49 research outputs found
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
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 NISAT_S observing sequence. This takes the full
wavelength ranges from both the NIS channels (308-381 Angtr. and 513-633
Angst.) with the 2 arcsec by 240 arcsec slit, which is the narrowest slit
available, yielding the best spectral resolution. In this work we contrast the
DEM from subregions of 2 by 80 arcsec with that obtained from the mean
spectrum of the whole raster (20 by 240 arcsec). We find that the DEM
maintains essentially the same shape in the subregions, differing by a constant
factor between 0.5 and 2 from the mean DEM, except in areas were the electron
density is below cm and downflow velocities of 50 km/s
are found in the transition region. Such areas are likely to contain plasma
departing from ionisation equilibrium, violating the basic assumptions
underlying the DEM method. The comparison between lines of Li-like and Be-like
ions may provide further evidence of departure from ionisation equilibrium. We
find also that line intensities tend to be lower where velocities of the order
of 30 km/s or higher are measured in transition region lines. The DEM analysis
is also exploited to improve the line identification performed by Brooks et al
(1999) and to investigate possible elemental abundance variations from region
to region. We find that the plasma has composition close to photospheric in all
the subregions examined.Comment: 18 pages, 9 figures, 7 tables. Table 5 is available only online. A
copy of Table 5 can be found at http://webusers.ct.astro.it/acl/table5.dat.
The ReadMe file is at http://webusers.ct.astro.it/acl/ReadMe. Accepted by
Astronomy and Astrophysic
The 3d-4f Transition in S VII Observed in a Laser-Produced Plasma
The energy levels of the 2p54f configuration in neon-like sulphur, S VII, have been derived from spectral lines in the region 330-375 Ă
. The lines, which were identified as belonging to the 3d-4f transition, were emitted from a laser-produced plasma. The structure in the 4f configuration has been studied through a parametric fit of Slater integrals
Lifetimes of 2p53p and 3d levels in Ne-like chlorine, Cl VIII
Experimental lifetimes of seven 2p53p and six 2p53d levels in Ne-like chlorine, Cl VIII, have been measured using the beam-foil technique. For the first time in the Ne-sequence, the ANDC method of cascade correction has been applied in the lifetime determination of the 3p levels. This procedure lowered the values by 10 to 30% compared to the results from multiexponential curve-fitting. For all levels studied, except 3p3D2 and 3D1, the experimental lifetimes are in good agreement with recent theoretical values. A comparison between experimental and theoretical lifetimes for some 3p and 3d levels along the isoelectronic sequence is presented
Sextet levels in the phosphorus-like ion Cu
Delayed spectra of foil-excited fast Cu ions have been studied
to find a number of , and levels
in the P-like ion Cu14+ (spectrum Cu XV).
Among these are levels,
which have never been observed before, although they are
the lowest excited states that have the same
parity as the ground configuration. The investigation combined
theory and experiment. The calculations used the Cowan code with
semi-empirically scaled parameters and
extensive MCDF computations
Relativistic calculation of 2p53s, 3p and 3d energy levels and transition wavelengths in Ti XIII, Fe XVII and some other neon-like ions
Average energies for the configurations 2p5 3s, 3p and 3d in a number of neon-like ions from Al IV to Xe XLV have been calculated by means of the MCDF computer code of Grant et al. The results have been compared with observations and previous non-relativistic calculations. Fine- structure levels and 3s-3p and ip-3d transition wavelengths have also been calculated with the MCDF code for Ti XIII and Fe XVII, both in the single-configuration approximation and in a multiconfiguration treatment including 2s 2p6 nl. The configuration interaction was found to affect 2p5 3p3S1 most seriously. A separate optimization for the 3p1S0 state was needed, due to the particular radial dependence of this state. The calculated wavelengths show excellent agreement with the observations, and the MCDF calculations are well suited for wavelength predictions in neon-like n = 3 system