J/A+A/624/A57 Convective blueshifts in solar atmos. (Loehner-Boettcher+, 2019)
Convective blueshifts in the solar atmosphere.
III. High-accuracy observations of spectral lines in the visible.
Loehner-Boettcher J., Schmidt W., Schlichenmaier R., Steinmetz T.,
Holzwarth R.
<Astron. Astrophys. 624, A57 (2019)>
=2019A&A...624A..57L 2019A&A...624A..57L (SIMBAD/NED BibCode)
ADC_Keywords: Solar system ; Sun ; Spectra, optical
Keywords: convection - Sun: atmosphere - Sun: activity -
methods: observational - techniques: spectroscopic - line: profiles
Abstract:
Convective motions in the solar atmosphere cause spectral lines to
become asymmetric and shifted in wavelength. For photospheric lines,
this differential Doppler shift varies from the solar disk center to
the limb.
Precise and comprehensive observations of the convective blueshift and
its center-to-limb variation improve our understanding of the
atmospheric hydrodynamics and ensuing line formation, and provide the
basis to refine 3D models of the solar atmosphere.
We performed systematical spectroscopic measurements of the convective
blueshift of the quiet Sun with the Laser Absolute Reference
Spectrograph (LARS) at the German Vacuum Tower Telescope. The spatial
scanning of the solar disk covered 11 heliocentric positions each
along four radial (meridional and equatorial) axes. The
high-resolution spectra of 26 photospheric to chromospheric lines in
the visible range were calibrated with a laser frequency comb to
absolute wavelengths at the 1m/s accuracy. Applying ephemeris and
reference corrections, the bisector analysis provided line asymmetries
and Doppler shifts with an uncertainty of only few m/s. To allow
for a comparison with other observations, we convolved the results to
lower spectral resolutions.
Description:
Solar spectra were observed in eight different spectral regions
(525nm, 538nm, 543nm, 557nm, 589nm, 614nm, 617nm, 630nm) with the
Laser Absolute Reference Spectrograph (LARS) at the VTT on Tenerife.
The observations were performed at different heliocentric position
mu=cos(alpha) from disk center (mu=1.0) to near the solar limb
(mu=0.3,0.2). These 20min-time-averaged observations were performed
along four radial axes (north, south, east, west). The calibration of
the solar spectra with a laser frequency comb results in an absolute
wavelength scale with an Doppler accuracy of 1m/s. The spectra were
recorded with the spectrographs (resolution greater than 700000) CCD
camera.
Vacuum Tower Telescope (VTT), Laser Absolute Reference Spectrograph
(LARS), May 2016 to May 2018.
IF Integrated sunlight of 10arcsec field of view AND Spectral
resolution greater than 700000, Temporal average over 20min at the
respective heliocentric position mu.
FITS files contain the average solar spectrum in the same form
throughout: *: 2048 pixel, dimension [*,0]: spectral intensity,
dimension [*,1]: standard deviation, dimension [*,2]: absolute
wavelength in Angstroem.
Data naming includes the instrument, date, time, spectral region,
heliocentric position mu, and abbreviated radial axis (except at disk
center)
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
list.dat 151 610 List of spectra
fits/* . 610 Individual fits spectra
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Byte-by-byte Description of file: list.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 4 I4 --- Nx Number of pixels along X-axis
6 I1 --- Ny Number of pixels along Y-axis
8- 30 A23 "datime" Obs.date Observation date
32- 33 I2 Kibyte size Size of FITS file
35- 92 A58 --- FileName Name of FITS file, in subdirectory fits
94-151 A58 --- Title Title of the FITS file
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Acknowledgements:
Johannes Lohner-Bottcher, jlb(at)leibniz-kis.de
References:
Loehner-Boettcher et al., Paper I 2018A&A...611A...4L 2018A&A...611A...4L
Stief et al., Paper II 2019A&A...622A..34S 2019A&A...622A..34S
(End) Patricia Vannier [CDS] 04-Feb-2019