The red edge of the instability strip of RR Lyrae stars

1982 ◽  
Vol 6 (1) ◽  
pp. 43-48 ◽  
Author(s):  
Xiong Da-run
Keyword(s):  
Instability Strip ◽  
Rr Lyrae Stars ◽  
Rr Lyrae ◽  
Red Edge ◽  
Lyrae Stars

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.

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 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.

Theoretical Problems of Beta Cephei Stars

1979 ◽  
Vol 46 ◽  
pp. 467-473
Author(s):  
Yoji Osaki
Keyword(s):  
Small Group ◽  
Spectral Type ◽  
Main Sequence ◽  
Massive Stars ◽  
Instability Strip ◽  
Rr Lyrae Stars ◽  
Rr Lyrae ◽  
M 10 ◽  
Classical Cepheids ◽  
Lyrae Stars

The Beta Cephei (or Beta Canis Majoris) stars are a small group of pulsating variables of early spectral type. There are some 20 “classical” β Cephei stars, and several new or suspected variables in this group. The classical β Cephei stars are confined in a narrow “instability strip” which lies about 1 mag above and nearly parallel to the zero-age main-sequence of massive stars (M~10-20 M⊙). They are thus located far away from other well-known pulsating variables such as classical Cepheids and RR Lyrae stars in the HR diagram.

scholarly journals Hydrodynamic Simulations of Convection

2002 ◽  
Vol 185 ◽  
pp. 458-459
Author(s):  
S.M. Asida
Keyword(s):  
Instability Strip ◽  
Rr Lyrae Stars ◽  
Hydrodynamic Simulations ◽  
Numerical Resolution ◽  
Rr Lyrae ◽  
Non Local ◽  
The Common ◽  
Red Giant ◽  
Mixing Length Theory ◽  
Lyrae Stars

Convection is one of the most problematic components of almost every model of a pulsating star. RR Lyrae stars, in particular, have a narrow convection zone at the outer layers, and a model without convection cannot get the red edge of the instability strip (see for example Kollath et al., 2000).In recent years, the common approach is to use non-local time-dependent extensions to the Mixing Length Theory of convection (Bono et al., 1997; Feuchtinger, 1999). These models have many free parameters that need to be calibrated. In this paper we report on a preliminary work in which a different approach is used: 2D hydro simulations similar to the red giant model in Asida (2000). This approach was used by Deupree (1975, 1977) but we used a much better numerical resolution and focused on comparison with MLT results.

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 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 Period Changes of RR Lyrae Stars in Globular Clusters

1975 ◽  
Vol 67 ◽  
pp. 545-552 ◽  
Author(s):  
B. Szeidl
Keyword(s):  
Globular Clusters ◽  
Evolutionary Track ◽  
Instability Strip ◽  
Rr Lyrae Stars ◽  
Rr Lyrae ◽  
Lyrae Stars

The dependence of the period changes of RR Lyrae stars, especially in globular clusters, on the evolutionary track through the instability strip has still found no explanation. The present paper is an attempt to give a review of the observed phenomena.

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