Formation and migration histories of giant exoplanets in multi-stellar systems

191 Pages·2017·10.69 MB·English

Formation and migration histories of giant
exoplanets in multi-stellar systems
Thesisby
Henry Hoang Khoi Ngo
InPartialFulfillmentoftheRequirementsforthe
Degreeof
DoctorofPhilosophy
CALIFORNIAINSTITUTEOFTECHNOLOGY
Pasadena,California
2017
Defended19May2017
ii
©2017
HenryHoangKhoiNgo
ORCID:0000-0001-5172-4859
Allrightsreserved
iii
ForMom,Dad,
Lauraandourlittlechip
iv
“Decide in your heart of hearts what really excites and challenges you, and start
moving your life in that direction. Every decision you make, from what you eat to
what you do with your time tonight, turns you into who you are tomorrow, and the
day after that. Look at who you want to be, and start sculpting yourself into that
person. You may not get exactly where you thought you’d be, but you will be doing
things that suit you in a profession you believe in. Don’t let life randomly kick you
intotheadultyoudon’twanttobecome.”
—ChrisHadfield,Commander,Expedition35,InternationalSpaceStation
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ACKNOWLEDGEMENTS
I am grateful for everyone who has supported me as I worked towards this disser-
tation. I want to thank my advisor, Heather Knutson, for her scientific advice and
mentorship during the past five years. She encourages her students to pursue inter-
estingresearchopportunities,tobecomeexcellentcolleagues,andtohaveahealthy
work-lifebalance. Heatherwillcontinuetobearolemodelformeinyearstocome.
IalsowanttothankDimitriMawet,whoagreedtojoinmythesiscommitteeduring
his first weeks at Caltech, for providing an opportunity to work with the vortex
coronagraphandforentrustinganexcitingnewplanetfindingprojectwithme.
I have benefited from the Planetary Science faculty’s open-door policy, which has
made it easy to build a mentoring network. I am thankful for the advice from
my committee members: Mike Brown, Geoff Blake and Konstantin Batygin. I
appreciate the friendship and mentorship from the postdocs, especially Courtney
Dressing, Gary Ruane, Björn Benneke, Brendan Bowler, and Sasha Hinkley. I am
also thankful for friends, collaborators and advisors at the University of British
ColumbiaandQueen’sUniversity.
ManypeopleintheGPSDivisionandPlanetaryScienceDepartmenthaveimproved
mygraduatestudentlife. Iamproudtobeamemberofthe“CaptainsPlanet”,with
Lu Pan, Mike Wong, Danielle Piskorz, and Joe O’Rourke. Thank you for working
with me on homework, studying with me for quals and providing moral support. I
alsoappreciatescientificandlifeadvicefromgradstudentsthatwentthroughbefore
me: AlexLockwood,AaronWolf,JoshKammer,andMikiNakajima. Ihaveenjoyed
fun scientific and not-so-scientific discussions with Peter Buhler, Chris Spalding,
Nancy Thomas, and Peter Gao. Extra thanks to Peter Gao for your friendship over
the last 10 years over two academic programs. Although I cannot name all the
awesomestudentsinourDivisionhere,Iamthankfulforourdodgeballteam(“The
Late Heavy Bombardment”), our softball team (“Strike-slip”), and all the social
events we do together. Special thanks to Mike Wong for collaborating with me
on many of these projects. Finally, I am extremely grateful for the wonderful and
caring staff members that have helped me along the way, both in the Division and
the department, especially Dian Buchness, Liz Boyd, Julie Lee, Julia Zuckerman,
AleenBoladian,MargaretCarlos,UlrikaTerrones,IrmaBlack,andMikeBlack.
MovingtoCaltechwasabigchangeforLauraandme,butthereweremanywonderful
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people that helped us feel at home. Thank you to Laura Flower Kim and Daniel
Yoder at the International Student Office; Natalie Gilmore, Felicia Hunt, and Kate
McAnulty at the Graduate Office; and Kurt Murdoch and Kevin Lee at Human
Resources. I am also grateful for the opportunity to improve graduate student life
withtheGraduateStudentCouncil. ThankyoutoallofmycolleaguesontheBoard
ofDirectorsoverthepastfouryears.
Iamverygratefulformyparents’loveandsupportoverthepast30years. Afterthe
Vietnam War, they took great risks and made huge sacrifices. They left everything
they knew behind to immigrate to Canada as refugees to create a better life for
themselves and their future children. They taught me the importance of education
andhardwork,whichhashelpedmebecomethepersonIamtoday.
Finally,andmostimportantly,noneofthiswouldhavebeenpossiblewithoutLaura.
Thankyouforalwaysbeingthereforme. WhenIfeeloverwhelmedbyachallenge,
I know I can always count on your unconditional love and support. No words can
capture how much love I have for you and how fortunate I feel to have you as my
life partner in every sense of the word. Over the past 15 years, we have had many
adventuresandIamlookingforwardtomanymoreintheyearstocome.
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ABSTRACT
Thefirstplanetsdiscoveredoutsideofoursolarsystemwereverydifferentfromthe
solar system planets. These discoveries raised new challenges to planet formation
models,whichweredesignedtoexplaintheoriginofthesolarsystemplanets. One
particularly intriguing population, the “hot Jupiters” were some of the first planets
discovered. These gas giant planets have masses similar to Jupiter and Saturn,
however, they were found on orbits 100 times closer to their star than Jupiter is to
the sun. Proposed formation scenarios involve models that argue for formation at
presentlyobservedlocations,butthesearechallengedbythelackofplanet-building
materialssoclosetothehoststar. Othermodelsassumetheseplanetsformatmore
moderate locations, perhaps in a manner similar to Jupiter and Saturn, followed by
inward migration via some other mechanism. These models are challenged by the
lackofaknownmigrationmechanism.
This dissertation compiles three studies conducted over the past five years to in-
vestigate the formation and migration histories of gas giant exoplanets. After the
discovery of the first hot Jupiter, additional discoveries revealed some population
characteristics that could provide evidence for certain formation or migration sce-
narios. A large fraction of hot Jupiters were found to have eccentric orbits and/or
misaligned orbits relative to the star’s spin axis. These properties suggest that a
gravitationalinteractionwithanadditionalmassiveobjectmayhaveplayedarolein
thedynamicalhistoryofthesehotJupiters. Studiesofstellarmultiplicityfornearby,
sun-likestarshavealsorevealedthatmulti-stellarsystemsarecommon.
The studies presented in this dissertation investigate whether stellar companions
to giant planet systems influence the planets. In the first and second study, we
conduct a survey for stellar companions around stars that host hot Jupiters detected
bythetransitingmethod. Thefirststudyexamineswhetherstarshostingmisaligned
planets are more likely to host a companion star. We found no such correlation,
suggestingthatstellarcompanionsdonotplayadominantroleincausingplanetary
misalignment. Inthesecondstudy,welookatthepopulationofstellarcompanions
as a whole to quantify the fraction of hot Jupiters that might have migrated due
to stellar interactions. We find that less than 20% of hot Jupiters might have
experiencedthismigrationscenario. However,wedofindthathotJupitersarethree
timesmorelikelytobeinawidemulti-stellarsystemcomparedtonearbystarsthat
do not host hot Jupiters, suggesting some other connection between the companion
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starandthegiantplanet.
Inthethirdstudy,wesearchforstellarcompanionsaroundstarsthathostgiantplanets
over a wide range of separations, from the close-in hot Jupiters to giant planets as
far away as Jupiter is to our sun. These planets were found via the radial velocity
method. We compare the giant planets’ orbital properties for single- and multi-
stellar systems to determine whether planets in multi-stellar systems show some
evidence for star-planet interactions. With the current dataset, we find no evidence
tosupportthehypothesisthatplanetsinmulti-stellarsystemshaveadifferentsetof
orbitalproperties.
Finally, we present preliminary results of an ongoing survey to understand giant
planetformationontheotherextremeend. InsteadofhotJupitersonclose-inorbits,
thissurveyseekstoexplaintheoriginoftheverydistantgiantplanetarymassobjects
found by direct imaging surveys. These objects are often found on separations that
are ten to one hundred times farther away than Neptune is to our sun. Due to their
distance and size, it’s not certain if these objects are some of the biggest planets in
existence or if they are the smallest stars. This new survey will search for planets
to serve as the link between known giant exoplanets and these unknown directly
imagedobjects.
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PUBLISHED CONTENT AND CONTRIBUTIONS
Ngo,H.,H.Knutson,S.Hinkley,etal.(2015).TheAstrophysicalJournal800,138.
doi:10.1088/0004-637X/800/2/138.
H. Ngo conducted the observations, processed the data, analyzed the results
and wrote the manuscript. H. Knutson advised this project. Reproduced with
permissionfromtheAmericanAstronomicalSociety(copyrightholder).
Ngo, H., H. A. Knutson, S. Hinkley, et al. (2016). The Astrophysical Journal 827,
8.doi:10.3847/0004-637X/827/1/8.
H. Ngo conducted the observations, processed the data, analyzed the results
and wrote the manuscript. H. Knutson advised this project. Reproduced with
permissionfromtheAmericanAstronomicalSociety(copyrightholder).
Ngo,H.,H.A.Knutson,M.L.Bryan,etal.(2017).TheAstronomicalJournal153,
242.doi:10.3847/1538-3881/aa6cac.
H. Ngo conducted the observations, processed the data, analyzed the results
and wrote the manuscript. H. Knutson advised this project. Reproduced with
permissionfromtheAmericanAstronomicalSociety(copyrightholder).
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TABLE OF CONTENTS
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . v
Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vii
PublishedContentandContributions . . . . . . . . . . . . . . . . . . . . . . ix
TableofContents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . x
ListofIllustrations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xii
ListofTables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xiii
ChapterI:Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.1 Exoplanetdiscoverieschallengeplanetformationmodels . . . . . . . 1
1.2 Exoplanetdetectionmethods . . . . . . . . . . . . . . . . . . . . . . 2
1.3 Populationpropertiesofgasgiantexoplanets . . . . . . . . . . . . . 6
1.4 FindingstellarcompanionsthroughKeckdirectimaging . . . . . . . 9
1.5 Organizationofthisdissertation . . . . . . . . . . . . . . . . . . . . 11
Chapter II: No correspondence between hot-Jupiter spin-orbit misalignment
andtheincidenceofdirectlyimagedstellarcompanions . . . . . . . . . . 14
2.1 Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
2.2 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
2.3 Observations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
2.4 Analysisofcompanionproperties . . . . . . . . . . . . . . . . . . . 23
2.5 Systemswithdetectedcompanions . . . . . . . . . . . . . . . . . . 40
2.6 Companionfraction . . . . . . . . . . . . . . . . . . . . . . . . . . 48
2.7 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
2.8 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
Chapter III: Stellar companions beyond 50 au might facilitate giant planet
formation,butmostareunlikelytocauseKozai-Lidovmigration . . . . . 68
3.1 Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68
3.2 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
3.3 Sampleselectionandobservations . . . . . . . . . . . . . . . . . . . 71
3.4 Analysisofcompanionproperties . . . . . . . . . . . . . . . . . . . 75
3.5 Notesondetectedcompanions . . . . . . . . . . . . . . . . . . . . . 87
3.6 Surveyresults . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92
3.7 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100
3.8 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105
3.9 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . 106
Chapter IV: No difference in orbital parameters of RV-detected giant planets
between0.1and5auinsinglevsmulti-stellarsystems . . . . . . . . . . . 114
4.1 Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114
4.2 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115
4.3 Observations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117
4.4 Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124