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Identification of moving groups from a sample of B, A and F type stars.
Figueras, F.; Torra, J.; Chen, B. +1 more
An algorithm to find moving groups has been developed and applied to a sample of 1924 B, A, and F main sequence stars, basically extracted from the Hipparcos Input Catalogue. This algorithm uses a non-parametric kernel estimator to describe the stellar distribution in a 4-dimensional space of velocities and age, although it can be used to detect t…
The Dwarf Irregular Galaxy Sextans A. I. HST Photometry of the Resolved Stars
Skillman, Evan D.; Saha, A.; Gallagher, J. +6 more
We have used the Hubble Space Telescope to observe the resolved stars of the nearby (D = 1.4 Mpc) dwarf irregular galaxy Sextans A (DDO 75, A 1008-04). The data consist of dithered WFPC2 images in 3 bands: F439W (1 hour), F555W (30 minutes), and F814W (30 minutes). The stellar photometry was extracted using the DoPHOT program developed by Schechte…
Radial velocities and iron abundances of field RR Lyraes. I.
Barnes, T. G.; Fernley, J.
We present systemic velocities and iron abundances for 56 RR Lyraes, the majority of which have been observed by the HIPPARCOS satellite. Comparison between our systemic velocities and previous values identifies several binary candidates only one of which, TU UMa, was previously suspected of being a binary. However, spectra of the unusual RR Lyrae…
The Extragalactic Distance Scale Key Project. VIII. The Discovery of Cepheids and a New Distance to NGC 3621 Using the Hubble Space Telescope
Illingworth, Garth D.; Huchra, John P.; Kennicutt, Robert C. +18 more
We report on the discovery of Cepheids in the field spiral galaxy NGC 3621, based on observations made with the Wide Field Planetary Camera 2 on board the Hubble Space Telescope (HST). NGC 3621 is one of 18 galaxies observed as a part of the HST Key Project on the Extragalactic Distance Scale, which aims to measure the Hubble constant to 10% accur…
On Calibrating Brightest Asymptotic Giant Branch Stars as Age Indicators: The Bulge Globular Cluster NGC 6553 and the Age of M32
Renzini, Alvio; Ortolani, Sergio; Guarnieri, Maria Donata
Bright asymptotic giant branch (AGB) stars can be used as an age indicator for stellar populations that are too far away for their main-sequence turnoffs to be reachable. However, the method requires an empirical calibration, as the brightness of the AGB termination depends on both age and metallicity in ways that cannot be predicted from first pr…
LASCO Observations of Disconnected Magnetic Structures Out to Beyond 28 Solar Radii During Coronal Mass Ejections
Llebaria, A.; St. Cyr, O. C.; Plunkett, S. P. +16 more
Two coronal mass ejections have been well observed by the LASCO coronagraphs to move out into the interplanetary medium as disconnected plasmoids. The first, on July 28, 1996, left the Sun above the west limb around 18:00 UT. As it moved out, a bright V-shaped structure was visible in the C2 coronagraph which moved into the field-of-view of C3 and…
Galaxy Morphology without Classification: Self-organizing Maps
Griffiths, Richard E.; Ratnatunga, Kavan U.; Naim, Avi
We examine a general framework for visualizing data sets of high (greater than 2) dimensionality and demonstrate the framework by taking the morphology of galaxies at moderate redshifts as an example. The distributions of various populations of such galaxies are examined in a space spanned by four purely morphological parameters. Galaxy images are…
Deep WFPC2 and Ground-Based Imaging of a Complete Sample of 3C Quasars and Galaxies.
Stockton, Alan; Ridgway, Susan E.
\tighten We present the results of an HST and ground-based imaging study of a complete 3C sample of z ~ 1 sources, comprising 5 quasars and 5 radio galaxies. We have observed all of the sample in essentially line-free bands at rest-frame 0.33 mu m with WFPC2 and in rest-frame 1 \micron\ images from the ground; we have also observed most of the sam…
The HIPPARCOS Mission
van Leeuwen, Floor
Coronal streamer belt asymmetries and seasonal solar wind variations deduced from Wind and Ulysses data
Steinberg, J. T.; Crooker, N. U.; Smith, E. J. +4 more
Solar wind measurements from Wind during March 1995 are combined with those from Ulysses' fast latitude scan to construct a map of the streamer belt. On the timescale of coronal change, the map is nearly a snapshot view of solar wind speed contours threaded by the trace of the heliospheric current sheet (HCS) in the +/-30° heliolatitude range. The…