Characterization of starspots on a young M-dwarf K2-25: multi-band observations of stellar photometric variability and planetary transits

Abstract

Detailed atmospheric characterization of exoplanets by transmission spectroscopy requires careful consideration of stellar surface inhomogeneities induced by starspots. This effect is particularly problematic for planetary systems around M-dwarfs, and their spot properties are not fully understood. We investigated the stellar activity of the young M-dwarf K2-25 and its effect on transit observations of the sub-Neptune K2-25b. From multi-band monitoring observations of stellar brightness variability using ground-based telescopes and TESS, we found that the temperature difference between the spots and photosphere is <190 K and the spot covering fraction is <61% (2$\sigma$). We also investigated the effect of starspot activity using multi-epoch, multi-band transit observations. We rule out cases with extremely low spot temperatures and large spot covering fractions. The results suggest that spots could distort the transmission spectrum of K2-25b by as much as $\sim$100 ppm amplitude, corresponding to the precision of JWST/NIRSPEC of the target. Our study demonstrates that simultaneous multi-band observations with current instruments can constrain the spot properties of M-dwarfs with good enough precision to support atmospheric studies of young M-dwarf planets via transmission spectroscopy.

24 pages, 24 figures, Accepted for publication in MNRAS

References in corpus (30)

• The Gaia mission
• Gaia Data Release 3: Summary of the content and survey properties
• The Transiting Exoplanet Survey Satellite
• The Zwicky Transient Facility: System Overview, Performance, and First Results
• The James Webb Space Telescope
• The generalised Lomb-Scargle periodogram. A new formalism for the floating-mean and Keplerian periodograms
• The Zwicky Transient Facility: Data Processing, Products, and Archive
• Kepler Flares II: The Temporal Morphology of White-Light Flares on GJ 1243
• PASTIS: Bayesian extrasolar planet validation. I. General framework, models, and performance
• High Tide or Riptide on the Cosmic Shoreline? A Water-Rich Atmosphere or Stellar Contamination for the Warm Super-Earth GJ~486b from JWST Observations
• Atmospheric Reconnaissance of TRAPPIST-1 b with JWST/NIRISS: Evidence for Strong Stellar Contamination in the Transmission Spectra
• ACCESS I: An Optical Transmission Spectrum of GJ 1214b Reveals a Heterogeneous Stellar Photosphere
• The Habitable-zone Planet Finder Reveals A High Mass and a Low Obliquity for the Young Neptune K2-25b
• Hubble WFC3 Spectroscopy of the Habitable-zone Super-Earth LHS 1140 b
• Near-Infrared Transmission Spectroscopy of HAT-P-18b with NIRISS: Disentangling Planetary and Stellar Features in the Era of JWST
• Mapping stellar surfaces I: Degeneracies in the rotational light curve problem
• Stellar surface inhomogeneities as a potential source of the atmospheric signal detected in the K2-18 b transmission spectrum
• From Starspots to Stellar Coronal Mass Ejections -- Revisiting Empirical Stellar Relations
• Mapping stellar surfaces II: An interpretable Gaussian process model for light curves
• Starspot mapping with adaptive parallel tempering. II. Application to TESS data for M-dwarf flare stars, AU Microscopii, YZ Canis Minoris, and EV Lacertae
• Near-infrared transmission spectrum of TRAPPIST-1 h using Hubble WFC3 G141 observations
• TOI-3884 b: A rare 6-R${}_{\oplus }$ planet that transits a low-mass star with a giant and likely polar spot
• Zodiacal Exoplanets in Time. XI. The Orbit and Radiation Environment of the Young M Dwarf-Hosted Planet K2-25b
• Zodiacal Exoplanets in Time (ZEIT) IX: a flat transmission spectrum and a highly eccentric orbit for the young Neptune K2-25b as revealed by Spitzer
• A Study of Flares in the Ultra-Cool Regime from SPECULOOS-South
• Spectral variability of photospheric radiation due to faculae II: Facular contrasts for cool main-sequence stars
• Forward modelling of Kepler-band variability due to faculae and spots
• Correcting the effect of stellar spots on ARIEL transmission spectra
• Wavelength Dependence of Activity-Induced Photometric Variations for Young Cool Stars in Hyades
• The young planetary system K2-25: constraints on companions and starspots

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• GEMS JWST: Transmission spectroscopy of TOI-5205b reveals significant stellar contamination and a metal-poor atmosphere
• Rapid characterization of exoplanet atmospheres with the Exoplanet Transmission Spectroscopy Imager (ETSI)