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Large-Amplitude Velocity Fluctuations in Coronal Loops: Flare Drivers?
Veltri, P.; Malara, F.; Nigro, G.
Recent space observations of coronal lines broadening during a flare occurrence suggest that unresolved nonthermal velocity rises well above the background level before the start of the flare, defined as the start of hard X-ray emission. Using a new shell model to describe the Alfvénic turbulence inside a coronal loop, it is shown that the occurre…
Nonthermal Velocities in Different Temperature Regions of the Solar Lower Transition Region
Doschek, G. A.; Mariska, J. T.; Akiyama, S.
We analyze the relationship between nonthermal velocities derived from spectral lines of ions formed at different temperatures in the solar lower transition region, using spectra from the Solar Ultraviolet Measurements of Emitted Radiation (SUMER) spectrometer on board the Solar and Heliospheric Observatory (SOHO). We find a high degree of correla…
ADAS analysis of the differential emission measure structure of the inner solar corona. II. A study of the "quiet Sun" inhomogeneities from SOHO CDS-NIS spectra
Lanzafame, A. C.; Brooks, D. H.; Lang, J.
We present a study of the differential emission measure (DEM) of a “quiet Sun” area observed in the extreme ultraviolet at normal incidence by the Coronal Diagnostic Spectrometer (CDS) on the SOHO spacecraft. The data used for this work were taken using the NISATS observing sequence. This takes the full wavelength ranges from both the N…
Oxygen Abundance in Coronal Streamers
Raymond, John C.; Vásquez, Alberto M.
In a previous work we developed a stationary proton-electron MHD model of the solar corona, suitable for the minimum-activity epochs. In the present work, we use empirically derived information from the past solar minimum for the oxygen parameters (temperatures and outflow velocity) to develop an oxygen model in the frame of our previous model. So…
Relation between the solar wind dynamic pressure at Voyager 2 and the energetic particle events at Voyager 1
Wang, C.; Richardson, J. D.; Stone, E. C. +2 more
Starting in 2001, Voyager 1 observed three events characterized by enhanced fluxes of energetic particles. These events suggest that Voyager 1 made a close approach to, or a crossing of, the termination shock. Although the plasma experiment on Voyager 1 is not providing useful data, plasma data from Voyager 2 may shed light on the plasma condition…
Spatial Evidence for Transition Radiation in a Solar Radio Burst
Fleishman, Gregory D.; Nita, Gelu M.; Gary, Dale E.
Microturbulence, i.e., enhanced fluctuations of plasma density and electric and magnetic fields, is of great interest in astrophysical plasmas, but occurs on spatial scales far too small to resolve by remote sensing, e.g., at ~1-100 cm in the solar corona. This Letter reports spatially resolved observations that offer strong support for the presen…
Turbulence in the Inner Solar Wind Determined from Frequency Fluctuations of the Downlink Signals from the ULYSSES and GALILEO Spacecraft
Plettemeier, D.; Bird, M. K.; Efimov, A. I. +2 more
The results of several sets of measurements of the frequency of radio signals during coronal-sounding experiments carried out from 1991 to 2000 using the ULYSSES and GALILEO spacecraft are presented and analyzed. The S-band signals (carrier frequency f = 2295 MHz) were received at the three 70-m widely spaced ground stations of the NASA Deep Space…
The 3-D shaping of NGC 6741: A massive, fast-evolving Planetary Nebula at the recombination-reionization edge
Sabbadin, F.; Turatto, M.; Cappellaro, E. +2 more
We infer the gas kinematics, diagnostics and ionic radial profiles, distance and central star parameters, nebular photo-ionization model, spatial structure and evolutionary phase of the Planetary Nebula NGC 6741 by means of long-slit ESO NTT+EMMI high-resolution spectra at nine position angles, reduced and analysed according to the tomographic and…
The proper motion of the Magellanic Clouds: The UCAC2-Hipparcos inconsistency
Momany, Y.; Zaggia, S.
Using the USNO CCD Astrograph all-sky Catalog (UCAC2), we measure the mean proper motion of the two Magellanic Clouds. Appropriately-selected LMC populations show a proper motion <µα,µδ>≃(+0.84,+4.32) that is significantly higher, in <µδ>, than currently accepted Hipparcos-like values; <µα,µδ>≃(+1.94…
Determination of confusion noise for far-infrared measurements
Lemke, D.; Klaas, U.; Kiss, Cs.
We present a detailed assessment of the far-infrared confusion noise imposed on measurements with the ISOPHOT far-infrared detectors and cameras aboard the ISO satellite. We provide confusion noise values for all measurement configurations and observing modes of ISOPHOT in the 90 µm ≤ λ ≤ 200 µm wavelength range. Based on these results…