J/A+A/560/A61 A frequency Comb calibrated solar atlas (Molaro+, 2013)
A frequency comb calibrated solar atlas.
Molaro P., Esposito M., Monai S., Lo Curto G., Gonzalez Hernandez J.I.,
Hansch T.W., Holzwarth R., Manescau A., Pasquini L., Probst R.A., Rebolo R.,
Steinmetz T., Udem T., Wilken T.
<Astron. Astrophys. 560, A61 (2013)>
=2013A&A...560A..61M 2013A&A...560A..61M
ADC_Keywords: Sun ; Atlases ; Spectroscopy
Keywords: instrumentation: spectrographs - techniques: spectroscopic - atlases -
Sun: photosphere - Sun: activity
Abstract:
The solar spectrum is a primary reference for the study of physical
processes in stars and their variation during activity cycles. High
resolution spectra of the Sun are easily obtained from spatially
selected regions of the solar disk, while those taken over the
integrated disk are more problematic. However, a proxy can be obtained
by using solar light reflected by small bodies of the solar system.
We first apply the LFC solar spectrum to characterize the CCDs of the
HARPS spectrograph. The comparison of the LFC and Th-Ar calibrated
spectra reveals S-type distortions on each order along the whole
spectral range with an amplitude of 40m/s. This confirms the pattern
found by Wilken et al. (2010MNRAS.405L..16W 2010MNRAS.405L..16W) on a single order and
extends the detection of the distortions to the whole analyzed region
revealing that the precise shape varies with wavelength. A new data
reduction is implemented to deal with CCD pixel inequalities to obtain
a wavelength corrected solar spectrum. By using this spectrum we
provide a new LFC calibrated solar atlas with 400 line positions in
the range of 476-530, and 175 lines in the 534-585nm range
corresponding to the LFC bandwidth. The new LFC atlas is consistent on
average with that based on FTS solar spectra, but it improves the
accuracy of individual lines by a significant factor reaching a mean
value of 10m/s.
The LFC-based solar line wavelengths are essentially free of major
instrumental effects and provide a reference for absolute solar line
positions at the date of Nov 2010, i.e. an epoch of low solar
activity. We suggest that future LFC observations could be used to
trace small radial velocity changes of the whole solar photospheric
spectrum in connection with the solar cycle and for direct comparison
with the predicted line positions of 3D radiative hydrodynamical
models of the solar photosphere. The LFC calibrated solar atlas can be
also used to verify the accuracy of ground or space spectrographs by
means of the solar spectrum.
Description:
In November 2010 (an epoch of low solar activity), an experiment with
a prototype of a Laser Frequency Comb (LFC) calibration system was
performed with the HARPS spectrograph of the 3.6m ESO telescope at
La Silla during which high signal-to-noise spectra of the Moon were
obtained. We exploit those Echelle spectra to study a portion of the
optical integrated solar spectrum and in particular to determine the
solar photospheric line positions.
The DAOSPEC program is used to measure solar line positions through
gaussian fitting in an automatic way. The solar spectra are calibrated
both with an LFC and a Th-Ar. The final atlas is corrected for all
motions (Sun, Moon, Earth).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table3.dat 27 575 LFC (Laser Frequency Comb) solar atlas in the
476.0-585.0nm wavelength region
table4a.dat 16 55067 Solar spectrum in 475/531nm region,
HARPS.2010-11-25T05:49:42.429s1dA blue
table4b.dat 16 52259 Solar spectrum in 533/586nm region,
HARPS.2010-11-25T05:49:42.429s1dA red
psf.dat 49 94208 Psf order by order
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See also:
J/A+A/525/A74 : 540-690nm Solar Atlas (Molaro+, 2011)
J/A+A/544/A125 : Solar lines from Ceres spectra (Molaro+, 2012)
Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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1- 3 I3 --- Seq [1/575] Sequence number
5- 14 F10.5 0.1nm lambda [4761/5849] Wavelength corrected for
all motions (in Å)
16- 19 F4.1 m/s sigma Standard Deviation
21- 23 I3 0.1pm EW Equivalent Width
25- 27 A3 --- El Element Identification (ionisation 1=neutral)
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Byte-by-byte Description of file: table4a.dat table4b.dat
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Bytes Format Units Label Explanations
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1- 9 F9.4 0.1nm lambda [4753/5860] Wavelength corrected for
all motions (in Å)
11- 16 I6 --- Flux Flux (arbitrary units)
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Byte-by-byte Description of file: psf.dat
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Bytes Format Units Label Explanations
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1- 22 E22.17 0.1nm lambda [4753/5860] Wavelength (Å)
24- 45 E22.17 --- Flux Flux (arbitrary units)
47- 49 I3 --- Order [105/128] Order
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Acknowledgements:
Sergio Monai, monai(at)ts.astro.it
(End) Patricia Vannier [CDS] 21-Oct-2013