Presentation on theme: "Polarimetric Calibration for Nasmyth instrument HiCIAO Jun Hashimoto (National Astronomical Observatory of Japan) and SEEDS, HiCIAO, AO team."— Presentation transcript:
Polarimetric Calibration for Nasmyth instrument HiCIAO Jun Hashimoto (National Astronomical Observatory of Japan) and SEEDS, HiCIAO, AO team
1/13 What is HiCIAO ? Near-infrared high contrast imaging instrument with a linear polarimetor at the 8.2m Subaru telescope. Targets: exoplanets and proto-planetary disks We use linear polarization for the detection of disks Required polarimetric accuracy: % –20-30 % polarization in disks GJ758 Thalmann et al ~10-30M J 30AU 100AU Muto+12 SAO PDS 70 Hashimoto+12 k And Carson+12 52AU HiCIAO results
2/13 Nasmyth polarimetor HiCIAO HiCIAO is mounted on Nasmyth platform. Instrumental polarization comes from the telescope and instruments. Correcting with Correction Matrix, not standard star. HiCIAO Nasmyth focus SUBARU Tertiary mirror 45º unpolarized light polarized light
3/13 What 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. Reflectance case of a bare silver mirror Mirror refractive index
4/13 Conceptual 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.
5/13 Instrumental polarization from Tertiary mirror Bare silver mirror 1.6um Tertiary mirror rotates with the telescope elevation Q/I (unpolarized light) ~0.3% instrumental polarization is generated by Tertiary Mirror
6/13 Instrumental polarization from Image Rotator Three silver mirrors to derotate images Over coating (SiO 2 ) –multi-reflection Wavelength dependency Linear polarization is changed to circular polarization at 1.6 um Conceptual figure of Image Rotator Conceptual figure of multi-reflection Phase Difference
7/13 Cross talk (Q, U => V) in Image Rotator Most incident linear polarization is changed to circular polarization at 45 degrees Observed linear polarization with a rotation angle Angle of Image rotator (degree)
8/13 Correction Construction of the matrix between observed values and true Stokes parameters –no need of observations for polarized standard star Incident Jones matrix Observed Jones matrix HiCIAO matrix observed values Incident Stokes parameters Deriving incident stokes QU by linear transformation. linear combination of IQUV
9/13 Matrix between observed values and Stokes parameter observable incident Stokes parameters p, q, u, v are functions of refractive indecs of Tertiary Mirror and Image Rotator Constant Values A, B, C, D are functions of parallactic angle and Telescope Elevation, Image Rotator angle, and wave-plate angle. Variable values
10/13 Stabilize instrumental polarization Optimizing the tracking of half-waveplate to stabilize time-variable instrumental polarization Two tracking mode –Sidereal tracking –Pupile tracking (ADI mode) Q/I Sidereal ADI star telescope spider time dependency of instrumental polarization No tracking half-waveplate Tracking half-waveplate No tracking half-waveplate Tracking half-waveplate
11/13 Performance Polarimetric standard star –Elias % %, 71.1º º (HiCIAO) 4.09% %, 71.0º º (Hough+88) –HDE % %, 63.0º º (HiCIAO) 2.59% %, 58.0º º (Whittet+92) Photometric standard star (not nearby star, may have interstellar polarization) –SAO93770 =0.70%, =0.20% –GSC01804 =0.52%, =0.13% Accuracy of polarization in HiCIAO PDI is sigma P < ~0.2%, sigma θ < ~5º. Instrumental polarization is corrected by our model.
12/13 Known 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
13/13 Conclusion HiCIAO 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 polarization Accuracy: a few 0.1% Thank you!
15/13 Performance 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 º Instrumental Polarization is corrected. The PI image of AB Aur is less affected by speckle noise (degree) (number)