Search Publications
Evidence for Chromospheric Evaporation in the Late Gradual Flare Phase from SOHO/CDS Observations
De Pontieu, B.; Czaykowska, A.; Alexander, D. +1 more
Using extreme-ultraviolet (EUV) spectroheliograms from the first intentional postflare observations with the Coronal Diagnostic Spectrometer (CDS) on board SOHO, we determine relative line-of-sight velocities and their temporal evolution during the gradual flare phase of an M6.8 two-ribbon flare that occurred on 1998 April 29. Dopplergrams in line…
Hubble Space Telescope Observations of the Broad Absorption Line QuasarPG 0946+301
Korista, Kirk T.; Arav, Nahum; de Kool, Martijn +2 more
We analyze Hubble Space Telescope (HST) and ground-based spectra of the brightest broad absorption line (BAL) quasar in the UV: PG 0946+301. A detailed study of the absorption troughs as a function of velocity is presented, facilitated by the use of a new algorithm to solve for the optical depth as a function of velocity for multiplet lines. We fi…
Evidence for a Massive Black Hole in the S0 Galaxy NGC 4342
Cretton, Nicolas; van den Bosch, Frank C.
We present axisymmetric dynamical models of the edge-on S0 galaxy NGC 4342. This small low-luminosity galaxy harbors, in addition to its outer disk, a bright nuclear stellar disk. A combination of observations from the ground and with the Hubble Space Telescope (HST) has shown that NGC 4342 rotates rapidly and has a strong central increase in velo…
High-resolution Imaging of the Solar Chromosphere/Corona Transition Region
Schrijver, C. J.; De Pontieu, B.; Title, A. M. +1 more
The properties of a previously unresolved extreme-ultraviolet (EUV) emission in solar active regions are examined using coordinated data sets from the Transition Region and Coronal Explorer (TRACE) satellite, the Michelson Doppler Imager on the Solar and Heliospheric Observatory satellite, the Soft X-Ray Telescope (SXT) on the Yohkoh satellite, an…
Dispersal of Magnetic Flux in the Quiet Solar Photosphere
Schrijver, C. J.; Shine, R. A.; Title, A. M. +1 more
We study the random walk of magnetic flux concentrations on two sequences of high-resolution magnetograms, observed with the Michelson Doppler Imager on board SOHO. The flux contained in the concentrations ranges from |Φ|=1018 Mx to |Φ|=1019 Mx, with an average of |Φ|=2.5×1018 Mx. Larger concentrations tend to move…
HUBBLE SPACE TELESCOPE Near-infrared and Optical Imaging of Faint Radio Sources in the Distant Cluster CL 0939+4713
Kneib, J. -P.; Ivison, R. J.; Morrison, G. +4 more
We present deep Hubble Space Telescope Near-Infrared Camera and Multiobject Spectrograph (NICMOS) and Wide Field and Planetary Camera 2 (WFPC2) optical imaging of a small region in the core of the distant rich cluster Cl 0939+4713 (z=0.41). We compare the optical and near-infrared morphologies of cluster members and find apparent small-scale optic…
EUV Spectral Line Profiles in Polar Coronal Holes from 1.3 to 3.0 Rsolar
Cranmer, S. R.; Fineschi, S.; Noci, G. +7 more
Spectral line profiles have been measured for H I λ1216, O VI λλ1032, 1037, and Mg X λ625 in a polar coronal hole observed during 1997 September 15-29, at projected heliographic heights ρ between 1.34 and 2.0 Rsolar. Observations of H I λ1216 and the O VI doublet from 1997 January for ρ=1.5-3.0 Rsolar are provided for compari…
Photospheric Magnetic Reconnection and Canceling Magnetic Features on the Sun
Litvinenko, Yuri E.
Parameters describing quasi-steady reconnecting current sheets in the plasma of the solar photosphere and chromosphere are computed using the VAL-C atmospheric model. In particular, the inflow speed for the Sweet-Parker magnetic reconnection is found for a sheet whose width is determined by the density scale height. The resulting speed of several …
Ultraviolet and Multiwavelength Variability of the Blazar 3C 279: Evidence for Thermal Emission
Maraschi, L.; Chiappetti, L.; Pian, E. +13 more
The γ-ray blazar 3C 279 was monitored on a nearly daily basis with IUE, ROSAT, and EGRET for 3 weeks between 1992 December and 1993 January. During this period, the blazar was at a historical minimum at all wavelengths. Here we present the UV data obtained during this multiwavelength campaign. A maximum UV variation of ~50% is detected, while duri…
Analysis of Transition-Region Emission-Line Profiles from Full-Disk Scans of the Sun Using the SUMER Instrument on SOHO
Peter, H.
We examine statistical properties of line profiles seen in full-disk observations with the UV spectrograph SUMER on board SOHO. In the SUMER data archive, full-disk data with complete spectral information are available only for wavelength regions including the He I (584 Å), Ne VIII (770 Å), C III (977 Å) and C IV (1548 Å) emission lines. In this p…