PhD Thesis Talk

Slides from my astronomy PhD Thesis Defense at the University of Washington.

For a video of the talk, see:
https://vimeo.com/133258086

Transcript

1. Spots and Flares: Stellar Activity in the Time Domain Era James R. A. Davenport University of Washington Department of Astronomy 1 "If the Sun did not have a magnetic field, it would be as uninteresting a star as most astronomers believe it to be." -R. B. Leighton PhD Final Exam 2015-July-10
2. Spots and Flares: Stellar Activity in the Time Domain Era 2 First: a short story about spots, flares, and magnetic activity
3. 3 Sunspot drawing by R. Carrington (1859)
4. SDO (2014) 4
5. 12 hours later… 5 Aurora Borealis - Frederic Edwin Church (1865) whoa…
6. 6 Raises many important questions! • How often do these giant spots appear? • How long do they live? • How often do huge flares happen? • Could they affect life? • What can spots & flares tell us about a star? • Are spots & flares on other stars the same? • How do they change over (astronomical) time?
7. Date Latitude 7 11-year “butterfly” pattern
8. Differential Rotation Law 8 Rotation Period (days) Lat (deg) 0 45 10 15 90
9. 9 Stellar Age versus Activity Level Lyra (2005) log Ca II Flux log age (yrs) ACTIVE! inactive Sun
10. 10 Kepler the greatest stellar mission in decades
11. Topics to Cover 11 Part 1: Starspots Part 2: Starspots + Transits Part 3: Flares
12. 12 Part 1: Starspots NASA - SDO
14. 14 Largest sunspot observed in “modern” times Hoge 1947, Mt. Wilson Observatory by-eye observation by G.W.
15. Strassmeier (1999) • Observed across range of 
 mass, evolutionary phase
 • Evolve on timescales from 
 days to years (perhaps longer!)
 • Trace surface B field geometry,
 rotation, differential rotation Starspots: a generic result of B fields SDO Carroll (2012) 15
16. – Stellar rotation rate – Spot sizes
 – Differential rotation rate – Spot Lifetimes
 – Stellar activity stellar cycles – Evolution of spots with stellar age 16 Starspots: Parameters/Physics of Interest
17. – Stellar rotation rate – S – Differential rotation rate – Spot Lifetimes – Stellar activity stellar cycles – Evolution of spots 17 Starspots: Parameters/Physics of Interest – Stellar rotation rate – Spot sizes

18. • Get rotation period, starspot sizes • Map back to surface features (at least longitudes) 18 Phase / Longitude Flux Starspots with Photometry Walkowicz+ (2010)
19. • Searching for 2nd order effects in light curve Rotation Period Starspot Size 19 Differential Rotation
20. 20 4 days GJ 1243 - M4 Prot=0.5926 days Flux Time
21. 21 Starspot Primary feature stable over years “Shoulder” evolves on ~100 day timescales 4 days Flux Time
22. Longitude (deg) or Phase Time 22 Phase-folded light curve over time Starspot 4 days Flux Time
23. pixel color Phase– Flux Map Time Phase-folded light curve over time Davenport+ (2015) 23 Longitude (deg) or Phase Spots moving in longitude Spot constant in longitude 0 1 0 100 200 300 0.5
24. Phase– Flux Map 24 Davenport+ (2015)
25. Time (days) Longitude (deg) 0 360 180 -180 0 540 25 Davenport+ (2015) Phase– Flux Map
26. 26 Time (days) Longitude (deg) 0 360 180 -180 0 540 Chop light curve in to time windows Davenport+ (2015)
27. Relative Flux Phase Fit for spot positions in each window Rotation Direction Phase 27 Davenport+ (2015) Relative Flux
28. 28 Longitude (deg) 360 180 -180 0 540 Time (days) Davenport+ (2015) Each pair of points = window with full MCMC solution!
29. 29 Longitude (deg) 360 180 -180 0 540 Time (days) Davenport+ (2015) Differential Rotation “Equator-Lap-Pole” times of ~1500 days 10x slower than on Sun!
30. Longitude (deg) 360 180 -180 0 540 Time (days) Spot lifetimes:150-500 days for 2nd spot many years for 1st spot 30 Davenport+ (2015)
31. Reiners (2006) Collier Cameron (2007) Küker & Rüdiger (2011) @jradavenport GJ 1245 B GJ 1245 A Lurie+ (2015) GJ 1243 Davenport+ (2015) 31 Diff. Rot. rate
32. Part 2: Starspots + Transits 32 Lessons learned from GJ 1243 analysis: • very hard to constrain latitude of starspots • can only track 2 (maybe 3) starspots • can only track very slow evolution • how dark (cool) to make the spots? Transits help with many of these problems!
33. 33 Out-of-transit modulation like for GJ 1243 The physical scenario, many spots! In-transit full of details!
34. Kepler 63 Sanchis-Ojeda (2013) Béky (2014) Hat-P-11 Mapping starspots with transits, previous work TrES-1 (oklo.org) Rabus (2009) 34
35. Basics of Starspot “bumps” darker (cooler) spots 35
36. darker (cooler) spots 70-80% Agrees with solar umbra! 36
37. Phase Relative Flux 37 Want to recover: • starspot positions on surface • differential rotation law • starspot evolution timescales First: Test our spot-fitting code using simulated data!
38. 38 Light curve model from Llama (2012), based on “butterfly pattern” Time (years) Latitude (deg) Flux Time (years) Plus solar-like differential rotation, spot evolution, migration, diffusion…
39. 39 Then add eclipsing planet (hot Jupiter like) Time (years) Flux
40. 40 A “Kepler” light curve based on Llama (2012) Time Flux • 4 years of data • 5 min samples • 10 day rotation (equator) • 2 day planet orbit • rp/rs = 0.1
41. 41 Use MCMC to fit every starspot (longitude, latitude, radius) x nspots planet orbit & stellar rotation fixed Flux Time
42. 42 Repeat for every time window Flux Time
43. 43 Longitude (deg) slower than mean period faster spot lifetime Time (days) rotating @ mean period Goal: measure differential rotation & spot evolution trace starspot longitudes with time
44. 44 Longitude (deg) slower than mean period faster spot lifetime Time (days) rotating @ mean period Goal: measure differential rotation & spot evolution trace starspot longitudes with time
45. 45 Longitude (deg) Time (days) Each set of points = full static MCMC solution! Point color & size = radius
46. 46 Longitude (deg) Time (days) Point color & size = radius
47. 47 Longitude (deg) Time (days) Colors = cluster grey points = no cluster Use Python sklearn “DBSCAN” to cluster DBSCAN = Density-based spatial clustering of applications with noise Each represents 1 starspot moving in longitude over time
48. Time (days) 48 Max slope = highest lat spot Recovers simulated differential rotation law coefficient, k=1 Longitude (deg)
49. 49 Can recover starspot decay profiles! Time (days) Largest sunspots Work in Progress related to diffusion timescale solar decay m odel Area sunspot decay Hathaway (2008)
50. 50 now some real data!
51. 51 Kepler 17 - G2 (same as our Sun!) Prot= 12.1 days (faster than Sun) Porb= 1.5 days (super fast) Mass = 2.5 MJ Rp/Rs = 0.13 Kepler 17b Désert et al. (2011) Properties very similar to the simulated system!
52. Kepler 17: Examples of Spot Evolution Every 8th Transit Prot = 12.1 d Porb = 1.5 d 52
53. Long Cadence Short Cadence Short Cadence Time (days) Flux 53
54. 54 Use MCMC to fit every starspot (longitude, latitude, radius) x 8 spots Flux Time
55. Results from Kepler 17 reminder: do this for every time window! 55
56. Bump Evolution Matched! Every 8th Transit 56
57. 57 Longitude (deg) Time (days) Starspot evolution with time: more complicated! Point color & size = radius slower faster mean period
58. 58 Longitude (deg) Time (days) For Kepler 17 find k=0.8 Compare with solar value of k=0.2
59. 59 Lessons from starspots • Starspots have contrasts similar to sunspots • With transits, can fit many starspots simultaneously • Track evolution of at least 100 spot groups over 4 years • Estimate differential rotation law • Decay profiles may constrain diffusion timescale
60. 60 Flare! SDO AIA 211 Part 3: Flares
61. Martens & Kuin (1989) Standard Solar Flare Model 61 N S Sunspots
62. Martens & Kuin (1989) 62 Stellar Surface Sunspots N S
63. Kepler: Stellar Flare Machine • Long continuous light curves
 (up to ~4years) • Very precise photometry
 (~0.01%) • Enormous sample
 (>100,000 solar-type stars) • Complete samples of flares!
 (impossible from ground) • Huge range of flare energy!
 (look for Carrington-like events) 63
64. Walkowicz+ (2010) Flares Observed by Kepler 4 M-dwarfs 64
65. Time (days) GJ 1243, M4 Prot=0.59 days, ~300days 1-min data 65 Davenport et al. (2014) Lots of flares! COLLECT THEM ALL!
66. Flares By EYE (FBEYE) 66 Davenport et al. (2014) github.com/jradavenport/FBeye • Pick flare start/stop times • Assign classifications • Help train “autofinder”
67. Interesting to compare users 67 Davenport et al. (2014) Time (days) Flux
68. Large Flare Sample! • 6107 unique flares, spanning 300 days of data
 most for any star, besides the Sun! • 15% flares are “complex”
 higher % for large energy flares! • big energy range: Log E = 28-33 erg
 large solar flares around 1E32 erg 68 Hawley et al. (2014) Davenport et al. (2014)
69. Flare Template: Study Morphology 69 Davenport et al. (2014) 885 “clean” flares Time (FWHM)
70. Rise Phase 2 Decay Phases exponentials Fit with 4th order polynomial Energy budget: rise=20%, decay1=41%, decay2=39% 70 Davenport et al. (2014) Time (FWHM) Time (FWHM)
71. Complex Flare Fitting 71 Davenport et al. (2014) Time (days) works well for “classical” events
72. Complex Flare Fitting Use to objectively determine “complex” vs “classical” events & decompose events! 72 Davenport et al. (2014) Time (days)
73. Relative Flux Some flares not well fit by template Caused by different physical morphology (e.g. arcade)? Active region rolling off limb? 73 Davenport et al. (2014) Time (days)
74. Hawley et al. (2014) No correlation between flares & spot 1 month short cadence 74
75. HST 75 Kepler John Lurie et al. (2015) Flares from partially resolved M5 + M5 binary in Kepler! Extending work: GJ 1245AB
76. Big questions still await us! • Dependence of flare morphology on stellar properties? • Structure of complex events? • “Triggered” flares? 
 “Sympathetic" flares? • Frequency of “Superflares”? • Flare rate vs age? 76
78. 78 Age vs. Activity Lyra (2005) log Ca II Flux log age (yrs) ACTIVE! inactive Sun More Flares Fewer Flares
79. 79 Magnetochronology: train on Kepler/K2, apply to LSST
80. 80 Can we recover solar cycles? Llama et al. (2012)
81. 81 Can we recover solar cycles? Misaligned orbit/rotation samples more latitudes, may be better! Brett Morris et al. (2016)
82. Phase Relative Flux (5 min smoothing) ~2.5x larger Ongoing work by L.Hebb, M. Gomez, J. Radigan, and P. McCullough In vs Out of Transit Scatter The Future: study all transiting systems 82
83. 83 Phase-tracking: many more stars possible in Kepler!
84. Summary Use transiting exoplanets to trace starspot motion & evolution Measuring differential rotation & spot lifetimes for active stars 84 Now is the golden age for statistical studies of stellar activity Largest sample of flares ever. New insights on flare morphology
85. 85 John R Nick Yumi Eddie Grace Brett John L Diana Nell Practice Talk Guinea Pigs: Thanks to the
86. New Mexico, the Land of Enchantment! 2007 2006 2010 2011 2012 2008 2014 2015
87. 87 Thanks to my committee, collaborators, and advisors. Especially: Leslie Suzanne &
90. Summary Use transiting exoplanets to trace starspot motion & evolution Measuring differential rotation & spot lifetimes for active stars 90 Now is the golden age for statistical studies of stellar activity Largest sample of flares ever. New insights on flare morphology