The Mira-based Distance to the Galactic Center

Abstract

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 center of R 0 =7.9±0.3 kpc, which is in good agreement with other literature values. The uncertainty has two components of ∼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 = P log 2.4, changes in the predicted K s magnitudes can be approximated byGyr 0.021 0.01 , and these coefficients are nearly independent of period. The expected overestimate in the Galactic center distance from using an LMC-calibrated relation is ∼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 solarneighborhood Miras work well in the near-infrared; though, there are offsets from the model predictions in the optical and mid-infrared.

A New Estimate of the Best Value for the Solar Galactocentric Distance

“…Nine R 0 estimates are derived from an analysis of the spatial distribution of variable stars. Four estimates were obtained for RR Lyr type variables [22,[28][29][30][31], two for type II Cepheids [32,33], one for Mira variables [34], and one for classical Cepheids [35]. In terms of the similarity of the approach, they are similar to the result obtained for the blue-giant branch stars [36].…”

“…A large sample of Mira variables was studied in [34]. These stars are pulsating variables that are in the late evolutionary stages of the asymptotic giant branch.…”

“…They belong to the Galactic halo. In [34], a large sample was formed, compiled from data from several observational programs (SAAO, MACHO, and OGLE). Calibration and absorption accounting was performed using photometry J, H, K s from the 2MASS catalog [44].…”

Predicted trends in Milky Way bulge proper motion rotation curves: future prospects for HST and LSST

“…The velocities are scaled by 0.48 to match the velocity dispersion in the MW bulge (see Debattista et al 2017). We place the observer at 8 kpc from the galactic centre in the mid-plane with the bar aligned to 27 • from the line of sight (LOS) of the observer to the galactic centre Qin et al 2018), with the near side of the bar at positive longitude.…”

Predicted Trends in Milky Way Bulge Proper Motion Rotation Curves: future Prospects for HST and LSST

“…The velocities are scaled by 0.48 to match the velocity dispersion in the MW bulge (see Debattista et al 2017). We place the observer at 8 kpc from the galactic centre in the mid-plane with the bar aligned to 27 • from the LOS of the observer to the galactic centre Qin et al 2018), with the near side of the bar at positive longitude.…”