Astrometry with the [ITAL]Hubble Space Telescope[/ITAL]: A Parallax of the Fundamental Distance Calibrator RR Lyrae

Abstract

We present an absolute parallax and relative proper motion for the fundamental distance scale calibrator, RR Lyr. We obtain these with astrometric data from FGS 3, a white-light interferometer on HST. We find π abs = 3.82 ± 0.2 mas. Spectral classifications and VRIJHKT 2 M and DDO51 photometry of the astrometric reference frame surrounding RR Lyr indicate that field extinction is low along this line of sight. We estimate <A V >= 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 the average field absorption, <A V >=0.07 ± 0.03, we obtain M RR V = 0.61 −0.11 +0.10 . This provides a distance modulus for the LMC, m-M=18.38 -18.53 −0.11 +0.10 with the average extinction-corrected magnitude of RR Lyr variables in the LMC, <V(RR)>, remaining a significant uncertainty. We compare this result to more than 80 other determinations of the distance modulus of the LMC.

Properties of RR Lyrae stars in the inner regions of the Large Magellanic Cloud

“…The distance to the star RR Lyrae is based on its trigonometric parallax. The current sources of parallax information for the star are as follows: ground-based: π = 3.0±1.9 mas (van Altena et al 1995); Hipparcos: π = 3.46±0.64 mas (van Leeuwen 2007); and HST: π = 3.82 ± 0.20 mas (Benedict et al 2002). The weighted average gives the π = 3.78 ±0.19 mas, which provides a distance modulus of (m − M) 0 = 7.1 ± 0.1 for the star.…”

Pulsating variable stars in the Magellanic Clouds

“…Benedict et al (2002) Table 4 summarizes some recent determinations of LMC distances based on pulsating variables. Far from being exhaustive, this table is only meant to highlight some recent advances in the distance determinations based on major types of pulsating variables found in the LMC.…”

Improving the cosmic distance ladder. Distance and structure of the Large Magellanic Cloud

“…thus extreme values such as those listed in Benedict et al (2002) are not very often seen in the recent literature (Clementini, 2009).…”

“…A number of analyses of the distances to the LMC as derived from different distance indicators have been performed (Gibson 2000;Benedict et al 2002;Clementini et al 2003;Schaefer 2008;De Grijs et al 2014). Clementini et al (2003) 18.49 ± 0.09 mag may be used for all practical purposes.…”

“…The famous phrase: "The Hubble Constant at any given time has always been known to 10 percent, despite having changed over the period by a factor of 10" should not be forgotten. For this reason the careful determination of the distance to the LMC is still crucially important, since this galaxy provides a sanity check of the validity of the lower rungs of the distance ladder (Walker, 2012 Benedict et al (2002). Colors represent the various methods, numbers refer to individual investigations (see Table 10 in Benedict et al 2002).…”