Astronomical Observing Techniques 2017 Lecture 12: Pink and …keller/Teaching/AOT... · 2017. 5....

AstronomicalObservingTechniques2017

Lecture12:PinkandotherColoredGlasses

ChristophU.Kellerkeller@strw.leidenuniv.nl

Content1. Broadband Filters 2. Plastic Filters 3. Colored Glass Filters 4.  Interference Filters 5. UBVRI Photometry 6. Precision Photometry 7. Extreme Photometry

keller@strw.leidenuniv.nl AstronomicalObservingTechniques2017:Imaging 2

Imaging•  2Dfield:starcluster,galaxy,protoplanetarydisk•  photometry•  astrometry•  filterstorestrictwavelengthrange

BroadbandColorFilters•  DyedgelaKn(KodakWraNen)

–  advantages:thin,cheap,largesizes–  disadvantages:limitedopKcalquality,heat-sensiKve

•  Coloredglass(SchoN,Corning)–  advantages:stable,rugged,hightransmission–  disadvantages:limitedbandpasses,limitedsizes

•  Interferencefilters–  advantages:verynarrowfilters,almostarbitrarybandpassshapeandwavelength

–  disadvantages:expensive,verylimitedsizes,temperature-sensiKve,humidity-sensiKve,aging

WraEenFilters

•  coloredplasKcsheets•  namedaUerFrederickWraNen,manufacturedbyKodakforabout100years

•  recently:WraNen2•  upto100mmby300mm•  canbeusedforexperiments•  improvedperformancewhenputbetweenglassplates

www.edmundopKcs.com/onlinecatalog/displayproduct.cfm?producKd=1326

TypicalWraEenFilters

www.edmundopKcs.com/onlinecatalog/displayproduct.cfm?producKd=1326

ColoredGlassFilters•  absorbspecificwavelengths•  madebyaddingsubstancestoglassduringglassmanufacturing

•  typicallyusefulfrom200-1200nm–  allglassesabsorbsignificantlybelow200nm

•  importantmanufacturers:–  SchoN–  Corning– Hoya

•  canalsobeusedfororderselecKoninspectroscopykeller@strw.leidenuniv.nl AstronomicalObservingTechniques2017:Imaging 7

SchoEColoredGlass•  UG:Blackandblueglasses,UVtransmi_ng•  BG:Blue,blue-green,andmulK-bandglasses•  VG:Greenglass•  GG:Nearlycolorlesstoyellowglasses,IRtransmi_ng•  OG:Orangeglasses,IRtransmi_ng•  RG:Redandblackglasses,IRtransmi_ng•  NG:NeutraldensityglasseswithuniformaNenuaKoninthevisiblerange

•  N-WG:ColorlessglasseswithdifferentcutoffsintheUV,transmi_nginthevisiblerangeandtheIR

•  KG:VirtuallycolorlessglasseswithhightransmissioninthevisibleandeffecKveabsorpKonintheIR(heatprotecKonfilters)

SchoEColoredGlass1

SchoEColoredGlass2

SchoEColoredGlass3

SchoEColoredGlass4

SchoEColoredGlass5

•  UBVbyJohnsonandMorgan(1953)•  VRIJKLMNQ(infrared)byJohnson(1960)•  (combinaKonsof)glassfilters•  inventedtoclassifystarswithphotomulKpliers•  zeropointofB-VandU-BcolorindicesdefinedtobezeroforA0Vstars

www.sbig.com/products/filters.htm

(Old)UBVRI

LimitaTonsofUBVRIPhotometry•  limitedspectralresoluKon•  effecKvecentralwavelengthchangeswithcolorofstar•  star'smagnitudesandcolordependonthestar'scolor•  short-wavelengthsideofUfilterextendsbelowatmospherictransmissioncutoff

•  properKesofskydefinewidthofbandpass,notfilter•  nocleanseparaKonofinformaKonfromdifferentfilters•  differentdetectorshavedifferentsensiKviKes•  today:BesselorCron/CousinsUBVRIwithCCDs

OtherFilterSystems•  havelessoverlapand/orhighertransmission

•  Johnsonsystemforstars

•  Thuan-GunnfiltersforfaintgalaxyobservaKons

OtherFilterSystems•  SloanDigitalSkySurvey(SDSS)forfaintgalaxyclassificaKon

•  StromgrenforbeNersensiKvitytostellarproperKes(metallicity,temperature,surfacegravity)

Fabry-PerotEtalon•  2parallelplateswithadjustableplateseparaKon•  highlyreflecKvecoaKngsoninsidesurfaces•  periodictransmissionpeaksduetoconstrucKveinterferenceof

successivelyreflectedbeams•  transmissionpeaklocaKonchangeslinearlywithplate

separaKon

ChristophU.Keller,keller@strw.leidenuniv.nl AstronomicalObservingTechniquesCrashCourse2016Part3 20

•  intensityreflecKvityr(transmissiont=1-r)•  transmissionasfuncKonofwavelengthk:m/2λ,m:orderofinterferometer,λ:wavelengthd:plateseparaKoni:angleofincidencen:indexofrefracKonofmaterialbetweenplates

•  ReflecKveFinessethehigherthebeNer

•  FreeSpectralRange:FSR=λ2/2nd•  SpectralResoluKon:R=λ/Δλ=λF/FSR=mF,R≈100-100’000

Fabry-PerotEtalon

( ) ( )1

0 cos2sin141

⎥⎦

⎤⎢⎣

⎡−

+⎟⎠⎞⎜

⎝⎛

−= idk

rrII π

−=1π

ChristophU.Keller,keller@strw.leidenuniv.nl AstronomicalObservingTechniquesCrashCourse2016Part3 21

ThinFilm

•  layerwiththickness≤λ•  extendsin2otherdim.>>λ•  materialwithdifferentindexofrefracKononthicksubstrate

•  maximumtransmissionwhenreflectedraysinterferedestrucKvely

•  maximumreflecKvitywhenreflectedraysinterfereconstrucKvely

InterferenceFilters•  stackofthinfilms•  canbetailoredtoalmostanyspecificaKons

•  sensiKvetotemperature,humidity,angleofincidence

•  tuneinwavelengthwithtemperature,angleofincidence

•  spectralresoluKonR~3–1000

n1, d1

n2, d2

nL, dL

n3, d3

Fabry-PerotTunableFilter•  mainingredientisFabry-PerotwithtunableplateseparaKon

•  stabilityofcavityspacingiscriKcal

•  oUencombinetwoormoretunableelements

•  alwaysneedinterferenceprefilter

www.arcetri.astro.it/science/solare/IBISphoto.jpeg

Photometry•  goal:determinefluxofanastronomicalobjectinwell-definedwavelengthrange

•  problems:–  seeing–  exKncKon–  skybackground–  telescope,instrument,detector

•  calibraKonwith(standard)stars•  all-skyphotometry:compareobjectsalloverthesky•  differenKalphotometry:compareobjectsonsameCCDexposure

SkyoverLaPalma

Atmosphere•  photometricnight=uniform,stableskycondiKons

•  thincloudsandcirrusarehardtoseeatnight•  bright,greyanddarkobservingKme•  seeingdefinessizeofstellarimageforlargetelescopes

•  image=convoluKonofsourceandPoint-SpreadFuncKon(PSF)

•  integraloverimage=integraloversourcekeller@strw.leidenuniv.nl AstronomicalObservingTechniques2017:Imaging 27

AirMass•  exKncKonduetoatmospherealongline-of-sight

•  airmass=amountofaironelooksthrough

•  atzenith(z=0):airmassX=1.0

•  atzenithdistancez,airmassX≈secz=1/cosz

•  X(z=60°)≈2keller@strw.leidenuniv.nl AstronomicalObservingTechniques2017:Imaging 28

AirMass•  absorpKoncoefficientK=2.5log(f(z)/f(z=0)),wheref(z)ismeasuredfluxasfuncKonofzenithdistancez

•  KΔX=ΔmchangeinmagnitudeisabsorpKoncoefficientKmeschangeinairmass

•  measuremagnitudefordifferentairmassesandextrapolatetozeroairmass(noatmosphere!)

•  linearextrapolaKondoesnotworkintheinfraredduetosaturated/overlappingmolecularlines

SimulatedNear-InfraredAbsorpTon

fromTokunagaetal.2002,adsabs.harvard.edu/abs/2002PASP..114..180T

DarkSkyinAlps

BrightSkyintheNetherlands

PhotometricObservaTons(1)•  observeobjectandstandardstarswithdifferentcolors

•  observestandardstarsatlowandhighairmasstodeterminetheir(color-dependent)exKncKoncoefficients

•  reduceimageswithbias,dark,flatfield•  measurefluxeswithaperturephotometry•  calculateinstrumentalmagnitudes:minst=-2.5log(fi/texp)

PhotometricObservaTons(2)•  calibrateinstrumentalmagnitudeforzeroairmass:m0=minst-Ksecz

•  zeropointfromstandardstars:mzp=mstd-mstd,inst•  removezeropoint:m=mzp+minst•  absolutephotometry:determineactualmagnitudeswithcalibraKonsderivedfromstandardstars

•  differenKalphotometry:doesnotrequirecalibraKons

SkyBackground•  useannulusaroundstar

•  usemedianinsteadofmeantoneglectcosmicrays

AperturePhotometry

•  determinelocaKonofstarbyfi_ng2-DGaussianorMoffatPSFmodel

•  determineandremoveskybackground

AperturePhotometry(conTnued)•  bestaperturesizedependsonbrightnessofstar•  trade-offbetweencapturingmorestarlightandaddingnoisefromskybackground,detectoretc.

•  plotresultasfuncKonofincreasingapertureandesKmateasymptoKcvalue

•  forvariabilitymeasurements(e.g.exoplanettransit)withdifferenKalphotometry(standardstarinsameimage):–  usefixedandidenKcalaperturesfortargetandreferencestar(s)

–  opKmumapertureminimizesscaNerinconstantpartsofmtarget-mstd

ColorCorrecTon•  exKncKondependsstronglyonwavelength(color)

•  measuredfluxthroughbroadfilterdependsonstellarspectrum

•  addiKonalcorrecKon m=m0+Ksecz+k2CseczwhereCiscolorindex(e.g.C=B-V)

ExtremePhotometry

keplerscience.arc.nasa.gov/PyKEprimerWalkthroughC.shtml90-daylong-cadenceKeplerSAPlightcurveofKIC3749404.keller@strw.leidenuniv.nl AstronomicalObservingTechniques2017:Imaging 39

SubtleInstrumentalEffects•  ThermalchangesinopKcs,electronics•  Smallguidingerrorscoupledwithsub-pixelgainvariaKons

•  CotrendingBasisVectors(CBV):Instrumentalparametersthathavebeenshowntocorrelatewithphotometryofstandardstars

16KeplerLightCurves

keplerscience.arc.nasa.gov/images/PyKE/PyKEprimerFig4.png

CotrendingBasisVectors

keplerscience.arc.nasa.gov/images/PyKE/PyKEprimerFig3.png

SubtracTonof2CBVs

SubtracTonof8CBVs

NoCBVFi]ngDuringEclipses

Astronomical Observing Techniques 2017 Lecture 12: Pink and …keller/Teaching/AOT... · 2017. 5....

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