Search Publications
On the Ionizing Continuum in Active Galactic Nuclei: Clues from the Infrared Space Observatory
Prieto, M. Almudena; Viegas, Sueli M.
The Infrared Space Observatory (ISO) coronal line spectrum of the brightest Seyfert galaxies from the CfA sample is presented and modeled. ISO observations of [O IV] 25.9 µm, [Ne V] 14.3 µm, [Mg VIII] 3.02 µm, and [Si IX] 2.58 µm lines are presented; their relationship with the soft part of the ionizing spectrum from 50 to …
Water and Dust Emission from W Hydrae
Elitzur, Moshe; Zubko, Victor
We construct a self-consistent model for the wind around W Hydrae by solving the coupled equations describing the hydrodynamics and dust radiative transfer problems. The model matches simultaneously the observed continuum radiation and wind velocity profile. The water line emission is calculated next using the water abundance as the only free para…
Extreme-Ultraviolet Spectral Line Widths in Quiet-Sun Coronal Plasmas at Distances of 1.03<=Rsolar<=1.45 along the Solar Equatorial Plane
Doschek, G. A.; Feldman, U.
We measure the full width at half-maximum intensity (FWHM) of extreme-ultarviolet (EUV) spectral line profiles as a function of height in the Sun's equatorial west limb streamer region using EUV spectra recorded by the Solar Ultraviolet Measurements of Emitted Radiation (SUMER) spectrometer on the Solar and Heliospheric Observatory (SOHO) spacecra…
HE 2-113: A Multipolar Planetary Nebula with Rings around a Cool Wolf-Rayet Star
Sahai, Raghvendra; Nyman, Lars-Åke; Wootten, Alwyn
We present Hα imaging and molecular-line (CO) observations of He 2-113, an object which belongs to a rare class of planetary nebulae with Wolf-Rayet type central stars. The Hα images, obtained with the Hubble Space Telescope Wide-Field Planetary Camera 2, show that He 2-113 has an overall bipolar shape and two bright, knotty, compact ringlike stru…
Far-Ultraviolet Echoes from the Frontier between the Solar Wind and the Local Interstellar Cloud
Ben-Jaffel, L.; Ratkiewicz, R.; Puyoo, O.
We propose that first-order Fermi acceleration of Lyα photons should occur at the interface region between the solar and interstellar winds. In this process, photons are Doppler-shifted toward shorter wavelengths each time they are scattered by hydrogen neutrals that have been decelerated by charge exchange with protons in the transition region wr…
Properties of Dust Grains in Planetary Nebulae. I. The Ionized Region of NGC 6445
Martin, P. G.; Ferland, Gary J.; Van de Steene, Griet C. +3 more
One of the factors influencing the spectral evolution of a planetary nebula is the fate of the dust grains that are emitting the infrared continuum. Several processes have been proposed that either destroy the grains or remove them from the ionized region. To test whether these processes are effective, we study new infrared spectra of the evolved …
Solar and Heliospheric Observatory Sungrazing Comets with Prominent Tails: Evidence on Dust-Production Peculiarities
Sekanina, Zdenek
A preliminary examination of the tails of 11 Solar and Heliospheric Observatory (SOHO) sungrazers, observed between 3 and 20 Rsolar on their approach to the Sun, provides information on dust ejected from these comets and on the forces to which the microscopic grains are subjected. Images taken at times of the SOHO spacecraft's transit a…
The Formation of a Multiple Planetary Nebula:Hubble Space Telescope/WFPC2 Observations of KJPN 8
López, J. A.; Steffen, W.; Meaburn, J. +3 more
KjPn 8 is an extreme polypolar planetary nebula with a large-scale structure characterized by a giant biconical envelope. Spasmodic bipolar ejections in changing directions have occurred over thousands of years to create this peculiar nebula. Narrowband images of the core of KjPn 8 have now been obtained with the Wide Field Planetary Camera 2 on b…
A Broad 22 Micron Emission Feature in the Carina Nebula H II Region
Onaka, Takashi; Chan, Kin-Wing
We report the detection of a broad 22 µm emission feature in the Carina Nebula H II region by the Infrared Space Observatory (ISO) short-wavelength spectrometer. The feature shape is similar to that of the 22 µm emission feature of newly synthesized dust observed in the Cassiopeia A supernova remnant. This finding suggests that both of…
Microscale Structures on the Quiet Sun and Coronal Heating
Vial, J. -C.; Bocchialini, K.; Velli, M. +3 more
We present some results concerning transient brightenings on the quiet Sun, based on data from the Extreme-Ultraviolet Imaging Telescope on board the Solar and Heliospheric Observatory. Histograms of intensity are found to be well fitted by χ2 distributions for small values of the intensity, while at high intensities power-law distribut…