Search Publications
Sustaining the Quiet Photospheric Network: The Balance of Flux Emergence, Fragmentation, Merging, and Cancellation
Shine, Richard A.; Title, Alan M.; Schrijver, Carolus J. +2 more
The magnetic field in the solar photosphere evolves as flux concentrations fragment in response to sheared flows, merge when they collide with others of equal polarity, or (partially) cancel against concentrations of opposite polarity. Newly emerging flux replaces the canceled flux. We present a quantitative statistical model that is consistent wi…
Ages of Globular Clusters from HIPPARCOS Parallaxes of Local Subdwarfs
Fusi Pecci, Flavio; Carretta, Eugenio; Clementini, Gisella +3 more
We report here initial but strongly conclusive results for absolute ages of Galactic globular clusters (GGCs). This study is based on high-precision trigonometric parallaxes from the HIPPARCOS satellite coupled with accurate metal abundances ([Fe/H], [O/Fe], and [α/Fe]) from high-resolution spectroscopy for a sample of about thirty subdwarfs. Syst…
Interstellar Abundance Gradients in NGC 2403: Comparison to M33
Garnett, D. R.; Skillman, E. D.; Dufour, R. J. +2 more
We present new long-slit spectra of 12 H II regions in the Scd spiral galaxy NGC 2403. Gas-phase element abundances for O, N, S, Ne, and Ar were estimated using direct measurements of electron temperature based on detections of [O III] λ4363, [S III] λ6312, and [O II] λ7320-7330, and from theoretical photoionization analysis. We find abundance gra…
A Pair of Lensed Galaxies at z = 4.92 in the Field of CL 1358+62
van Dokkum, Pieter G.; Franx, Marijn; Kelson, Daniel D. +2 more
The cluster CL 1358+62 displays a prominent red arc in WFPC2 images obtained with the Hubble Space Telescope. Keck spectra of the arc show Lyα emission at 7204 Å, a continuum drop blueward of the line, and several absorption lines to the red. We identify the arc as a gravitationally lensed galaxy at a redshift of z = 4.92. It is the highest redshi…
The Structure and Appearance of Protostellar Accretion Disks: Limits on Disk Flaring
Henning, Th.; Bell, K. R.; Cassen, P. M. +1 more
Vertical structure models are used to investigate the structure of protostellar, α-law, accretion disks. Conditions investigated cover a range of mass fluxes (10-9 to 10-5 M⊙ yr-1), viscous efficiencies (α = 10-2 and 10-4), and stellar masses (0.5-3 M⊙). Analytic formulae…
Discovery of Extended Blue Horizontal Branches in Two Metal-rich Globular Clusters
Rich, R. Michael; Renzini, Alvio; Piotto, Giampaolo +7 more
We have used WFPC2 to construct B, V color-magnitude diagrams of four metal-rich globular clusters, NGC 104 (47 Tuc), NGC 5927, NGC 6388, and NGC 6441. All four clusters have well populated red horizontal branches (RHB), as expected for their metallicity. However, NGC 6388 and 6441 also exhibit a prominent blue horizontal-branch (BHB) extension, i…
The Nature of Compact Galaxies in the Hubble Deep Field. II. Spectroscopic Properties and Implications for the Evolution of the Star Formation Rate Density of the Universe1,
Illingworth, Garth D.; Faber, S. M.; Koo, David C. +5 more
We present a spectroscopic study of 51 compact field galaxies with redshifts z < 1.4 and apparent magnitudes I814 < 23.74 in the flanking fields of the Hubble Deep Field. These galaxies are compact in the sense that they have small apparent half-light radii (r1/2 <= 0.5") and high surface brightnesses (µI8…
A Powerful Nuclear Starburst in the Seyfert Galaxy Markarian 477: Implications for the Starburst-Active Galactic Nucleus Connection
Leitherer, C.; Wilson, A. S.; Heckman, T. M. +5 more
There have been many suggestions that starbursts may play an important role in Seyfert galaxies. Recent analyses of the UV, optical, and near-IR ``featureless continuum'' (FC) in type 2 Seyfert nuclei have provided indirect evidence that the FC may be produced by a compact starburst and that this starburst may provide a power source for the pronou…
Evidence of an Erupting Magnetic Flux Rope: LASCO Coronal Mass Ejection of 1997 April 13
St. Cyr, O. C.; Paswaters, S. E.; Simnett, G. M. +7 more
A coronal mass ejection (CME) observed by LASCO exhibits evidence that its magnetic field geometry is that of a flux rope. The dynamical properties throughout the fields of view of C2 and C3 telescopes are examined. The results are compared with theoretical predictions based on a model of solar flux ropes. It is shown that the LASCO observations a…
Synthetic Spectra of Hydrodynamic Models of Type Ia Supernovae
Baron, E.; Branch, David; Hauschildt, Peter H. +2 more
We present detailed non-LTE synthetic spectra of hydrodynamic supernovae (SNe) Ia models. We make no assumptions about the form of the spectrum at the inner boundary. We calculate both Chandrasekhar-mass deflagration models and sub-Chandrasekhar ``helium detonators.'' Gamma-ray deposition is handled in a simple, accurate manner. We have parameteri…