J/A+A/664/A34 Sun and HD128621 spectra (Al Moulla+, 2022)
Measuring precise radial velocities on individual spectral lines.
III. Dependence of stellar activity signal on line formation temperature.
Al Moulla K., Dumusque X., Cretignier M., Zhao Y., Valenti J.A.
<Astron. Astrophys. 664, A34 (2022)>
=2022A&A...664A..34A 2022A&A...664A..34A (SIMBAD/NED BibCode)
ADC_Keywords: Sun ; Stars, nearby ; Spectroscopy ; Optical
Keywords: stars: activity - stars: individual: Sun -
stars: individual: HD128621 - techniques: radial velocities -
techniques: spectroscopic
Abstract:
To enable radial velocity (RV) precision on the order of ∼0.1m/s
required for the detection of Earth-like exoplanets orbiting
solar-type stars, the main obstacle lies in mitigating the impact of
stellar activity.
This study investigates the dependence of derived RVs with respect to
the formation temperature of spectral line segments.
Using spectral synthesis, we compute for each observed wavelength
point of unblended spectral lines the stellar temperature below which
50% of the emergent flux originates. We can then construct RV time
series for different temperature ranges, using template matching.
With HARPS-N solar data and HARPS alpha Cen B measurements, we
demonstrate on time intervals of prominent stellar activity that the
activity-induced RV signal has different amplitude and periodicity
depending on the temperature range considered. We compare the solar
measurements with simulated contributions from active surface regions
seen in simultaneous images, and find that the suppression of
convective motion is the dominant effect.
From a carefully selected set of spectral lines, we are able to
measure the RV impact of stellar activity at various stellar
temperatures ranges. We are able to strongly correlate the effect of
convective suppression with spectral line segments formed in hotter
temperature ranges. At cooler temperatures, the derived RVs exhibit
oppositely directed variations compared to the average RV time series
and stronger anti- correlations with chromospheric emission.
Description:
We make use of daily-binned spectra of the Sun and alpha Cen B
(HD128621), obtained with the HARPS-N and HARPS spectrographs,
respectively. The spectra are continuum normalized with the RASSINE
code, and corrected for telluric contamination and instrumental
systematics with the YARARA code. The FITS files contain the binned
spectra, with the following data fields: 'wave': wavelength points in
angstrom, 'flux': normalized flux, 'flux_err': normalized flux
uncertainty.
Objects:
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RA (2000) DE Designation(s)
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14 39 35.06 -60 50 15.1 HD128621 = * alf Cen B
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File Summary:
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FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
list.dat 132 155 List of fits spectra
fits/* . 155 Individual fits spectra
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Byte-by-byte Description of file: list.dat
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Bytes Format Units Label Explanations
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1- 8 A8 --- Name Star name (HD128621 or Sun)
10- 32 A23 "datime" Obs.Date Observation date
34- 39 I6 --- Nx Number of wavelength points
41- 43 F3.1 Mbyte Size Size of FITS file
45- 90 A46 --- FileName Name of FITS file
92-132 A41 --- Title Title of the fits file
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Acknowledgements:
Khaled Al Moulla, khaled.almoulla[at]unige.ch
References:
Dumusque, Paper I 2018A&A...620A..47D 2018A&A...620A..47D
Cretignier et al., Paper II 2020A&A...633A..76C 2020A&A...633A..76C
(End) Patricia Vannier [CDS] 16-May-2022