Distance scale zero points from Galactic RR Lyrae star parallaxes

摘要

We present new absolute trigonometric parallaxes and proper motions for seven Population II variable stars - five RRLyr variables: RZCep, XZCyg, SUDra, RRLyr, and UV Oct; and two type 2 Cepheids: VYPyx and κPav. We obtained these results with astrometric data from Fine Guidance Sensors, white-light interferometers on Hubble Space Telescope. We find absolute parallaxes in milliseconds of arc: RZCep, 2.12 ± 0.16mas; XZCyg, 1.67 ± 0.17mas; SUDra, 1.42 ± 0.16mas; RRLyr, 3.77 ± 0.13mas; UV Oct, 1.71 ± 0.10mas; VYPyx, 6.44 ± 0.23mas; and κ Pav, 5.57 ± 0.28mas; an average σ_π/π = 5.4. With these parallaxes, we compute absolute magnitudes in V and K bandpasses corrected for interstellar extinction and Lutz-Kelker-Hanson bias. Using these RRLyrae variable star absolute magnitudes, we then derive zero points for M_V -Fe/H and M_K -Fe/H-log P relations. The technique of reduced parallaxes corroborates these results. We employ our new results to determine distances and ages of several Galactic globular clusters and the distance of the Large Magellanic Cloud. The latter is close to that previously derived from Classical Cepheids uncorrected for any metallicity effect, indicating that any such effect is small. We also discuss the somewhat puzzling results obtained for our two type 2 Cepheids.