Astronomy and Astrophysics – Astronomy
Scientific paper
Jan 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009aas...21332501k&link_type=abstract
American Astronomical Society, AAS Meeting #213, #325.01; Bulletin of the American Astronomical Society, Vol. 41, p.380
Astronomy and Astrophysics
Astronomy
Scientific paper
Mean colors and magnitudes of 3525 RR Lyrae stars in Galactic bulge fields from the MACHO database are presented. Accurate mean reddenings are computed for these stars using their nearly-constant V-R color at minimum V-band light. Using 3256 stars located in the Galactic Bulge, we derive the selective extinction coefficient R_{V,VR} = A_V/E(V-R) = 4.2 ± 0.2.
We use the Fourier parameters of light curves of RR Lyrae stars to find the [Fe/H] metallicity of 2690 RR0 Lyrae with an error of ˜0.2 dex. A correlation between metallicity and galactocentric distance is found, in a sense that for the metal-poor RR0 Lyrae stars, the closer a star is to the Galactic center, on average, the more metal rich it is. However, for the metal-rich RR0 Lyrae stars, this trend is reversed. Using mean magnitudes of MACHO RR Lyrae stars, we searched for the evidence of the Galactic bar, and found marginal evidence of a bar. The absence of a strong bar indicates that the RR Lyrae in the bulge represent a different population than the majority of the bulge stars, which are metal rich and are part of a bar.
We derive the distance to the northern extension of Sgr from 150 Sgr RR0 Lyrae stars found in the MACHO database. Their distances are determined differentially with respect to 194 MACHO Galactic Bulge RR0 Lyrae. We find a distance modulus difference of 2.41 mags at l = 5° and b = -8°. Assuming R_{GC} = 8 kpc, this implies the distance to these stars is (m-M)_0 = 16.94 ± 0.07 mags, which corresponds to D = 24.3 ± 0.8 kpc. This estimate is smaller than previous determinations for this galaxy and agrees with previous suggestions that Sgr's body is truly closer to us.
Chaboyer Brian C.
Kunder Andrea Malaika
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