Hunt for Starspots in HARPS Spectra of G and K Stars

Abstract

We present a method for detecting starspots on cool stars using the cross-correlation function (CCF) of high resolution molecular spectral templates applied to archival high-resolution spectra of G and K stars observed with HARPS/HARPS-N. We report non-detections of starspots on the Sun even when the Sun was spotted, the solar twin 18 Scorpii, and the very spotted Sun-like star HAT-P-11, suggesting that Sun-like starspot distributions will be invisible to the CCF technique, and should not produce molecular absorption signals which might be confused for signatures of exoplanet atmospheres. We detect strong TiO absorption in the T Tauri K-dwarfs LkCa 4 and AA Tau, consistent with significant coverage by cool regions. We show that despite the non-detections, the technique is sensitive to relatively small spot coverages on M dwarfs and large starspot areas on Sun-like stars.

arXiv comment12 pages, 8 figures, accepted to AJ

References in corpus (32)

• Astropy: A Community Python Package for Astronomy
• The NumPy array: a structure for efficient numerical computation
• The chemical composition of the Sun
• The Astropy Project: Building an inclusive, open-science project and status of the v2.0 core package
• A new extensive library of PHOENIX stellar atmospheres and synthetic spectra
• The orbital motion, absolute mass, and high-altitude winds of exoplanet HD209458b
• A high accuracy computed water line list
• The signature of orbital motion from the dayside of the planet tau Bootis b
• The Transit Light Source Effect: False Spectral Features and Incorrect Densities for M-dwarf Transiting Planets
• Structure and Evolution of Nearby Stars with Planets II. Physical Properties of ~1000 Cool Stars from the SPOCS Catalog
• ExoMol Molecular linelists -- XXXIII. The spectrum of Titanium Oxide
• Toroidal versus poloidal magnetic fields in Sun-like stars: a rotation threshold
• Starspots, spin-orbit misalignment, and active latitudes in the HAT-P-11 exoplanetary system
• Deriving precise parameters for cool solar-type stars. Optimizing the iron line list
• FastChem: A computer program for efficient complex chemical equilibrium calculations in the neutral/ionized gas phase with applications to stellar and planetary atmospheres
• Placing the spotted T Tauri star LkCa 4 on an HR diagram
• A search for TiO in the optical high-resolution transmission spectrum of HD 209458b: Hindrance due to inaccuracies in the line database
• SunPy - Python for Solar Physics
• The Starspots of HAT-P-11: Evidence for a Solar-like Dynamo
• Linking the evolution of terrestrial interiors and an early outgassed atmosphere to astrophysical observations
• Disentangling the planet from the star in late type M dwarfs: A case study of TRAPPIST-1g
• The radius and mass of the close solar twin 18 Sco derived from asteroseismology and interferometry
• The full spectral radiative properties of Proxima Centauri
• Kepler and Ground-based Transits of the Exo-Neptune HAT-P-11b
• The 0.8-4.5$\mu$m broadband transmission spectra of TRAPPIST-1 planets
• Chromospheric activity and evolutionary age of the Sun and four solar twins
• The Sun-like activity of the solar twin 18 Scorpii
• Chromospheric Activity of HAT-P-11: an Unusually Active Planet-Hosting K Star
• Stellar Properties of Active G and K Stars: Exploring the Connection Between Starspots and Chromospheric Activity
• Estimating the p-mode frequencies of the solar twin 18 Sco
• Non-detection of Contamination by Stellar Activity in the Spitzer Transit Light Curves of TRAPPIST-1
• Modelling the solar twin 18 Sco

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