Astrometry with the Hubble Space Telescope: A Parallax of the Fundamental Distance Calibrator RR Lyrae
McArthur, B. E.; Franz, O. G.; Bradley, A. J.; Hemenway, P. D.; Jefferys, W. H.; Nelan, E.; Shelus, P. J.; Story, D.; Whipple, A. L.; Duncombe, R. L.; Fredrick, L. W.; Benedict, G. Fritz; Lee, J.; Harrison, T. E.; Patterson, R. J.; Wasserman, L. H.; van Altena, W.; Slesnick, C. L.; Rhee, J.
United States
Abstract
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 MRRV=0.61-0.11+0.10. This provides a distance modulus for the Large Magellanic Cloud (LMC) of m-M=18.38-18.53-0.11+0.10, 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. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555.