Asterseismologyand Gaiaastroweb.cwru.edu/heather/323.17/asteroseismology.pdf · Asteroseismology...
Transcript of Asterseismologyand Gaiaastroweb.cwru.edu/heather/323.17/asteroseismology.pdf · Asteroseismology...
Asterseismology andGaia
Asteroseismology candeliveraccuratestellarradiiandmassesHuberetal2017compareresultsondistancesfromGaiaand
asteroseismology for2200Kepler stars
Asteroseismology
Surfaceconvectionzonesexcitenon-radialoscillations– standingsoundwaves
DanielHuber
Individual modes of oscillation are described in terms of spherical harmonics. The oscillations are described by their frequency ν and three quantum numbers: the radial order n indicating the number of nodes in the radial direction, the spherical degree l indicating the number of nodal lines on the surface, and the azimuthal order m indicating the number of nodal lines that pass through the rotation axis.
Hekker 2017
DanielHuberTtemperature,mumolecularweight
DanielHuber
DanielHuber
DanielHuber
DanielHuber
Sizeofcavity=stellarradius!
Dispersionrelation
Applieswhenwavesofdifferentwavelengthshavedifferentvelocities- Oneexampleispropagationoflightthroughglass- Anotherisstandingwavesinastar
Frequencyfrelatedto
soundspeed=wavelengthxfrequency
Relatesfrequency,soundspeed,radius
Integrate1/(soundspeed)throughthestar
DanielHuber
DanHuber
Asteroseismology givesadirectmeasureofstellarmeandensity
Measuringlogg
Hekker 2017
IfwecanmeasureTeff,wecanobtainlogg,mass
Stellarradiusfromfrequencydata
Huberetal2017
Asteroseismology summary
• FrequenciesofFourierspectrumofoscillationsgivestellarmeandensityandradiusdirectly
• WiththeadditionofTeff,wecanalsoobtainloggandstellarmass
Gaiasatellite• LaunchedDec2013• OrbitsL2(secondLagrangepoint,dynamicallystable,noEarthoccultation)• GaiaDataRelease1(DR1),includingTGAS(astrometricsolutionincludingpropermotionsderivedfromTychoandDR1positions)released2016• DR2expectedApril2018
Gaiaprecision
GaiaDR1paper2016– TGASerrorsoforder.3mas
Hipparcos hadgeometricdistortionsinreferenceframe… muchlesswithGaia
Brownetal17,GaiaDR1
Hipparcos linkedtoaccurateradioVLBIreferenceframeusingonly12radiostars!Gaiahas295“defining”compactradiosourcestotieitintotheVLBIframe
Kovalevskyetal97
Radiusandlogg fromKeplerAsteroseismic satellite
SpectroscopicTeff and[Fe/H]fromSDSSAPOGEE
griz photometry2MASSJHKs
Parallaxfromasteroseismology?
RadiusfromasteroseismologyTeff fromhigh-resspectra->L
BolometriccorrectionfrommodelsusingTeff,logg,[Fe/H],Av
LandBCgiveMv,thenusem-M=5logd– 5+Av
RadiusfromGaia?
• Bayesiandistancesfrom1/parallax• Thendocalculationinreverse
• ORestimatereddeningusingisochronesandsyntheticphotometryingriz,JHKs,comparewithactualvaluesofmagnitudes/colors
Extinctionestimatefrom3Dmodelincl Schlafly correction
Notethatthesearesmall…..
Test
TestBCsusingtwomethods
SystematicerrorsduetoBCs<1%
GaiaparallaxesvsSeismologyderivedones
Asteroseismic-derivedparallaxesarealittlelarger
Eclipsingbinaryresultnotsupported(reddashesordots)
Strongestoffsetforlargeparallax(dwarfs)
CheckoutTeff :distancesscaleasTeff^2.5
CanderiveTeff usingspectroscopicmethods(donehere)ORphotometric.
Inparticular,theInfraRed FluxMethod(IRFM)isaphotometricmethodwhichiswelltiedtofundamentalphysicsbuthasanoffsetoforder100Kfromspectroscopictemperatures
Redidasteroseismic parallaxestimatesusingdifferenttemperaturescale,for(morediscrepant)dwarfsandsubgiants only
HotterTeff scale(IRFM)reducesdifferencebetweenparallaxesto2%“Asteroseismic andTGASdistancesagreewithinafewpercentoverseveralordersofmagnitude”
Thefuture:asteroseismic distancesbetterthanGaia’send-of-missiononesford>3kpc
Summary
Gaia’sTGASparallaxesareprettydarngood… comparisonwithindependentlyestimatedasteroseismic parallaxesshowdifferencesatonlyafewpercent
AttheendoftheGaiamission,asteroseismic distancesforredgiantswillstillbemoreprecisethanGaiaparallaxes.