Search Publications
The Luminosity Function of Star Clusters in Spiral Galaxies
Larsen, Søren S.
Star clusters in six nearby spiral galaxies are examined using archive images from the Wide Field Planetary Camera 2 (WFPC2) on board the Hubble Space Telescope (HST). The galaxies have previously been studied from the ground and some of them are known to possess rich populations of ``young massive clusters.'' Comparison with the HST images indica…
Deviations from the Local Hubble Flow. I. The Tip of the Red Giant Branch as a Distance Indicator
Méndez, Bryan; Davis, Marc; Moustakas, John +3 more
The properties of the velocity field in the local volume (cz<550 km s-1) have been difficult to constrain because of a lack of a consistent set of galaxy distances. The sparse observations available to date suggest a remarkably quiet flow, with little deviation from a pure Hubble law. However, velocity field models based on the distr…
The Halo Stars in NGC 5128. III. An Inner Halo Field and the Metallicity Distribution
Harris, William E.; Harris, Gretchen L. H.
We present new Hubble Space Telescope WFPC2 (V,I) photometry for field stars in NGC 5128 at a projected distance of 8 kpc from the galaxy center, which probes a mixture of its inner halo and outer bulge. The color-magnitude diagram shows an old red giant branch that is even broader in color than our two previously studied outer halo fields (at 21 …
Internal Dynamics, Structure, and Formation of Dwarf Elliptical Galaxies. I. A Keck/Hubble Space Telescope Study of Six Virgo Cluster Dwarf Galaxies
Geha, M.; van der Marel, R. P.; Guhathakurta, P.
Spectroscopy with the Keck II 10 m telescope and Echelle Spectrograph and Imager is presented for six Virgo Cluster dwarf elliptical (dE) galaxies in the absolute magnitude range -15.7<=MV<=-17.2. The mean line-of-sight velocity and velocity dispersion are resolved as a function of radius along the major axis of each galaxy, nearl…
Astrometry with the Hubble Space Telescope: A Parallax of the Fundamental Distance Calibrator RR Lyrae
McArthur, B. E.; Franz, O. G.; Bradley, A. J. +16 more
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 astr…
Hubble Space Telescope Images of the HH 34 Jet and Bow Shock: Structure and Proper Motions
Bally, John; Morse, Jon; Reipurth, Bo +2 more
We present new, deep Hα and [S II] images of the HH 34 jet and bow shock obtained with the Wide Field Planetary Camera 2 on board the Hubble Space Telescope (HST), which reveal the structure of this fine HH flow with unprecedented detail. Many of the knots in the jet appear to form small working surfaces with bright [S II] cores and thin Hα filame…
Hubble Space Telescope WFPC2 Proper Motions in Two Bulge Fields: Kinematics and Stellar Population of the Galactic Bulge
Rich, R. Michael; Kuijken, Konrad
We report proper-motion dispersions for stars in the direction of two fields of the Galactic bulge, using Hubble Space Telescope Wide Field Planetary Camera 2 images taken 6 years apart. Our two fields are Baade's window [(l,b)=(1.13d,-3.77d)] and Sgr I [(l,b)=(1.25d,-2.65d)]. Our proper-motion dispersions are in good agreement with prior ground- …
A High Angular Resolution Multiplicity Survey of the Open Clusters α Persei and Praesepe
Ghez, A. M.; Matthews, K.; Patience, J. +1 more
Two hundred forty-two members of the Praesepe and α Persei clusters have been surveyed with high angular resolution 2.2 µm speckle imaging on the 3 m Infrared Telescope Facility, the 5 m Hale, and the 10 m Keck telescopes, along with direct imaging using the near-infrared camera (NICMOS) aboard the Hubble Space Telescope. The observed stars …
The Star Formation History and Spatial Distribution of Stellar Populations in the Ursa Minor Dwarf Spheroidal Galaxy
Aparicio, Antonio; Martínez-Delgado, David; Alonso-García, Javier +1 more
As a part of a project devoted to the study of the Ursa Minor dwarf spheroidal (dSph) galaxy, the star formation history of the galaxy is presented. The analysis uses wide-field photometry, encompassing about 1°×1° (the total covered area being 0.75 deg2), which samples the galaxy out to its tidal radius. Derivation of the star formatio…
Astrometry with the Hubble Space Telescope: A Parallax of the Fundamental Distance Calibrator δ Cephei
McArthur, B. E.; Franz, O. G.; Bradley, A. J. +16 more
We present an absolute parallax and relative proper motion for the fundamental distance scale calibrator δ Cep. We obtain these with astrometric data from FGS 3, a white-light interferometer on the Hubble Space Telescope (HST). Utilizing spectrophotometric estimates of the absolute parallaxes of our astrometric reference stars and constraining δ C…