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The optical counterpart to γ-ray burst GRB970228 observed using the Hubble Space Telescope
Livio, Mario; Kouveliotou, Chryssa; Sahu, Kailash C. +7 more
Although more than 2,000 astronomical γ-ray bursts (GRBs) have been detected, and numerous models proposed to explain their occurrence1, they have remained enigmatic owing to the lack of an obvious counterpart at other wavelengths2-5. The recent ground-based detection6,7 of a transient optical source in the vicinit…
An Empirical Study of the Electron Temperature and Heavy Ion Velocities in the South Polar Coronal Hole
Gloeckler, George; Geiss, Johannes; Fisk, Lennard A. +2 more
The solar wind ions flowing outward through the solar corona generally have their ionic fractions `freeze-in' within 5 solar radii. The altitude where the freeze-in occurs depends on the competition between two time scales: the time over which the wind flows through a density scale height, and the time over which the ions achieve ionization equili…
Steps toward Determination of the Size and Structure of the Broad-Line Region in Active Galactic Nuclei. XI. Intensive Monitoring of the Ultraviolet Spectrum of NGC 7469
Shull, J. M.; Malkan, M. A.; Nandra, K. +54 more
From 1996 June 10 to July 29, the International Ultraviolet Explorer monitored the Seyfert 1 galaxy NGC 7469 continuously in an attempt to measure time delays between the continuum and emission-line fluxes. From the time delays, one can estimate the size of the region dominating the production of the UV emission lines in this source. We find the s…
Patchy intergalactic He II absorption in HE 2347-4342. II. The possible discovery of the epoch of He-reionization
Reimers, D.; Wamsteker, W.; Rodriguez-Pascual, P. +3 more
We report on observations of redshifted Heii303.8 Angstroms absorption in the high-redshift QSO HE2347-4342 (z=2.885, V=16.1) with the Goddard High Resolution Spectrograph on board HST in its low resolution mode (bigtriangleup lambda = 0.7 Angstroms). With f_λ=3.6\ 10(-15) ergcm(-2) s(-1) Angstroms(-1) at the expected position of Heii304 Angstroms…
The Ultraviolet Properties of the Narrow-Line Quasar I Zw 1
Laor, Ari; Green, Richard F.; Jannuzi, Buell T. +1 more
I Zwicky 1 (I Zw 1) is the prototype narrow-line quasar. Its narrow-line profiles minimize blending effects and thus allow a significantly more accurate study of individual quasar emission lines. We report here the results of our study of the 1150-3250 Å emission of I Zw 1 using a high signal-to-noise (50-120) spectrum obtained with the Faint Obje…
The Nature of Compact Galaxies in the Hubble Deep Field. I. Global Properties1,
Illingworth, Garth D.; Faber, S. M.; Koo, David C. +5 more
We present 10 m Keck spectroscopy and photometry for a sample of 61 small (r1/2 <= 0.5"), faint (I814 <= 23.74), high-surface brightness (µI814 < 22.2 mag arcsec-2) galaxies in fields flanking the Hubble Deep Field. The majority of this empirically defined sample of compact galaxies lies a…
The Abundance of Interstellar Nitrogen
Sofia, Ulysses J.; Meyer, David M.; Cardelli, Jason A.
Using the Hubble Space Telescope Goddard High Resolution Spectrograph (GHRS), we have obtained high S/N echelle observations of the weak interstellar N I λλ1160, 1161 absorption doublet toward the stars γ Cas, λ Ori, ι Ori, κ Ori, δ Sco, and κ Sco. In combination with a previous GHRS measurement of N I toward ζ Oph, these new observations yield a …
External supply of oxygen to the atmospheres of the giant planets
Lellouch, E.; Encrenaz, T.; de Graauw, T. +3 more
The atmospheres of the giant planets are reducing, being mainly composed of hydrogen, helium and methane. But the rings and icy satellites that surround these planets, together with the flux of interplanetary dust, could act as important sources of oxygen, which would be delivered to the atmospheres mainly in the form of water ice or silicate dust…
A Catalog of Morphological Types in 10 Distant Rich Clusters of Galaxies
Smail, Ian; Ellis, Richard S.; Dressler, Alan +4 more
We present catalogs of objects detected in deep images of 11 fields in 10 distant clusters obtained using WFPC-2 on board the Hubble Space Telescope. The clusters span the redshift range z = 0.37-0.56 and are the subject of a detailed ground- and space-based study to investigate the evolution of galaxies as a function of environment and epoch. The…
A Coronal Spectrum in the 500--1610 Angstrom Wavelength Range Recorded at a Height of 21,000 Kilometers above the West Solar Limb by the SUMER Instrument on Solar and Heliospheric Observatory
Wilhelm, K.; Curdt, W.; Schühle, U. +4 more
We present a solar coronal spectrum recorded by the extreme UV spectrometer SUMER on the Solar and Heliospheric Observatory. The spectrum was taken between 21:28 UT on 1996 June 25 and 02:47 UT on 1996 June 26, at a height of 21,000 km above the west equatorial limb with the slit oriented in the north-south direction. At the time of the observatio…