Search Publications
The afterglow, redshift and extreme energetics of the γ-ray burst of 23 January 1999
Kelson, D. D.; Malkan, M. A.; Harrison, F. A. +26 more
Long-lived emission, known as afterglow, has now been detected from about a dozen γ-ray bursts. Distance determinations place the bursts at cosmological distances, with redshifts, z, ranging from ~1 to 3. The energy required to produce these bright γ-ray flashes is enormous: up to ~10 53erg, or 10 per cent of the rest-mass energy of a n…
A giant periodic flare from the soft γ-ray repeater SGR1900+14
Cline, T.; Hurley, K.; Golenetskii, S. +11 more
Soft γ-ray repeaters are transient sources of high-energy photons; they emit sporadic and short (about 0.1s) bursts of `soft' γ-rays during periods of activity, which are often broken by long stretches of quiescence. These objects are associated with neutron stars in young supernova remnants. The event of 5 March 1979 was the most intense burst to…
Accretion of low-metallicity gas by the Milky Way
Savage, B. D.; Wakker, B. P.; Peletier, R. F. +7 more
Models of the chemical evolution of the Milky Way suggest that the observed abundances of elements heavier than helium (`metals') require a continuous infall of gas with metallicity (metal abundance) about 0.1 times the solar value. An infall rate integrated over the entire disk of the Milky Way of ~1 solar mass per year can solve the `G-dwarf pro…
Discovery of a massive equatorial torus in the η Carinae stellar system
de Graauw, Th.; Waters, L. B. F. M.; Mutschke, H. +10 more
The enigmatic object η Carinae is believed to represent an important, but short-lived, unstable phase in the life of the most massive stars, occurring shortly before they explode as supernovae or collapse directly to black holes. The putative binary system believed to constitute η Carinae survived an outburst in the previous century that lasted 20…
Disappearance of stellar debris disks around main-sequence stars after 400 million years
Kessler, M. F.; Siebenmorgen, R.; Metcalfe, L. +7 more
Almost 5 billion years ago, the Sun formed in a local contraction of a cloud of molecular gas. A rotating disk of gas and dust is believed to have fed material onto the proto-Sun for the first few million years of its life, and to have formed the planets, comets and other Solar System objects. Similar disks, but with less mass, have been observed …
Spectroscopic identification of a galaxy at a probable redshift of z = 6.68
Chen, Hsiao-Wen; Lanzetta, Kenneth M.; Pascarelle, Sebastian
The detection and identification of distant galaxies is an important goal of observational cosmology, as such galaxies are seen at a time when the Universe was very young. The development of new techniques and instrumentation permits the search for ever-fainter galaxies, and so aids attempts to determine when the first stars and galaxies formed. H…
Discovery of molecular hydrogen in a high-velocity cloud of the Galactic halo
de Boer, K. S.; Grewing, M.; Richter, P. +4 more
The Milky Way's halo contains clouds of neutral hydrogen with high radial velocities which do not follow the general rotational motion of the Galaxy. Few distances to these high-velocity clouds are known, so even gross properties such as total mass are hard to determine. As a consequence, there is no generally accepted theory regarding their origi…
A distance to the galaxy NGC4258 from observations of Cepheid variable stars
Zepf, Stephen E.; Davis, Marc; Madore, Barry F. +5 more
Cepheid variable stars pulsate in a way that is correlated with their intrinsic luminosity, making them useful as `standard candles' for determining distances to galaxies; the potential systematic uncertainties in the resulting distances have been estimated to be only 8-10%. They have played a crucial role in establishing the extragalactic distanc…
Stability of Neptune's ring arcs in question
Schneider, Glenn; Dumas, Christophe; Terrile, Richard J. +2 more
Although all four of the gas-giant planets in the Solar System have ring systems, only Neptune exhibits `ring arcs'-stable clumps of dust that are discontinuous from each other. Two basic mechanisms for confining the dust to these arcs have been proposed. The firstrelies on orbital resonances with two shepherding satellites, while the second invok…