Search Publications
Measurements of Solar Magnetic Element Motion from High-Resolution Filtergrams
Berger, Thomas E.; Title, Alan M.; Löfdahl, Mats G. +1 more
Solar photospheric flowfield properties on sub-0.5" scales are measured using local correlation tracking (LCT) and object tracking of magnetic bright points (MBPs: photospheric bright points associated with magnetic elements). The dataset is a 70 minute time series of cospatial and cotemporal G-band 4305 Å and wideband 4686 Å filtergrams obtained …
Binary Stars in the Orion Trapezium Cluster Core
Beckwith, Steven V. W.; Petr, Monika G.; Coudé du Foresto, Vincent +2 more
We have obtained high angular resolution (0.13" FWHM) near-infrared images of the central ~40" × 40" of the Trapezium cluster, using a speckle holography technique that we describe in detail. A search for close binary systems was made in Ks (2.16 µm) and H (1.65 µm) mosaic images, in which 45 and 35 stars were detected, resp…
The absolute magnitudes of RR Lyraes from HIPPARCOS parallaxes and proper motions
Garrido, R.; Evans, D. W.; Solano, E. +5 more
We have used HIPPARCOS proper motions and the method of Statistical Parallax to estimate the absolute magnitude of RR Lyrae stars. In addition we used the HIPPARCOS parallax of RR Lyrae itself to determine it's absolute magnitude. These two results are in excellent agreement with each other and give a zero-point for the RR Lyrae M_v,[Fe/H] relatio…
Galaxy-Galaxy Lensing in the Hubble Deep Field: The Halo Tully-Fisher Relation at Intermediate Redshift
Gwyn, Stephen D. J.; Hudson, Michael J.; Dahle, Håkon +1 more
A tangential distortion of background source galaxies around foreground lens galaxies in the Hubble Deep Field is detected at the 99.3% confidence level. An important element of our analysis is the use of photometric redshifts to determine distances of lens and source galaxies and rest-frame B-band luminosities of the lens galaxies. The lens galax…
The Relationship between Galaxies and Low-Redshift Weak Lyα Absorbers in the Directions of H1821+643 and PG 1116+215
Tripp, Todd M.; Savage, Blair D.; Lu, Limin
To study the nature of low-z Lyα absorbers in the spectra of QSOs, we have obtained high signal-to-noise ratio (S/N) UV spectra of H1821+643 (zem = 0.297) and PG 1116+215 (zem = 0.177) with the Goddard High-Resolution Spectrograph on the Hubble Space Telescope. The spectra have minimum S/Ns of ~70-100 and 3 σ limiting equival…
The Distance to the Large Magellanic Cloud from the Eclipsing Binary HV 2274
Ribas, I.; Fitzpatrick, E. L.; Guinan, E. F. +6 more
The distance to the Large Magellanic Cloud (LMC) is crucial for the calibration of the cosmic distance scale. We derive a distance to the LMC based on an analysis of ground-based photometry and Hubble Space Telescope (HST)-based spectroscopy and spectrophotometry of the LMC-eclipsing binary system HV 2274. Analysis of the optical light curve and t…
Quantitative spectroscopy of Wolf-Rayet stars in HD97950 and R136a - the cores of giant HII regions
Crowther, P. A.; Dessart, Luc
We present quantitative analyses of Wolf-Rayet stars in the cores of two giant Hii regions - HD97950 in NGC3603 and R136a in 30 Doradus - based on archive Hubble Space Telescope (HST) spectroscopy. We confirm previous WN6h+abs classifications for components A1, B and C in HD97950, while classifications for R136a1-3 are revised from O3If^*/WN6 to W…
Large-scale coronal heating by the small-scale magnetic field of the Sun
Schrijver, C. J.; Tarbell, T. D.; Shine, R. A. +6 more
Magnetic fields play a crucial role in heating the outer atmospheres of the Sun and Sun-like stars, but the mechanisms by which magnetic energy in the photosphere is converted to thermal energy in the corona remain unclear. Observations show that magnetic fields emerge onto the solar surface as bipolar regions with a broad range of length scales. …
Detection of Abundant CO2 Ice in the Quiescent Dark Cloud Medium toward Elias 16
de Graauw, Th.; Prusti, T.; van Dishoeck, E. F. +9 more
We report the first detection of solid carbon dioxide (CO2) in quiescent regions of a dark cloud in the solar neighborhood, a result that has important implications for models of ice formation and evolution in the interstellar medium. The K-type field star Elias 16 was previously known to display solid-state absorption features of H
Measurement of the electron temperature gradient in a solar coronal hole
Wilhelm, K.; Fludra, A.; Lemaire, P. +3 more
It has long been established that the high speed solar wind streams observed at 1 A.U. originate from the coronal hole regions of the Sun. Theoretical modelling of the acceleration mechanism depends critically on the value of the maximum of temperature existing close to the Sun. Measurements of the temperature in coronal holes prior to SOHO are un…