Search Publications
What is Moss?
Fletcher, L.; Schrijver, C. J.; De Pontieu, B. +3 more
TRACE observations of active regions show a peculiar extreme ultraviolet (EUV) emission over certain plage areas. Termed `moss' for its spongy, low-lying, appearance, observations and modeling imply that the phenomenon is caused by thermal conduction from 3-5 MKcoronal loops overlying the plage: moss is the upper transition region emission of hot …
PRONAOS observations of MCLD 123.5 + 24.9: cold dust in the Polaris cirrus cloud
Boulanger, F.; Abergel, A.; Giard, M. +10 more
We present submillimeter observations between 200 and 600 microns obtained with the French balloon-borne instrument SPM/PRONAOS toward the high latitude cirrus cloud MCLD 123.5+24.9 in the Polaris Flare. These sensitive measurements allow for the first time to study in details the submillimeter dust emission of cirruses at the arc minute scale. Th…
Ring Diagram Analysis of Near-Surface Flows in the Sun
Basu, Sarbani; Antia, H. M.; Tripathy, S. C.
Ring diagram analysis of solar oscillation power spectra obtained from Michelson Doppler Imager data is carried out to study the velocity fields in the outer part of the solar convection zone. The three-dimensional power spectra are fitted to a model that has a Lorentzian profile in frequency and includes the advection of the wave front by horizon…
Galactic bulges from Hubble Space Telescope NICMOS observations: ages and dust
Burkert, A.; Balcells, Marc; Peletier, Reynier F. +4 more
We present optical and near-infrared colour maps of the central regions of bulges of S0 and spiral galaxies obtained with WFPC2 and NICMOS on the Hubble Space Telescope (HST). By combined use of HST and ground-based data, the colour information spans a region from a few tens of pc to a few kpc. In almost all galaxies, the colour profiles in the ce…
Properties of Quiet-Sun Coronal Plasmas at Distances of 1.03<=Rsolar<=1.50 along the Solar Equatorial Plane
Wilhelm, K.; Schühle, U.; Doschek, G. A. +1 more
We determine the physical properties, i.e., electron temperature, density, line-of-sight emission measure, and element-abundance variation with height, in the Sun's equatorial west limb streamer region from extreme-ultraviolet (EUV) spectra recorded by the Solar Ultraviolet Measurements of Emitted Radiation (SUMER) spectrometer on the Solar and He…
The Fading Optical Counterpart of GRB 970228, 6 Months and 1 Year Later
Fruchter, Andrew S.; Mutchler, Max; Livio, Mario +20 more
We report on observations of the fading optical counterpart of the gamma-ray burst GRB 970228, made with the Hubble Space Telescope (HST) and the Keck I telescope. The gamma-ray burst (GRB) was observed approximately 6 months after outburst, on 1997 September 4, using the HST/STIS CCD, and approximately 1 year after outburst, on 1998 February 24, …
Effect of the variation of electric-dipole moments on the shape of pressure-broadened atomic spectral lines
Kielkopf, J. F.; Allard, N. F.; Royer, A. +1 more
We derive a classical path expression for a pressure-broadened atomic spectral line shape that allows for an electric-dipole moment that is dependent on the position of perturbers. The theory is applied to the atomic hydrogen Lyman-α and Lyman-β lines broadened by collisions with neutral and ionized atomic hydrogen. The far wings of the Lyman seri…
HST luminosity functions of the globular clusters M10, M22, and M55. A comparison with other clusters
Zoccali, M.; Piotto, G.
From a combination of deep Hubble Space Telescope V and I images with groundbased images in the same bands, we have obtained color-magnitude diagrams of M10, M22, and M55, extending from just above the hydrogen burning limit to the tip of the red giant branch, down to the white dwarf cooling sequence. We have used the color-magnitude arrays to ext…
Plasma Diagnostics of Transition Region ``Moss'' using SOHO/CDS and TRACE
De Pontieu, Bart; Fletcher, Lyndsay
Recent observations of solar active regions with the Transition Region and Coronal Explorer (TRACE) have revealed finely textured, low-lying EUV emission, called the ``moss,'' appearing as a bright dynamic pattern with dark inclusions. The moss has been interpreted as the upper transition region by Berger and coworkers. In this study we use SOHO C…
Nuclear Disks of Gas and Dust in Early-Type Galaxies and the Hunt for Massive Black Holes: Hubble Space Telescope Observations of NGC 6251
Ferrarese, Laura; Ford, Holland C.
We discuss Hubble Space Telescope (HST) optical images and spectra of NGC 6251, a giant E2 galaxy and powerful radio source at a distance of 106 Mpc (for H0=70 km s-1 Mpc-1). The galaxy is known to host a very well-defined dust disk; the exceptional resolution of our V and I images allows a detailed study of the di…