J/A+A/432/1063 Analysis of inner solar corona in Extreme-UV (Lanzafame+, 2005)
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.
<Astron. Astrophys. 432, 1063 (2005)>
=2005A&A...432.1063L 2005A&A...432.1063L
ADC_Keywords: Sun ; Spectra, ultraviolet ; Atomic physics
Keywords: Sun: atmosphere - Sun: corona - Sun: UV radiation - Sun: abundances -
atomic data - techniques: spectroscopic
Abstract:
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 NIS channels (308-381Å and 513-633Å) 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*80arcsec2 with that obtained from the mean spectrum
of the whole raster (20*240arcsec2). 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 2*107cm-3 and downflow velocities of
50km/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 30km/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. (1999A&A...347..277B 1999A&A...347..277B) 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.
Description:
Comparison of the observed intensities with those derived from the DEM
for the mean spectrum.
Lines used for the integral inversion are indicated with "i". Those
compared with observations in the forward sense, i.e. by comparing the
intensities predicted using the DEM with the observed intensities, are
indicated with "f".
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table5.dat 110 180 Comparison of the observed intensities with those
derived from the DEM for the mean spectrum.
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See also:
J/A+AS/113/237 : Ultraviolet Spectrum of the Sun (Samain, 1995)
J/A+AS/131/431 : Accurate wavelengths in Sun spectrum (Allende Prieto+ 1998)
Byte-by-byte Description of file: table5.dat
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Bytes Format Units Label Explanations
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1 A1 --- Blend Blend data (1)
2 A1 --- n_Blend [S] S when the record contains information
about the blend
3- 4 A2 --- EL Element symbol (2)
6- 7 I2 --- Z1 ? Ion charge + 1 (2)
10- 16 F7.3 0.1nm lambda ? Adopted laboratory wavelength (2)
18 A1 --- r_lambda Reference for lambda (3)
21- 30 A10 --- Conf1 Lower level electronic configuration (2)
32- 37 A6 --- Term1 Lower level term (2)
38 A1 --- --- [-]
40- 49 A10 --- Conf2 Upper level electronic configuration (2)
51- 55 A5 --- Term2 Upper level term (2)
58- 61 F4.2 [K] logT ? Temperature (log) of peak of line
formation (2)
64- 65 A2 --- n_lambdaObs [2x ] For Si 11 303.326 only
66- 72 F7.3 0.1nm lambdaObs ? Observed wavelength
77- 81 F5.1 mW/m2/sr IntTh Theoretical intensity
85- 89 F5.1 mW/m2/sr IntObs ? Observed intensity
93- 97 F5.1 mW/m2/sr e_IntObs ? Observational uncertainty
101-106 E6.2 --- Chi2 ? Chisquare
110 A1 --- Note Note (4)
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Note (1): A same letter identifies the lines of the blend.
Note (2): For data of blended lines (S), these quantities are not reported
Note (3): The source for the adopted wavelengths, lambda, is denoted as follows:
E = Edlen, 1983, Phys. Scripta, 28, p. 51 and p. 48,
1984, Phys. Scripta, 30, 135, 1985, Phys. Scripta, 31, 345,
1985, Phys. Scripta, 32, p. 59 and p. 86.
F = Fawcett, 1975, Atomic Data and Nuclear Data Tables, 16, 138.
J = Jupen et al., 1993MNRAS..264..627.
K = Kelly, 1987, J. Phys. Chem. Ref. Data 16, Supp. 1.
M = Moore, 1993, in Tables of Spectra of Hydrogen, Carbon,
Nitrogen and Oxygen Atoms and Ions, ed. J.W. Gallacher, CRC
Series in Evaluated Data in Atomic Physics (CRC Press).
N = Martin et al.. 1995, NIST Database for Atomic Spectroscopy,
Version 1.0.
O = Wiese, 1985, Spectroscopic Data for Iron, ORNL No. 6089/V4
(Oak Ridge National Laboratory).
S = Shirai et al., 1990, J. Chem. Phys. Ref. Data, 19, 127.
Note (4): Note has the following meaning:
i = the line has been used for the integral inversion
f = the line has been compared with observations in the
forward sense, i.e. by comparing the intensities predicted using
the DEM with the observed intensities.
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Acknowledgements: Alessandro Lanzafame, alanzafame(at)ct.astro.it
References:
Lanzafame et al, Paper I 2002A&A...384..242L 2002A&A...384..242L
(End) Alessandro Lanzafame [Catania Univ.], Patricia Vannier [CDS] 30-Nov-2004