Absolute Magnitude of RR Lyrae in Globular Clusters from Pulsational Properties

2000 ◽  
pp. 269-274
Author(s):  
V. Ripepi ◽  
F. Caputo ◽  
V. Castellani ◽  
M. Marconi
Keyword(s):  
Globular Clusters ◽  
Absolute Magnitude ◽  
Rr Lyrae

scholarly journals The Absolute Magnitudes of RR Lyrae Stars and the Age of the Galaxy

1989 ◽  
Vol 111 ◽  
pp. 121-140
Author(s):  
Allan Sandage
Keyword(s):  
Globular Cluster ◽  
Globular Clusters ◽  
Main Sequence ◽  
Absolute Magnitude ◽  
Cluster System ◽  
Apparent Magnitude ◽  
Rr Lyrae ◽  
Globular Cluster System ◽  
The Absolute ◽  
Absolute Magnitudes

AbstractIt is shown that the intrinsic spread in the absolute magnitudes of the RR Lyrae variables in a given globular cluster can reach 0.5 magnitudes at a given period or at a given color, due to luminosity evolution away from the zero age horizontal (ZAHB). The size of this intrinsic luminosity spread is largest in clusters of the highest metallicity.The absolute magnitude of the ZAHB itself also differs from cluster to cluster as a function of metallicity, being brightest in clusters of the lowest metallicity. Three independent methods of calibrating the ZAHB RR Lyrae luminosities each show a strong variation of MV(RR) with [Fe/H]. The pulsation equation of P<ρ>0.5 = Q(M,Te, L) used with the observed periods, temperatures, and masses of field and of cluster RR Lyraes gives the very steep luminosity-metallicity dependence of dMv(RR)/d[Fe/H] = 0.42. Main sequence fitting of the color-magnitude diagrams of clusters which have modern main-sequence photometry gives a confirming steep slope of 0.39. A summary of Baade-Wesselink MV(RR) values for field stars determined in four independent recent studies also shows a luminosity-metallicity dependence, but less steep with a slope of dMV(RR)/d[Fe/H] = 0.21.Observations show that the magnitude difference between the main sequence turn-off point and the ZAHB in a number of well observed globular clusters is independent of [Fe/H], and has a stable value of dV = 3.54 with a disperion of only 0.1 magnitudes. Using this fact, the absolute magnitude of the main sequence turn-off is determined in any given globular cluster from the observed apparent magnitude of the ZAHB by adopting any particular MV(RR) = f([Fe/H]) calibration.Ages of the clusters are shown to vary with [Fe/H] by amounts that depend upon the slopes of the MV(RR) = f([Fe/H]) calibrations. The calibrations show that there would be a steep dependence of the age on [Fe/H] if MV(RR) does not depend on [Fe/H]. No dependence of age on metallicity exists if the RR Lyrae luminosities depend on [Fe/H] as dMV(RR)/d[Fe/H] = 0.37. If Oxygen is not enhanced as [Fe/H] decreases, the absolute average age of the globular cluster system is 16 Gyr, independent of [Fe/H], using the steep MV(RR)/[Fe/H] calibration that is favored. If Oxygen is enhanced by [O/Fe] = – 0.14 [Fe/H] + 0.40 for [Fe/H] < –1.0, as suggested from the observations of field subdwarfs, then the age of the globular cluster system decreases to 13 Gyr, again independent of [Fe/H], if the RR Lyrae ZAHB luminosities have a metallicity dependence of dMV(RR)/d[Fe/H] = 0.37.

scholarly journals Observational Aspects of RR Lyrae Variables in Globular Clusters

1973 ◽  
Vol 21 ◽  
pp. 51-67 ◽  
Author(s):  
L. Rosino
Keyword(s):  
Globular Clusters ◽  
Absolute Magnitude ◽  
Good Test ◽  
Rr Lyrae Stars ◽  
Pulsating Stars ◽  
Rr Lyrae ◽  
Powerful Means ◽  
The Galaxy ◽  
Points Of View ◽  
Lyrae Stars

RR Lyrae variables play a prominent role in many of the problems of globular clusters, and from several points of view. In the first place they can be considered as pretty good indicators of population and distance; although they do not form a completely homogeneous set of stars, the knowledge of their mean absolute magnitude gives a powerful means of establishing distances within and outside the Galaxy, and hence of determining the form and size of the Galaxy itself. Moreover, the number of RR Lyrae stars in clusters, the relative frequency of RRc and RRab, types, the length of the transition periods, the array of colors, when correctly interpreted, give important information on the degree of evolution, age and chemical composition of the clusters. Placed as they are in a peculiar region of the H — R diagram of Population II, the RR Lyr variables can be used as a good test of the theories of advanced evolution or the models of pulsating stars.

The Luminosity-Metallicity Relation for RR Lyrae Stars and its Implications for the Astronomical Distance Scale

1989 ◽  
Vol 111 ◽  
pp. 255-255
Author(s):  
G. Clementini ◽  
C. Cacciari
Keyword(s):  
Globular Clusters ◽  
Galactic Center ◽  
Absolute Magnitude ◽  
Rr Lyrae Stars ◽  
Rr Lyrae ◽  
Visual Magnitude ◽  
Phase Range ◽  
The Absolute ◽  
Lyrae Stars ◽  
Magnitude Difference

AbstractThe surface brightness version of the Baade-Wesselink method, has been applied to 7 field RR Lyrae stars with metallicity ranging from [Fe/H]= −0.2 to −1.5. V magnitudes, V-R and V-I colors and CORAVEL radial velocities were used, and the analysis was performed over a restricted phase range in order to avoid the complications caused by the pulsating atmospheres. The combination with previous results of the B-W method, which used comparable criteria (Jones, Carney, & Latham, 1988, preprint; Jameson, Fernley, & Longmore 1987, in press M.N.R.A.S; Cohen & Gordon 1987, Ap.J., 318, 215) leads to the following relation between the absolute luminosity and metallicity:Mv = (1.0 ± 0.05) + (0.17 ± 0.05) [Fe/H]This relation is in very good agreement with the preliminary results found by Liu and Janes (this volume). The application of the above relation to the RR Lyraes in M31 and the Magellanic Clouds leads to distance moduli of (m–M)o= 24.21 ± 0.20 for M31, (m–M)o = 18.26 ± 0.20 for the LMC, and (m–M)o =18.85 ± 0.20 for the SMC, and the distance to the galactic center turns out to be approximately 7.2 kpc. From the absolute magnitude of the RR Lyraes and adopting a constant visual magnitude difference between the RR Lyraes and the turn-off ΔV = 3.55 (Buonanno 1986, Mem.S.A.It., 57, 333), we estimate ages of 18.8 and 15.7 Gyr for globular clusters of metallicity [Fe/H] = −2.2 (e.g. M92) and [Fe/H] = −0.8 (e.g. 47 Tuc) respectively, using the age-turnoff luminosity relation derived by Sandage (1982, Ap.J., 252, 553) or 20.9 and 16.9 Gyr using Buonanno’s relation.

scholarly journals Variable Stars and Evolution in Globular Clusters

1973 ◽  
Vol 21 ◽  
pp. 187-195
Author(s):  
Pierre Demarque
Keyword(s):  
Globular Clusters ◽  
Main Sequence ◽  
Absolute Magnitude ◽  
Variable Stars ◽  
Rr Lyrae Stars ◽  
The Past ◽  
Rr Lyrae ◽  
Lyrae Stars ◽  
Distance Indicators

Traditionally, cluster variables have been used as distance indicators and have in this sense played an important role in our understanding of stellar evolution. In particular, the determination of the distance moduli of globular clusters and of the absolute magnitude of the main sequence turnoff, thus yielding the ages of the cluster, have relied heavily in the past on observations of RR Lyrae stars.

scholarly journals The Luminosities of Horizontal Branches and RR Lyrae Stars in Globular Clusters

2004 ◽  
Vol 193 ◽  
pp. 525-529 ◽  
Author(s):  
D.H. McNamara ◽  
M.B. Rose ◽  
P.J. Brown ◽  
D.I. Ketcheson ◽  
J.E. Maxwell ◽  
...  
Keyword(s):  
Globular Clusters ◽  
Absolute Magnitude ◽  
Apparent Magnitude ◽  
Rr Lyrae Stars ◽  
Blue Stragglers ◽  
Rr Lyrae ◽  
The Absolute ◽  
The Difference ◽  
Absolute Magnitudes ◽  
Lyrae Stars

AbstractWe have utilized the latest stellar models of the Y2 (Yonsei-Yale) collaborators and color-magnitude diagrams of globular clusters to infer ages and absolute magnitudes of their horizontal branches (HB). The intrinsic (B – V) color indices of the turn-offs, of the globular clusters were used to find ages. For 47 clusters that appear to be coeval (within ±0.7 Gyr), we find an average age of 12.5 Gyr. We adopt this age and infer the absolute magnitudes of the turn-offs, from the clusters [Fe/H] values. The absolute magnitude of the horizontal branches or RR Lyrae stars are then determined from the difference between the apparent magnitudes of the horizontal branches (or RR Lyrae stars) and the apparent magnitude of the turn-offs, VTO. We conclude: 1) The slope of the MV(HB), [Fe/H] relation is ~0.3 for clusters with [Fe/H] values between —0.5 to —1.5. The relation has zero slope for [Fe/H] values smaller than −1.5. 2) For [Fe/H] < -1.3, the MV(HB) or MV values of RRLyrae stars are not only a function of [Fe/H], but the horizontal-branch type in the sense that the clusters with the blue horizontal branches have more luminous horizontal branches than clusters with red horizontal branches. The same results are found by inferring the luminosities of the HBs from pulsating blue stragglers.

scholarly journals RR Lyrae Stars in the Globular NGC 3201: Light Curves, Reddening, and Distance

2002 ◽  
Vol 185 ◽  
pp. 122-123
Author(s):  
Andrew Layden
Keyword(s):  
Globular Clusters ◽  
Absolute Magnitude ◽  
Progress Report ◽  
Light Curves ◽  
High Quality ◽  
Rr Lyrae Stars ◽  
Rr Lyrae ◽  
Standard Candle ◽  
Trigonometric Parallaxes ◽  
Lyrae Stars

RR Lyrae stars (RRL) are a favourite standard candle for globular clusters and other old stellar populations, yet recent absolute magnitude calibrations, MV(RR), span more than 0.2 mag. Precise distance estimates for nearby globular clusters will eventually be available through satellite-based trigonometric parallaxes (Layden, these proceedings), thus providing a resolution to this old problem.Here, we present a progress report on our high quality time-series photometry of RRL in the nearby globular cluster NGC 3201 - the first obtained for this cluster with a CCD. The resulting light curves provide accurate intensity-mean apparent magnitudes and reddening estimates, which will in turn be used to calibrate MV(RR) once a satellite-based parallax for NGC 3201 is available.

scholarly journals On the Existence of Luminosity Differences between HB Field and Cluster Stars

2000 ◽  
Vol 176 ◽  
pp. 265-265
Author(s):  
E. Carretta ◽  
R. G. Gratton ◽  
G. Clementini
Keyword(s):  
Globular Clusters ◽  
Main Sequence ◽  
Absolute Magnitude ◽  
Distance Scale ◽  
Horizontal Branch ◽  
Rr Lyrae Stars ◽  
Rr Lyrae ◽  
Intrinsic Difference ◽  
General Field ◽  
Lyrae Stars

AbstractThe discrepancy between the long distance scale as derived, e.g., from Hipparcos-based distances to globular clusters via main sequence fitting to local subdwarfs, and the short distance scale as derived, e.g., from the absolute magnitude of field RR Lyrae stars via statistical parallaxes and the Baade–Wesselink method, could be accounted for if an intrinsic difference in luminosity of about 0.1−0.2 mag were found to exist between horizontal branch (HB) stars populating the sparse general field and the dense globular clusters.

scholarly journals The Period-Luminosity Relation for Cepheids in Globular Clusters

1973 ◽  
Vol 21 ◽  
pp. 180-184
Author(s):  
B. V. Kukarkin ◽  
A. S. Rastorgouev
Keyword(s):  
Globular Clusters ◽  
Apparent Distance ◽  
Absolute Magnitude ◽  
Rr Lyrae ◽  
Method Of Determination ◽  
The Absolute ◽  
Absolute Magnitudes

The period-luminosity relation for Cepheids in globular clusters has been investigated many times (e.g. Fernie, 1964; Kwee, 1968; Frolov, 1970; Demers, 1971).The method of determination of the apparent distance moduli was recently revised by Kukarkin and Russev (1972). Instead of using a single absolute magnitude for RR Lyrae variables, the magnitudes according to pulsation theory (Christy, 1966, 1971) were adopted. The inhomogeneity of the absolute magnitudes of the RR Lyrae variables had already been established long ago (Pavlovskaya, 1953), but it attracted attention only recently. The different methods for determining the distance moduli of globular clusters were calibrated according to the new absolute magnitudes of the RR Lyrae variables. The problem consisted in the determination of the absolute magnitudes of the Cepheids in globular clusters according to the apparent distance moduli.

scholarly journals General Properties of the Two Groups of Globular Clusters and Their Variable Stars

1975 ◽  
Vol 67 ◽  
pp. 541-543
Author(s):  
A. V. Mironov ◽  
N. N. Samus'
Keyword(s):  
Chemical Composition ◽  
Globular Clusters ◽  
Variable Stars ◽  
Rr Lyrae Stars ◽  
General Properties ◽  
Rr Lyrae ◽  
Lyrae Stars

The dependences of the numbers of variable stars in globular clusters on the chemical composition are studied. For given metallicity the numbers of RR Lyrae stars reduced to some definite total number of stars in the cluster are different for the two groups of globular clusters introduced by Mironov.

scholarly journals RR Lyrae variables in Galactic globular clusters

2005 ◽  
Vol 437 (3) ◽  
pp. 1017-1021 ◽  
Author(s):  
M. Castellani ◽  
V. Castellani ◽  
S. Cassisi
Keyword(s):  
Globular Clusters ◽  
Rr Lyrae ◽  
Galactic Globular Clusters
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