Variability of Elemental Abundances in the Local Neighborhood and its Effect on Planetary ...

195 Pages·2014·4.24 MB·English

VariabilityofElementalAbundancesintheLocalNeighborhood
anditsEffectonPlanetarySystems
by
MichaelPagano
ADissertationPresentedinPartialFulfillment
oftheRequirementfortheDegree
DoctorofPhilosophy
ApprovedApril2014bythe
GraduateSupervisoryCommittee:
PatrickYoung,Chair
Sang-HeonShim
JenniferPatience
StevenDesch
ArielAnbar
ARIZONASTATEUNIVERSITY
May2014
ABSTRACT
Asthedetectionofplanetsbecomecommonplacearoundourneighboringstars,sci-
entists can now begin exploring their possible properties and habitability. Using statistical
analysis I determine a true range of elemental compositions amongst local stars and how
this variation could affect possible planetary systems. Through calculating and analyzing
thevariationinelementalabundancesofnearbystars,theactualrangeinstellarabundances
canbedeterminedusingstatisticalmethods. Thisresearchemphasizesthediversityofstel-
lar elemental abundances and how that could affect the environment from which planets
form. An intrinsic variation has been found to exist for almost all of the elements studied
bymostabundance-findinggroups.
Specifically, this research determines abundances for a set of 458 F, G, and K stars
from spectroscopic planet hunting surveys for 27 elements, including: C, O, Na, Mg, Al,
Si, S, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Mo, Ba, La, Ce, Nd, Eu, and Hf.
Abundancesoftheelementsinmanyknownexosolarplanethoststarsarecalculatedforthe
purpose investigating new ways to visualize how stellar abundances could affect planetary
systems, planetary formation, and mineralogy. I explore the Mg/Si and C/O ratios as well
asplacetheseabundancesonternarydiagramswithFe.
Lastly, I emphasize the unusual stellar abundance of τ Ceti. τ Ceti is measured to
have 5 planets of Super-Earth masses orbiting in near habitable zone distances. Spectro-
scopic analysis finds that the Mg/Si ratio is extremely high ( 2) for this star, which could
„
lead to alterations in planetary properties. τ Ceti’s low metallicity and oxygen abundance
account for a change in the location of the traditional habitable zone, which helps clarify a
newdefinitionofhabitableplanets.
i
DEDICATION
Idedicatethistothosewhohavestoodbymeandhelpedmethroughthisprocess.
.
.
.
Tomyfamilyforalwaysbeingthereforme,forallthephonecallsandallthetimesIsaid
“I’llbedonewhenI’mdone”
.
.
.
ToLiz,mymoonlight,forfindingawaytogetthroughallthiscrazinessandkeepmesane.
.
.
.
Toallmyfriendswhohavemademygraduatelifeamazing.
“Forsmallcreaturessuchaswe,thevastnessisbearableonlythroughlove”
￿CarlSagan
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ACKNOWLEDGMENTS
Iwouldliketothankmyadvisor,PatrickYoung,whotookmeinwhenIwaslost
atthestartofmygraduatecareerandmademefeellikeItrulybelongedhere. Ihopethis
projecthasnotonlytakenmyself,butalsomyadvisor,intonewdirectionsofexploration.
Tomycommittee: SteveDesch,ArielAnbar,JennyPatience,andDanShim. Allofyou
havehelpedshapemyunderstandingofscienceandhowtostayopentoadvisefromany
field. Throughmixingallyourspecialtieswecanstarttounderstandsomuchmoreabout
theuniversearoundus. IwouldliketothankPaulButlerandtheCarnegieInstituteof
Washingtonforallowingmetousetheirspectraandteachingmehowtoreducethem.
ThankstoEricBubarandJadeBondwhoreallytaughtmehowtomeasure,understand,
andinterpretstellarabundances.
I’mextremelygratefulforNatalieHinkel(Mew! Mew! Mew!),whostartedoffas
afriendandquicklybecamemymostimportantcolleague(andIhopewewillalways
remainboth). Yourhelpduringthislastyearhasreallykeptmecalmandmadealotof
thispossible. ThankstoPriyaChallaandJoshuaGonzalez,whosehelpwasinstrumental
ingettingmyabundancecodestandardizedandworking. Theybothhaveagoodfuture
aheadofthem. ThankyoutoNahksTr’Ehnlforbeingsuchagreatoffice-mateandreally
makingmethinkabouttheconnectionsbetweenartandsceince. Itwaslonelyinthat
officewithoutyou.
ThankyoutoalloftheFollowtheElementsteams. Ienjoyedeverymeetingand
everynewpieceofinformationIlearnedabouttopicsIneverwouldhaveconsidered. I
stilllookforwardtothemeetingwhenIgetaskedifIhaveabundancesforacertain
element(Phosphorus)andIactuallyhavethemtoshow. I’velearnedalotfromworking
withthatgroup.
Idon’tknowwhereI’dbewithoutCarenBurgermeister,whosefriendshipand
supportcangetmethroughanything. ThankyouErinneBlakemanforallyourhelpand
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friendship. Thankstomyroommatesovertheyears,especiallyDrew,Caleband
Jean-Franc¸ois. Forallmyfriends,whichisalisttoolongtowritehere,andforthatIam
blessed.
IwouldliketoacknowledgessupportfromtheFollowtheElements”grantthrough
theNASAAstrobiologyInstituteandArielAnbar(08-NAI5-0018),andfromGPSAfor
multipletravelgrantstopresentmymaterialatconferences.
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TABLEOFCONTENTS
Page
LISTOFTABLES ............................................................ viii
LISTOFFIGURES ........................................................... ix
CHAPTER
1 INTRODUCTION...................................................... 1
1.1 TheSolarComposition ............................................ 3
1.2 StellarAbundances ................................................ 5
1.3 SourcesofAbundanceVariations ................................... 7
2 ELEMENTALABUNDANCEVARIATIONSINNEARBYSTARS ........ 11
2.1 Introduction ...................................................... 11
2.2 AbundanceAnalysis............................................... 15
2.2.1 IntrinsicVariation .......................................... 15
2.3 IndividualElements ............................................... 19
2.3.1 Carbon.................................................... 19
2.3.2 Oxygen ................................................... 21
2.3.3 Sodium,Magnesium,andAluminum......................... 23
2.3.4 Silicon,Sulfur ............................................. 26
2.3.5 Calcium................................................... 28
2.3.6 Titanium .................................................. 28
2.3.7 Chromium,Scandium,Vanadium,Manganese ................ 29
2.3.8 NickelandCobalt .......................................... 30
2.3.9 sandrprocess ............................................. 31
2.3.10 OutlierStars ............................................... 32
2.4 Conclusions ...................................................... 33
3 ABUNDANCESOFNEARBYSTARS .................................. 42
v
CHAPTER Page
3.1 StellarData....................................................... 42
3.1.1 TargetStarsandObservations ............................... 42
3.1.2 AbundanceAnalysis........................................ 42
3.1.3 StellarParameters .......................................... 44
3.1.4 AbundanceDetermination .................................. 46
3.2 Results ........................................................... 46
3.2.1 ComparisontoPlanetHosts ................................. 49
3.2.2 IntrinsicVariation .......................................... 50
4 ABUNDANCESOFPLANETHOSTS................................... 64
4.1 StellarData....................................................... 64
4.1.1 TargetStarsandObservations ............................... 64
4.1.2 AbundanceAnalysis........................................ 64
4.2 Results ........................................................... 65
4.3 ExoplanetaryMineralogy .......................................... 67
4.4 Conclusions ...................................................... 71
5 THEEXTREMEEXAMPLEOFTAUCETI.............................. 75
5.1 AbundanceDeterminations ........................................ 77
5.1.1 Observations .............................................. 77
5.1.2 Abundances ............................................... 78
5.2 InternalStructureandDynamicsofMg-richTerrestrialPlanets ........ 79
5.3 HabitableZone ................................................... 82
5.4 Conclusions ...................................................... 87
6 CONCLUSIONS ....................................................... 90
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CHAPTER Page
REFERENCES ............................................................... 94
APPENDIX .................................................................. 102
A TABLES .............................................................. 102
A.1 LineList ......................................................... 103
A.2 FullAbundanceStudy ............................................. 108
A.3 PlanetHostAbundanceStudy ...................................... 177
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LISTOFTABLES
Table Page
2.1 Intrinsicvariationofabundanceratiosfordifferentabundancefindinggroups.
Valueisfor[X/Fe]. ................................................... 37
2.2 StatisticsforabundancefindingstudiesofBondetal.(2006,2008);Gonza´lez
Herna´ndezetal.(2010);Misheninaetal.(2008);DelgadoMenaetal.(2010). 38
2.3 Table of outlier stars for the surveys of Bond et al. (2006, 2008); Gonza´lez
Herna´ndezetal.(2010);Misheninaetal.(2008);DelgadoMenaetal.(2010). 39
3.1 Tableofstatistics ..................................................... 51
5.1 AbundancesofTauCeti ............................................... 80
5.2 HabitableZoneProperties ............................................. 87
A.1 LineList............................................................. 103
A.2 Allstarsparameters................................................... 108
A.3 AllstarsabundancesforFe,C,O,Na,Mg,Al,Si,andS. ................. 118
A.4 AllstarsabundancesforCa,Sc,Ti,V,Cr,MnandCo..................... 130
A.5 AllstarsabundancesforNi,Cu,Zn,Y,Zr,MoandBa. ................... 142
A.6 AllstarsabundancesforLa,Ce,Nd,Eu,Hf,Mg/SiratioandC/Oratio..... 154
A.7 Absoluteabundancesnormalizedto106 Siatoms ........................ 166
A.8 Planethostparameters ................................................ 177
A.9 PlanethostabundancesforFe,C,O,Na,Mg,Al,Si,SandCa............. 178
A.10 PlanethostabundancesforCa,Sc,Ti,V,Cr,MnanCo. .................. 179
A.11 PlanethostabundancesforNi,Cu,Zn,Y,Zr,MoandBa.................. 180
A.12 PlanethostabundancesforLa,Ce,Nd,Eu,Hf,Mg/SiratioandC/Oratio .. 181
A.13 Absoluteabundancesnormalizedto106 Siatoms ........................ 182
viii
LISTOFFIGURES
Figure Page
2.1 IntrinsicVariationforthestudiesofBondetal.(2006,2008);Misheninaet
al.(2008);Gonza´lezHerna´ndezetal.(2010);Nevesetal.(2009). ......... 40
2.2 Plot of [O/Fe] vs. [Fe/H] for the studies of Bond et al. (2008); Gonza´lez
Herna´ndezetal.(2010);Misheninaetal.(2008);Ram´ırezetal.(2007)(top
to bottom). The solid line represents the linear best fit and the dotted lines
aretheu valuesawayfromthebestfitline. ........................ 41
intrinsic
3.1 Left: Carbon to hydrogen ratio with respect to solar, [C/H], as a function
of [Fe/H]. Red data points are exosolar planet host stars. Right: Carbon to
iron ratio with respect to solar, [C/Fe] as a function of [Fe/H]. The solid
lineisaleast-squaredlinearfittotheentiredistribution. .................. 52
3.2 Left: Oxygen to hydrogen ratio with respect to solar, [O/H], as a function
of [Fe/H]. Red data points are exosolar planet host stars. Right: Oxygen
to iron ratio with respect to solar, [O/Fe] as a function of [Fe/H]. The solid
lineisaleast-squaredlinearfittotheentiredistribution. .................. 53
3.3 Left: Sodium to hydrogen ratio with respect to solar, [Na/H], as a function
of [Fe/H]. Red data points are exosolar planet host stars. Right: Sodium to
iron ratio with respect to solar, [Na/Fe] as a function of [Fe/H]. The solid
lineisaleast-squaredlinearfittotheentiredistribution. .................. 54
3.4 Left: Magnesiumtohydrogenratiowithrespecttosolar,[Mg/H],asafunc-
tion of [Fe/H]. Red data points are exosolar planet host stars. Right: Mag-
nesium to iron ratio with respect to solar, [Mg/Fe] as a function of [Fe/H].
Thesolidlineisaleast-squaredlinearfittotheentiredistribution. ......... 55
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