Slides from 1-hour talk about ongoing research on stellar activity with data from NASA's Kepler space telescope. Stellar flares and starspots are the subject of investigation here.

1. Spots & Flares
Stellar Activity with Kepler
Leslie Hebb (Hobart & William Smith)
James R. A. Davenport (University of Washington)
!1
Suzanne L. Hawley (University of Washington)
Boston University — 2014 February 25

2. Spots & Flares
Observable byproducts of magnetic fields
"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 (or E. Parker)
!2

3. Spots & Flares
Build our intuition from the Sun
!3

4. Source of solar B field?
Convective Envelope
(differential rotation)
Radiative Zone
(solid body rot.)
Tachocline (interface)
!4

5. Evolution of the B field
with mass, age, rotation?
!5

6. !6

7. !7

8. Flares - why we care?
A few reasons…
• Insight into properties of stellar dynamo/interior
• Habitability (of our planet, and others)
• Potential age-tracer for stars
!8

9. Martens & Kuin (1989)
Standard Solar Flare Model
!9

10. Martens & Kuin (1989)!10

11. Martens & Kuin (1989)!11

12. Kepler: Stellar Flare Machine
• Long continuous light curves
(up to ~4years)
• Very precise photometry
(~0.01%)
• Enormous sample
(>100,000 solar-type stars)
!12

13. Kepler: Stellar Flare Machine
• Long continuous light curves
(up to ~4years)
• Very precise photometry
(~0.01%)
• Enormous sample
(>100,000 solar-type stars)
• Look for outliers (super-flares)
• Complete samples!
!13

14. (Walkowicz+ 2010)
Flares Observed by Kepler
4 M-dwarfs
!14

15. Davenport in prep
GJ 1243
M4, Prot=0.59 days, ~300days 1-min data
!15

16. Davenport in prep
GJ 1243
M4, Prot=0.59 days, ~300days 1-min data
!16

17. Flares By EYE (FBEYE)
Davenport in prep!17

18. Davenport in prep
Compare Users
!18

19. Massive Flare Sample!
• 6107 flares, spanning 300 days
• most of any star besides the Sun!
• 15% complex
• energy range: Log E = 27-33 erg
• complete to Log E ~31
!19

20. tstart tstop
Determined by people for every flare
!20

21. Amplitude
t1/2 (FWHM)
Place in scale units for time & flux
tpeak
!21

22. Davenport in prep
Median Combine: Flare Template
!22

23. Rise Phase Decay Phase
Davenport in prep
e-1t
e-0.3t
Fit with 4th order
polynomial
Energy budget:
rise=20%,
decay1=41%,
decay2=39%
!23

24. Davenport in prep
Complex Flare Fitting
!24

25. Davenport in prep
Complex Flare Fitting
Objective way to determine
complex vs classical
!25

26. RelativeFlux
Some flares not well fit by template
Davenport in prep
Caused by different physical
morphology (e.g. arcade)?
Active region rolling off limb? !26

27. Hawley in prep
No correlation between flares & spot
1 month short cadence
!27

28. Big questions still await us!
• Dependence of morphology
on stellar properties?
• Does decay rate depend on
total flare energy?
• Can we resolve peak shape?
• More detailed understanding
of complex events
!28

29. GJ 1245 AB(C):
a novel system for spots & flares
2 distinct periods
Lurie in prep!29

30. GJ 1245 AB(C):
a novel system for spots & flares
2 distinct periods
!30

31. GJ 1245 AB(C):
a novel system for spots & flares
HST
2”
Kepler Pixel
!31

32. GJ 1245 AB(C):
a novel system for spots & flares
HST
2”
Kepler Pixel
!32

33. HST
Kepler
Lurie in prep!33

34. Flux
Time (days)
Preliminary separated light curves
Lurie in prep!34

35. Starspots
!35

36. Strassmeier (1999)
• Observed across range of
mass, evolutionary phase
• Trace B field geometry,
rotation, differential rotation
!
• Evolve on timescales from
days to years (perhaps longer!)
Starspots
a generic result of B fields
SDO
Carroll (2012)
!36

37. – Stellar rotation rate
– Spot sizes
– Differential rotation rate
– Spot Lifetimes
– Spot evolution over stellar cycles
– Evolution with stellar age
Starspots:
Parameters/Physics of Interest
!37

38. Davenport in prep
GJ 1243: M4, Prot=0.59 days,
300days1-min data, 13 Quarters 30-min data
!38

39. GJ 1243
Flatten with polynomial fits
!39

40. Davenport in prep
GJ 1243
!40

41. Phase
Davenport in prep
GJ 1243 - spot evolution in phase
!41

42. Phase
Davenport in prep
GJ 1243 - spot phase map
Primary Spot
Secondary Spot(s)
!42

43. Phase
Davenport in prep
GJ 1243 Differential Rotation!
!43

44. Phase
Davenport in prep
GJ 1243 Differential Rotation!
“Equator-Lap-Pole” time of
700-1200 days
(assume Solar-like diff. rot.)
!44

45. Phase
Davenport in prep
GJ 1243 Differential Rotation!
Spot lifetimes: 150-500 days for 2nd spot
>4 years for 1st spot
!45

46. Davenport in prep
GJ 1243 2-spot lightcurve model
Phase
1-spot model preferredunclear
!46

47. Time
Time
Phase
Phase
Some other M dwarfs
with Prot<2 day
!
A wide range of starspot-
phase evolution!
~20 other short P dM’s
in Kepler 30-min data
!47

48. Davenport & Hebb in prep
Kepler 63
Differential Rotation
transits
!48
G2, Prot=5.4d

49. Kepler 63
Differential Rotation
Davenport & Hebb in prep !49

50. Kepler 63
Differential Rotation
Primary !
Spot
Secondary !
Spots
Davenport & Hebb in prep !50

51. Kepler 63
Differential Rotation
Davenport & Hebb in prep
Different slopes:
Likely 3 different
spot latitudes
Faster !
differential !
rotation
Slower !
differential !
rotation
!51

52. Kepler 63
Differential Rotation
Davenport & Hebb in prep
Faster !
differential !
rotation
Slower !
differential !
rotation
“Equator-Lap-Pole” times: 40-80 days
Spot lifetimes: 100-500 days
!52

53. Kepler 63
Davenport & Hebb in prep
Faster !
differential !
rotation
Slower !
differential !
rotation
Might be
Anti-Solar diff. rot., polar primary spot
Solar diff. rot., equatorial primary spot
!53

54. Kepler 63: 40-80 days ! ! (G2, P=5d)!
Sun: 115 days !! ! ! ! (G2, P=25d)!
!
AB Dor: 110 days ! ! ! ! (K0, P=0.5d)!
Speedy Mic: 191 days ! ! (K3, P=0.4d)!
!
GJ 1243: 700-1200 days ! (M4, P=0.6d)!
HK Aqr: [-1449-449] days ! (M0, P=0.4d)
Expectation: lap times increase with
later spectral type
e.g. Kueker (2011), Barnes (2005)
See excellent recent paper by
Timo Reinhold et al. (2013)
Equator-Lap-Pole time comparisons
!54

55. Transiting Starspots
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56. Hebb & Davenport in prep!56

57. Hebb & Davenport in prep!57

58. Kepler 17
!58

59. Advantage: Spot lat/lon better constrained
(if planet properties known)
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60. Key: fit transit “bumps” &
out-of-transit flux together
!60

61. Hebb & Davenport in prep
Spot contrast-radius-latitude
degeneracy (partially) broken!
vary both spot
radius & contrast
!61

62. Hebb & Davenport in prep
Spot contrast-radius-latitude
degeneracy (partially) broken!
!62

63. Hebb & Davenport in prep
Spot contrast-radius-latitude
degeneracy (partially) broken!
!63

64. Hebb & Davenport in prep
Spot contrast-radius-latitude
degeneracy (partially) broken!
Finding 70-80%
!64

65. Fitting
challenges…
• MCMC very expensive
• Parameter space “target” very small
• Need to run over many “windows” of time
• Spots can evolve on few-transit
(or few rotation) timescales
!65

66. The future: measure contrast
from umbra & penumbra?
NewSolarTelescope(2010)
!66

67. Time
PhaseThe future: automate the diff. rot.
& spot timescale measurement?
!67

68. The future: compare detailed spot
properties with gyrochronology
• Spot timescales
• Spot contrast(s)
• Differential rotation rate
& direction
(Prot spin down with stellar age)
!68

69. The future: find flares in every Kepler
target, learn about B fields en masse
• Comparable to transit-finding
(just inverted)
• Tackle flare physics questions
(e.g. dependence on star properties)
• Include gyrochronology, flares as age indicator?
(viable for LSST?)
!69

70. Proposed K2 fields
Ideal to test flares as age-indicator!
!70

71. Summary
Thanks!
• Largest sample of flares on any star,
create flare template
• One of slowest differential rotation
rates ever measured
• Detailed starspot properties
observable in transiting systems
• Kepler opening door to statistical
understanding of stellar activity!
!71