The 222 000 I -band light curves of variable stars detected by the ogle - ii survey in the direction of the Galactic Bulge have been fitted and have also been correlated with the denis and 2mass all-sky release databases and with lists of known objects .
Lightcurves , and the results of the lightcurve fitting ( periods and amplitudes ) and denis and 2mass data are presented for 2691 objects with I -band semi-amplitude larger than 0.45 magnitude , corresponding to classical Mira variables .
The Mira period distribution of 6 fields at similar longitude but spanning latitudes from -1.2 to -5.8 are statistically indistinguisable indicating similar populations with initial masses of 1.5-2 M _ { \odot } ( corresponding to ages of 1-3 Gyr ) .
A field at similar longitude at b = -0.05 from Glass et al .
( 2001 ) does show a significantly different period distribution , indicating the presence of a younger population of 2.5-3 M _ { \odot } and ages below 1 Gyr .
The K -band period-luminosity relation is presented for the whole sample , and for sub-fields .
The zero point depends on Galactic longitude .
Simulations are carried out to show that the observed dependence of the zero point with l , and the number of stars per field are naturally explained using the model of disk and bulge stars of Binney et al .
( 1997 ) , for a viewing angle ( major-axis Bar - axis perpendicular to the line-of-sight to the Galactic Centre ) of 43 \pm 17 degrees .
The simulations also show that biases in the observed zero point are small , < 0.02 mag .
A comparison is made with similar objects in the Magellanic Clouds , studied in a previous paper .
The slope of the PL -relation in the Bulge and the MCs agree within the errorbars .
Assuming the zero point does not depend on metallicity , a distance modulus difference of 3.72 between Bulge and LMC is derived .
This implies a LMC DM of 18.21 for an assumed distance to the Galactic Centre ( GC ) of 7.9 kpc , or , assuming a LMC DM of 18.50 , a distance to the GC of 9.0 kpc .
From the results in Groenewegen ( 2004 ) it is found for carbon-rich Miras that the PL -relation implies a relative SMC-LMC DM of 0.38 , assuming no metallicity dependence .
This is somewhat smaller than the often quoted value near 0.50 .
Following theoretical work by Wood ( 1990 ) a metallicity term of the form M _ { K } \sim \beta \log Z is introduced .
If a relative SMC-LMC DM of 0.50 is imposed , \beta = 0.4 is required , and for that value the distance to the GC becomes 8.6 \pm 0.7 kpc ( for a LMC DM of 18.50 ) , within the errorbar of the geometric determination of 7.9 \pm 0.4 kpc ( Eisenhauer et al .
2003 ) .
An independent estimate using the absolute calibration of Feast ( 2004b ) leads to a distance estimate to the GC of 8.8 \pm 0.4 kpc .