Search Publications
Determination of the Formation Temperature of Si IV in the Solar Transition Region
Wilhelm, K.; Schühle, U.; Lemaire, P. +4 more
Using spectra obtained with the Solar Ultraviolet Measurements of Emitted Radiation (SUMER) spectrometer flown on the Solar and Heliospheric Observatory spacecraft, we deduce the temperature of formation of the Si IV ion in the solar transition region from the Si IV ultraviolet spectral line intensity ratio, 3p 2P3/2-3d …
The Amount of CH Produced during CH+ Synthesis in Interstellar Clouds
Welty, D. E.; Federman, S. R.; Cardelli, Jason A.
A particularly useful constraint for models of CH+ formation in interstellar clouds is knowledge of the amount of CH associated with CH+ synthesis. For lines of sight with no detectable CN absorption, this column of CH can be inferred through a combined analysis of C I excitation and simplified chemical models. The approach i…
Abell 2218: X-Ray Lensing, Merger, or Both?
Markevitch, Maxim
Comparison of the high-resolution X-ray image of A2218 obtained with the ROSAT HRI with the optical HST image shows several interesting correlations. The X-ray emission within a 1' radius core is resolved into several components; the central dominant galaxy does not coincide with either of them or with the emission centroid. The major X-ray peak i…
Signatures of Acoustic and Magnetic Waves in Solar and Stellar Coronae
Judge, Philip G.; Hansteen, Viggo H.; Wikstøl, Øivind
Time-dependent dynamical calculations of the radiating gas in solar coronal flux tubes are used to identify features of UV spectral-line profiles that can reveal the direction in which wave energy flows through the solar transition region. The profile features survive spatial and temporal averaging through nonlinear dependencies of line emission c…
An Anomalous Ultraviolet Extension in NGC 6251
Crane, P.; Vernet, J.
Deep U-band Faint Object Camera (FOC) images of the nuclear region of NGC 6251 have revealed a region of extended emission that is most probably radiation scattered from a continuum source in the nucleus. This radiation lies interior to a dust ring, is nearly perpendicular to the radio jet axis, and is seen primarily in the FOC U and B filters. Th…
Atomic Physics with the Goddard High Resolution Spectrograph on the Hubble Space Telescope. III. Oscillator Strengths for Neutral Carbon
Federman, S. R.; Cardelli, Jason A.; Zsargo, J.
High quality spectra of interstellar absorption from C I toward β1 Sco, ρ Oph A, and χ Oph were obtained with the Goddard High Resolution Spectrograph on HST. Many weak lines were detected within the observed wavelength intervals: 1150-1200 Å for β1 Sco and 1250-1290 Å for ρ Oph A and χ Oph. Curve-of-growth analyses were perf…
Lyα Absorption-Line Systems in the Gravitational Lens Q0957+5611
Bruhweiler, F. C.; Michalitsianos, A. G.; Kazanas, D. +6 more
Far-ultraviolet spectra of the gravitational lens components Q0957+561A and B were obtained with the Hubble Space Telescope Faint Object Spectrograph (HST FOS). Two previously known absorption-line systems were detected at redshifts zdamped = 1.3911 and zLyα = 1.1249. Their prominent absorption features are superposed on inte…
The Nature of the Far-Infrared Emission from Seyfert Galaxies
Pérez García, A. M.; Rodríguez Espinosa, J. M.
Optical R-band imaging data and far-infrared (FIR) Infrared Space Observatory data from Seyfert galaxies are combined to show that the compact optical emission from the nuclear and circumnuclear region correlates reasonably well with the warm FIR emission that is observed in these objects, while the extended optical emission, which essentially ori…
The Hardness-Intensity Correlation in Bright Gamma-Ray Bursts
Hurley, K.; Sunyaev, R.; Boer, M. +10 more
The presence of a hardness-intensity correlation (HIC) is demonstrated in a sample of 77 bright bursts observed by the Phebus and Ulysses gamma-ray burst (GRB) experiments. Using simulations, we find a significant correlation (5 σ) between the peak spectral hardness and the peak intensity in Phebus. Moreover, the HIC is compatible with a single re…
Effects of Non-LTE Radiative Loss and Partial Ionization on the Structure of the Transition Region
Chae, J.; Yun, H. S.; Poland, A. I.
In this paper we address the question of how non-LTE radiative losses with partial ionization of hydrogen and helium affects the energetics and structure of the solar transition region. To accomplish this we have constructed theoretical models of a thin rigid magnetic flux tube with a steady material flow, which is embedded vertically in the solar…