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.