Presentation on theme: "What is HiCIAO ? Near-infrared high contrast imaging instrument with a linear polarimetor at the 8.2m Subaru telescope. Targets: exoplanets and proto-planetary."— Presentation transcript:
0Polarimetric Calibration for Nasmyth instrument HiCIAO Jun Hashimoto(National Astronomical Observatory of Japan)and SEEDS, HiCIAO, AO team
1What is HiCIAO ?Near-infrared high contrast imaging instrument with a linear polarimetor at the 8.2m Subaru telescope.Targets: exoplanets and proto-planetary disksWe use linear polarization for the detection of disksRequired polarimetric accuracy: %20-30 % polarization in disksGJ758HiCIAO results（Thalmann et al. 2009）PDS 70k AndSAO206462~10-30MJ100AU52AUHashimoto+1230AUCarson+12Muto+12
2Nasmyth polarimetor HiCIAO HiCIAO is mounted on Nasmyth platform.Instrumental polarization comes from the telescope and instruments.Correcting with Correction Matrix, not standard star.SUBARUunpolarized lightHiCIAOpolarized light45ºNasmyth focusTertiary mirror
3What is instrumental polarization ? The amplitude and phase of incident light are changed at mirrors (Fresnel reflection).Rs and Rp: the reflection coefficient of perpendicular and parallel wave to the plane of incidence.Reflectancecase of a bare silver mirrorrefractive indexMirror
4Conceptual figure of the optical path Instrumental polarization in HiCIAO mainly comes from Tertiary Mirror and Image Rotator.Rotating during tracking objects, thus, time variable.Other optics generate static instrumental polarization.Corrected by flat-fielding uging non-polarized light.
5Instrumental polarization from Tertiary mirror Bare silver mirror1.6umTertiary mirror rotates with the telescope elevationQ/I (unpolarized light)~0.3% instrumental polarizationis generated by Tertiary Mirror
6Instrumental polarization from Image Rotator Three silver mirrors to derotate imagesOver coating (SiO2)multi-reflectionWavelength dependencyLinear polarization is changed to circular polarization at 1.6 umConceptual figure of Image RotatorConceptual figure of multi-reflectionPhase Difference
7Cross talk (Q , U => V) in Image Rotator Observed linear polarization with a rotation angleAngle of Image rotator (degree)Most incident linear polarization is changed to circular polarization at 45 degrees
8Deriving incident stokes QU by linear transformation. CorrectionConstruction of the matrix between observed values and true Stokes parametersno need of observations for polarized standard starIncident Jones matrixObserved Jones matrixIncident StokesparametersHiCIAO matrixobserved valueslinear combinationof IQUVDeriving incident stokes QU by linear transformation.
9refractive indecs of Tertiary Mirror and Image Rotator Constant Values Matrix between observed values and Stokes parameterobservableincidentStokes parametersp, q, u, v are functions ofrefractive indecs of TertiaryMirror and Image RotatorConstant ValuesA, B, C, D are functions ofparallactic angle andTelescope Elevation, ImageRotator angle, andwave-plate angle.Variable values
10Stabilize instrumental polarization Optimizing the tracking of half-waveplate to stabilize time-variable instrumental polarizationTwo tracking modeSidereal trackingPupile tracking (ADI mode)starSiderealtime dependency ofinstrumental polarizationADItelescope spiderTrackinghalf-waveplateTrackinghalf-waveplateQ/IQ/INo trackinghalf-waveplateNo trackinghalf-waveplate
11Performance Polarimetric standard star Elias 164.22% %, 71.1º º (HiCIAO)4.09% %, 71.0º º (Hough+88)HDE2.67% %, 63.0º º (HiCIAO)2.59% %, 58.0º º (Whittet+92)Photometric standard star (not nearby star, may have interstellar polarization)SAO93770<P>=0.70%, <sigmaP>=0.20%GSC01804<P>=0.52%, <sigmaP>=0.13%Accuracy of polarization in HiCIAO PDI is sigmaP < ~0.2%, sigmaθ < ~5º.Instrumental polarization iscorrected by our model.
12Known problem Large wavelength dependency in Image Rotator Blue or red sources may have large uncertainty.Tracking Image Rotator around ‘0’ degree.MKO H band filter
13ConclusionHiCIAO is the Nasmyth polarimetor at the Subaru telescope.Instrumental polarization including cross talk is corrected by Correction Matrix.For better correction, half-waveplate is tracked to stabilize the variable instrumental polarizationAccuracy: a few 0.1%Thank you!
15Performance Polarization vector pattern of AB Aur. Detecting polarization at the vicinity of the mask edge (r >0.15" : 22 AU)Center: 90.1º º ,FWHM: 4.3º ºInstrumental Polarization is corrected.The PI image of AB Aur is less affected by speckle noise.(number)(degree)