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HUBBLE SPACE TELESCOPE Observations of Galactic Globular Cluster Cores. II. NGC 6273 and the Problem of Horizontal-Branch Gaps
Djorgovski, S. G.; Zoccali, M.; Rich, R. M. +4 more
We present observations of the center of the Galactic globular cluster NGC 6273, obtained with the Hubble Space Telescope Wide Field Planetary Camera 2 as part of the snapshot program GO-7470. A BV color-magnitude diagram (CMD) for ~28,000 stars is presented and discussed. The most prominent feature of the CMD, identified for the first time in thi…
Hubble Space Telescope Observations of the Oldest Star Clusters in the Large Magellanic Cloud
Somerville, Rachel S.; Stetson, Peter B.; Bolte, Michael +2 more
We present V, V-I color-magnitude diagrams (CMDs) for three old star clusters in the Large Magellanic Cloud (LMC): NGC 1466, NGC 2257, and Hodge 11. Our data extend ~3 mag below the main-sequence turnoff, allowing us to determine accurate relative ages and the blue straggler frequencies. Based on a differential comparison of the CMDs, any age diff…
Very High Resolution Ultraviolet Spectroscopy of a Chemically Peculiar Star: Results of the chi LUPI Pathfinder Project
Wahlgren, Glenn M.; Proffitt, Charles R.; Brage, Tomas +2 more
We summarize here the results of a major eight-year investigation of the extraordinarily detailed UV spectrum of the sharp-lined, nonmagnetic, main-sequence, chemically peculiar star chi Lupi (B9.5p HgMn + A2 Vm). The UV observations are composed of 345 Å of the spectrum acquired with the Goddard High Resolution Spectrograph (GHRS) on board the Hu…
A refurbished convergent-point method for finding moving groups in the HIPPARCOS Catalogue
de Bruijne, Jos H. J.
The Hipparcos data allow a major step forward in the research of `moving groups' in the Solar neighbourhood, as the common motion of group members causes converging proper motions. Previous knowledge of these coherent structures in velocity space has always been limited by the availability, reliability and accuracy of ground-based proper-motion me…
Long-term drift of the coronal source magnetic flux and the total solar irradiance
Lockwood, M.; Stamper, R.
We test the method of Lockwood et al [1999] for deriving the coronal source flux from the geomagnetic aa index and show it to be accurate to within 12% for annual means and 4.5% for averages over a sunspot cycle. Using data from four solar constant monitors during 1981-1995, we find a linear relationship between this magnetic flux and the total so…
First Comparison of Ionization and Metallicity in Two Lines of Sight toward HE 1104-1805 AB at z=1.66
Rauch, Michael; Lopez, Sebastian; Smette, Alain +2 more
Using new Hubble Space Telescope Faint Object Spectrograph, the New Technology Telescope ESO Multi Mode Instrument, and Keck HIRES spectra of the gravitationally lensed double QSO HE 1104-1805 AB (zem=2.31) and assuming UV photoionization by a metagalactic radiation field, we derive physical conditions (ionization levels, metal abundanc…
WFPC2 Observations of Compact Star Cluster Nuclei in Low-Luminosity Spiral Galaxies
Ballester, Gilda E.; Krist, John E.; Crisp, David +15 more
We have used the Wide Field Planetary Camera 2 (WFPC2) aboard the Hubble Space Telescope to obtain F450W and F814W (B- and I-band) observations of the compact star cluster nuclei of the nearby, late-type, low-luminosity spiral galaxies NGC 4395, NGC 4242, and ESO 359-029. In addition, we analyze archival WFPC2 observations of the compact star clus…
A Consistency Test of Spectroscopic Gravities for Late-Type Stars
Lambert, David L.; Allende Prieto, Carlos; García López, Ramón J. +1 more
Chemical analyses of late-type stars are usually carried out following the classical recipe: LTE line formation and homogeneous, plane-parallel, flux-constant, and LTE model atmospheres. We review different results in the literature that have suggested significant inconsistencies in the spectroscopic analyses, pointing out the difficulties in deri…
High-Resolution Infrared Space Observatory Spectroscopy of the Unidentified 21 Micron Feature
Volk, Kevin; Kwok, Sun; Hrivnak, Bruce J.
We present Infrared Space Observatory SWS06 mode observations of the 21 µm feature in eight sources, including a first detection of the feature in IRAS Z02229+6208. The observed feature peak-to-continuum ratios range from 0.13 in IRAS Z02229+6208 to 1.30 in IRAS 07134+1005. The normalized spectra, obtained by the removal of the underlying co…
The Solar Origin of Corotating Interaction Regions and Their Formation in the Inner Heliosphere
Bochsler, P.; Balogh, A.; Lucek, E. +20 more
Corotating Interaction Regions (CIRs) form as a consequence of the compression of the solar wind at the interface between fast speed streams and slow streams. Dynamic interaction of solar wind streams is a general feature of the heliospheric medium; when the sources of the solar wind streams are relatively stable, the interaction regions form a pa…