T. B. Williams

Maximum disk mass models for spiral galaxies

We present axisymmetric maximum disk mass models for a sample of 74 spiral galaxies taken from the southern sky Fabry-Perot Tully-Fisher survey by Schommer et al. The sample contains galaxies spanning a large range of morphologies and having rotation widths from 180 km s -1 to 680 km s -1. For each galaxy we have an I-band image and a two-dimensional Hα velocity field. We decompose the disk and bulge by fitting models directly to the I-band image. This method utilizes both the distinct surface brightness profiles and shapes of the projected disk and bulge in the galaxy images. The luminosity profiles and rotation curves are derived using consistent centers, position angles, and inclinations derived from the photometry and velocity maps. The distribution of mass is modeled as a sum of disk and bulge components with distinct, constant mass-to-light ratios. No dark matter halo is included in the fits. The models reproduce the overall structure of the rotation curves in the majority of galaxies, providing good fits to galaxies that exhibit pronounced structural differences in their surface brightness profiles. Of galaxies for which the rotation curve is measured to R23.5 or beyond 75% are well fitted by a mass-traces-light model for the entire region within R23.5. The models for about 20% of the galaxies do not fit well; the failure of most of these models is traced directly to nonaxisymmetric structures, primarily bars but also strong spiral arms. The median I-band M/L of the disk plus bulge is 2.4 ± 0.9 h75 in solar units, consistent with normal stellar populations. These results require either that the mass of dark matter within the optical disk of spiral galaxies is small or that its distribution is very precisely coupled to the distribution of luminous matter.

Detection of h-alpha emission from the magellanic stream: evidence for an extended gaseous galactic halo

We have detected faint, diffuse H

The 1990 Calán/Tololo supernova search

\alpha emission from several points along the Magellanic Stream, using the Rutgers Fabry--Perot Interferometer at the CTIO 1.5-m telescope. At points on the leading edges of the H I clouds MS II, MS III, and MS IV, we detect H

Optical and infrared photometry of the nearby type Ia supernovae 1999ee, 2000bh, 2000ca, and 2001ba

\alpha emission of surface brightness

Photometric Decomposition of Barred Galaxies

0.37 \pm 0.02

Optical Light Curves of the Type I[CLC]a[/CLC] Supernovae SN 1990N and SN 1991T

Rayleighs,

UNCOVERING PLANETARY NEBULAE IN EARLY-TYPE GALAXIES USING THE RUTGERS FABRY-PEROT

0.21 \pm 0.04

Optical light curves of the type ia supernovae 1990n and 1991t

R, and

Optical emission from high velocity clouds and the ionization sources in the Galactic halo

0.20 \pm 0.02

Distance Constraints for High Velocity Clouds from Optical Emission Lines

R respectively, corresponding to emission measures of 1.0 to 0.5 \cmsixpc. We have observed several positions near the MS IV concentration, and find that the strongest emission is on the sharp leading-edge density gradient. There is less emission at points away from the gradient, and halfway between MS III and MS IV the H