Dissertation (2019): The Effects of Stellar Magnetic Activity and Variability on Observations of Exoplanets

(Dissertation final presentation)

The search for life in the Universe outside of the Solar System focuses on the study of potentially habitable exoplanets. Exoplanets have been discovered principally via the transit method, which reveals planetary radii and orbital periods, among other things. In transiting multi-planet systems, we can measure the masses of exoplanets without expensive spectroscopy by using transit timing variations. The orbit of a single transiting planet around a single star would be (nearly) perfectly periodic, but if there's more than one planet in the system, the gravitational influence of each planet on each other changes the orbital shape and orientation. The apparent variation in the exoplanet transit times thus transmits information about the mass and orbit of the perturbing planet. Transits can also reveal the composition of exoplanet atmospheres via transmission spectroscopy. When the planet passes in front of the host star, it will appear largest at wavelengths where the planet's atmosphere is opaque, and smallest at wavelengths where the atmosphere is transparent. Thus by measuring the apparent radius of the planet as a function of wavelength, we can obtain a spectrum of an exoplanet's atmosphere. However, there are additional signals generated by magnetic activity and variability at the stellar surface which inject confounding time- and wavelength-dependent signals into the spectrophotometry of exoplanet host stars which complicate all of the aforementioned measurements. We must understand heterogeneous stellar surfaces in order to accurately answer astrobiological questions such as: does this planet have a surface, and what is the composition of its atmosphere?The goal of this dissertation is to explore stellar magnetic activity and variability and their impacts on measurements of exoplanets with implications for astrobiology. I used the transiting planet HAT-P-11 b to measure the size and latitude distributions of starspots on its active K4 dwarf host star, to find that its magnetic activity mirrors the Sun's. I measured the chromospheric activity of HAT-P-11 and compared it to stars of similar temperature and rotation period to find that it's the most active of its peers, perhaps suggestive of star-planet interaction. I directly measured starspot coverage on a sample of bright stars via TiO molecular band modeling. I identified the possibility of detecting stellar activity cycles of nearby stars using precision astrometry. I devised a technique for measuring robust exoplanet radii even in the presence of significant starspot distributions by reparameterizing the transit light curve of Mandel & Agol (2002). Finally, I devised a simulator for James Webb Space Telescope observations of transiting exoplanets, to explore the limits imposed by stellar magnetic activity on transit timing and transmission spectroscopy measurements for three systems with potentially habitable exoplanets.

Transcript

1. The Effects of Stellar Magnetic Activity and Variability on Observations of Exoplanets Brett M. Morris Eric Agol & Suzanne Hawley
 
 Rory Barnes, David Catling, Leslie Hebb, Andrew Nestingen
2. Sun ? HAT-P-11 TRAPPIST-1 2
3. Sun ? HAT-P-11 TRAPPIST-1 Stars we know more about 2
6. 3 Hinode's Solar Optical Telescope
7. 3 Hinode's Solar Optical Telescope
8. 3 Hinode's Solar Optical Telescope
9. 4 NASA Goddard Space Flight Center
10. 4 NASA Goddard Space Flight Center
11. ? Sun HAT-P-11 TRAPPIST-1 Stars we know more about 5
12. ? Sun HAT-P-11 TRAPPIST-1 Stars we know more about 5
13. ? Sun HAT-P-11 TRAPPIST-1 Stars we know more about Stars with potentially characterizable Earths 5
14. 6 1) Transits 2) Transmission spectroscopy 3) Transit timing variations Intro: Exoplanet Characterization Techniques
15. 7 Time Flux Intro: Exoplanet Radius Ingress Egress Depth
16. 8 Time Flux Intro: Exoplanet Radius
17. 8 Time Flux Intro: Exoplanet Radius
18. 9 Wavelength Radius Intro: Atmospheric Composition
19. 10 Wavelength Radius Blue Filter Intro: Atmospheric Composition
20. 11 Wavelength Radius Red Filter Intro: Atmospheric Composition
21. 12 Wavelength Radius Intro: Atmospheric Composition
22. Intro: Atmospheric Composition 13
23. Intro: Atmospheric Composition 13
24. 14 Wavelength Radius Intro: Atmospheric Composition
25. 15 Wavelength Radius Blue Filter Intro: Atmospheric Composition
26. 16 Wavelength Radius Red Filter Intro: Atmospheric Composition
27. 16 Wavelength Radius Red Filter Intro: Atmospheric Composition
28. Intro: Exoplanet Mass 17
29. ? Sun HAT-P-11 TRAPPIST-1 Stars we know more about Stars with potentially characterizable Earths 18
30. ? Sun • p-mode oscillations HAT-P-11 • starspot occultations • stellar activity cycle TRAPPIST-1 • Accurate exoplanet radii • New form of stellar activity? • Planning for JWST 19
31. Sun ESA’s PLATO 20 Q: When we discover an Earth-sized planet orbiting a Sun-like star, with what precision can we know its radius, mass?
32. 21 Solar p-mode oscillations • Standing pressure waves observed by SOHO/VIRGO
33. 21 Solar p-mode oscillations • Standing pressure waves observed by SOHO/VIRGO
34. Supergranulation Granulation p-modes 22 Solar p-mode oscillations • Standing pressure waves observed by SOHO/VIRGO Δν νmax 5 m in 1 day 1 m onth Morris et al. 2019b
35. 23 Solar p-mode oscillations • Standing pressure waves observed by SOHO/VIRGO • Result: • Radius precision: 4% • 60% larger timing uncertainties than white noise Code: github.com/bmorris3/shocksgo Morris et al. 2019b
36. 24 Sun: Summary • p-mode oscillations limit: • radius precision • timing precision Sun: Bibliography The Solar Benchmark: Rotational Modulation of the Sun Reconstructed from Archival Sunspot Records
 Morris, B.M.; Davenport, J.R.A.; Giles, H.A.C.; Hebb, L.; Hawley, S.L; Angus, R.; Gilman, P.; Agol, E., Monthly Notices of the Royal Astronomical Society (2018) The Stellar Variability Noise Floor for Transiting Exoplanet Photometry with PLATO Morris, B.M.; Bobra, M.G.; Agol, E.; Lee, Y.J.; Hawley, S.L. (2019, in review) Generating Stellar Light Curves with Granulation and Oscillations Morris, B.M.; Agol, E.; Huber, D.; Hawley, S.L. (2019, in prep.)
37. ? Sun HAT-P-11 TRAPPIST-1 Stars we know more about Stars with potentially characterizable Earths 25
38. 26 HAT-P-11 Kepler Q: Are the starspots of the “Sun-like” star HAT-P-11 similar to sunspots?
39. 27 HAT-P-11: Scaled-Down Sun 0° +15° –15° • Ṃ = 0.8 M⨀ • Prot = 29 d (like Sun!) Winn et al. 2010 Sanchis-Ojeda et al. 2011
40. Misaligned exoplanets reveal active latitudes • Timing encodes active latitude positions • Amplitude encodes spot contrast 28 NASA/SDO/HMI
41. Misaligned exoplanets reveal active latitudes • Timing encodes active latitude positions • Amplitude encodes spot contrast 28 NASA/SDO/HMI
42. Misaligned exoplanets reveal active latitudes • Timing encodes active latitude positions • Amplitude encodes spot contrast 28 NASA/SDO/HMI
43. 29 HAT-P-11: Sun-like active latitudes Morris et al. 2017a STSP • STSP: forward model for starspot occultations
44. 29 HAT-P-11: Sun-like active latitudes Morris et al. 2017a STSP • STSP: forward model for starspot occultations
45. 30 HAT-P-11: Sun-like active latitudes Morris et al. 2017a Posterior Samples STSP • XSEDE/Open Science Grid: 740,000 core hours
46. 31 HAT-P-11: Sun-like active latitudes • Active latitudes: similar positions, widths to Sun’s Morris et al. 2017a
47. 32 HAT-P-11: Sunspot-like sizes Morris et al. 2017a • Most spots have similar sizes to the largest spots on the Sun at solar max
48. 33 HAT-P-11: More spotted than Sun Morris et al. 2017a 33 • Spot coverage 100x greater than Solar
49. 34 HAT-P-11 ARC 3.5 m Telescope at Apache Point Observatory Q: Can we approach Kepler-like precision from the ground?
50. 35 • Precise photometry from the ground HAT-P-11: Holographic Diffuser
51. Rotation Axis ˆ X ˆ Y 0° +15° –15° HAT-P-11b Transit chord 36 Morris et al. 2018a • Precise photometry from the ground • Most spotted view of HAT-P-11 yet: fs=14% HAT-P-11: Holographic Diffuser
52. 37 HAT-P-11 ARC 3.5 m Telescope at Apache Point Observatory Q: Is the activity cycle of HAT-P-11 similar to the Sun’s activity cycle?
53. 38 CH G band, λ = 4300 Å CaII H, λ = 3933 Å HAT-P-11: Chromospheric Activity Hall (2008)
54. 38 CH G band, λ = 4300 Å CaII H, λ = 3933 Å HAT-P-11: Chromospheric Activity Hall (2008)
55. • R~30,000 spectroscopy 39 Morris et al. 2017b HAT-P-11: Chromospheric Activity
56. • Sun-like activity cycle 40 Morris et al. 2017b HAT-P-11: Chromospheric Activity
57. 41 “Active” “Inactive” Böhm-Vitense 2007 ̥ Sun Cycle period/rotation is between sequences Morris et al. 2017b Is HAT-P-11 “normal”?
58. 41 “Active” “Inactive” Böhm-Vitense 2007 ̥ Sun HAT-P-11 Cycle period/rotation is between sequences Morris et al. 2017b Is HAT-P-11 “normal”?
59. Rotation Axis ˆ X ˆ Y 0° +15° –15° HAT-P-11b Transit chord 42 HAT-P-11: Summary • Sun-like spot latitude distribution • Sun-like spot radius distribution • Sun-like activity cycle duration • 100x solar spot coverage HAT-P-11: Bibliography The Starspots of HAT-P-11: Evidence for a Solar-like Dynamo
 Morris, B.M., Hebb L., Davenport J.R.A., Rohn G., Hawley S.L., The Astrophysical Journal, 846, 2 (2017) Chromospheric Activity of HAT-P-11: an Unusually Active Planet-Hosting K Star
 Morris, B.M., Hawley S.L., Hebb L., Saraki C., Davenport J.R.A., Isaacson H., Howard A.W., Montet B.T., Agol E., The Astrophysical Journal, 846, 99 (2017) Large Starspot Groups on HAT-P-11 in Activity Cycle 1
 Morris, B.M., Hawley S.L., Hebb L. Research Notes of the AAS, 2, 1 (2018)
60. ? Sun HAT-P-11 TRAPPIST-1 Stars we know more about Stars with potentially characterizable Earths 43
62. ? TRAPPIST-1 45 Q: Are there dark or bright spots on the surface of TRAPPIST-1? Spitzer
63. Delrez et al. 2018 46
64. What if we are really unlucky? Morris et al. 2018 47
65. What if we are really unlucky? Morris et al. 2018 47
66. What if we are really unlucky? Depth? 6= ✓ Rp R? ◆2 Morris et al. 2018 47
67. Ingress/egress durations v = 2⇡a/P Time Flux Morris et al. 2018 Spotless Spotted 48
68. Ingress/egress durations v = 2⇡a/P ⌧ ⇡ 2Rp v = P ⇡ Rp R? R? a Time Flux Ingress Duration Morris et al. 2018 Spotless Spotted 𝜏 48
69. Ingress/egress durations v = 2⇡a/P ⌧ ⇡ 2Rp v = P ⇡ Rp R? R? a Can solve for planet radius from ingress/egress duration alone with sufficient precision on: P, a/Ṛ Time Flux Ingress Duration Morris et al. 2018 Spotless Spotted 𝜏 48
70. • Spitzer depths consistent with ingress durations • Spot occultations not detected • Spots the size of the smallest sunspots are not ruled out Morris et al. 2018b Ingress/egress durations 49 Rp/Ṛ
71. ? TRAPPIST-1 50 Q: Are there dark or bright spots on the surface of TRAPPIST-1? Spitzer Kepler
72. Best dark spot model Bright Regions on TRAPPIST-1 Best bright spot model Kepler Spitzer 51
73. Best dark spot model Bright Regions on TRAPPIST-1 Best bright spot model Kepler Spitzer 51
74. Flare-flux correlation 52 Morris et al. 2018 Flare Flare Flare Flare Flare Flare Flare Flare Flare • Flares occur when brightness is increasing
75. Flare-flux correlation 53 Morris et al. 2018 • Flares occur when brightness is increasing
76. 54 TRAPPIST-1: Summary • No evidence for significant spot 
 coverage in transit chords • Evidence for bright regions • Flare/flux correlation? TRAPPIST-1: Bibliography Non-detection of Contamination by Stellar Activity in the Spitzer Transit Light Curves of TRAPPIST-1 Morris, B.M., Agol E., Hebb, L., Hawley, S.L., Gillon, M., Ducrot, E., Delrez, L., Ingalls, J., Demory, B.O., The Astronomical Journal Letters (2018) Robust Transiting Exoplanet Radii in the Presence of Starspots from Ingress and Egress Durations Morris, B.M., Agol E., Hebb, L., Hawley, S.L., The Astronomical Journal (2018) Possible Bright Starspots on TRAPPIST-1 Morris, B.M., Agol E., Davenport J.R.A., Hawley, S.L., The Astrophysical Journal (2018) Photometric Analysis and Transit Times of TRAPPIST-1 b and c
 Morris, B.M., Agol, E., Hawley S.L. Research Notes of the AAS, 2, 1 (2018) ?
77. 55 PLATO James Webb Space Telescope 2021 2026 TESS 2018- Future Work
78. Transmission spectra w/ JWST Morris et al. 2019c (in prep) 56 CO2 CO2 CO2 CO2 CO2 CO2 CO2 CO2 CO2 CO2 CO2 O3 O3 H2O H2O CO CO H2O H2O H2O O3 CO
79. 57 Conclusions • Stellar variability and activity limits 
 exoplanet characterization • Exoplanet transits reveal stellar activity • Stars are astrophysical signal generators, 
 not noise makers Stars Planets
80. 58 Suzanne Hawley Leslie Hebb Eric Agol Acknowledgements The author acknowledges the traditional, ancestral territory of the Puget Sound Salish and Duwamish peoples, on which this work was completed.
81. 59 Acknowledgements
82. 60 Acknowledgements
83. 61 Acknowledgements
84. 62 ARC 3.5 m Telescope at Apache Point Observatory Special thanks to observing specialists: Russet McMillan, Candace Gray, Jack Dembicky and Ted Rudyk Acknowledgements