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.

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 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 The Instability Strip of M3

2000 ◽  
Vol 176 ◽  
pp. 255-256 ◽  
Author(s):  
G. Á. Bakos ◽  
J. Jurcsik
Keyword(s):  
Globular Cluster ◽  
Horizontal Branch ◽  
Instability Strip ◽  
Ccd Photometry ◽  
Perfect Agreement ◽  
Rr Lyrae Stars ◽  
Precise Position ◽  
Rr Lyrae ◽  
Lyrae Stars ◽  
Theoretical Results

AbstractWe present new multicolour CCD photometry of the central part of the globular cluster M3, mapping the precise position of ~ 120 RR Lyrae stars (RRab, RRd, RRc) on the horizontal branch (HB). The location of the double-mode variables (RRd) is in perfect agreement with recent theoretical results. We find a significant internal spread of metallicity amongst the RRab variables.

scholarly journals Classical Cepheids: Period Changes and Mass Loss

1985 ◽  
Vol 82 ◽  
pp. 67-70
Author(s):  
H. Deasy
Keyword(s):  
Mass Loss ◽  
Secular Variation ◽  
Separate Study ◽  
Instability Strip ◽  
Rr Lyrae Stars ◽  
Rr Lyrae ◽  
Classical Cepheids ◽  
Random Fluctuations ◽  
Lyrae Stars

The period is an ideal parameter for monitoring minute changes in the structure of a star passing through the instability strip, as it can be measured with an accuracy of up to one part per million. The view of Parenago (1956) that only abrupt period changes occur in cepheids is no longer prevalent, and it is generally accepted that random period changes are superposed on the secular variation due to evolution. One possible mechanism for the random fluctuations in period or phase is convection or semiconvection, which Sweigert & Renzini (1979) showed could account for the period changes of RR Lyrae stars. Other mechanisms include the influence of binary companions and mass loss. The latter mechanism forms the basis for a separate study involving the use of IUE spectra to search for evidence of matter being ejected from cepheids.

scholarly journals The Unusual Period Distribution of the RR Lyrae Variables in NGC 5897

1989 ◽  
Vol 111 ◽  
pp. 287-287
Author(s):  
Amelia Wehlau
Keyword(s):  
Light Curves ◽  
Instability Strip ◽  
Rr Lyrae Stars ◽  
Rr Lyrae ◽  
Period Distribution ◽  
Unusual Distribution ◽  
Photoelectric Observations ◽  
Lyrae Stars ◽  
Branch Star ◽  
Central Concentration

AbstractAttention is called to the rather unusual distribution of the periods of the RR Lyrae variables in NGC 5897, a metal-poor halo globular cluster with a very low central concentration. Of the seven RR Lyrae stars known in the cluster, three have periods between 0.797 and 0.856 day and two have periods of 0.45 and 0.42 day. The other two have periods of 0.34 and 0.35 day with much lower amplitudes of variation. Due to the lack of crowding in this cluster photoelectric observations and Fourier decompositions of the resulting light curves should be possible for at least six of the RR Lyrae variables. In addition, the cluster appears to contain a non-variable horizontal branch star, SK 120, lying within the instability strip. As this is the only well documented case of such a star, photoelectric observations of this star would also be desirable.

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 Convective effects and the RR lyrae instability strip

1984 ◽  
Vol 105 ◽  
pp. 461-463
Author(s):  
R. F. Stellingwerf
Keyword(s):  
Nonlinear Behavior ◽  
Instability Strip ◽  
Unstable Region ◽  
Rr Lyrae Stars ◽  
Rr Lyrae ◽  
Red Edge ◽  
Diffusive Convection ◽  
Structure Equations ◽  
Lyrae Stars

The effects of nonlinear, nonlocal, diffusive convection have been included in the structure equations of pulsational hydrodynamic analyses of a series of RR Lyrae models. We find a well-defined red edge of the unstable region that depends on mode of pulsation. It is shown that this result has strong implications for the nonlinear behavior of RR Lyrae stars.

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