J/A+A/644/A109 Quiet-sun hydrogen Lyman-alpha line profile (Gunar+, 2020)
Quiet-sun hydrogen Lyman-alpha line profile derived from SOHO/SUMER solar-disk
observations.
Gunar S., Schwartz P., Koza J., Heinzel P.
<Astron. Astrophys. 644, A109 (2020)>
=2020A&A...644A.109G 2020A&A...644A.109G (SIMBAD/NED BibCode)
ADC_Keywords: Sun ; Spectroscopy
Keywords: Sun: UV radiation - Sun: filaments - prominences - Sun: atmosphere -
methods: data analysis - Techniques: spectroscopic
Abstract:
The solar radiation in the Lyman-alpha spectral line of hydrogen plays
a significant role in the illumination of chromospheric and coronal
structures, such as prominences, spicules, chromospheric fibrils,
cores of coronal mass ejections, and solar wind. Moreover, it is
important for the investigation of the heliosphere, Earth's
ionosphere, and the atmospheres of planets, moons, and comets.
We derive a reference quiet-Sun Lyman-alpha spectral profile that is
representative of the Lyman-alpha radiation from the solar disk during
a minimum of solar activity. This profile can serve as an incident
radiation boundary condition for the radiative transfer modelling of
chromospheric and coronal structures. Because the solar radiation in
the Lyman lines is not constant over time but varies significantly
with the solar cycle, we provide a method for the adaptation of the
incident radiation Lyman line profiles (Lyman-alpha and higher lines)
to a specific date. Moreover, we analyse how the change in the
incident radiation influences the synthetic spectra produced by the
radiative transfer modelling.
We used SOHO/SUMER Lyman-alpha raster scans obtained without the use
of the attenuator in various quiet-Sun regions on the solar disk. The
observations were performed on three consecutive days (June 24, 25,
and 26, 2008) during a period of minimum solar activity. The reference
Lyman-alpha profile was obtained as a spatial average over eight
available raster scans. To take into account the Lyman-alpha variation
with the solar cycle, we used the LISIRD composite Lyman-alpha index.
To estimate the influence of the change in the incident radiation in
the Lyman lines on the results of radiative transfer models, we used a
2D prominence fine structure model.
We present the reference quiet-Sun Lyman-alpha profile and a table of
coefficients describing the variation of the Lyman lines with the
solar cycle throughout the lifetime of SOHO. The analysis of the
influence of the change in the incident radiation shows that the
synthetic spectra are strongly affected by the modification of the
incident radiation boundary condition. The most pronounced impact is
on the central and integrated intensities of the Lyman lines. There,
the change in the synthetic spectra can often have the same amplitude
as the change in the incident radiation itself. The impact on the
specific intensities in the peaks of reversed Lyman-line profiles is
smaller but still significant. The hydrogen Halpha line can also be
considerably affected, despite the fact that the Halpha radiation from
the solar disk does not vary with the solar cycle.
Description:
The reference quiet-Sun Lyman-alpha profile obtained as an average
over eight SOHO/SUMER raster scans obtained between 2008/06/24 and
2008/06/26. The central wavelength lambda0 of the Lyman-alpha line
is 1215.67Å (121.567nm).
The symmetrized reference quiet-Sun Lyman-alpha profile obtained by
symmetrization of the full profile from Table A1. Only the right half
of the profile is provided. The central wavelength lambda0 of the
Lyman-alpha line is 1215.67Å (121.567nm).
table B1 ∼List of coefficients describing the variation of the solar
radiation in the Lyman-alpha and higher Lyman lines. The coefficients
were derived from 400-day averaged LISIRD Lyman-alpha composite index
(Machol et al., 2019E&SS....6.2263M 2019E&SS....6.2263M). We provide coefficients for
selected dates throughout the lifetime of SOHO. Coefficients for the
Lyman-alpha line are computed with respect to the date 2008/06/25.
Coefficients for the higher Lyman lines are computed with respect to
the date 1996/05/15 used in Warren et al. (1998ApJS..119..105W 1998ApJS..119..105W).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
tablea1.dat 25 87 Reference quiet-Sun Lyman-alpha profile
tablea2.dat 25 31 Symmetrized reference Lyman-alpha half-profile
tableb1.dat 43 79 Coefficients - variation with solar cycle
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See also:
VI/152 : SOVAP-PICARD total solar irradiance (Meftah+, 2016)
J/A+A/581/A26 : Solar Lyman irradiance line profiles (Lemaire+, 2015)
J/A+A/611/A1 : SOLAR/SOLSPEC Spectral Irradiance - 0.5-3000nm (Meftah+, 2018)
J/A+A/624/A36 : EUV irradiances of the quiet Sun (Del Zanna, 2019)
Byte-by-byte Description of file (#): tablea?.dat
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Bytes Format Units Label Explanations
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1- 5 F5.2 0.1nm lambda Wavelength in the vacuum
12- 15 F4.2 10-8mW/m2/Hz I(Hz) Specific Intensity
22- 25 F4.2 10+6mW/m2/nm I(0.1nm) Specific Intensity
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Byte-by-byte Description of file (#): tableb1.dat
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Bytes Format Units Label Explanations
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1- 10 A10 "date" Date Specified date
17- 21 F5.3 10-2W/m2 Irradiance LISIRD Lyman-alpha index (smoothed) (1)
28- 32 F5.3 --- Coeff-L1 Coefficient for Lyman-alpha for 2008/06/24
39- 43 F5.3 --- Coeff-higher Coefficient for higher Lyman lines
for 1996/05/15
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Note (1): LISIRD composite Lyman-alpha index (Machol et al.,
2019E&SS....6.2263M 2019E&SS....6.2263M) was smoothed by a running average over 400 days.
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Acknowledgements:
Stanislav Gunar, gunar(at)asu.cas.cz
Pavol Schwartz, pschwartz(at)astro.sk
(End) Patricia Vannier [CDS] 19-Oct-2020