Search Publications
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 intergalactic red-giant-branch stars in the Virgo cluster
Ferguson, Henry C.; von Hippel, Ted; Tanvir, Nial R.
It has been suspected for nearly 50 years that galaxy clusters contain a population of intergalactic stars ripped from the galaxies during cluster formation, or when the galactic orbits pass through the cluster centre. Observational support for theexistence of such a stellar population is provided both by measurements of the diffuse light in clust…
The sun's shape and brightness
Kuhn, J. R.; Bush, R. I.; Scherrer, P. +1 more
We present satellite data that show that the sun's shape and temperature vary with latitude in an unexpectedly complex way. Although the solar oblateness shows no evidence of varying with the solar cycle, we find a significant hexadecapole shape term which may vary. We also see a variation of about 1.5 K in the surface temperature with latitude. B…
Long-lived giant cells detected at the surface of the Sun
Scherrer, P. H.; Duvall, T. L.; Beck, J. G.
Giant convective cells have been predicted to exist in the Sun. Such cells should span the entire zone unstable to convective motions - now known to cover the outer 29 per cent of the Sun's radius - and could be dredging up the magnetic flux that is thought to be the source of solar activity (sunspots). Several studies have failed to detect these …
Birth and early evolution of a planetary nebula
Bobrowsky, Matthew; Sahu, Kailash C.; Parthasarathy, M. +1 more
The final expulsion of gas by a star as it forms a planetary nebula - the ionized shell of gas often observed surrounding a young white dwarf - is one of the most poorly understood stages of stellar evolution,. Such nebulae form extremely rapidly (about 100 years for the ionization) and so the formation process is inherently difficult to observe. …
Global warming on Triton
Olkin, C. B.; Franz, O. G.; Buie, M. W. +11 more
Triton, Neptune's largest moon, has been predicted to undergo significant seasonal changes that would reveal themselves as changes in its mean frost temperature. But whether this temperature should at the present time be increasing, decreasing or constant depends on a number of parameters (such as the thermal properties of the surface, and frost m…
A Cepheid distance to the Fornax cluster and the local expansion rate of the Universe
Illingworth, Garth D.; Madore, Barry F.; Freedman, Wendy L. +13 more
Both galaxy distances and velocities are required for the determination of the expansion rate of the Universe, as described by the Hubble constant H0. The radial velocities of galaxies arise not just from this expansion but also from random components and large-scale flows. To reach out to distances dominated by the overall cosmic expan…
Constraints on the Hubble constant from observations of the brightest red-giant stars in a Virgo-cluster galaxy
Harris, William E.; Durrell, Patrick R.; Pierce, Michael J. +1 more
The nearest large groups of elliptical galaxies, in the Virgo and Fornax clusters, play a central role in determinations of the Hubble constant, H0, and hence the cosmological rate of expansion. Because the relative distances between these two clusters and more remote clusters are well known, absolute distance determinations to Virgo an…
Star formation triggered by galaxy collisions
Lutz, Dieter; Genzel, Reinhard; Tacconi, Linda
It is becoming increasingly clear that collisions between galaxies play an important role in galaxy evolution. The ultraluminous infrared galaxies are predominantly powered by enormous star-formation events that are triggered in the last phases of such collisions. These bursts occur just before the galaxies merge to form single elliptical galaxies.
Unexpected stellar velocity distribution in the warped Galactic disk
Lattanzi, M. G.; Drimmel, R.; Smart, R. L. +1 more
It is now over 40 years since radio observations of neutral hydrogen revealed the gaseous disk of our Galaxy to be warped. Subsequently, the warp has been detected in the distribution of Galactic dust, molecular clouds, and luminous stars,. Roughly half of all spiral galaxies have similarly warped disks, which suggests that warps are a common and …