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Younger and Brighter - New Distances to Globular Clusters Based on HIPPARCOS Parallax Measurements of Local Subdwarfs
Reid, I. Neill
We have used new parallax measurements, obtained by the Hipparcos satellite, of fifteen nearby, metal-poor stars to re-define the subdwarf main-sequence. All of these stars have parallaxes determined to an accuracy of at least 12%. Comparing these measurements against previous ground-based data for nine stars reveals a systematic offset of 5%, in …
NGC 2419, M92, and the age gradient in the galactic halo
Bond, Howard E.; Stetson, Peter B.; Richer, Harvey B. +7 more
The WFPC2 camera on HST has been used to obtain photometry of the low-metallicity ([Fe/H] =-2.14), outer-halo globular cluster NGC 2419. Our color-magnitude diagram in (V, V-I) reaches Vlim =~ 27.8, clearly delineating the subgiant and turnoff region and about three magnitudes of the unevolved main sequence. A differential fit of the NG…
A New Pulsation Spectrum and Asteroseismology of delta Scuti.
Templeton, Matthew R.; Bradley, Paul A.; Guzik, Joyce A. +3 more
We present the results of a five-year Strömgren y photometric campaign on δ Scuti. Our data set consists of 6515 discrete differential magnitudes, and spans the period of 1983 June to 1988 September. We found the primary pulsation mode at 59.731129±0.000002 µHz, in close agreement with the frequency determination of Fitch (1976, IAU Colloqui…
Multicolor CCD Photometry of the Poorly Studied Globular Cluster NGC 6541
Alcaino, G.; Liller, W.; Alvarado, F. +3 more
We have carried out the first accurate multicolor (UBVRI) CCD photometry for more than 3000 stars (12m.3<V<21m.0) in the field of the globular cluster NGC 6541. This cluster was neglected in photometric studies after two photographic investigations by Alcaino (1971, A&A;, 13, 399; 1979, A&AS, 35, 233). The color…
Systematic Errors in the FK5 Catalog as Derived from CCD Observations in the Extragalactic Reference Frame.
Stone, Ronald C.
This paper presents new positions for 689 FK5 stars determined directly in the extragalactic reference system from CCD scan observations made with the Flagstaff Astrometric Scanning Transit Telescope (FASTT). All the observations were made in 1994-1996 with an accuracy of ∼±40 mas in each coordinate. When these positions are compared with their co…
The Program to Link the HIPPARCOS Reference Frame to an Extragalactic Reference System Using the Fine Guidance Sensors of the Hubble Space Telescope
Benedict, G. F.; Franz, O. G.; Hemenway, P. D. +19 more
The Hipparcos Satellite Mission has produced positions, proper motions, and parallaxes of unprecedented accuracy for 118,000 stars. For the positions and proper motions to represent true directions and physical motions in space, they must refer to an accurate realization of a nonrotating (inertial) reference frame. One of the major problems confro…
Chromospherically Active Stars. XVI. The Double-Lined Binary 42 Capricorni
Fekel, Francis C.
New spectroscopic observations of the chromospherically active binary, 42 Capricorni, have resulted in the detection of lines of the secondary, improved orbital elements, and the determination of fundamental properties of the components. 42 Cap has an orbital period of 13.174004 d, an eccentricity of 0.176, and a mass ratio A/B of 1.375. No eviden…