Near-infrared Characterization of the Atmospheres of Alien Worlds

153 Pages·2011·6.33 MB·English

Near-infrared Characterization of the Atmospheres of Alien Worlds
by
Bryce Croll
A thesis submitted in conformity with the requirements
for the degree of Doctor of Philosophy
Graduate Department of Astronomy and Astrophysics
University of Toronto
Copyright (cid:13)c 2011 by Bryce Croll
Abstract
Near-infrared Characterization of the Atmospheres of Alien Worlds
Bryce Croll
Doctor of Philosophy
Graduate Department of Astronomy and Astrophysics
University of Toronto
2011
In this thesis I present near-infrared detections of the thermal emission of a number of
hot Jupiters and likely transit depth differences from different wavelength observations of a
super-Earth. I have pioneered “Staring Mode” using the Wide-field Infrared Camera on the
Canada-France-Hawaii Telescope to achieve the most accurate photometry to-date in the near-
infrared from the ground. I also discuss avenues that should allow one to achieve even more
accurate photometry in the future. Using WIRCam on CFHT my collaborators and I have
detected the thermal emission of the following hot Jupiters: TrES-2b and TrES-3b in Ks-band,
WASP-12b in the J, H & Ks-bands, and WASP-3b in the Ks-band on two occasions. Near-
infrared detections of the thermal emission of hot Jupiters are important, because the majority
of these planets’ blackbodies peak in this wavelength range; near-infrared detections allow us to
obtain the most model-independent constraints on these planets’ atmospheric characteristics,
their temperature-pressure profiles with depth and an estimate of their bolometric luminosities.
With these detections we are able to answer such questions as: how efficiently these planets
redistribute heat to their nightsides, if they’re being inflated by tidal heating, whether there’s
any evidence that one of these planets is precessing, and whether another experiences extreme
weather and violent storms?
My collaborators and I have also observed several transits of the super-Earth GJ 1214b.
We find a deeper transit depth in one of our near-infrared bands than the other. This is likely
indicativeofaspectralabsorptionfeature. Forthedifferencesinthetransitdepthtobeaslarge
asweobserved, theatmosphereofGJ1214bmusthavealargescaleheight, lowmeanmolecular
weight and thus have a hydrogen/helium dominated atmosphere. Given that other researchers
have not found similar transit depth differences, we also discuss the most likely atmospheric
ii
makeup for this planet that results from a combination of all the observations to date.
Lastly,bysearchingforlong-termlineartrendsinradialvelocitydata,Iconstrainthetheory
that most hot Jupiters migrated to their present positions via the Kozai mechanism with tidal
heating.
iii
Acknowledgements
When it came time to write my thesis, the prospect of writing the dedication and acknowl-
edgements was the most intimidating part. I read these sections from the theses of a number
of my peers, and something about their unabashedly sanguine tone – without mentioning the
adversity – did not ring true to me. These last five years have been a series of long, difficult,
even occasionally unpleasant, and often solitary slogs. Ultimately though, it is these challenges,
and the sacrifices that have been necessary to confront them head-on, that has made this pro-
cess worthwhile; after all, we do these things “not because they are easy, but because they are
hard.” In between these slogs, I’ve had a great deal of fun, and in quiet moments of reflection
it is the successes that have resulted from overcoming these hardships that I’ll cherish and that
have made my time in Toronto so rewarding.
My parents and family are not scientists, but they have nonetheless taught me an immea-
surable number of life lessons that are reflected in these pages. A classic example is one of the
lessons from what I refer to as the “The Four Rules of Dad.” I’m not sure that these are the
messages that my Father would be aware that I have taken away from our time together, but
theyarenonetheless the lessonsthat I’vetakentoheart. At leastoneofthese “RulesofDad”is
unprintable, butonethatisn’tis: “Ifyouaregoingtodoajob, thendoitright.” Itisperhapsa
slightly less eloquent version of Dr. Martin Luther King, Jr.’s: “If a man is called to be a street
sweeper, he should sweep streets even as Michelangelo painted, or Beethoven composed music,
or Shakespeare wrote poetry. He should sweep streets so well that all the hosts of heaven and
earth will pause to say, here lived a great street sweeper who did his job well.” This thesis, and
my efforts over the past five years, have been my earnest attempt to honour that fine tradition
bequeathed to me by my Father and my Family.
Bothofmythesisadvisorsdeservemyconsiderablegratitudeforassistingmeonthisjourney
over these past five years. I would like to thank Norman Murray for always having five minutes
(that often turned into half-an-hour), even on Saturday and Sunday evenings of long weekends,
to talk though the intriguing mysteries that my observations uncovered throughout my thesis.
RayJayawardhanadeservesmythanksforallowingandinsistingthatIdotheworkmyself, and
reinforcing the notion that it is not shameful to chase ”sexy” science. I’m grateful to both my
advisors for having enough faith in me to allow me to choose my own projects and effectively
blaze my own trail. As a result, this thesis has been an exercise in appreciating the plaque that
adorned Harry Truman’s desk: “The buck stops here.” This brings me to another printable
iv
“Rule of Dad”: “It is only the people who don’t do anything, that never make mistakes.” I’m
proud to say that any mistakes in this thesis are wholly mine - I wouldn’t have it any other
way.
When I look back on my years in Toronto, the non-academic achievements will certainly
rankasbeingasrewardingasanythingIachievedinthesepages. I’mproudofmyworkwiththe
Free Astronomy Public Tours, the UofT Triathlon Club and the GSU Council. I’ve attempted
simply to leave these institutions in slightly better shape then when I found them - I sincerely
hope I’ve succeeded.
Thanks go out to a great many friends and colleagues in the Department of Astronomy at
the University of Toronto and outside of it, who taught me a great many professional and life
lessons - whether by taking five minutes out of their busy schedules when I came knocking on
their office doors, or shared over hour-long morning coffee discussions, or even late at night
after one or more beers.
None of this, would have been possible without my numerous scientific mentors throughout
the years who sent me down this path in the first place. Dr. Dale Stevenson and Dr. Gordon
Walker both deserve special mention for having faith in me, before I had faith in myself.
I’llconcludewiththeoneandonlyquotationthatIknewwouldclosemyacknowledgements
from the very beginning of the writing process - the conclusion of Tennyson’s “Ulysses” and
words to live by: “To strive, to seek, to find, and not to yield.”
v
Contents
1 Introduction 1
1.1 The first Alien Worlds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.1.1 Fulfilling the promise of Otto Struve . . . . . . . . . . . . . . . . . . . . . 2
1.2 Transmission Spectroscopy. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.3 Thermal Emission from hot Jupiters . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.3.1 Two classes of hot Jupiters? . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.3.2 Thermal emission of hot Jupiters in the near-infrared . . . . . . . . . . . 7
1.3.3 Future prospects of near-infrared thermal emission detections from the
ground . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
2 Near-infrared Thermal Emission of TrES-2b 13
2.1 Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
2.2 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
2.3 Observations and data reduction . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
2.4 Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
2.5 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
3 Near-infrared Thermal Emission of TrES-3b 28
3.1 Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
3.2 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
3.3 Observations and data reduction . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
3.4 Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
3.5 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
3.5.1 TrES-3b’s Ks-band thermal emission . . . . . . . . . . . . . . . . . . . . . 38
3.5.2 An upper-limit on TrES-3b’s H-band thermal emission . . . . . . . . . . . 40
3.5.3 Comparisons to atmospheric models . . . . . . . . . . . . . . . . . . . . . 41
3.5.4 Future prospects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
vi
4 Detections of the Thermal Emission of WASP-12b in Ks, H & J 45
4.1 Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
4.2 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
4.3 Observations and Data Reduction . . . . . . . . . . . . . . . . . . . . . . . . . . 49
4.4 Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
4.5 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
4.5.1 Eccentricity and Precession of WASP-12b . . . . . . . . . . . . . . . . . . 56
4.5.2 A longer duration secondary eclipse; possible signs of material stripped
from the planet? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
4.5.3 The properties of WASP-12b’s atmosphere . . . . . . . . . . . . . . . . . 64
4.5.4 Future Prospects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67
5 Broadband Transmission Spectrum of GJ 1214b 69
5.1 Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
5.2 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
5.3 Observations and Data Reduction . . . . . . . . . . . . . . . . . . . . . . . . . . 72
5.4 Results. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75
5.4.1 WIRCam non-linearity correction . . . . . . . . . . . . . . . . . . . . . . . 77
5.5 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78
5.5.1 GJ 1214b’s transit depth in the near-infrared . . . . . . . . . . . . . . . . 78
5.5.2 The effect of stellar spots on transit observations of GJ 1214b . . . . . . . 79
5.5.3 A larger transit depth in Ks-band than J-band . . . . . . . . . . . . . . . 82
5.5.4 WIRCam transit depths suggest a low mean molecular weight . . . . . . . 83
5.5.5 Comparison to observations at other wavelengths . . . . . . . . . . . . . . 86
5.5.6 Possible atmospheric compositions of GJ 1214b . . . . . . . . . . . . . . . 87
5.5.7 Consequences of a hydrogen/helium dominated atmosphere . . . . . . . . 89
5.6 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90
6 Two Near-infrared Secondary Eclipses of WASP-3b 92
6.1 Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92
6.2 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93
6.3 Observations and data reduction . . . . . . . . . . . . . . . . . . . . . . . . . . . 96
6.3.1 Canada-France-Hawaii Observations . . . . . . . . . . . . . . . . . . . . . 96
6.3.2 Variation of the eclipse depth with aperture size . . . . . . . . . . . . . . 97
6.4 Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100
6.5 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101
6.5.1 WASP-3b’s near-infrared thermal emssion . . . . . . . . . . . . . . . . . . 101
vii
6.5.2 Comparison of near-infrared detection of the thermal emission of hot
Jupiters to date . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105
7 The Limits on precise Ground-based Near-infrared Photometry 108
7.1 Systematics that hinder near-infrared precision . . . . . . . . . . . . . . . . . . . 109
7.2 Systematics in our CFHT/WIRCam photometry . . . . . . . . . . . . . . . . . . 111
7.2.1 Differential Electronic Response . . . . . . . . . . . . . . . . . . . . . . . 111
7.2.2 Background trends . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111
7.2.3 Variable photometric precision . . . . . . . . . . . . . . . . . . . . . . . . 112
7.3 Possible avenues to achieve even more accurate photometry . . . . . . . . . . . . 114
8 The hot Jupiter Kozai Mechanism Connection Constrained 116
8.1 Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116
8.2 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116
8.3 Data & Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119
8.3.1 California & Carnegie Radial Velocity Data . . . . . . . . . . . . . . . . . 119
8.3.2 Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119
8.4 Monte Carlo tests. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121
8.5 Results. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122
8.5.1 Frequency of Exoplanet systems with long-term linear trends . . . . . . . 124
8.6 Constraints from other methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . 128
8.6.1 Rossiter-McLaughlin measurements of hot Jupiters . . . . . . . . . . . . . 128
8.6.2 Directly imaged companions to exoplanetary systems . . . . . . . . . . . . 128
8.7 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129
8.7.1 Constraints from long-term RV trends . . . . . . . . . . . . . . . . . . . . 129
8.7.2 Combined constraints from Rossiter-McLaughlin measurements, directly
imaged companions and long-term RV trends . . . . . . . . . . . . . . . . 130
8.7.3 Fate of the connection between hot Jupiters and the Kozai Mechanism
with Tidal Heating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130
Bibliography 132
viii
List of Tables
2.1 TrES-2 Reference Stars . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
2.2 TrES-2b’s best-fit secondary eclipse parameters . . . . . . . . . . . . . . . . . . . 22
3.1 TrES-3b’s best-fit secondary eclipse parameters . . . . . . . . . . . . . . . . . . . 36
4.1 WASP-12b’s best-fit secondary eclipse parameters . . . . . . . . . . . . . . . . . 53
4.2 WASP-12b’s orbital parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
5.1 CFHT/WIRCam near-infrared transit depths of GJ 1214b . . . . . . . . . . . . . 78
6.1 WASP-3b’s best-fit secondary eclipse parameters . . . . . . . . . . . . . . . . . . 99
7.1 Photometric Precision of CFHT/WIRCam data-sets . . . . . . . . . . . . . . . . 113
8.1 Fraction of exoplanetary systems displaying RV linear trends . . . . . . . . . . . 125
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List of Figures
2.1 X and Y pixel position of the centroid of the target star TrES-2 . . . . . . . . . . 16
2.2 Raw photometry of TrES-2 and its reference stars. . . . . . . . . . . . . . . . . . 17
2.3 The CFHT/WIRCam full frame array . . . . . . . . . . . . . . . . . . . . . . . . 18
2.4 Correlation with flux of the x and y pixel position of TrES-2’s centroid . . . . . . 19
2.5 RMS of the out-of-eclipse photometry of TrES-2 . . . . . . . . . . . . . . . . . . 19
2.6 Constraints on the phase of the secondary eclipse of TrES-2b . . . . . . . . . . . 21
2.7 TrES-2b’s Ks-band secondary eclipse . . . . . . . . . . . . . . . . . . . . . . . . . 21
2.8 Joint constraints on TrES-2b’s albedo and reradiation factor . . . . . . . . . . . . 24
2.9 Comparison to atmospheric models of TrES-2b . . . . . . . . . . . . . . . . . . . 26
3.1 X and Y pixel positions of the centroid of the target star TrES-3 in the Ks and
H-bands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
3.2 Raw photometry of TrES-3 and its reference stars. . . . . . . . . . . . . . . . . . 32
3.3 RMS of the out-of-eclipse photometry of TrES-3 . . . . . . . . . . . . . . . . . . 34
3.4 The depth of TrES-3b’s Ks-band secondary eclipse and an upper limit on its
H-band eclipse depth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
3.5 Constraints on the mid-eclipse phase of TrES-3b’s secondary eclipse . . . . . . . 35
3.6 Joint constraints on TrES-3b’s Bond albedo and reradiation factor . . . . . . . . 38
3.7 Comparison to atmospheric models of TrES-3b . . . . . . . . . . . . . . . . . . . 42
4.1 Raw Photometry of WASP-12 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
4.2 RMS of the out-of-eclipse photometry of WASP-12 . . . . . . . . . . . . . . . . . 50
4.3 WASP-12b’s Ks-band secondary eclipse . . . . . . . . . . . . . . . . . . . . . . . 54
4.4 WASP-12b’s H-band secondary eclipse . . . . . . . . . . . . . . . . . . . . . . . . 54
4.5 WASP-12b’s J-band secondary eclipse . . . . . . . . . . . . . . . . . . . . . . . . 55
4.6 Constraints on the phase of the mid-eclipse of WASP-12b . . . . . . . . . . . . . 55
4.7 Observational constraints on the precession signal of WASP-12b. . . . . . . . . . 58
4.8 Constraints on the eccentricity of the orbit of WASP-12b . . . . . . . . . . . . . 60
4.9 Possible longer duration eclipse of WASP-12b in the Ks-band . . . . . . . . . . . 61
x