The photometric selecon of M-dwarfs using Gaia, …...2018/07/06  · The photometric selecon of...

Thephotometricselec.onofM-dwarfsusingGaia,WISEand

2MASSphotometryJohnBentleySupervisors:

Prof.ChrisTinneyDr.DuncanWright

Whichstars?

•  TESSislookingforexoplanets•  MillionsofpotenBalexoplanet-hosBngstars– OnlyafracBonwillhaveplanetsthatwecandetect

•  M-dwarfs– ~75%ofmainsequencedwarfsinthegalaxy(excludingbrowndwarfs)

– ~50%ofthemareexpectedtohaveHZplanets

ClassificaBon

•  SpectroscopicclassificaBon– OnestarataBmeisveryBmeconsuming

•  MulB-starsurveys– FunnelWebesBmatesthousandsofstarspernight– Easiertoremovethestarswedon’twantthantoonlyselectcandidateswedowant

SelecBoncriteria

•  AsimplewaytoselectM-dwarfs•  Absolutemagnitude– Requiresphotometryandparallaxes– ViablewithGaiaDR2butnotDR1

•  ColourselecBon– Largephotometricsurveys– Photometryisreadilyavailableforalargenumberofstars

– 2MASS-J,H,&K;WISE-W1,&W2;Gaia-G

ColourselecBon

•  Starsshouldoccupyuniquecolourranges•  SelectM-dwarfsbyselecBngstarswithinthecolourrangethat

M-dwarfsoccupy•  Simplepolygon

ContaminaBon

•  Confusionwillphotometricallyscaberstars•  Somestarswillbeputintoregionsoccupiedbyothertypesofstars

•  Somecoloursaremoreusefulasspectraltypesarefurtherapart,reducingcontaminaBon– e.g.W1-W2placesM-giantsfurtherawayfromM-dwarfsthanH-K

Galaxia

•  Needalarge,unbiased,andclassifieddataset•  Mostsurveysareeitherlargeandunclassified,orsmallandbiased

•  SyntheBcgalaxycanfulfillallthreerequirements

•  SelectregionfromGalaxiaandseehowmanystarsthisselectsinobservaBonaldata

ContaminaBonandcompleteness

•  Highcompleteness– 99%ofmanyM-dwarfs– ContaminaBonlessimportant

•  LowcontaminaBon– BalancingcontaminaBonwithcompleteness

ColourResultsCompleteness(%) Contamina.on(%) M-dwarfs(%) DR1(#)

Highcompleteness 99.3 55.6 44.4 78340

LowcontaminaBon 98.0 35.9 64.1 40505

•  LowcontaminaBonselectsfewerstars• Mostoftheexcludedwillbecontaminates

Absolutemagnitude

•  NocontaminaBonfromgiants•  Highcompleteness– Dashedline

•  LowcontaminaBon– Dobedline

AbsolutemagnituderesultsCompleteness(%) Contamina.on(%)

Highcompleteness 99.96 29.4

LowcontaminaBon 54.7 16.8

•  LowcontaminaBonselects55%ofM-dwarfs•  FocusoncompletenessovercontaminaBon

ComparisonGalaxia(#) Contamina.on(%)

Colour 54255 55.6

Absolutemagnitude 34324 29.4

Colour+Abs.magnitude 32351 25.6

•  AbsolutemagnitudealmosthalvesthecontaminaBonrate•  CombinaBonofcolourandabsolutemagnitudegivesbestresults•  VeryviablewithFunnelweb

LimitaBonsandGaiaDR2

•  ObservaBonaldatawillbeslightlybiased– RequirescrossmatchwithWISEand2MASS– Removed4%ofstars

•  DR2–  ImprovecolourselecBon– CheckAbsolutemagnituderesults

Conclusion

•  ContaminaBonisthefocusforcolourselecBon•  CompletenessisrequiredforabsolutemagnitudeselecBon

•  VeryachievablenumbersforFunnelweb