Solar Photospheric Spectrum Microvariability I. Theoretical searches for proxies of radial-velocity jittering
arXiv:2308.10937 · doi:10.1051/0004-6361/202347142
Abstract
Extreme precision radial-velocity spectrometers enable extreme precision stellar spectroscopy. Searches for low-mass exoplanets around solar-type stars are limited by the physical variability in stellar spectra, such as the short-term jittering of apparent radial velocities. To understand the physical origins of such jittering, the solar spectrum is assembled, as far as possible, from basic principles. Surface convection is modeled with time-dependent 3D hydrodynamics, followed by the computation of hyper-high resolution spectra during numerous instances of the simulation sequences. The behavior of different classes of photospheric absorption lines is monitored to identify commonalities or differences between different classes of lines: weak or strong, neutral or ionized, high- or low-excitation, atomic or molecular. For Fe I and Fe II lines, the radial-velocity jittering over the small simulation area typically amounts to +-150 m/s, scaling to about 2 m/s for the full solar disk. Most photospheric lines vary in phase but with different amplitudes among different classes of lines. Radial-velocity excursions are greater for stronger and for ionized lines, decreasing at longer wavelengths. The differences between various line-groups are about one order of magnitude less than the full jittering amplitudes. By matching very precisely measured radial velocities to the characteristic jittering patterns between different line-groups should enable to identify and to remove a significant component of the stellar noise originating in granulation. To verify the modeling toward such a filter, predictions of solar center-to-limb dependences of jittering amplitudes are presented for different classes of lines, testable with spatially resolving solar telescopes connected to existing radial-velocity instruments.
18 pages, 20 figures, accepted for publication in Astronomy & Astrophysics
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