Search Publications
Accurate Optical Positions of Extragalactic Radio Reference Frame Sources
Zacharias, N.; Zacharias, M. I.; Hall, D. M. +3 more
Optical positions on the 50 mas level in the Hipparcos system have been obtained for 327 extragalactic, radio reference frame sources for both hemispheres from a 2-step procedure. Positions of secondary reference stars in the 10<=V<=14 magnitude range were obtained from photographic plates taken at the Hamburg astrograph (Northern Hemisphere…
Toward an Understanding of the Mid-Infrared Surface Brightness of Normal Galaxies
Dale, Daniel A.; Rubin, Robert H.; Malhotra, Sangeeta +3 more
We report a mid-infrared color and surface brightness analysis of IC 10, NGC 1313, and NGC 6946, three of the nearby galaxies studied under the Infrared Space Observatory Key Project on Normal Galaxies. Images with less than 9" (170 pc) resolution of these nearly face-on, late-type galaxies were obtained using the LW2 (6.75 µm) and LW3 (15 &…
The Luminosity Function of omega Centauri
de Marchi, Guido
Deep Hubble Space Telescope (HST) Wide Field Planetary Camera 2 observations of the stellar population in the globular cluster omega Cen (NGC 5139) have been used to measure the luminosity function of main-sequence stars at the low-mass end. Two fields have been investigated, located ~4.6‧ and ~7', respectively, away from the cluster center or nea…
Hubble Space Telescope and VLA Observations of Two Optical Continuum Knots in the Jet of 3C 380
Baum, Stefi A.; O'Dea, Christopher P.; Biretta, John A. +1 more
We present Hubble Space Telescope Wide Field Planetary Camera 2 broadband red and linear ramp filter (isolating redshifted [O II] lambda3727) observations and subarcsecond-resolution 15, 22, and 43 GHz VLA observations of the radio-loud quasar 3C 380. We confirm the report of de Vries et al. that there is good correspondence between the locations …
A Dwarf Irregular Galaxy at the Edge of the Local Group: Stellar Populations and Distance of IC 5152
Minniti, Dante; Zijlstra, Albert A.
We have obtained V- and I-band photometry for about 700 stars in the field of the dwarf irregular galaxy IC 5152, previously considered a possible member of the Local Group. Deep VI color-magnitude diagrams are presented of the main body of this galaxy and of a nearby field. We infer a distance by comparison with the VI color-magnitude diagrams of…
A Near- and Mid-Infrared Study of the Interacting Galaxy Pair UGC 12914/12915: ``Taffy''
Helou, G.; Condon, J. J.; Jarrett, T. H. +2 more
We report on an infrared 1 to 17 µm study of the nearby (cz=4600 km s-1) interacting spiral galaxy system UGC 12914/12915, using the ground-based Palomar 200 inch (5 m) telescope and PFIRCAM near-infrared detector and space-based mid-infrared imaging and spectral observations using ISOCAM and PHT-S on the Infrared Space Observator…
The Twin Astrographic Catalog on the HIPPARCOS System
Zacharias, N.; Zacharias, M. I.
The Twin Astrographic Catalog (TAC) is an astrometric, photographic catalog covering most of the sky between declinations +90 deg and -18 deg to an average limiting magnitude of about V=11 and B=12. This release 2 is based on the same 4912 plates as release 1, which were taken with the US Naval Observatory Twin Astrograph (blue and yellow lens) be…
Hubble Space Telescope Imaging Polarimetry of eta Carinae
Hillier, D. J.; Nota, A.; Clampin, M. +3 more
Linear polarization measurements have been a key to our understanding of the massive star system eta Carinae and its surrounding Homunculus nebula. We here present the results of (linear) polarimetric imaging of eta Carinae in the V band (F555W) with the Hubble Space Telescope's Wide Field Planetary Camera 2 (HST/WFPC2). The data agree well with p…
Near-Infrared Observations of Hot Spots in the Circumnuclear Rings of NGC 2997 and NGC 6951
Elmegreen, Debra Meloy; Chromey, Frederick R.; Sawyer, Jessica E. +1 more
Near-infrared observations of NGC 2997 and NGC 6951 reveal complete rings of symmetrically placed hot spots, which are star-forming complexes. The masses of the complexes range from a few times 10^4 to a few times 10^5 M_solar in both galaxies. The regular hot-spot spacings of about 200 pc in a ring 55 pc thick in NGC 2997 and 380 pc in a ring 150…
Deep Hubble Space Telescope Observations of Blue Star Clusters in NGC 3597
Ballester, Gilda E.; Crisp, David; Grillmair, Carl J. +15 more
We have analyzed HST/WFPC2 images of NGC 3597 and find ~700 compact objects surrounding the galaxy with an average (B-R)_0~0.6. We propose that the majority of these objects are young globular clusters. They have a spread in colors that is consistent with that expected for a population of young clusters with a common age and spread induced by phot…