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 A survey of RR Lyrae models

1993 ◽  
Vol 139 ◽  
pp. 262-262
Author(s):  
G. Bono ◽  
R.F. Stellingwerf
Keyword(s):  
Convective Transport ◽  
Time Dependent ◽  
Instability Strip ◽  
Rr Lyrae Stars ◽  
Rr Lyrae ◽  
Non Linear ◽  
Non Local ◽  
Lyrae Stars

AbstractAn extensive grid of non-linear pulsating models of RR Lyrae stars have been computed. To simulate the outer regions of these variables a non-local and time-dependent treatment of convective transport has been adopted. In this poster we briefly describe some new features of the instability strip (IS).

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.

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.

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 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 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 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.

Sign in / Sign up

Export Citation Format

Share Document