Exoplanets around Flare Stars

[Presented at Know Thy Star, Know Thy Planet conference]
Searches for rocky, habitable zone exoplanets have naturally moved to surveying lower-mass stars such as M dwarfs. While geometrically favorable for exoplanet studies, these small stars present serious challenges for habitability characterization and transit detection due to surface magnetic activity, especially from flares. To fully "Know Thy Star" we must therefore understand its magnetic activity. I will review how exoplanet missions such as Kepler have begun a revolution in our understanding of stellar activity, including the first models of flare rate evolution over time. I will also discuss how flares have impacted the search for planets around M dwarfs including Proxima Cen and TRAPPIST-1 in the optical and IR, and the prospects for future work on active stars.

Transcript

1. Exoplanets Around Flare Stars James R. A. Davenport NSF Astronomy & Astrophysics Postdoctoral Fellow, Western Washington University DIRAC Fellow, University of Washington jradavenport UNIVERSITY OF WASHINGTON
2. Exoplanets Around Flare Stars jradavenport Casey Reed/NASA
3. Age vs. Activity log Ca II Flux ACTIVE! inactive Sun More Flares Fewer Flares See poster Adam Schneider: The UV Evolution of Mid-Type M Dwarfs with GALEX log age (yrs) Lyra (2005) jradavenport
4. so many flares! jradavenport GJ 1243, M4 300 days of 1-min data Prot = 0.59 days +6100 flares! some Kepler data Time (days) Relative Flux
5. find every flare in Kepler: appaloosa *why “appaloosa”? Ask me later jradavenport http://github.com/jradavenport/appaloosa
6. 3 steps to find flares in Kepler: 1. Detrend 2. Detect 3. Distrust find every flare in Kepler: appaloosa – iterative removal of “noise” – find “significant” peaks – artificial flare injection and recovery jradavenport
7. Cumulative Flare Rate Davenport 2016 log Flare Energy 68% Completeness Test Limit individual quarters of data Flare Frequency Distribution (for 1 star) jradavenport
8. A break in the powerlaw? (talk with Dave Soderblom) jradavenport
9. Flare Frequency vs. Rotation Fast (1-day) Slow (18-day) Cumulative Flare Rate log Flare Energy jradavenport
10. Flare Frequency vs. Rotation jradavenport
11. Add terms for mass and age Fit with powerlaw flare rate slope specific flare rate *Age from gyrochronology model jradavenport
12. log flare rate (#/day) Lbol-corrected Flare Rate vs. (Mass, Age) Davenport et al. (2017 in prep) jradavenport
13. Proxima Alpha Cen A&B Proxima b jradavenport P = 11.186 days m sin i = 1.27 M⨁ habitable zone! transit? ESO
14. Proxima Alpha Cen A&B jradavenport Proxima b ESO/M. Kornmesser
15. MOST jradavenport 2014 & 2015 37.6 days on Proxima ~1min cadence Microvariability and Oscillations of STars
16. jradavenport Over 60 flares found Flares! gaps due to orbit Proxima Cen
17. jradavenport See poster: Ward Howard Stellar Activity for Every TESS Star in the Southern Sky
18. Kipping+2016 No conclusive evidence for a transit from MOST data original data reduction alternate data reduction jradavenport ~1.5% chance of a Transit Flares really hurting us Need more continuous data Go to infrared ?
19. Flares in the Optical & IR jradavenport
20. U g r i J H K Tofflemire et al. (2012) AD Leo (M4) Davenport et al. (2012) Observations Models jradavenport Flares in the Optical & IR
21. b c e f g h d TRAPPIST–1 jradavenport NASA
22. Gillon et al. (2017) jradavenport Luger+2017 TRAPPIST–1 K2 light curve Spitzer ~20 days ~79 days
23. TRAPPIST–1 jradavenport BIG flare(s) K2 light curve
24. TRAPPIST–1 Luger+2017 jradavenport Flare K2 light curve
25. Flares from Spitzer TRAPPIST–1 jradavenport
26. Similar K2 flare Flares from Spitzer TRAPPIST–1 jradavenport
27. TRAPPIST–1 jradavenport Comparable rates between optical & IR
28. b Incredible - flares overlapping 2 transits! TRAPPIST–1 jradavenport
29. Summary Flares make transit searches hard(er) Flare rates change with stellar age! Flares may be bad for habitability! Flares are visible in the IR!