The Zero Point of Extinction toward Baade's Window from RR Lyrae Stars

AbstractWe have applied the Baade–Wesselink method to two field RR Lyrae stars, i.e. SW And and RR Cet, and derived their distances and physical parameters. With respect to previous B–W analyses we have applied the following improvements: i) use of all sets of available data, after proper comparison for homogeneity and compatibility; ii) use of the most recent and accurate model atmospheres, with turbulent velocity Vturb = 4 km s−1 and the no-overshooting approximation, and comparison with other treatments of convection; iii) use of the instantaneous gravity along the pulsation cycle rather than the mean value; iv) comparison with modified radial velocity curves according to various assumptions on radial velocity gradients in the atmosphere; and v) careful reanalysis of the temperature scale. The main aim of this study is to evaluate the effect of the above items on the B–W results and verify whether any (or a combination) of them can possibly account for the discrepancy of the absolute magnitude zero-point with respect to other independent determinations.

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The kinematics and zero point of the log P –〈MK〉 relation for galactic field RR Lyrae variables via statistical parallax

International Astronomical Union Colloquium ◽

10.1017/s0252921100010472 ◽

2004 ◽

Vol 193 ◽

pp. 128-132 ◽

Cited By ~ 1

Author(s):

A.K. Dambis ◽

O.V. Vozyakova

Keyword(s):

Zero Point ◽

Log P ◽

Distance Modulus ◽

Proper Motions ◽

Galactocentric Distance ◽

Rr Lyrae Stars ◽

Rr Lyrae ◽

Solar Galactocentric Distance ◽

Lyrae Stars ◽

Maximum Likelihood Technique

AbstractThe kinematical parameters of the local field RR Lyrae population and the zero point of the log P –〈MK〉 relation for these variables are inferred by applying the statistical parallax (maximum-likelihood) technique to a sample of 379 RR Lyrae stars with known periods, radial-velocities, metallicities, K-band photometry, and absolute proper motions on the ICRS system. Hipparcos, Tycho-2, SPM, UCAC1 and NPM1 were used as the sources of proper motions. The K-band magnitudes were adopted from the 2MASS All-Sky Data Release. The parameters of the velocity distribution are found to be (U0 = −13 ± 9, V0 = −41 ± 7, W0 = −19±4) kms−1, (σU = 66±9, σV = 47±7, σW = 23±5) km s−1 and (U0 = −11±10, V0 = −224±8, W0 = −8±6) km s−1 (σU = 158±9, σV = 95±5, σW = 88±5) km s−1 for the thick-disk (the purest disk sample, 56 stars) and halo (the purest halo sample, 264 stars) objects, respectively. The zero point of the infrared PL relation of Jones et al. (1992 – based on the results obtained using the Baade-Wesselink method) is confirmed: we find 〈MK〉 = −2.33⋅log PF−0.89±0.09, which is only brighter than found using the Baade-Wesselink method (Jones et al. 1992). A conversion of the resulting log P –〈MK〉 relation to V-band luminosities yields the metallicity-luminosity relation 〈MV〉 = +1.12 + 0.18 ⋅ [Fe/H] ± 0.10. Our results imply a solar Galactocentric distance of R0 = 7.8±0.4 kpc and an LMC distance modulus of DMLMC = 18.17 ±0.10 (cluster RR Lyraes) or DMLMC = 18.10±0.10 (field RR Lyraes), thereby favoring the so-called short distance scale.

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Double-Mode RR Lyrae Stars in IC 4499

Symposium - International Astronomical Union ◽

10.1017/s0074180900043229 ◽

1988 ◽

Vol 126 ◽

pp. 591-592

Author(s):

Christine M. Clement ◽

James M. Nemec ◽

Robert J. Dickens ◽

Elizabeth A. Bingham

Keyword(s):

Zero Point ◽

Distance Modulus ◽

Type I ◽

Rr Lyrae Stars ◽

Average Mass ◽

Rr Lyrae ◽

Cluster Distance ◽

Metal Abundances ◽

The Mean ◽

Lyrae Stars

Thirteen double-mode RR Lyrae (RRd) stars, with mean magnitudes c = 18.30 ± 0.10 and <V>c = 17.80 ± 0.15, have been identified in the variable-rich Oosterhoff type I globular cluster IC 4499. The stars have surprisingly uniform properties, and are considerably different from RRd stars found in Oo II systems. The mean first-overtone period (Fig.1) is <P1>=0.357d ± 0.005d (cf. <P1>=0.40d for Oo II RRd stars), and the mean ratio of the first-overtone period to the fundamental period is <P1/P0>= 0.7443 ± 0.0002. The mean double-mode pulsation mass for the 13 stars, using the King Ia (Y=0.279, Z=0.001) mass calibration, is 0.535 ± 0.003 M⊙. Such an average mass is 0.11 M⊙ smaller (i.e. ~17% smaller) than that for RRd stars found in Oo II systems, and possibly ~0.01 M⊙smaller than the mean mass for the two RRd stars in M3 (it is important to note that the zero point of these mass determinations is uncertain by at least 15%). The metal abundances for the RRd stars, and for the system of RR Lyrae stars as a whole, are found to be consistent with <[Fe/H]>=-1.38 ± 0.20, determined from δS spectroscopy. In the Peterson diagram (Fig.2), all known RRd stars now divide (apparently by mass) into two groups (split according to Oosterhoff type). With a reddening of EB-V=0.26 ± 0.03, the cluster distance modulus is (m-M)o=16.23m ± 0.23m.

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The Unusual Period Distribution of the RR Lyrae Variables in NGC 5897

International Astronomical Union Colloquium ◽

10.1017/s0252921100011957 ◽

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.

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

Symposium - International Astronomical Union ◽

10.1017/s0074180900010743 ◽

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.

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