Distances of nearby Groups and Clusters, and the Local Value of the Hubble Ratio

1977 ◽  
Vol 37 ◽  
pp. 301-307
Author(s):  
G. de Vaucouleurs
Keyword(s):  
Globular Clusters ◽  
Zero Point ◽  
Rr Lyrae ◽  
Galactic Clusters ◽  
The Galaxy ◽  
Nearby Galaxies ◽  
Absolute Magnitudes ◽  
Extragalactic Distance Scale ◽  
Zero Points ◽  
Local Value

AbstractThe correct approach to build up the extragalactic distance scale is to use all available primary (novae, cepheids, RR Lyrae) and secondary indicators (brightest stars, globular clusters, largest HII rings) to calibrate without arbitrary extrapolation all reliable tertiary indicators (magnitudes and diameters of galaxies), precisely corrected for all known effects of type, luminosity class, orientation, internal and galactic extinction and redshift. Such data are now available for over 1000 galaxies in the Second Reference Catalogue.Revised distances to members of the Local Group from primary indicators and new estimates of distances to the nearest groups from primary and secondary indicators are used to calibrate the tertiary indicators via a new, composite luminosity index.The distances derived from globular clusters for 3 galaxy clusters dominated by ellipticals (Vir I, For I, Hya I) with mean corrected velocities 1000 ≤ Vo ≤ 3650 km s-1 give a mean Hubble ratio <H> = 88 (1 ± 0.15) km s-1 Mpc-1. This value rests entirely on the calibration of the globular clusters luminosity function in the Galaxy as a gaussian of dispersion σ = 1.1 mag. and mean <MB>(⊕) = -6.55, with <(B-V)o > = 0.75, based on the adopted RR Lyrae zero point <Mv> (RR) = + 0.86 ± 0.15.The distances derived from tertiary indicators to 19 field spirals and 28 nearby groups dominated by spirals with corrected velocities Vo < 1800 km s-1 give <H> = 82 (1 ± 0.15) km s-1 Mpc-1. This value rests on the relations between luminosity index and fully corrected absolute magnitudes or linear diameters of galaxies derived without extrapolation and calibrated in ~20 nearby galaxies by seven secondary indicators. The zero points were derived from the 3 primary indicators, including 15 galactic novae with <M15> = -5.5 ± 0.15, and 13 cepheids in 8 galactic clusters with <MB> (logPo = 0.8) = -2.92 ± 0.15 (for an adopted Hyades modulus of 3.16 ± 0.05).The low values of Ho≃50 to 55 can be explained by an accumulation of complex systematic errors arising from a multiplicity of sources. These errors, all but one acting in the same sense, have been identified and evaluated; a full report will appear elsewhere.

scholarly journals Pulsating Stars and the Distance Scale - II

1995 ◽  
Vol 155 ◽  
pp. 209-220
Author(s):  
Michael Feast
Keyword(s):  
Globular Clusters ◽  
Zero Point ◽  
Distance Scale ◽  
Age Difference ◽  
Distance Modulus ◽  
Pulsating Stars ◽  
Rr Lyrae ◽  
Galactic Globular Clusters

AbstractThe current Cepheid zero-point is equivalent to an LMC distance modulus of 18.57 ± 0.10. The zero-point from corrected Baade-Wesselink data is probably not significantly different from this. A reexamination of the Baade-Wesselink data for RR Lyrae variables leads to an LMC modulus of 18.51, an age difference between β- and α-group galactic globular clusters of +1.46±0.70 Gyr, and an Mv - [Fe/H] slope in agreement with theory. Other questions discussed include; Avoiding bias in using the Cepheid PL relation; Metallicity spread amongst Cepheids; Cepheids and Ho.

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.

Recently Developed Distance Criteria

1983 ◽  
Vol 6 ◽  
pp. 289-300 ◽  
Author(s):  
G. Paturel
Keyword(s):  
Globular Clusters ◽  
Zero Point ◽  
Great Distance ◽  
Distance Scale ◽  
The Earth ◽  
Distant Galaxies ◽  
Preceding Step ◽  
External Galaxies ◽  
Nearby Galaxies

The problem of the determination of distances in astronomy (the so-called problem of the distance scale) is a very old and important problem. About 280 BC Aristarchus of Samos, the famous greek astronomer of the Alexandrian school, already devised a method to find the relative distances to the Sun and Moon in terms of the size of the Earth. Later, Eratosthenes (about 200 BC), another greek astronomer, measured the Earth’s diameter; so the zero-point of this first distance scale was fixed.Now we are interested by extragalactic distances but the same approach is made : (i) determination of relative distances (ii) determination of the zero-point to obtain absolute distances.Some distance criteria can be used to determine the zero-point. These criteria cannot generally be used at a great distance. They permit a comparison between galactic objects, like Cepheids, Novae, Supergiants ..., globular clusters..., and the same counterparts recognized in external galaxies. Often application is limited to nearby galaxies. In a first section we will briefly present this kind of distance criteria. For more distant galaxies other criteria must be employed, the zero-point being here fixed with nearby galaxies whose distances are known from the preceding step. We will discuss these criteria in a second section.

scholarly journals Globular clusters in the Sagittarius stream

2020 ◽  
Vol 636 ◽  
pp. A107 ◽  
Author(s):  
M. Bellazzini ◽  
R. Ibata ◽  
K. Malhan ◽  
N. Martin ◽  
B. Famaey ◽  
...  
Keyword(s):  
Globular Clusters ◽  
Main Body ◽  
Rr Lyrae ◽  
The Galaxy ◽  
Tidal Stream ◽  
Galactic Globular Clusters

We reconsider the case for the association of Galactic globular clusters to the tidal stream of the Sagittarius dwarf spheroidal galaxy (Sgr dSph) using Gaia DR2 data. We used RR Lyrae variables to trace the stream in 6D and we selected clusters matching the observed stream in position and velocity. In addition to the clusters residing in the main body of the galaxy (M 54, Ter 8, Ter 7, Arp 2) we confirm the membership of Pal 12 and Whiting 1 to the portion of the trailing arm populated by stars lost during recent perigalactic passages. NGC 2419, NGC 5634, and NGC 4147 are very interesting candidates, possibly associated with more ancient wraps of the Sagittarius stream. With the exception of M 54, which lies within the stellar nucleus of the galaxy, we note that all these clusters are found in the trailing arm of the stream. The selected clusters are fully consistent with the [Fe/H] versus [Mg/Fe], [Ca/Fe] patterns and the age-metallicity relation displayed by field stars in the main body of Sgr dSph.

scholarly journals Turnoffs and Ages of Globular Clusters

1988 ◽  
Vol 126 ◽  
pp. 635-636
Author(s):  
F. Buonanno ◽  
C. E. Corsi ◽  
F. Fusi Pecci
Keyword(s):  
Globular Clusters ◽  
Horizontal Branch ◽  
Rr Lyrae Stars ◽  
Rr Lyrae ◽  
The Absolute ◽  
The Difference ◽  
Absolute Magnitudes ◽  
Lyrae Stars ◽  
The Way

The way to arrive at (even relative) ages for globular clusters involves the determination of their (relative) distances. We would like to see a theory which would fit the absolute magnitudes of RR Lyrae stars as determined from observations (Sandage effect). We have examined a sample of 17 CM diagrams of galactic globular clusters, 11 of which were observed at ESO and reduced with the program, ROMAFOT and 6 of which were taken from the literature. In Fig. 1 the difference in bolometric magnitude between the turnoff point and the location of the zero-age horizontal branch (ZAHB), δV RRTO (bo1) is plotted versus [Fe/H]. It turns out that δV RRTO ≃ δ RRTO (bo1) + 0.1 = 3.56 ±0.15. We are faced with the problem of determining how the horizontal branch scales with metallicity in order to understand the constant value of 3.56 in this relation.

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.

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 The LMC Globular Cluster Hodge 11 (=SL 868)

1984 ◽  
Vol 108 ◽  
pp. 43-44
Author(s):  
L. L. Stryker ◽  
J. M. Nemec ◽  
J. E. Hesser ◽  
R.D. McClure
Keyword(s):  
Globular Clusters ◽  
Main Sequence ◽  
Star Cluster ◽  
Open Clusters ◽  
Rr Lyrae Stars ◽  
Rr Lyrae ◽  
Magnitude Diagram ◽  
The Galaxy ◽  
Lyrae Stars ◽  
Termination Point

The age of the star cluster H11 has been controversial for a number of years. The color-magnitude diagram (CMD) of Walker (1979) to V=21.5 was interpreted as an “…evolved main-sequence, whose termination point corresponds to an age of about 0.6 Gyr, but with a giant branch which is displaced blueward by about Δ (B-V)o=0.4 from the positions of the giant branches of open clusters of similar age in our Galaxy.” On the other hand, the integrated colors are similar to those of metal-poor globular clusters in the Galaxy (Freeman and Gascoigne 1977, and references therein), and “…incompatible with an age of say 0.3 Gyr.” Searle, Wilkinson and Bagnuolo (1980) classify it as Group VII, the oldest group. The system has no RR Lyrae stars (Graham and Nemec 1984).

scholarly journals The Infrared Period - 2.2/µm Magnitude Relation for RR Lyrae Stars

1993 ◽  
Vol 139 ◽  
pp. 21-29
Author(s):  
A.J. Longmore
Keyword(s):  
Theoretical Prediction ◽  
Theoretical Basis ◽  
Globular Clusters ◽  
Galactic Centre ◽  
Reference List ◽  
Rr Lyrae Stars ◽  
Rr Lyrae ◽  
Full Reference ◽  
Absolute Magnitudes ◽  
Lyrae Stars

AbstractThe observational and theoretical basis for the log P vs. K-mag relation is reviewed. The observed gradient in all well observed globular clusters agrees well with the theoretical prediction. An indistinguishable result is found for field RR Lyrae stars whose absolute magnitudes have been determined from infrared Baade-Wesselink analyses. A full reference list is given for the source of these magnitudes. Application of the results to find the distance to globular clusters and the Galactic Centre is discussed.

scholarly journals The Zero-Point of the Cepheid Luminosity Scale from a Calibration of the Luminosities of Early-Type Stars

1985 ◽  
Vol 82 ◽  
pp. 201-202
Author(s):  
L. A. Balona ◽  
R. R. Shobbrook
Keyword(s):  
Zero Point ◽  
Photometric System ◽  
Early Type ◽  
Early Type Stars ◽  
The Absolute ◽  
Absolute Magnitudes ◽  
Zero Points

AbstractA new calibration of the absolute magnitudes of early-type stars in terms of the (β, c0) photometric system is used to establish the distance moduli of clusters containing Cepheids. The zero points of the period – luminosity and period – luminosity – colour relations are calculated and compared to previous determinations.

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