J/A+A/590/A118 Differences of atlases of solar spectrum (Doerr+, 2016)
How different are the Liege and Hamburg atlases of the solar spectrum?
Doerr H.-P., Vitas N., Fabbian D.
<Astron. Astrophys. 590, A118 (2016)>
=2016A&A...590A.118D 2016A&A...590A.118D (SIMBAD/NED BibCode)
ADC_Keywords: Sun ; Atlases ; Line Profiles
Keywords: atlases - Sun: general - techniques: spectroscopic - line: profiles -
Sun: abundances
Abstract:
The high-fidelity solar spectral atlas prepared by Delbouille et. al
(1973, Liege atlas, Atlas photometrique du spectre solaire de λ
3000 a λ 10000, 1973apds.book.....D 1973apds.book.....D) and the atlas by Neckel
(1999, Hamburg atlas, 1999SoPh..184..421N 1999SoPh..184..421N) are widely recognised as
the most important collection of reference spectra of the Sun at disc
centre in the visible wavelength range. The two datasets serve as
fundamental resources for many researchers, in particular for chemical
abundance analyses. But despite their similar published specifications
(spectral resolution and noise level), the shapes of the spectral
lines in the two atlases differ significantly and systematically.
Knowledge of any instrumental degradations is imperative to fully
exploit the information content of spectroscopic data. We seek to
investigate the magnitude of these differences and explain the
possible sources. We provide the wavelength-dependent correction
parameters that need to be taken into account when the spectra are to
be compared with synthetic data, for instance.
Description:
A parametrically degraded version of the Hamburg spectrum was fitted
to the Liege spectrum. The parameters of the model (wavelength shift,
broadening, intensity scaling, intensity offset) represent the
different characteristics of the respective instruments, observational
strategies, and data processing. The fits were carried out for all
identified solar lines in the line list provided by Pierce and
Breckinridge (1973, The Kitt-Peak Table of Solar Spectrum Wavelengths,
Vol. Contribution No. 559 (Kitt Peak National Observatory); hereafter
PB73) for an interval of ±15pm around the line cores. From an initial
testrun we found that the offset parameter (stray-light) is compatible
with zero. The final fits were carried out with only three free
parameters. The results from that run are provided in the file
'fitres.dat'.
A second file (liegepar.dat) contains derived parameters (spectral
resolving power, position of the continuum) for the Liege spectrum
that can be used in studies that compare Liege data to other data
(e.g. synthetic spectra).
For instance, synthetic spectra have to be degraded to match the
spectral resolving power of the Liege spectrum for a valid
comparison. Our analysis showed that a Gaussian convolution kernel
with a full-width at half-maximum (FWHM) of lambda/R (lambda:
wavelength; R: spectral resolving power) is a very good approximation
to the actual instrumental profile of the Liege atlas.
Likewise, the continuum of the Liege atlas at a particular wavelength
can be matched to the continuum of the Hamburg atlas by division with
the parameter 'C' from liegepar.dat. The correction parameters in
liegepar.dat should be interpolated to the desired wavelength range
before being applied in any data analysis.
We want to stress that the parameters provided here result from the
fitting-procedure as described in the paper, with no further
consistency checks or corrections applied. Some fits are affected by
nearby telluric blends. We recommend to apply an outlier-rejection
(e.g. a median filter) and/or smoothing before using the data. The
results need to be carefully checked.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
fitpar.dat 77 7634 Results of the model fitting procedure
liegepar.dat 26 7634 Derived parameters of the Liege atlas
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See also:
J/A+AS/113/237 : Ultraviolet Spectrum of the Sun (Samain, 1995)
J/A+AS/113/71 : Lines in the infrared solar spectrum (Ramsauer+, 1995)
J/A+A/375/591 : SUMER Spectral Atlas of Solar Disk Features (Curdt+, 2001)
J/ApJS/181/351 : Solar flux model in 30-1300nm wavelength range (Killen+, 2009)
J/A+A/525/A74 : 540-690nm Solar Atlas (Molaro+, 2011)
J/ApJS/213/11 : UV spectrum of the quiet Sun above the limb (Warren+, 2014)
J/other/ApSS/353.347 : 398-710nm Sun spectral atlases (Fathivavsari+, 2014)
J/A+A/587/A65 : Visible and near-infrared solar spectra (Reiners+, 2016)
Byte-by-byte Description of file: fitpar.dat
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Bytes Format Units Label Explanations
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1- 9 F9.5 nm lambda Wavelength of spectral line from PB73 (1)
12- 19 F8.5 pm L Fit parameter L (wavelength shift)
23- 29 F7.5 pm e_L 1-sigma error of L
32- 37 F6.4 --- S Fit parameter S (intensity scaling)
40- 45 F6.4 --- e_S 1-sigma error of S
48- 53 F6.3 pm B Fit parameter B (broadening)
57- 61 F5.3 pm e_B 1-sigma error of B
64- 68 F5.1 --- rchi2 Reduced chi2 (chi2/ndof) of fit
71- 77 F7.5 --- rms RMS of the residuals of the fit
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Note (1): PB73 for Pierce and Breckinridge (1973, The Kitt-Peak Table of Solar
Spectrum Wavelengths, Vol. Contribution No. 559
(Kitt Peak National Observatory, 1973apds.book.....D 1973apds.book.....D).
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Byte-by-byte Description of file: liegepar.dat
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Bytes Format Units Label Explanations
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1- 9 F9.5 nm lambda Wavelength of spectral line from PB73
12- 18 F7.0 --- R Estimated spectral resolving power
21- 26 F6.4 --- C Estimated position of the continuum (1)
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Note (1): continuum relative to the maximum intensity level of the Liege
data. C is identical with S in file fitpar.dat.
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Acknowledgements:
Hans-Peter Doerr, doerr(at)mps.mpg.de
(End) Hans-Peter Doerr [MPS, Germany], Patricia Vannier [CDS] 22-Apr-2016