Date of Original Version
We present an absolute parallax and relative proper motion for the fundamental distance scale calibrator, RR Lyrae. We obtain these with astrometric data from FGS 3, a white-light interferometer on the Hubble Space Telescope. We find πabs = 3.82 ± 0.2 mas. Spectral classifications and VRIJHKT2M and DDO 51 photometry of the astrometric reference frame surrounding RR Lyr indicate that field extinction is low along this line of sight. We estimate AV = 0.07 ± 0.03 for these reference stars. The extinction suffered by RR Lyr becomes one of the dominant contributors to the uncertainty in its absolute magnitude. Adopting theaverage field absorption AV = 0.07 ± 0.03, we obtain M = 0.61. This provides a distance modulus for the Large Magellanic Cloud (LMC) of m - M = 18.38–18.53, with the average extinction-corrected magnitude of RR Lyrae variables in the LMC, V(RR), remaining a significant uncertainty. We compare this result with more than 80 other determinations of the distance modulus of the LMC.
Benedict, G. F., McArthur, B. E., Fredrick, L. W., Harrison, T. E., Lee, J., Slesnick, C. L., Rhee, J.,...Bradley, A. J. (2002). Astrometry with the Hubble Space Telescope: A Parallax of the Fundamental Distance Calibrator RR Lyrae. The Astronomical Journal, 123(1), 473-484. doi: 10.1086/338087
Available at: http://dx.doi.org/10.1086/338087