamie M. Howard
Keyword(s):  
Mass Loss ◽  
Horizontal Branch ◽  
Constant Mass ◽  
Instability Strip ◽  
Rr Lyrae Stars ◽  
Rr Lyrae ◽  
Mass Dispersion ◽  
Low Mass ◽  
Lyrae Stars ◽  
Loss Rates

Horizontal branch (HB) models were evolved using the Yale stellar evolution code, YREC, to test the possibility that mass loss during the RR Lyrae phase is able to produce the observed color (mass) dispersion on the HB (Willson and Bowen 1984) and the anomalous period changes in RR Lyrae stars (Laskarides 1974). Models of total mass 0.64, 0.66, 0.68, 0.70, and 0.72 M⊙ (YMS = 0.23, Z = 0.001) were evolved with constant mass loss rates of 0, 10-10, and 10-9 M⊙ yr-1. Mass loss was assumed to occur only in the RR Lyrae phase, and the instability strip was defined by 3.800 < log Teff < 3.875.HB stars which lose mass evolve further to the blue. Low mass loss rates do not affect the shape of the tracks significantly. Stars, which without mass loss could not become blue HB stars, were able to emerge from the instability strip on the blue side.

On the Two Oosterhoff Groups of Globular Clusters

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.

scholarly journals The effect of stellar evolution on the light curves’ shapes of RR Lyrae stars in M3

2004 ◽  
Vol 193 ◽  
pp. 171-175
Author(s):  
Johanna Jurcsik
Keyword(s):  
Light Curve ◽  
Stellar Evolution ◽  
Light Curves ◽  
Horizontal Branch ◽  
Homogeneous Sample ◽  
Rr Lyrae Stars ◽  
Rr Lyrae ◽  
Lyrae Stars

AbstractThe light curve characteristics of a homogeneous sample of variables in M3 are studied in detail. Accurate light curves and mean magnitudes of about 100 RRab and 50 RRc stars which do not show any type of modulation are analyzed. According to their mean magnitudes and Fourier parameters the variables can be sorted into four groups, representing different stages of the horizontal branch stellar evolution.

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

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.

scholarly journals Humps and bumps: the effects of shocks on the optical light curves of fundamental-mode RR Lyrae stars

2020 ◽  
Vol 635 ◽  
pp. A66 ◽  
Author(s):  
Z. Prudil ◽  
I. Dékány ◽  
R. Smolec ◽  
M. Catelan ◽  
E. K. Grebel ◽  
...  
Keyword(s):  
Main Shock ◽  
Period Change ◽  
Light Curves ◽  
Horizontal Branch ◽  
Instability Strip ◽  
Rr Lyrae Stars ◽  
Change Rate ◽  
Rr Lyrae ◽  
Red Edge ◽  
Lyrae Stars

We present the most extended and homogeneous study carried out so far of the main and early shocks in 1485 RR Lyrae stars in the Galactic bulge observed by the Optical Gravitational Lensing Experiment. We selected nonmodulated fundamental-mode RR Lyrae stars with good-quality photometry. Using a self-developed method, we determined the centers and strengths of main and early shock features in the phased light curves. We found that the positions of both humps and bumps are highly correlated with the pulsation properties of the studied variables. Pulsators with a pronounced main shock are concentrated in the low-amplitude regime of the period–amplitude diagram, while stars with a strong early shock have average and above-average pulsation amplitudes. A connection between the main and early shocks and the Fourier coefficients is also observed. In the color–magnitude diagram, we see a separation between stars with strong and weak shocks. Variables with a pronounced main shock cluster close to the fundamental red edge of the instability strip (IS), while stars with a strong early shock tend to clump in the center and near the fundamental blue edge of the IS. The appearance of shocks and their properties appear to be independent of the direction of evolution estimated from the period change rate of the studied stars. In addition, the differences in the period change rate between the two main Oosterhoff groups found in the Galactic bulge suggest that stars of Oosterhoff type I are located close to the zero-age horizontal branch while Oosterhoff type II variables are on their way toward the fundamental red edge of the instability strip, and have therefore already left the zero-age horizontal branch.

scholarly journals Contamination of RR Lyrae stars from Binary Evolution Pulsators

2015 ◽  
Vol 5 (1) ◽  
pp. 24-28
Author(s):  
P. Karczmarek
Keyword(s):  
Mass Transfer ◽  
Binary System ◽  
Synthesis Method ◽  
Population Synthesis ◽  
Rr Lyrae Stars ◽  
Rr Lyrae ◽  
Low Mass ◽  
Binary Evolution ◽  
Lyrae Stars ◽  
Range Of Values

A Binary Evolution Pulsator (BEP) is a low-mass (0.26 𝔐☉) member of a binary system, which pulsates as a result of a former mass transfer to its companion. The BEP mimics RR Lyrae-type pulsations, but has completely different internal structure and evolution history. Although there is only one known BEP (OGLE-BLG-RRLYR-02792), it has been estimated that approximately 0.2% of objects classified as RR Lyrae stars can be undetected Binary Evolution Pulsators. In the present work, this contamination value is re-evaluated using the population synthesis method. The output falls inside a range of values dependent on tuning the parameters in the StarTrack code, and varies from 0.06% to 0.43%.

scholarly journals RR Lyrae Stars in the Globular Cluster NGC 6101

2012 ◽  
Vol 29 (1) ◽  
pp. 72-77 ◽  
Author(s):  
M. T. Fitzgerald ◽  
J. Criss ◽  
T. Lukaszewicz ◽  
D. J. Frew ◽  
M. Catelan ◽  
...  
Keyword(s):  
Secondary School ◽  
Globular Cluster ◽  
High Ratio ◽  
School Students ◽  
Rr Lyrae Stars ◽  
Rr Lyrae ◽  
Upper Secondary ◽  
Independent Estimate ◽  
Red Giant ◽  
Lyrae Stars

AbstractV- and I-band observations were taken over 9 months to study the RR Lyrae population in the metal-poor diffuse globular cluster NGC 6101. We identify one new variable, which is either a potential long-period red giant variable or eclipsing binary, and recover all previously identified RR Lyraes. One previously studied RR Lyrae is reclassified as an RRc type, while two period estimations have been significantly refined. We confirm that NGC6101 is Oosterhoff type II with a high ratio of n(c)/n(ab + c) = 0.833 with a very long mean RRab period of 0.86 d. By using theoretical RRLyrae period-luminosity-metallicity relations, we use our V- and I-band RR Lyrae data to gain an independent estimate of the reddening towards this cluster of E(B − V) = 0.15 ± 0.04 and derive a distance of 12.8 ± 0.8 kpc. The majority of the work in this study was undertaken by upper secondary school students involved in the Space to Grow astronomy education project in Australia.

scholarly journals Period Changes of RR Lyrae Stars in the LMC Globular Cluster NGC 2257

1984 ◽  
Vol 108 ◽  
pp. 39-40 ◽  
Author(s):  
James M. Nemec ◽  
Martha H. Liller ◽  
James E. Hesser
Keyword(s):  
Physical Properties ◽  
Globular Cluster ◽  
Period Change ◽  
Stellar Systems ◽  
Horizontal Branch ◽  
Rr Lyrae Stars ◽  
Rr Lyrae ◽  
Horizontal Branch Stars ◽  
Lyrae Stars

The period changes of RR Lyrae stars can be compared with models of horizontal branch stars as a means of investigating the physical properties of the stars themselves, and of the stellar systems in which they are found (Smith and Sandage 1981). The present study is the first in which period change rates of extragalactic RR Lyraes have been estimated.

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