the photometric selecon of m-dwarfs using gaia, …...2018/07/06 · the photometric selecon of...
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Thephotometricselec.onofM-dwarfsusingGaia,WISEand
2MASSphotometryJohnBentleySupervisors:
Prof.ChrisTinneyDr.DuncanWright
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Whichstars?
• TESSislookingforexoplanets• MillionsofpotenBalexoplanet-hosBngstars– OnlyafracBonwillhaveplanetsthatwecandetect
• M-dwarfs– ~75%ofmainsequencedwarfsinthegalaxy(excludingbrowndwarfs)
– ~50%ofthemareexpectedtohaveHZplanets
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ClassificaBon
• SpectroscopicclassificaBon– OnestarataBmeisveryBmeconsuming
• MulB-starsurveys– FunnelWebesBmatesthousandsofstarspernight– Easiertoremovethestarswedon’twantthantoonlyselectcandidateswedowant
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SelecBoncriteria
• AsimplewaytoselectM-dwarfs• Absolutemagnitude– Requiresphotometryandparallaxes– ViablewithGaiaDR2butnotDR1
• ColourselecBon– Largephotometricsurveys– Photometryisreadilyavailableforalargenumberofstars
– 2MASS-J,H,&K;WISE-W1,&W2;Gaia-G
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ColourselecBon
• Starsshouldoccupyuniquecolourranges• SelectM-dwarfsbyselecBngstarswithinthecolourrangethat
M-dwarfsoccupy• Simplepolygon
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ContaminaBon
• Confusionwillphotometricallyscaberstars• Somestarswillbeputintoregionsoccupiedbyothertypesofstars
• Somecoloursaremoreusefulasspectraltypesarefurtherapart,reducingcontaminaBon– e.g.W1-W2placesM-giantsfurtherawayfromM-dwarfsthanH-K
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Galaxia
• Needalarge,unbiased,andclassifieddataset• Mostsurveysareeitherlargeandunclassified,orsmallandbiased
• SyntheBcgalaxycanfulfillallthreerequirements
• SelectregionfromGalaxiaandseehowmanystarsthisselectsinobservaBonaldata
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ContaminaBonandcompleteness
• Highcompleteness– 99%ofmanyM-dwarfs– ContaminaBonlessimportant
• LowcontaminaBon– BalancingcontaminaBonwithcompleteness
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ColourResultsCompleteness(%) Contamina.on(%) M-dwarfs(%) DR1(#)
Highcompleteness 99.3 55.6 44.4 78340
LowcontaminaBon 98.0 35.9 64.1 40505
• LowcontaminaBonselectsfewerstars• Mostoftheexcludedwillbecontaminates
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Absolutemagnitude
• NocontaminaBonfromgiants• Highcompleteness– Dashedline
• LowcontaminaBon– Dobedline
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AbsolutemagnituderesultsCompleteness(%) Contamina.on(%)
Highcompleteness 99.96 29.4
LowcontaminaBon 54.7 16.8
• LowcontaminaBonselects55%ofM-dwarfs• FocusoncompletenessovercontaminaBon
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ComparisonGalaxia(#) Contamina.on(%)
Colour 54255 55.6
Absolutemagnitude 34324 29.4
Colour+Abs.magnitude 32351 25.6
• AbsolutemagnitudealmosthalvesthecontaminaBonrate• CombinaBonofcolourandabsolutemagnitudegivesbestresults• VeryviablewithFunnelweb
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LimitaBonsandGaiaDR2
• ObservaBonaldatawillbeslightlybiased– RequirescrossmatchwithWISEand2MASS– Removed4%ofstars
• DR2– ImprovecolourselecBon– CheckAbsolutemagnituderesults
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Conclusion
• ContaminaBonisthefocusforcolourselecBon• CompletenessisrequiredforabsolutemagnitudeselecBon
• VeryachievablenumbersforFunnelweb