Bertaux, J.L.; Kyrola, E.; Quemerais, E.; Pellinen, R.; Lallement, R.; Schmidt, W.; Berthe, M.; Dimarellis, E.; Goutail, J.P.; Taulemesse, C.; Bernard, C.; Leppelmeier, G.; Summanen, T.; Hannula, H.; Huomo, H.; Kehla, V.; Korpela, S.; Leppala, K.; Strommer, E.; Torsti, J.; Viherkanto, K.; Hochedez, J.F.; Chretiennot, G.; Peyroux, R.; Holzer, T.
Sol. Phys. vol.162, no.1-2, 403
On board the SOHO spacecraft poised at the L1 Lagrange point, the SWAN instrument is mainly devoted to the measurement of large scale structures of the solar wind, and in particular the distribution with heliographic latitude of the solar wind mass flux. This is obtained from an intensity map of the sky Lyman alpha emission, which reflects the shape of the ionization cavity carved in the flow of interstellar H atoms by the solar wind. The methodology, inversion procedure and related complications are described. The subject of latitude variation of the solar wind is briefly reviewed: earlier Lyman alpha results from Prognoz in 1976 are confirmed by Ulysses. The importance of the actual value of the solar wind mass flux for the equation of dynamics in a polar coronal hole is stressed. The instrument is composed of one electronic unit commanding two identical sensor units, each of them allowing to map a full hemisphere with a resolution of 1 degrees , thanks to a two-mirrors periscope system. The design is described in some detail, and the rationale for choice between several variants are discussed. A hydrogen absorption cell is used to measure the shape of the interplanetary Lyman alpha line and other Lyman alpha emissions. Other types of observations are also discussed: the geocorona, comets (old and new), the solar corona, and a possible signature of the heliopause. The connection with some other SOHO instruments, in particular LASCO, UVCS, SUMER, 5 is briefly discussed.
1995-13: The Ultraviolet Coronagraph Spectrometer for the Solar and Heliospheric Observatory
KOHL, J. L.; ESSER, R.; GARDNER, L. D.; HABBAL, S.; DAIGNEAU, P. S.; DENNIS, E. F.; NYSTROM, G. U.; PANASYUK, A.; RAYMOND, J. C.; SMITH, P. L.; STRACHAN, L.; VAN BALLEGOOIJEN, A. A.; NOCI, G.; FINESCHI, S.; ROMOLI, M.; CIARAVELLA, A.; MODIGLIANI, A.; HUBER, M. C. E.; ANTONUCCI, E.; BENNA, C.; GIORDANO, S.; TONDELLO, G.; NICOLOSI, P.; NALETTO, G.; PERNECHELE, C.; SPADARO, D.; POLETTO, G.; LIVI, S.; VON DER LUHE, O.; GEISS, J.; TIMOTHY, J. G.; GLOECKLER, G.; ALLEGRA, A.; BASILE, G.; BRUSA, R.; WOOD, B.; SIEGMUND, O. H. W.; FOWLER, W.; FISHER, R.; JHABVALA,
1995, M. Journal: solar Physics, v. 162, p. 313-356.
complete
on-line version
The SOHO Ultraviolet Coronagraph Spectrometer (UVCS/SOHO) is composed of three reflecting telescopes with external and internal occultation and a spectrometer assembly consisting of two toric grating spectrometers and a visible light polarimeter. The purpose of the UVCS instrument is to provide a body of data that can be used to address a broad range of scientific questions regarding the nature of the solar corona and the generation of the solar wind. The primary scientific goals are the following: to locate and characterize the coronal source regions of the solar wind, to identify and understand the dominant physical processes that accelerate the solar wind, to understand how the coronal plasma is heated in solar wind acceleration regions, and to increase the knowledge of coronal phenomena that control the physical properties of the solar wind as determined by in situ measurements. To progress toward these goals, the UVCS will perform ultraviolet spectroscopy and visible polarimetry to be combined with plasma diagnostic analysis techniques to provide detailed empirical descriptions of the extended solar corona from the coronal base to a heliocentric height of 12 solar radii.
1995-12: Microchannel plates for the UVCS and SUMER instruments on the SOHO satellite
Siegmund, O. H., Gummin, M. A.,
Sasseen, T.,
Jelinsky, P. N.,
Gaines, G. A., Hull, J.,
Stock, J. M.,
Edgar, M. L., Welsh, B. Y.,
Jelinsky, S. R.,
Vallerga, J. V.
1995, in The International Society for Optical Engineering, EUV, X-Ray, and Gamma-Ray Instrumentation for Astronomy VI, 2518, 344, ed. O. H. Siegmund, J. V. Vallerga
The microchannel plates for the detectors in the SUMER and UVCS instruments aboard the Solar Orbiting Heliospheric Observatory (SOHO) mission to be
launched in late 1995 are described. A low resistance Z stack of microchannel
plates (MCPs) is employed in a detector format of 27 mm multiplied by 10 mm
using a multilayer cross delay line anode (XDL) with 1024 by 360 digitized
pixels. The MCP stacks provide gains of greater than 2 multiplied by
10(superscript 7) with good pulse height distributions (as low as 25% FWHM)
under uniform flood illumination. Background rates of approximately equals 0.6
event cm(superscript -2) sec(superscript -1) are obtained for this configuration.
Local counting rates up to approximately equals 800 events/pixel/sec have been
achieved with little drop of the MCP gain. MCP preconditioning results are
discussed, showing that some MCP stacks fail to have gain decreases when
subjected to a high flux UV scrub. Also, although the bare MCP quantum
efficiencies are close to those expected (approximately equals 10%), we found
that the long wavelength response of KBr photocathodes could be substantially
enhanced by the MCP scrubbing process. Flat field images are characterized by a
low level of MCP fixed pattern noise and are stable. Preliminary calibration
results for the instruments are shown.
1995-11: Ultraviolet Coronagraph Spectrometer
for the Solar and Heliospheric Observatory: instrument description and
calibration overview KOHL, J. L.; ESSER, R.; GARDNER, LARRY D.; HABBAL, S.; DAIGNEAU, P. S.; NYSTROM, GEORGE U.; RAYMOND, JOHN C.; STRACHAN, LEONARD; VAN BALLEGOOIJEN, A. A.; NOCI, G.; FINESCHI, SILVANO; ROMOLI, MARCO; CIARAVELLA, A.; MODIGLIANI, A.; HUBER, MARTIN C.; ANTONUCCI, E.; BENNA, C.; GIORDANO, S.; VON DER LUEHE, OSKAR; TONDELLO, GIUSEPPE; NICOLOSI, PIERGIORGIO; NALETTO, GIAMPIERO; PERNECHELE, CLAUDIO; GEISS, J.; GLOECKLER, G.; POLETTO, G.; SPADARO, D.; ALLEGRA, A.; BASILE, G.; BRUSA, R.; WOOD, B.; SIEGMUND, OSWALD H.
1995, Proc. SPIE Vol. 2517, p. 40-61,
X-Ray and EUV/FUV Spectroscopy and Polarimetry, Silvano Fineschi; Ed. The SOHO ultraviolet coronagraph spectrometer (UVCS/SOHO) is composed of three reflecting telescopes with external and internal occultation and
a spectrometer assembly consisting of two toric grating spectrometers and a visible light polarimeter. The UVCS will perform ultraviolet spectroscopy and visible polarimetry to be combined with plasma diagnostic analysis techniques to provide detailed empirical descriptions of the extended solar corona from the coronal base to a heliographic height of 12 R. In this paper, the salient features of the design of the UVCS instrument are described. An overview of the UVCS test and calibration activities is presented. The results from the calibration activity have demonstrated that the UVCS can achieve all its primary scientific observational goals. E. Antonucci, M.A. Dodero
1995, The Astrophysical Journal, 438, 480
Analyzes the intensities and profiles of a number of soft X-ray lines, O VIII, Ne IX, Mg XI, Si XIII, S XV, Ca XIX, and Fe XXV, which have been observed during solar flares with the Flat Crystal Spectrometer (FCS) of the Solar Maximum Mission. These lines are emitted in the temperature range from 3*10/sup 6/ K to 5*10/sup 7/ K. The temperature distribution of the flare plasma computed on basis of the FCS line intensities, consists of two plasma components at different temperatures, 5-8*10/sup 6/ K and 16-25*10/sup 6/ K, respectively, in agreement with previous studies. Significant nonthermal motions in the flare plasma are inferred from the presence of nonthermal broadenings in the observed lines. The broadening is deduced by comparing observed profiles to synthetic ones derived using the differential emission measure calculated from a series of FCS line intensities. The Doppler temperature, inferred from the observed line width is found to exceed systematically the average temperature of line formation characterizing the width of the reconstructed thermal lines. The established relation between velocity of the nonthermal plasma motions and temperature, indicating a positive correlation both locally in flare plasmas and throughout the solar atmosphere, supports the idea that nonthermal velocities are very likely a manifestation of the heating process.
E. Antonucci,and R. Martin
1995, Adv. Space Res. 15, (7)37
Evidence for variations in iron and calcium abundances during the impulsive phase of solar flares has been obtained by analyzing the Ca XIX and Fe XXV spectra, detected with the Bent Crystal Spectrometer of the Solar Maximum Mission. The plasma thermal conditions have been investigated by considering different temperature indicators: namely, the temperatures T/sub Ca/ and T/sub Fe/, derived from the intensity ratios of the dielectronic recombination satellites to the resonance line, and the temperature T/sub Ca,Fe/, calculated from the ratio of the resonance lines of Ca XIX and Fe XXV, which is also depending on the Fe/Ca abundance ratio. The observed values of T/sub Ca/ and T/sub Fe/ can be ascribed to the specific characteristics of the plasma thermal distribution, the corresponding values of T/sub Ca,Fe/ can be explained by allowing also for variations in the Fe/Ca abundance ratio relative to the photospheric ratio by a factor within 0.2 and 2.4. According to the observed abundance variations, the events analyzed can be divided in Ca-rich and Fe-rich flares.
E. Antonucci, R. Martin
1995, The Astrophysical Journal, 451, 402
The temperature distribution of the coronal plasma during solar flares is studied for a set of energetic events of class M and X observed with the bent crystal spectrometer (BCS) flown on the Solar Maximum Mission (SMM) satellite. From the analysis of Ca XIX and Fe XXV spectra, emitted in the regions from 3.165 to 3.231 AA and from 1.840 to 1.894 AA, respectively, the authors can derive different indicators of the thermal conditions of the flare plasma: the temperature T/sub Ca,Fe/, derived from the ratio of the intensities of the Ca XIX and Fe XXV resonance lines, and the temperatures T/sub Ca/ and T/sub Fe/ obtained from the ratio of the dielectronic satellites to the resonance line in the Ca XIX and Fe XXV spectrum. In most of the analyzed flares, the temperature indicators T/sub Ca,Fe/, T/sub Ca/ and T/sub Fe/ are considerably different. The study shows that a difference in T/sub Ca/ and T/sub Fe/ is a signature of departure from quasi-isothermal conditions and the variability from flare to flare of the quantity T/sub Ca,Fe/ is a signature of the variability of the iron to calcium relative abundance. The authors develop a model of plasma differential emission measure which accounts for the enhancements of T/sub Fe/ with respect to T/sub Ca/ by assuming the presence of a "superhot" component at temperature greater than 2*10/sup 7/ K. The difference of the observed value of T/sub Ca,Fe/ and that derived from the model can be accounted for by varying the relative abundance of iron to calcium.
D. Marocchi, E. Antonucci,
R.P.W. McWhirter Il Nuovo Cimento, 17D, 10, 1139-1148, 1995
The Li-like to He-like ion population ratio for calcium at the onset of solar flares is observed to be about 60% higher than in steady-state ionization balance. The measurement of the duration of this initial period of transient ionization and of the population ratios of adjacent ionization states allows an estimate of the electron density of the coronal plasma at flare onset. The density found in the present study, within 1*10/sup 9/ and 7*10/sup 9/ cm/sup -3/, is comparable with the density typical of pre-flare active regions.
M.A.Dodero, E. Antonucci,
D.Marocchi, R.Martin Il Nuovo Cimento, 17D, 9, 999-1006
The development of multilayer optics has profound implications for soft-X-ray/UV astronomy, since it allows to extend the use of normal-incidence telescopes to cover the XUV region where lines are formed at greatly different temperatures (10/sup 5/-10/sup 7/ K). A multilayer mirror consists of alternating thin layers of suitable materials deposited on a substrate and its performance depends not only on the optical properties of the materials but also on the design of the multilayer. In this study we have computed the reflectivity of multilayer mirrors to select both the materials and the multilayer design to achieve the best performance in the wavelength range from 30 to 350 AA. Our calculations show that high theoretical reflectivities, from 0.2 to 0.8 and relatively narrow bandpasses, from ~1 AA to ~30 AA, can be obtained, in the wavelength range from 30 to 350 AA, by a suitable choice of the materials and of the multilayer design.
E. Antonucci, M.A. Dodero,
B.V. Somov, A. Verneta Il Nuovo Cimento, 17D, 10, 1149-1153, 1995
Computes the intensity of the emission in the O VI, Mg X, Si XII, Fe XIII, Fe XVI transitions and the profiles of these spectral lines for a plasma flowing out of reconnecting current sheets that originate in the active region corona either during transient brightenings or in preflare conditions. The characteristic of these lines is a significant non-thermal broadening consistent with plasma non-thermal velocities of the order of 300 km s/sup -1/. Hence, it is possible to infer the occurrence of magnetic reconnection in the solar corona by investigating the broadening of transition region and coronal lines in the sites where reconnection is presumed to take place.
M.Romoli, A.Ciaravella, G.Noci,
D.Spadaro, R.Ventura, J.L.Kohl
1995, in the 2nd Rencontres du Vietnam, ``The
Sun and Beyond'' The Ultraviolet Spectrometer
Coronagraph (UVCS) of the SOHO mission has the capability of measuring intensities and profiles of O VI, Mg X, Fe XII, and Si XII ion lines in the solar corona between 1.4 and 10 solar radii. Spectroscopic diagnostics on these ion lines will give the unprecedented opportunity of determining densities, velocities and temperatures of the coronal plasma, and, therefore, of addressing some of the still unsolved questions such as the coronal elemental abundances, and the mechanisms of acceleration of the solar wind. In the following, expected count rates and exposure times for the above lines are given in the worst case scenario of a coronal hole, and, for comparison, in a streamer at O VI wavelength. The calculated count rates are based on the coronal intensities derived from empirical models, and on the efficiencies measured during component level and system level tests.
PERNECHELE, CLAUDIO; NALETTO, GIAMPIERO; NICOLOSI, PIERGIORGIO; POLETTO, L.; TONDELLO, GIUSEPPE
1995, SPIE Vol. 2517, p. 79-88, X-Ray and EUV/FUV Spectroscopy and Polarimetry, Silvano Fineschi; Ed.
The optical performances of the spectrometer for the SOHO/UVCS instrument have been tested. The flight unit of the spectrometer assembly consisting of the structure equipped with the entrance slit assembly, the grating drive mechanism mounting a pair of toroidal grating, and two photon counting cross-delay line detector has been integrated and aligned. Both tests with visible and UV radiation have been performed. Aberration and stray light measurements have shown satisfactory performances of the instrument, practically in compliance with the scientific requirements.
PERNECHELE, CLAUDIO; POLETTO, L.;
NICOLOSI, PIERGIORGIO; NALETTO, GIAMPIERO
1995, SPIE Vol. 2517, p. 62-70, X-Ray and EUV/FUV Spectroscopy and Polarimetry, Silvano Fineschi; Ed.
A new technique has been developed for improving the spectral resolution of spectrographs mounting discrete array detectors. The basic idea is to acquire various spectroscopic images each spectrally displaced on the detector by a fraction of the pixel and to apply suitable numerical procedures in order to extract a spectral profile with subpixel resolution. This technique has been applied to a vacuum spectrograph adopting the Johnson-Onaka configuration. The dispersion element is a concave toroidal grating which can rotate around a pivot axis displaced from its vertex, in order to keep always a good spectral focus on the detector. The latter is a multi-anode microchannel-plate array (MAMA), operating in photon counting mode. Several stigmatic images of the H I Ly(alpha) line at 1216 angstrom emitted by a D(subscript 2) lamp have been acquired for various rotation of the grating. The results of the application of this new technique and the numerical algorithm are presented and discussed in terms of potentialities and limitations due to signal to noise (S/N) ratio and intrinsic spectral broadening of the signals.
Wang, A.-H., Wu, S.-T., Suess, S.-T., Poletto, G.
1995, Solar Phys., 161, 365-381 Examines how the initial state (pre-event corona) affects the numerical MHD simulation for a coronal mass ejection (CME). Earlier simulations based on a pre-event corona with a homogeneous density and temperature distribution at the lower boundary (i.e., solar surface) have been used to analyze the role of streamer properties in determining the characteristics of loop-like transients. The present paper extends these studies to show how a broader class of global coronal properties leads not only to different types of CMEs, but also modifies the adjacent quiet corona and/or coronal holes. The authors consider four pre-event coronal cases: (1) constant boundary conditions and a polytropic gas with gamma =1.05; (2) non-constant (latitude dependent) boundary conditions and a polytropic gas with gamma =1.05; (3) constant boundary conditions with a volumetric energy source and gamma =1.67; (4) non-constant (latitude dependent) boundary conditions with a volumetric energy source and gamma =1.67. In all models, the pre-event magnetic fields separate the corona into closed field regions (streamers) and open field regions. The CME`s initiation is simulated by introducing at the base of the corona, within the streamer region, a standard pressure pulse and velocity change. Boundary values are determined using MHD characteristic theory. The simulations show how different CMEs, including loop-like transients, clouds and bright rays, might occur. There are significant new features in comparison to published results. The authors conclude that the pre-event corona is a crucial factor in dictating CMEs properties.
1995-10: Temperature dependence of non-thermal motions in solar flares plasmas observed with the Flat Crystal Spectrometer on SMM
1995-09: Variations in Iron and Calcium Abundances During Solar Flares
1995-08: Differential emission measure and iron to calcium abundance in solar flare plasmas
1995-07: Non-equilibrium ionization and electron density in the coronal plasma
during solar flares
1995-06: Study of the reflectivity in the XUV domain of normal incidence multilayer mirrors
1995-05: XUV lines emitted from plasma accelerated during magnetic reconnection
1995-04: Spectroscopy of Minor Ions in the Solar Corona with SOHO/UVCS,
1995-03: VUV optical performances of the spectrometer of the UVCS instrument for SOHO
1995-02: Spectral resolution improvement technique for a spectrograph mounting
a discrete array detector
1995-01: Numerical modeling of Coronal Mass Ejections based on various pre-event
atmospheres