Asterseismologyand Gaiaastroweb.cwru.edu/heather/323.17/asteroseismology.pdf · Asteroseismology...
30
Asterseismology and Gaia Asteroseismology can deliver accurate stellar radii and masses Huber et al 2017 compare results on distances from Gaia and asteroseismology for 2200 Kepler stars
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.
