ar X iv : a st ro - p h / 99 08 14 0 v 2 1 2 A ug 1 99 9 A Cepheid distance to NGC 4258

ar X iv : a st ro - p h / 98 08 21 9 v 1 2 0 A ug 1 99 8 Sgr A ∗ : A supermassive black hole or a spatially extended object ?

ar X iv : a st ro - p h / 98 03 03 9 v 1 4 M ar 1 99 8 Cosmology With High - Redshift Water Masers

Multi-epoch VLBA observations of the maser in NGC 4258 have yielded a 4% geometrical distance to the galaxy. The potential scientific payoffs of finding similar objects at large distances, in the Hubble flow, are considerable. In this contribution, I discuss the plausibility of detecting high-redshift water masers, and describe a search strategy that we have implemented to realize this objective.

ar X iv : a st ro - p h / 99 08 29 3 v 1 2 7 A ug 1 99 9 The DIRECT Project : Influence of Blending on the Cepheid Distance Scale

We investigate the influence of blending on the Cepheid distance scale. Blending leads to systematically low distances to galaxies observed with HST, and therefore to systematically high estimates of H0. High-resolution HST images are compared to our ground-based data, obtained as part of the DIRECT project, for a sample of 22 Cepheids in the M31 galaxy. The average (median) V -band flux contri...

X iv : a st ro - p h / 99 08 34 3 v 1 3 1 A ug 1 99 9 A robust method for measuring the Hubble parameter

We obtain a robust, non-parametric, estimate of the Hub-ble constant from galaxy linear diameters calibrated using HST Cepheid distances. Our method is independent of the parametric form of the diameter function and the spatial distribution of galaxies and is insensitive to Malmquist bias. We include information on the galaxy rotation velocities ; unlike Tully-Fisher, however, we retain a fully...

ar X iv : a st ro - p h / 96 08 03 6 v 2 1 2 A ug 1 99 6 TABLE 1 Properties of LMC Double - Mode