scholarly journals Masses of c-type RR Lyrae Variables in Globular Clusters

1993 ◽  
Vol 139 ◽  
pp. 324-324
Author(s):  
C. Cacciari ◽  
A. Bruzzi
Keyword(s):  
Stellar Evolution ◽  
Globular Clusters ◽  
Stellar Mass ◽  
Type I ◽  
Pulsation Period ◽  
Rr Lyrae ◽  
Stellar Pulsation ◽  
Controversial Problem ◽  
The One ◽  
Image Position

The mass of RR Lyrae variables has been a controversial problem for about a decade: while the stellar evolution theory predicts masses ranging between 0.65 and 0.75 M⊙ for Oosterhoff type I and II clusters respectively, the stellar pulsation theory predicts smaller masses (0.55 and 0.65 respectively) using the double-mode pulsators. Simon (1990, M.N.R.A.S. 246, 70), comparing hydrodynamical models with observed stars by means of Fourier parameters, has found relations between the stellar mass and its luminosity, pulsation period, Helium content and Fourier parameter ϕ31. Combining his equations we obtain:(1)from which one can estimate the stellar mass by using the observable quantities P and ϕ31 and a luminosity scale, e.g. the one derived by Cacciari, Clementini and Fernley (1992, Astrophys. J. in press).

scholarly journals Pulsation Period Change & Classical Cepheids: Probing the Details of Stellar Evolution

2014 ◽  
Vol 9 (S307) ◽  
pp. 224-225
Author(s):  
Hilding R. Neilson ◽  
Alexandra C. Bisol ◽  
Ed Guinan ◽  
Scott Engle
Keyword(s):  
Mass Loss ◽  
Real Time ◽  
Stellar Evolution ◽  
Stellar Mass ◽  
Period Change ◽  
Pulsation Period ◽  
Instability Strip ◽  
Loss Mechanism ◽  
Stellar Pulsation ◽  
Classical Cepheids

AbstractMeasurements of secular period change probe real-time stellar evolution of classical Cepheids making these measurements powerful constraints for stellar evolution models, especially when coupled with interferometric measurements. In this work, we present stellar evolution models and measured rates of period change for two Galactic Cepheids: Polaris and l Carinae, both important Cepheids for anchoring the Cepheid Leavitt law (period-luminosity relation). The combination of previously-measured parallaxes, interferometric angular diameters and rates of period change allows for predictions of Cepheid mass loss and stellar mass. Using the stellar evolution models, We find that l Car has a mass of about 9 M⊙ consistent with stellar pulsation models, but is not undergoing enhanced stellar mass loss. Conversely, the rate of period change for Polaris requires including enhanced mass-loss rates. We discuss what these different results imply for Cepheid evolution and the mass-loss mechanism on the Cepheid instability strip.

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 Semiconvection and the RR Lyrae Variables

1973 ◽  
Vol 21 ◽  
pp. 221-228
Author(s):  
A. V. Sweigart ◽  
P. Demarque
Keyword(s):  
Time Scale ◽  
Globular Clusters ◽  
Pulsation Period ◽  
Horizontal Branch ◽  
Composition Distribution ◽  
Rates Of Change ◽  
Rr Lyrae ◽  
Horizontal Branch Stars ◽  
Convective Core ◽  
Source Models

Theoretical computations (Hoyle and Schwarzschild, 1955; Faulkner, 1966; Iben and Rood, 1970; Demarque and Mengel, 1971a, b) have identified the horizontal-branch stars in globular clusters with the evolution phase in which helium burns within a convective core and hydrogen burns in a shell outside the convective core. Most computations for such double-energy-source models have indicated that the evolution proceeds smoothly on a nuclear time scale during the horizontal-branch phase, leading to small predicted rates of change in the RR Lyrae pulsation period (Iben and Rood, 1970). Sweigart and Demarque (1972) have recently considered the effects of semiconvection on the horizontal-branch evolution of typical Population II stars and have suggested that changes in the composition distribution within the core may occur on a time scale considerably shorter than the nuclear time scale during the phase immediately preceding core-helium exhaustion. It has been found that the composition distribution generated by the growth of a semiconvective zone in the layers surrounding the convective core can become unstable when Yc, the helium abundance within the convective core, decreases below roughly 0.12. The changes in the internal structure caused by this instability result in relatively rapid movement of the models in the HR diagram and consequently produce large predicted rates of change in the RR Lyrae pulsation period. The possibility that RR Lyrae period changes may be associated with the behavior of the semiconvective zone has been previously suggested by Schwarzschild (1970). A similar instability may occur in the late core-hydrogen burning phase for stars around 10 M⊙. Percy (1970) has noted the coincidence of β Cephei stars with stellar models containing semiconvective zones. It is tempting to suggest that such an instability in the semiconvective zone could also be related to the β Cephei phenomenon.

scholarly journals Low Amplitude New Type Variable Stars in Globular Clusters

1993 ◽  
Vol 134 ◽  
pp. 163-165
Author(s):  
Yao Bao-An ◽  
Zhang Chung-Sheng ◽  
Qin Dao ◽  
Tong Jian-Hua
Keyword(s):  
Globular Clusters ◽  
Variable Stars ◽  
Instability Strip ◽  
Rr Lyrae Stars ◽  
Rr Lyrae ◽  
Stellar Pulsation ◽  
Type Variable ◽  
New Type ◽  
New Challenges ◽  
Low Amplitude

Rapid progress in the stellar pulsation research has presented many new challenges to traditional pulsation theory. The following progress made by us should belong to one of the new challenges: 1)There are many variable stars located at the Horizontal Branch (HB) but outside the instability strip with amplitude larger than 0.02 mag.Maybe some astronomers have already doubted of the 1950’s conclusion-the RR Lyrae stars are confined to the narrow instability strip in the C-M diagram, the boundaries of the gap are extremely sharp and definite, beyond the edges no light variations occur with ranges greater than 0.02 mag. We are changing the conclusion by observations. Here we do not mean the microvariability. We still raise the question from the classical viewpoint. We want to show that there are variable stars outside the strip with peak to peak amplitudes larger than 0.02 mag.

scholarly journals The Helium Abundance in the Envelopes of the Bluest RR Lyrae Stars in Globular Clusters and Dependence of Globular Cluster Variable Star Properties on Chemical Composition

1973 ◽  
Vol 21 ◽  
pp. 229-234
Author(s):  
A. V. Mironov
Keyword(s):  
Chemical Composition ◽  
Globular Clusters ◽  
Variable Star ◽  
Variable Stars ◽  
Type I ◽  
Helium Abundance ◽  
Type Ii ◽  
Rr Lyrae Stars ◽  
Rr Lyrae ◽  
Lyrae Stars

AbstractThe helium abundance Y in the envelopes of RR Lyrae stars in globular clusters has been estimated. The values of Y range from 0.07 to 0.59. The properties of variable stars in globular clusters of two types distinguished by a type of dependence of the horizontal branch form on the chemical composition are compared. The clusters of type I are shown to be on the average poorer in RR Lyrae stars than those of type II. The RR Lyrae stars in type I clusters are on the average brighter by 0.1 mag. It is found that as Y increases, the cluster richness in W Virginis variables decreases.

scholarly journals Amplitude of RR Lyrae Star Light Curves: Comparison between Observations and One—Zone Model Predictions

1993 ◽  
Vol 139 ◽  
pp. 339-339
Author(s):  
E. Antonello ◽  
S. Cermiti
Keyword(s):  
Short Note ◽  
High Amplitude ◽  
Zone Model ◽  
Atmospheric Models ◽  
Rr Lyrae ◽  
Stellar Pulsation ◽  
Model Predictions ◽  
The One ◽  
Scuti Stars ◽  
Present Poster

Stellingwerf's one–zone model is a simple and useful tool for reproducing the main observed pulsational characteristics of RR Lyrae and high amplitude δScuti stars, in particular their light and color curves (Stellingwerf et al., 1987, Ap.J.313, L75; Antonello, 1990, Astr. Ap.230, 127). In the present poster we show in better detail a comparison of the observed amplitudes of the light curve at various wavelengths with those predicted by the one–zone model; a preliminary result on this subject was reported in the short note by Grieco and Antonello (1990, in Confrontation between Stellar Pulsation and Evolution p. 101). As in the previous applications, here we use the published grids of atmospheric models (Kurucz, 1979, Ap.J.Suppl. 40, 1) and we do not consider possible shock effects.

scholarly journals IR characteristics of Type II Cepheids in the LMC and in the Galaxy

1991 ◽  
Vol 148 ◽  
pp. 109-111
Author(s):  
C. David Laney
Keyword(s):  
Globular Clusters ◽  
Distance Modulus ◽  
Type I ◽  
Type Ii ◽  
Normal Type ◽  
Rr Lyrae Stars ◽  
Galactic Field ◽  
Rr Lyrae ◽  
The Galaxy ◽  
Lyrae Stars

JHK observations have been obtained of Type II Cepheids in the LMC, in globular clusters, and in the galactic field. The P-L relations at J and H imply an LMC distance modulus consistent with Mv˜0.6 for RR Lyrae stars. Modest excesses at K are seen in some LMC objects. One previously reported LMC Type II Cepheid appears to be a Type I Cepheid, and two others are much redder in J-H than normal Type II Cepheids. HV11211 is a Type I Cepheid in the SMC.

scholarly journals Gaia Data Release 2

2019 ◽  
Vol 622 ◽  
pp. A60 ◽  
Author(s):  
G. Clementini ◽  
V. Ripepi ◽  
R. Molinaro ◽  
A. Garofalo ◽  
T. Muraveva ◽  
...  
Keyword(s):  
Time Series ◽  
Fundamental Mode ◽  
Globular Clusters ◽  
Pulsation Period ◽  
Rr Lyrae Stars ◽  
Rr Lyrae ◽  
Classical Cepheids ◽  
Data Release ◽  
Lyrae Stars ◽  
Multi Band

Context. The Gaia second Data Release (DR2) presents a first mapping of full-sky RR Lyrae stars and Cepheids observed by the spacecraft during the initial 22 months of science operations. Aims. The Specific Objects Study (SOS) pipeline, developed to validate and fully characterise Cepheids and RR Lyrae stars (SOS Cep&RRL) observed by Gaia, has been presented in the documentation and papers accompanying the Gaia first Data Release. Here we describe how the SOS pipeline was modified to allow for processing the Gaia multi-band (G, GBP, and GRP) time-series photometry of all-sky candidate variables and produce specific results for confirmed RR Lyrae stars and Cepheids that are published in the DR2 catalogue. Methods. The SOS Cep&RRL processing uses tools such as the period–amplitude and the period–luminosity relations in the G band. For the analysis of the Gaia DR2 candidates we also used tools based on the GBP and GRP photometry, such as the period–Wesenheit relation in (G, GRP). Results. Multi-band time-series photometry and characterisation by the SOS Cep&RRL pipeline are published in Gaia DR2 for 150 359 such variables (9575 classified as Cepheids and 140 784 as RR Lyrae stars) distributed throughout the sky. The sample includes variables in 87 globular clusters and 14 dwarf galaxies (the Magellanic Clouds, 5 classical and 7 ultra-faint dwarfs). To the best of our knowledge, as of 25 April 2018, the variability of 50 570 of these sources (350 Cepheids and 50 220 RR Lyrae stars) has not been reported before in the literature, therefore they are likely new discoveries by Gaia. An estimate of the interstellar absorption is published for 54 272 fundamental-mode RR Lyrae stars from a relation based on the G-band amplitude and the pulsation period. Metallicities derived from the Fourier parameters of the light curves are also released for 64 932 RR Lyrae stars and 3738 fundamental-mode classical Cepheids with periods shorter than 6.3 days.

scholarly journals Horizontal Branch Evolution and RR Lyrae Star Pulsation

1995 ◽  
Vol 10 ◽  
pp. 590-593 ◽  
Author(s):  
Arthur N. Cox
Keyword(s):  
Stellar Evolution ◽  
Globular Clusters ◽  
Deep Convection ◽  
Big Bang ◽  
Helium Abundance ◽  
Horizontal Branch ◽  
Rr Lyrae ◽  
Red Giant ◽  
The Masses ◽  
The Big Bang

For many years there has been a confrontation between stellar evolution and pulsation theories concerning the masses, luminosities, and compositions of the horizontal branch RR Lyrae variables. Masses obtained by Cox, Hodson & Clancy (CHC, 1983) were very low, but Kovacs (1985) and later Kovacs & Buchler (1988) suggested somewhat larger ones. Even later Simon & Cox (1991) verified CHC results, though still using the Los Alamos opacities. Petersen (1991, 1992) has also discussed this mass problem in some detail. The persistent discrepancy of 0.1 Mʘ or more between the evolution and pulsation masses was mostly ignored because neither theory could find any significant flaw in its analysis. Cox (1991), Kovacs, Buchler & Marom (1991), and Kovacs, Buchler, Marom, Iglesias & Rogers (1992) finally showed that larger double-mode pulsation masses, are consistent with evolution calculations to reproduce color-magnitude diagrams of globular clusters. Evolution tracks by many for years, especially the recent ones by Lee, Demarque & Zinn (1990), did require a much lower primordial helium abundance near the big bang value near Y = 0.23, and now this value, slightly enhanced by deep convection dredge-up in the earlier red giant stage, is also found to be appropriate for pulsation studies.

scholarly journals The First Billion Years project: Finding infant globular clusters at z = 6

2020 ◽  
Vol 641 ◽  
pp. A132 ◽  
Author(s):  
Frederika Phipps ◽  
Sadegh Khochfar ◽  
Anna Lisa Varri ◽  
Claudio Dalla Vecchia
Keyword(s):  
Globular Clusters ◽  
High Redshift ◽  
Formation Rate ◽  
Stellar Mass ◽  
Mass Relation ◽  
Stellar Content ◽  
Host Galaxies ◽  
Cosmological Simulations ◽  
Satisfactory Description ◽  
The One

Aims. We aim to conduct an assessment of the demographics of substructures in cosmological simulations to identify low-mass stellar systems at high redshift, with a particular focus on globular cluster (GC) candidates. Methods. We explored a suite of high-resolution cosmological simulations from the First Billion Years Project (FiBY) at z ≥ 6. All substructures within the simulations have been identified with the SUBFIND algorithm. From our analysis, two distinct groups of objects emerge. We hypothesise that the substructures in the first group, which appear to have a high baryon fraction (fb ≥ 0.95), are possible infant GC candidates. Objects belonging to the second group have a high stellar fraction (f* ≥ 0.95) and show a potential resemblance to infant ultra-faint dwarf galaxies. Results. The high baryon fraction objects identified in this study are characterised by a stellar content similar to the one observed in present-day GCs, but they still contain a high gas fraction (fgas ∼ 0.95) and a relatively low amount of dark matter. They are compact systems, with densities higher than the average population of FiBY systems at the same stellar mass. Their sizes are consistent with recent estimates based on the first observations of possible proto-GCs at high redshifts. These types of infant GC candidates appear to be more massive and more abundant in massive host galaxies, indicating that the assembly of galaxies via mergers may play an important role in building several GC-host scaling relations. Specifically, we express the relation between the mass of the most massive infant GC and its host stellar mass as log(Mcl) = (0.31 ± 0.15) log (M*, gal + (4.17 ± 1.06). We also report a new relation between the most massive infant GC and the parent specific star formation rate of the form log(Mcl) = (0.85 ± 0.30) log (sSFR)+α that describes the data at both low and high redshift. Finally, we assess the present-day GC mass (GC number) – halo mass relation offers a satisfactory description of the behaviour of our infant GC candidates at high redshift, suggesting that such a relation may be set at formation.

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