J/A+A/643/A146 The solar gravitational redshift (Gonzalez Hernandez+, 2020)
The solar gravitational redshift from HARPS-LFC Moon spectra.
A test of the general theory of relativity.
Gonzalez Hernandez J.I., Rebolo R., Pasquini L., Lo Curto G., Molaro P.,
Caffau E., Ludwig H.-G., Steffen M., Esposito M., Suarez Mascarenno A.,
Toledo-Padron B., Probst R.A., Hansch T.W., Holzwarth R., Manescau A.,
Steinmetz T., Udem T., Wilken T.
<Astron. Astrophys. 643, A146 (2020)>
=2020A&A...643A.146G 2020A&A...643A.146G (SIMBAD/NED BibCode)
ADC_Keywords: Solar system ; Sun ; Equivalent widths ; Line Profiles
Keywords: instrumentation: spectrographs - techniques: spectroscopic -
Sun: granulation - Sun: photosphere - Sun: activity - atlases
Abstract:
The General Theory of Relativity predicts the redshift of spectral
lines in the solar photosphere, as a consequence of the gravitational
potential of the Sun.
This effect can be measured from a solar disk-integrated flux spectrum
of the Sun's reflected light on solar system bodies.
The laser frequency comb (LFC) calibration system attached to the
HARPS spectrograph offers the possibility to perform an accurate
measurement of the solar gravitational redshift (GRS) by observing the
Moon or other solar system bodies.
We have analysed the line shift observed in Fe absorption lines from
five high-quality HARPS-LFC spectra of the Moon.
We select an initial sample of 326 photospheric Fe lines in the
spectral range 476-585nm and measure their line positions and
equivalent widths (EWs).
Accurate line shifts are derived from the wavelength position of the
core of the lines compared with the laboratory wavelengths of Fe
lines. We also use a CO5BOLD 3D hydrodynamical model atmosphere of
the Sun to compute 3D synthetic line profiles of a subsample of about
200 spectral Fe lines centred at their laboratory wavelengths.
We fit the observed relatively weak spectral Fe lines (with
EW<180mÅ) with the 3D synthetic profiles.
Convective motions in the solar photosphere do not affect the line
cores of Fe lines stronger than about 150mÅ.
In our sample, only 15 FeI lines have EWs in the range
150<EW(mÅ)<550, providing a measurement of the solar GRS at
639±14m/s, consistent with the expected theoretical value on Earth
of 633.1m/s.
A final sample of about 98 weak Fe lines with EW<180mÅ allows us to
derive a mean global line shift of 638±6m/s in agreement with the
theoretical solar GRS.
These are the most accurate measurements of the solar GRS so far.
Ultrastable spectrographs calibrated with the LFC over a larger
spectral range, such as HARPS or ESPRESSO, together with a further
improvement on the laboratory wavelengths, could provide a more robust
measurement of the solar GRS and further tests for the 3D
hydrodynamical models.
Description:
Line data and velocity shifts of the FeI and FeII lines, with
laboratory wavelengths, λlab, from Nave et al.
(1994ApJS...94..221N 1994ApJS...94..221N, 2013ApJS..204....1N 2013ApJS..204....1N) and excitation potentials,
oscillator strengths from the VALD database (Piskunov et al.
1995A&AS..112..525P 1995A&AS..112..525P).
In Table A.1 we provide the mean line core shifts, vcoreobs,
measured on the spectral lines from the observed HARPS-LFC spectra of
the MOON and computed with respect to the original laboratory
wavelengths (Nave et al. 1994ApJS...94..221N 1994ApJS...94..221N, 2013ApJS..204....1N 2013ApJS..204....1N).
We also give the recalibrated wavelengths, lambda_nist, computed from
recalibrated wavenumber measurements and Ritz wavelengths,
lambda_ritz, computed from recalibrated energy levels, with their
corresponding wavelengths uncertainties, extracted from the NIST
database (Kramida et al. 2019APS..DMPN09004K).
In Table A.2, we give the line core shifts measured on the observed
spectral lines, vcoreobs_n, estimated using the recalibrated
wavelengths, lambda_nist, as reference laboratory wavelengths, the 3D
profiles, v_core,3D, and the global line shifts, vfit3D_n, from
fitting the observed spectral lines using 3D profiles, and corrected
using the recalibrated wavelengths lambda_nist as reference laboratory
wavelengths.
Wavelengths are given in Angstroms, wavelength uncertainties in
miliAngstroems, excitation potentials in eV, equivalent widths (EW) in
miliAngstroems, and velocity shifts in m/s.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
tablea1.dat 75 188 Line data and line shifts of 188 FeI-II lines
tablea2.dat 74 97 Line data and line shifts of 97 FeI-II lines
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See also:
J/ApJS/94/221 : New multiplet table for FeI (Nave+, 1994)
Byte-by-byte Description of file: tablea1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 9 F9.4 0.1nm lambda-lab Original wavelengths (1)
11- 19 F9.4 0.1nm lambda-nist Recalibrated wavelengths (2)
21- 23 F3.1 0.1pm e_lambda-nist Uncertainty in lambda_nist (2)
25- 33 F9.4 0.1nm lambda-ritz Recalibrated Ritz wavelengths (2)
35- 37 F3.1 0.1pm e_lambda-ritz Uncertainty in lambda_ritz (2)
39- 40 A2 --- El Chemical element
42 I1 --- Ion Element Ion
44- 47 F4.2 eV ExPot Excitation potential (3)
49- 53 F5.2 [-] loggf Oscillator strength (3)
55- 59 F5.1 0.1pm EW Equivalent widths
61- 64 F4.1 0.1pm e_EW Uncertainty in EW
66- 70 F5.1 m/s v-core-obs Line core shift (4)
72- 75 F4.1 m/s e_v-core-obs Uncertainty in vcoreobs
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Note (1): original wavelengths of FeI lines extracted from
Nave et al. (1994ApJS...94..221N 1994ApJS...94..221N, Cat. J/ApJS/94/221) and of FeII lines
extracted from Nave & Johansson (2013ApJS..204....1N 2013ApJS..204....1N).
Note (2): recalibrated wavelengths of FeI-II lines, lambda-nist, computed from
recalibrated wavenumber measurements and Ritz wavelengths, lambda_ritz,
computed from recalibrated energy levels, with their corresponding
wavelengths uncertainties, all values extracted from the NIST database
(Kramida et al. 2019APS..DMPN09004K).
Note (3): excitation potentials and oscillator strengths from the VALD database
(Piskunov et al. 1995A&AS..112..525P 1995A&AS..112..525P).
Note (4): Mean line core shift computed with respect to the original laboratory
wavelengths of FeI lines from Nave et al. (1994ApJS...94..221N 1994ApJS...94..221N,
Cat. J/ApJS/94/221) and FeII lines from Nave & Johansson (2013ApJS..204....1N 2013ApJS..204....1N).
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Byte-by-byte Description of file: tablea2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 9 F9.4 0.1nm lambda-lab Original wavelengths (1)
11- 19 F9.4 0.1nm lambda-nist Recalibrated wavelengths (2)
21- 22 A2 --- El Chemical element
24 I1 --- Ion Element Ion
26- 29 F4.2 eV ExPot Excitation potential (3)
31- 35 F5.2 [-] loggf Oscillator strength (3)
37- 41 F5.1 0.1pm EW Equivalent width
43- 45 F3.1 0.1pm e_EW Uncertainty in EW
47- 51 F5.1 m/s v-core-obs-n Line core shift (4)
53- 56 F4.1 m/s e_v-core-obs-n Uncertainty in vcoreobs
58- 63 F6.1 m/s v-core-3D Line core shift; 3D line profile (5)
65- 69 F5.1 m/s v-fit-3D-n Global line shift; 3D profile fit (6)
71- 74 F4.1 m/s e_v-fit-3D-n Uncertainty in vfit3D_n
--------------------------------------------------------------------------------
Note (1): original wavelengths of FeI lines extracted from
Nave et al. (1994ApJS...94..221N 1994ApJS...94..221N, Cat. J/ApJS/94/221) and of FeII lines
extracted from Nave & Johansson (2013ApJS..204....1N 2013ApJS..204....1N).
Note (2): recalibrated wavelengths of FeI-II lines, lambda_nist, computed from
recalibrated wavenumber measurements, with their corresponding
wavelengths uncertainties, all values extracted from the NIST database
(Kramida et al. 2019APS..DMPN09004K).
Note (3): excitation potentials and oscillator strengths from the VALD database
(Piskunov et al. 1995A&AS..112..525P 1995A&AS..112..525P).
Note (4): Mean line core shift computed with respect to the recalibrated
wavelengths of FeI-II lines, lambda-nist, extracted from the NIST
database (Kramida et al. 2019APS..DMPN09004K).
Note (5): Line core shift computed from the 3D line profiles interpolated to
the observed equivalent width of the FeI-II lines.
Note (6): Global line shift estimated from fitting the observed FeI-II lines
with 3D line profiles computed using a CO5BOLD 3D model atmosphere
of the Sun. The line shift are corrected using the recalibrated
wavelengths of FeI-II lines, lambda_nist, extracted from the NIST
database (Kramida et al. 2019APS..DMPN09004K)
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Acknowledgements:
Jonay I. Gonzalez Hernandez, jonay(at)iac.es
References:
Kramida et al., 2019APS..DMPN09004K,
NIST's atomic databases for applied and fundamental science
Nave, G., et al., 1994ApJS...94..221N 1994ApJS...94..221N,
A New Multiplet Table for Fe I
Nave, G., & Johansson, S., 2013ApJS..204....1N 2013ApJS..204....1N,
The Spectrum of Fe II
Piskunov, N. E. et al., 1995A&AS..112..525P 1995A&AS..112..525P,
VALD: The Vienna Atomic Line Data Base
(End) Jonay Gonzalez Hernandez [IAC, Spain], Patricia Vannier [CDS] 24-Sep-2020