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تسجيل مستخدم جديدThe Mira-based distance to the Galactic centre
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Mira variables are useful distance indicators, due to their high luminosities and well-defined period-luminosity relation. We select 1863 Miras from SAAO and MACHO observations to examine their use as distance estimators in the Milky Way. We measure a distance to the Galactic centre of $R_0 = 7.9 pm 0.3$ kpc, which is in good agreement with other literature values. The uncertainty has two components of $sim$0.2 kpc each: the first is from our analysis and predominantly due to interstellar extinction, the second is due to zero-point uncertainties extrinsic to our investigation, such as the distance to the Large Magellanic Cloud (LMC). In an attempt to improve existing period-luminosity calibrations, we use theoretical models of Miras to determine the dependence of the period-luminosity relation on age, metallicity, and helium abundance, under the assumption that Miras trace the bulk stellar population. We find that at a fixed period of $log P = 2.4$, changes in the predicted $K_s$ magnitudes can be approximated by $Delta M_{Ks} approx -0.109(Delta rm{[Fe/H]}) + 0.033( {Delta}t/rm{Gyr}) + 0.021 ({Delta}Y/0.01)$, and these coefficients are nearly independent of period. The expected overestimate in the Galactic centre distance from using an LMC-calibrated relation is $sim$0.3 kpc. This prediction is not validated by our analysis; a few possible reasons are discussed. We separately show that while the predicted color-color diagrams of solar-neighbourhood Miras work well in the near-infrared, though there are offsets from the model predictions in the optical and mid-infrared.
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We report the results of a near-infrared survey for long-period variables in a field of view of 20 arcmin by 30 arcmin towards the Galactic Centre (GC). We have detected 1364 variables, of which 348 are identified with those reported in Glass et al.
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