Convective blueshifts in the solar atmosphere: III. High-accuracy observations of spectral lines in the visible

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 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. Typically, a blueshifted "C"-shaped curve at disk center transforms into a less blueshifted "\"-shape toward the solar limb. The comparison of all lines reveals the systematic dependence of the convective blueshift on the line depth. Synthetic models yield considerable deviations from the observed center-to-limb variation. The obtained Doppler shifts of the quiet Sun can serve as an absolute reference for other observations, the relative calibration of Dopplergrams, and the necessary refinement of atmospheric models. Based on this, the development of high-precision models of stellar surface convection will advance the detection of (potentially habitable) exoplanets by radial velocity measurements.

References in corpus (19)

• The Imaging Magnetograph eXperiment (IMaX) for the Sunrise balloon-borne solar observatory
• The Sunrise Mission
• Using the Sun to estimate Earth-like planets detection capabilities II. Impact of plages
• Planetary detection limits taking into account stellar noise. I. Observational strategies to reduce stellar oscillation and granulation effects
• Measuring precise radial velocities on individual spectral lines. I. Validation of the method and application to mitigate stellar activity
• The Sun as a planet-host star: Proxies from SDO images for HARPS radial-velocity variations
• HARPS-N observes the Sun as a star
• The origin of the reversed granulation in the solar photosphere
• The quiet solar atmosphere observed and simulated in NaD1
• Stellar Surface Magneto-Convection as a Source of Astrophysical Noise II. Center-to-Limb Parameterisation of Absorption Line Profiles and Comparison to Observations
• Solar velocity references from 3D HD photospheric models
• Convective Nature of Sunspot Penumbral Filaments: Discovery of Downflows in the Deep Photosphere
• Convective blueshifts in the solar atmosphere, I. Absolute measurements with LARS of the spectral lines at 6302 Å
• Explanation of the activity sensitivity of Mn I 5394.7 Å
• The GREGOR Fabry-Pérot Interferometer and its companion the Blue Imaging Solar Spectrometer
• LARS - An Absolute Reference Spectrograph for solar observations, Upgrade from a prototype to a turn-key system
• Absolute velocity measurements in sunspot umbrae
• Convective blueshifts in the solar atmosphere II. High-accuracy observations of the Fe i 6173.3Å line and deviations of full-disk Dopplergrams
• Measuring the surface magnetic fields of magnetic stars with unresolved Zeeman splitting

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