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The Interaction of New and Old Magnetic Fluxes at the Beginning of Solar Cycle 23
Kosovichev, A. G.; Benevolenskaya, E. E.; Hoeksema, J. T. +1 more
The 11 yr cycle of solar activity follows Hale's law by reversing the magnetic polarity of leading and following sunspots in bipolar regions during the minima of activity. In the 1996-1997 solar minimum, most solar activity emerged in narrow longitudinal zones--``active longitudes'' but over a range in latitude. Investigating the distribution of s…
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…
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…
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…
Direct Analysis of Spectra of the Type IC Supernova SN 1994I
Filippenko, Alexei V.; Kirshner, R. P.; Suntzeff, N. B. +12 more
Synthetic spectra generated with the parameterized supernova synthetic-spectrum code SYNOW are compared to observed photospheric-phase spectra of the Type Ic supernova SN 1994I. The observed optical spectra can be well matched by synthetic spectra that are based on the assumption of spherical symmetry. We consider the identification of the infrare…
The Age and Metallicity Range of Early-Type Galaxies in Clusters
Charlot, Stéphane; Ferreras, Ignacio; Silk, Joseph
We present an unbiased method for evaluating the ranges of ages and metallicities that are allowed by the photometric properties of the stellar populations that dominate the light of early-type galaxies in clusters. The method is based on the analysis of morphologically classified early-type galaxies in 17 clusters at redshifts 0.3<~z<~0.9 a…
NICMOS Imaging of the Dusty Microjansky Radio Source VLA J123642+621331 at z = 4.424
Stern, D.; Spinrad, H.; Windhorst, R. A. +3 more
We present the discovery of a radio galaxy at a likely redshift of z=4.424 in one of the flanking fields of the Hubble Deep Field (HDF). Radio observations with the Very Large Array and MERLIN centered on the HDF yielded a complete sample of microjansky radio sources, of which about 20% have no optical counterpart to I<=25 mag. In this Letter, …
The ``Water-Fountain Nebula'' IRAS 16342-3814: Hubble Space Telescope/Very Large Array Study of a Bipolar Protoplanetary Nebula
Sahai, Raghvendra; Morris, Mark; Zijlstra, Albert +2 more
We present Hubble Space Telescope (HST) Wide-Field and Planetary Camera 2 images and VLA OH maser emission-line maps of the cold infrared object IRAS 16342-3814, believed to be a protoplanetary nebula. The HST images show an asymmetrical bipolar nebula, with the lobes separated by a dark equatorial waist. The two bright lobes and the dark waist ar…
The ISO/SWS Spectrum of IRC +10216: The Vibrational Bands of C2H2 and HCN
Cernicharo, José; Yamamura, Issei; González-Alfonso, Eduardo +4 more
We present the Infrared Space Observatory/Short-Wavelength Spectrometer full grating resolution spectrum of IRC +10216, which is dominated by strong absorption/emission bands of C2H2 and HCN. All C2H2 bands and the strong near-infrared stretching bands of HCN are observed in absorption, whereas the funda…