1,715 research outputs found
A Relationship Between Stellar Age and Spot Coverage
We investigate starspot distributions consistent with space-based photometry
of F, G, and K stars in six stellar associations ranging in age from 10 Myr to
4 Gyr. We show that a simple light curve statistic called the "smoothed
amplitude" is proportional to stellar age as , following a
Skumanich-like spin-down relation. We marginalize over the unknown stellar
inclinations by forward modeling the ensemble of light curves for direct
comparison with the Kepler, K2 and TESS photometry. We sample the posterior
distributions for spot coverage with Approximate Bayesian Computation. We find
typical spot coverages in the range 1-10% which decrease with increasing
stellar age. The spot coverage is proportional to where , also statistically consistent with a Skumanich-like decay of
starspot coverage with age. We apply two techniques to estimate the spot
coverage of young exoplanet-hosting stars likely to be targeted for
transmission spectroscopy with the James Webb Space Telescope, and estimate the
bias in exoplanet radius measurements due to varying starspot coverage.Comment: 21 pages, 11 figures, accepted in ApJ, software in review at JOSS
https://github.com/openjournals/joss-reviews/issues/210
Hunt for Starspots in HARPS Spectra of G and K Stars
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.Comment: 12 pages, 8 figures, accepted to A
Non-detection of Contamination by Stellar Activity in the Spitzer Transit Light Curves of TRAPPIST-1
We apply the transit light curve self-contamination technique of Morris et
al. (2018) to search for the effect of stellar activity on the transits of the
ultracool dwarf TRAPPIST-1 with 2018 Spitzer photometry. The self-contamination
method fits the transit light curves of planets orbiting spotted stars,
allowing the host star to be a source of contaminating positive or negative
flux which influences the transit depths but not the ingress/egress durations.
We find that none of the planets show statistically significant evidence for
self-contamination by bright or dark regions of the stellar photosphere.
However, we show that small-scale magnetic activity, analogous in size to the
smallest sunspots, could still be lurking in the transit photometry undetected.Comment: Accepted for publication in ApJ
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