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 = 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, =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, , remaining a significant uncertainty. We compare this result to more than 80 other determinations of the distance modulus of the LMC.

We report on a sub-stellar companion search utilizing interferometric fringe-tracking astrometry acquired with Fine Guidance Sensor 3 (FGS 3) on the Hubble Space Telescope. Our targets were Proxima Centauri and Barnard's Star. We obtain absolute parallax values for Proxima Cen π abs = 0. ′′ 7687 ± 0. ′′ 0003 and for Barnard's Star π abs = 0. ′′ 5454 ± 0. ′′ 0003.Once low-amplitude instrumental systematic errors are identified and removed, our companion detection sensitivity is less than or equal to one Jupiter mass for periods longer than 60 days for Proxima Cen. Between the astrometry and the Kürster et al. 1999 radial velocity results we exclude all companions with M > 0.8M Jup for the range of periods 1 < P < 1000 days. For Barnard's Star our companion detection sensitivity is less than or equal to one Jupiter mass for periods longer than 150 days. Our null results for Barnard's Star are consistent with those of Gatewood (1995).

2 -Received ; accepted to appear in Ap. J. , xx. -3 -ABSTRACT TV Columbae (TV Col) is a 13th magnitude Intermediate Polar (IP) Cataclysmic Variable (CV), with multiple periods found in the light curves. Past estimates predicted a distance of 400 parsec to greater than 500 parsec. Recently completed Hubble Space Telescope (HST) Fine Guidance Sensor (FGS) interferometric observations allow us to determine the first trigonometric parallax to TV Col. This determination puts the distance of TV Col at 368 −15 +17 parsecs.CD-32 2376, a 10th magnitude Tycho Catalog star, is a reference star in the TV Col frame. We find a distance of 127.7 −1 +1 parsecs.

With Hubble Space T elescope Fine Guidance Sensor 3 we have determined a parallax for the white dwarfÈM dwarf interacting binary, Feige 24. The white dwarf (DA) component has an e †ective temperature K. A weighted average with past parallax determinations mas) T eff D 56,000 (n abs \ 14.6^0.4 narrows the range of possible radius values, compared with past estimates. We obtain R DA \ 0.0185 with uncertainty in the temperature and bolometric correction the dominant contributorŝ 0.0008 R _ to the error. Fine Guidance Sensor 3 photometry provides a light curve entirely consistent with reÑec-tion e †ects. A recently reÐned model mass-luminosity relation for low-mass stars provides a mass estimate for the M dwarf companion, where the mass range is due to metallicity M dM \ 0.37^0.20 M _ , and age uncertainties. Radial velocities from Vennes and Thorstensen provide a mass ratio from which we obtain Independently, our radius and recent log g determinations yield 0.44 M DA \ 0.49~0 .05 0.19 M _ . In each case, the minimum DA mass is that derived by Vennes & Thorstensen M _ \ M DA \ 0.47 M _ . from their radial velocities and Keplerian circular orbits with i ¹ 90¡. Locating Feige 24 on an (M, R)-plane suggests a carbon core. Our radius and these mass estimates yield a value of inconsistent with c grav that derived by Vennes & Thorstensen. We speculate on the nature of a third component whose existence would resolve the discrepancy.

No abstract