Coronal Loop System Research Articles

Impulsive phase soft X-ray blueshifts at a loop footpoint

Solar Maximum Mission (SMM) observations of a solar flare that occurred on May 24, 1987 are described. The event was noteworthy in that it was observed during the impulsive phase with the SMM X-ray Poly-chromator (XRP) pointed at a location associated with the chromospheric footpoints of a system of coronal loops. Density-sensitive line ratios at the flare site imply an initially large electron density of 5 x 10 to the 12th/cu cm, which decreased an order of magnitude during the flare. Spectral scans of the soft X-ray Mg XI line at the site reveal asymmetric blueshifted (200 km/s) profiles concurrent with impulsive hard X-ray emission. The blueshift amplitude was correlated with the intensity of hard X-rays (with a phase delay of about 30 s) and showed fluctuations on a time scale comparable with the variation of hard X-ray emission. These observations are interpreted as evidence for chromospheric evaporation produced by heating and expansion of footpoint plasma.

SOFT X-RAY IMAGES OF THE SOLAR CORONA USING NORMAL INCIDENCE OPTICS

A solar coronal loop system has been photographed in soft X-rays using a normal incidence telescope based on multilayer mirror technology. The telescope consisted of a spherical objective rnirror of 4 cm aperture and 1 m focal length, a film cassette, and a focal plane shutter. A metallized thin plastic film filter was used to exclude visible light. The objective mirror was covered with a multilayer coating consisting of alternating layers of tungsten and carbon whose combined thicknesses satisfied the Bragg diffraction condition for 44 A... radiation The image was recorded during a rocket flight on 1985 October 25, and was dominated by emission lines arising from the Si XII spectrum. The rocket also carried a high resolution soft X-ray spectrograph that confirmed the presence of Si XII line radiation in the source. This image represents the first successful use of multilayer technology for astrophysical observations.

Simultaneous VLA-satellite observations of the sun

The Very Large Array (VLA) and satellite-borne telescopes can be used in the 1990s to provide unique observations of the quiescent and active corona with comparable resolution in time and space. Recently available 90-cm VLA data specify closed and open magnetic structures in the low solar corona, providing unique information about the initiating source of coronal mass ejections observed by satellite coronagraphs. The physical properties of quiescent coronal loops can be inferred from combined soft X-ray (electron density and temperature) and 20-cm VLA (magnetic field strength and structure) data. Systems of coronal loops within a single active region have different temperatures and different radiation mechanisms that can only be detected by observations in both spectral domains. The combined VLA-satellite observations will also specify magnetic interaction and particle acceleration before and during flares, including magnetic triggering in the corona (VLA) and preflare heating (VLA-satellite).

Soft X-Ray Images of the Solar Corona Using Normal Incidence Optics

AbstractA solar coronal loop system has been photographed in soft X-rays using a normal incidence telescope based on multilayer mirror technology. The telescope consisted of a spherical objective mirror of 4 cm aperture and 1 m focal length, a film cassette, and a focal plane shutter. A metallized thin plastic film filter was used to exclude visible light. The objective mirror was covered with a multilayer coating consisting of alternating layers of tungsten and carbon whose combined thicknesses satisfied the Bragg diffraction condition for 44 Å radiation. The image was recorded during a rocket flight on 1985 October 25, and was dominated by emission lines arising from the Si XII spectrum. The rocket also carried a high resolution soft X-ray spectrograph that confirmed the presence of Si XII line radiation in the source. This image represents the first successful use of multilayer technology for astrophysical observations.

X-ray spectrum of sigma Geminorum: an RS Canum Venaticorum type binary

The binary system σ Gem has been observed on three occasions during 1984 November 17–21 with the medium-energy and the low-energy detectors on the EXOSAT Observatory. Spectral analysis of the data obtained over the energy range of 0.05–6.0 keV shows evidence for a bimodal temperature distribution of emission measure in an optically thin thermal equilibrium plasma with one component |$\sim5\times {10}^{6}$| K and the other one of |$\sim40\times {10}^{6}$| K. It is found that the lower-temperature component is the dominant source of X-ray emission. The data are interpreted in terms of emission from two types of hot coronal loops with constant pressure on the surface of the visible red giant star in the binary. The two systems of coronal loops correspond to the two temperature plasma components measured. The observed variations in the luminosity of the system are probably due to the rotational effects on the smaller, cooler loops confined to certain regions on the surface of the late-type giant star.

Temperature-Density Structure in Coronal Helmets: the Quiescent Prominence and Coronal Cavity

view Abstract Citations (39) References (11) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Temperature-Density Structure in Coronal Helmets: the Quiescent Prominence and Coronal Cavity Pneuman, G. W. Abstract Physical processes which are most important in determining temperature and density distributions in closed coronal loop systems are studied within the context of how this type of magnetic geometry influences the local balance of mechanical energy flux, conductive flux, and radiative losses. For regions above the temperature maximum, there can be no net conductive loss since closed field lines prevent outward beat conduction and the vanishing temperature gradient at the level of the temperature maximum prohibits downward heat conduction there. Hence, the mechanical energy input at the base must ultimately be radiated away. This requirement, in addition to a condition on the lateral distribution of gas pressure at the level of T , is used in a computation which yields the density and temperature distribution throughout the helmet as a function of the mechanical energy input and magnetic field geometry. It is demonstrated that the quiescent prominences normally observed at the base of coronal helmets as well as the low-density cavity surrounding these structures are the natural consequences of the adjustment of density and temperature structui e in the helmet required to satisfy energy and mass balance conditions as modulated by the magnetic field. Publication: The Astrophysical Journal Pub Date: November 1972 DOI: 10.1086/151756 Bibcode: 1972ApJ...177..793P full text sources ADS |