The impact of unresolved magnetic spots on high-precision radial velocity measurements

Lisogorskyi, Maksym; Saikia, S. Boro; Jeffers, S. V.; Jones, H. R. A.; Morin, J.; Mengel, M. W.; Reiners, A.; Vidotto, A. A.; Petit, P.

doi:10.1093/mnras/staa2184

Cited by 7 publications

(5 citation statements)

References 50 publications

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“…Magnetic activity influences planetary evolution through the amount of high-energy radiation emitted during the phase when the planetary atmosphere is young because intense highenergy radiation and winds can evaporate the atmosphere of a planet in a close orbit (Sanz-Forcada et al 2011;Johnstone et al 2015). Magnetic fields and their variability are among the main obstacles for the radial velocity detection of low-mass planets (Reiners et al 2013;Lisogorskyi et al 2020;Haywood et al 2020;Crass et al 2021).…”

Section: Introductionmentioning

confidence: 99%

Magnetism, rotation, and nonthermal emission in cool stars

Reiners

Shulyak

Käpylä

et al. 2022

A&A

102

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Stellar dynamos generate magnetic fields that are of fundamental importance to the variability and evolution of Sun-like and low-mass stars, and for the development of their planetary systems. As a key to understanding stellar dynamos, empirical relations between stellar parameters and magnetic fields are required for comparison to ab initio predictions from dynamo models. We report measurements of surface-average magnetic fields in 292 M dwarfs from a comparison with radiative transfer calculations; for 260 of them, this is the first measurement of this kind. Our data were obtained from more than 15 000 high-resolution spectra taken during the CARMENES project. They reveal a relation between average field strength, ⟨B⟩, and Rossby number, Ro, resembling the well-studied rotation–activity relation. Among the slowly rotating stars, we find that magnetic flux, ΦB, is proportional to rotation period, P, and among the rapidly rotating stars that average surface fields do not grow significantly beyond the level set by the available kinetic energy. Furthermore, we find close relations between nonthermal coronal X-ray emission, chromospheric Hα and Ca H&K emission, and magnetic flux. Taken together, these relations demonstrate empirically that the rotation–activity relation can be traced back to a dependence of the magnetic dynamo on rotation. We advocate the picture that the magnetic dynamo generates magnetic flux on the stellar surface proportional to rotation rate with a saturation limit set by the available kinetic energy, and we provide relations for average field strengths and nonthermal emission that are independent of the choice of the convective turnover time. We also find that Ca H&K emission saturates at average field strengths of ⟨B⟩≈800 G while Hα and X-ray emission grow further with stronger fields in the more rapidly rotating stars. This is in conflict with the coronal stripping scenario predicting that in the most rapidly rotating stars coronal plasma would be cooled to chromospheric temperatures.

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Section: Introductionmentioning

confidence: 99%

Magnetism, rotation, and nonthermal emission in cool stars

Reiners

Shulyak

Käpylä

et al. 2022

A&A

102

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“…The amplitude diminishes with increased averaging times (Bastien et al 2016;Cranmer et al 2014). Further phenomena such as starspots or faculae are adding to the confusion (Işık et al 2020;Korhonen et al 2015;Lagrange et al 2010;Lisogorskyi et al 2020;Meunier et al 2010;Milbourne et al 2019;Norris et al 2017).…”

Section: The Quest For Earth-like Exoplanetsmentioning

confidence: 99%

“…Furthermore, bright flares may appear in chromospheric emission lines (Czesla et al 2015;Klocová et al 2017). The presence of emerging and decaying starspots complicates exoplanet discoveries (Barnes et al 2017;Dumusque et al 2011b;Herrero et al 2016;Işık et al 2018;Lagrange et al 2010;Lanza et al 2011;Lisogorskyi et al 2020;Suárez Mascareño et al 2017;Tal-Or et al 2018), and magnetic activity cycles also add to the complications (Lovis et al 2011). As we explained in Paper I, one of the ambitions of the current project is to recover spatially resolved spectra also of starspots and stellar magnetic regions (including Zeeman signatures in magnetically sensitive spectral lines), which requires simultaneous precision photometry to identify the exact time of starspot transit.…”

Section: Stellar Magnetic Activitymentioning

confidence: 99%

Spatially resolved spectroscopy across stellar surfaces

Dravins

Ludwig

Freytag

2021

A&A

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Context. High-precision stellar analyses require hydrodynamic 3D modeling. Testing such models is feasible by retrieving spectral line shapes across stellar disks, using differential spectroscopy during exoplanet transits. Observations were presented in Papers I, II, and III, while Paper IV explored synthetic data at hyper-high spectral resolution for different classes of stars, identifying characteristic patterns for Fe I and Fe II lines. Aims. Anticipating future observations, the observability of patterns among photospheric lines of different strength, excitation potential and ionization level are examined from synthetic spectra, as observed at ordinary spectral resolutions and at different levels of noise. Time variability in 3D atmospheres induces changes in spectral-line parameters, some of which are correlated. An adequate calibration could identify proxies for the jitter in apparent radial velocity to enable adjustments to actual stellar radial motion. Methods. We used spectral-line patterns identified in synthetic spectra at hyper-high resolution in Paper IV from 3D models spanning Teff = 3964–6726 K (spectral types ~K8 V–F3 V) to simulate practically observable signals at different stellar disk positions at various lower spectral resolutions, down to λ/Δλ = 75 000. We also examined the center-to-limb temporal variability. Results. Recovery of spatially resolved line profiles with fitted widths and depths is shown for various noise levels, with gradual degradation at successively lower spectral resolutions. Signals during exoplanet transit are simulated. In addition to Rossiter-McLaughlin type signatures in apparent radial velocity, analogous effects are shown for line depths and widths. In a solar model, temporal variability in line profiles and apparent radial velocity shows correlations between jittering in apparent radial velocity and fluctuations in line depth. Conclusions. Spatially resolved spectroscopy using exoplanet transits is feasible for main-sequence stars. Overall line parameters of width, depth and wavelength position can be retrieved already with moderate efforts, but a very good signal-to-noise ratio is required to reveal the more subtle signatures between subgroups of spectral lines, where finer details of atmospheric structure are encoded. Fluctuations in line depth correlate with those in wavelength, and because both can be measured from the ground, searches for low-mass exoplanets should explore these to adjust apparent radial velocities to actual stellar motion.

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“…Using magnetohydrodynamic models, it is shown that in the case of HD 261941, outflow and accretion take place, and for V590 Mon, the line origins mainly in the stellar wind from the disk. Lisogorskyi et al (2020) consider the effect of stellar activity on the accuracy of radial velocity measurements in exoplanet searches. Simulation is carried out under the assumption of a different set of unresolved magnetic spots in a rotating star of the K2 Eri type.…”

Section: Magnetic White Dwarfsmentioning

confidence: 99%

Magnetic Fields of Chemically Peculiar and Related Stars. VII. Main Results of 2020 and Near-Future Prospects

Romanyuk

2021

Astrophys. Bull.

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We present a review of the papers written in the field of stellar magnetism studies in 2020. More than 70 original papers related to different areas of the specified scientific topics have been analyzed. Instruments, methods of analysis, and software are considered, as well as: chemically peculiar stars and their identification; magnetic fields, chemical abundance, and photometry of chemically peculiar stars; magnetic white dwarfs, active cool stars and other objects. In the field of stellar magnetism research, 6–7 scientific groups continue to work actively using the world’s largest telescopes, which fact indicates the relevance and importance of the problem under study.

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The impact of unresolved magnetic spots on high-precision radial velocity measurements

Cited by 7 publications

References 50 publications

Magnetism, rotation, and nonthermal emission in cool stars

Magnetism, rotation, and nonthermal emission in cool stars

Spatially resolved spectroscopy across stellar surfaces

Magnetic Fields of Chemically Peculiar and Related Stars. VII. Main Results of 2020 and Near-Future Prospects

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