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HST - AO - Coronography

HST - AO - Coronography. Exoplanets and circumstellar disks: Past and future science G. Duch êne (Obs. Grenoble). Outline (2 classes). AO: why and how? AO: data processing Coronography: why and how? Exoplanets: current observations Disks: interpreting images

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HST - AO - Coronography

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  1. HST - AO - Coronography Exoplanets and circumstellar disks: Past and future science G. Duchêne (Obs. Grenoble)

  2. Outline (2 classes) • AO: why and how? • AO: data processing • Coronography: why and how? • Exoplanets: current observations • Disks: interpreting images • The big picture (interferometry, ELTs) HST/AO/coronography: disks and planets

  3. Coronography : Why and How? HST/AO/coronography: disks and planets

  4. Need to improve contrast! • Achievable contrast is not yet sufficient for planets (or disks) • Need to go inside! HST/AO/coronography: disks and planets

  5. Block the central star! • A simple idea to prevent saturation on detectors and go deeper • However, just hiding it is not enough… • Try the Sun with anything you can to hide it! HST/AO/coronography: disks and planets

  6. Lyot coronography • 1930s design, dedicated for the Sun • Key element: the Lyot stop!! • Blocks scattered light HST/AO/coronography: disks and planets

  7. Lyot coronography • Optical concept: Occulting mask Lyot stop Image plane Pupil (Fourier) plane HST/AO/coronography: disks and planets

  8. Lyot coronography • Strong improvement on achievable contrast inside outside HST/AO/coronography: disks and planets

  9. Lyot coronography • Occulting spot not always circular • STIS wedge, allows range of spot sizes HST/AO/coronography: disks and planets

  10. Modern coronographs • HST and ground-based AO systems all have coronographic modes • Typical occulting spot size: 0.3-3’’ • Importance of space • Stable PSF and ‘perfect’ positioning • Much more data from HST than ground-based AO HST/AO/coronography: disks and planets

  11. Modern coronographs ACS Direct (V) STIS Coronagraph (U→I) Palomar AO Coronagraph (2.2 mm) Courtesy: J. Krist ACS Coronagraph (V) NICMOS Coronagraph (J) HST/AO/coronography: disks and planets

  12. Modern coronographs • Coronography can be combined with • PSF subtraction • Roll subtraction, ADI • Polarization Courtesy: G. Scheider HST/AO/coronography: disks and planets

  13. Improving on Lyot • Residuals in coronographic images come from diffraction off sharp edges • Introduce a smoothing function • Apodization • Smoother profiles • Lower resolution HST/AO/coronography: disks and planets

  14. New coronograph designs • Disk phase mask: cancel the star with itself (destructive interference) • Size of spot is selected to match fluxes • Size = 0.53 /D HST/AO/coronography: disks and planets

  15. New coronograph designs • 4-quadrant phase mask • A different flavor of the same idea  =   = 0  = 0  =  2 /D, in lab HST/AO/coronography: disks and planets

  16. New coronograph designs • Shaped pupil coronographs Ring Barcode Cross-barcode Spiderweb Starshape PSF Early ripple designs S-K ripple1 ripple2 ripple3 Mask PSF HST/AO/coronography: disks and planets

  17. Coronography: limitations • Fine design and alignment! HST/NICMOS Aligned Lyot Stopl Misaligned Lyot Stop Observed HST/AO/coronography: disks and planets

  18. Coronography: limitations • Chromaticity of transmission optics! • Limited to narrow-band filters • Sensitivity? • Shaped pupil corono are OK HST/AO/coronography: disks and planets

  19. Coronography : Data processing HST/AO/coronography: disks and planets

  20. How to treat such datasets? • Need to subtract remaining stellar flux • Similar to AO images • Regular PSF subtraction • Time/color constraints • Roll subtraction • Not possible on all telescopes HST/AO/coronography: disks and planets

  21. Example:  Pictoris Courtesy: J. Krist Roll 1 Beta Pictoris Roll 2 Alpha Pic 1 - 2 Smith & Terrile (1984) Beta - Alpha Pic 1984 HST/AO/coronography: disks and planets

  22. Contrast gain • Direct complementary images needed to probe the inner regions HST/AO/coronography: disks and planets

  23. Some little defects • Need perfect centering and focusing breathing centering Courtesy: J. Krist HST/AO/coronography: disks and planets

  24. Some little defects • Need to adjust flux of central star to within 1-2% • Hard to estimate!! Courtesy: G. Scheider HST/AO/coronography: disks and planets

  25. Science: Exoplanets (direct detection) HST/AO/coronography: disks and planets

  26. Exoplanets: basics • Current state of the art • See N. Santo’s talks (Thursday & Friday) • Planets are frequent • Planets are massive • Planets are close in /d on 8m (2.2 m) Beuzit et al. (PPV) HST/AO/coronography: disks and planets

  27. What do we want to know? • Physical properties • M, R: composition • Physico-chemistry • Colors: surface Uranus Neptune HST/AO/coronography: disks and planets

  28. dependence on particle size, impact on clouds ! What do we want to know? • Physical properties • M, R: composition • Physico-chemistry • Colors: surface • Atmosphere (features) • Geology? Biology? HST/AO/coronography: disks and planets

  29. Search for wide planets • Ongoing for ~15 years • A high contrast challenge (106 - 109) • A few BD companions HST/AO/coronography: disks and planets

  30. What can we do now? • Search around nearby young stars • Forming planets are brighter! young old Burrows et al. HST/AO/coronography: disks and planets

  31. AB Pic A AB Pic B AB Pic • 30 Myr-old star (Tuc-Hor association) • Companion 260AU away • 10-20 MJup BACH98 (M dwarfs) K ~ 8 mag Sep. ~ 5’’ DUSTY (L dwarfs) COND (T dwarfs) Chauvin et al. (2005) HST/AO/coronography: disks and planets

  32. AB Pic • 30 Myr-old star (Tuc-Hor association) • Companion 260AU away • 10-20 MJup K ~ 8 mag Sep. ~ 5’’ Teff ~ 1700 K Chauvin et al. (2005) HST/AO/coronography: disks and planets

  33. 2MASSWJ 1207334-39325 • 5-10 Myr-old 24 MJup primary (53pc) • Teff ~ 1600K, 8 MJup companion Chauvin et al. (2004) HST/AO/coronography: disks and planets

  34. GQ Lup • An example of technical improvements! ESO/Come-On+ 1994 Neuhauser et al. (2005) Janson et al. (2007) HST/AO/coronography: disks and planets

  35. GQ Lup • An example of technical improvements! • ~5 Myr-old 25 MJup ESO/Come-On+ 1994 Neuhauser et al. (2007) Neuhauser et al. (2005) Janson et al. (2007) HST/AO/coronography: disks and planets

  36. What are these objects? • Too far from their parent star to form in a disk through core accretion • Are they really planets? • Similar to “free-floating” VLM objects in  Ori, for instance • Come very low-mass prestellar cores • No very low-mass objects found HST/AO/coronography: disks and planets

  37. What next? • Need even higher contrast at shorter separations • Dedicated instruments (future AO) Simulated 99.9999% Strehl Image in H Band 8 m Telescope Simulated 95% Strehl in H band 8m telescope HST/AO/coronography: disks and planets

  38. What next? • Not just images: need spectroscopy!! Lenslet array Image slicing VLT/SINFONI Keck/OSIRIS HST/AO/coronography: disks and planets

  39. Stars Brown Dwarfs Planets M2 (Mjup) Physical separation (AU) Wait for a few years!! 5 Gyr 1 Gyr 0.5 Gyr HST/AO/coronography: disks and planets

  40. Circumstellar disks : Scientific results HST/AO/coronography: disks and planets

  41. Coronography: a family picture HR 4796 AB Aur  Pic Schneider et al. (1999) Kalas et al. (2000) Clampin et al. (2003) Fukagawa et al. (2004) Fomalhaut HD 100546 AU Mic Fitzgerald et al. (2007) Kalas et al. (2006) Grady et al. (2001) HST/AO/coronography: disks and planets

  42. HST/AO: a family picture Perrin et al. (2006) • ‘Natural’ coronograph • Edge-on disks PDS 144 Burrows et al. (1996) IM Lup HK Tau HV Tau GG Tau Stapelfeldt et al. (2003) Courtesy: C. Pinte Courtesy: C. McCabe Krist et al. (2005) HST/AO/coronography: disks and planets

  43. What type of observations? VLT/VISIR 11.3 m S. Wolf’s courses R. Akeson’s course L. Testi’s courses Spitzer 10 m Interferometry Courtesy: C. Pinte HST/AO/coronography: disks and planets

  44. Interpreting disk images • Images are very important but need to be quantitatively analyzed • Obtaining an image is a not a goal in itself • This usually requires exact radiative transfer modeling • If possible in conjunction with SED… • See S. Wolf’s lectures HST/AO/coronography: disks and planets

  45. Basic parameters • Disk radii: 10s to 1000s of AU • Disk height: H/R ~ 0.1 • Masses cannot be easily determined • Young disks are optically thick… • Radio regime! • L Testi’s courses IRAS 04158+2805 ~ 1100 AU HV Tau ~ 40 AU Stapelfeldt et al. (2003) Glauser et al. (2007) HST/AO/coronography: disks and planets

  46. Structural information Perrin et al. (2006) PDS 144 • Flared geometry • Hydrostatic equilibrium • Truncation in binaries? • Presence of spiral arms • Companions? Instability? HV Tau AB Aur Stapelfeldt et al. (2003) Fukagawa et al. (2004) HST/AO/coronography: disks and planets

  47. Structural information • A word of caution about asymmetries: • What you see is not what you have! • Asymmetries are real, but may not be in density (optically thick?) HD 100546 AB Aur Optically thin! Piétu et al. (2005) Grady et al. (2001) Fukagawa et al. (2004) HST/AO/coronography: disks and planets

  48. Dust information • We receive scattered stellar photons • Scattering depends on /2a • ‘Phase function’ varies: • Large grains scatter forward • Small grains scatter isotropicaly • Scattering off small grains polarize more than large grains • Scattering also depends on geometry HST/AO/coronography: disks and planets

  49. Dust information • An exemple: the GG Tau ring • A case where  < 2a (‘large’ grains) Silber et al. (2000) HST/AO/coronography: disks and planets

  50. Dust information • Basic strategy: image same disk over a wide range of wavelengths • Each image probes a different grain size • Dust opacity decreases at longer wavelengths (reddening) • Longer wavelength images probe deeper layers of the disk! HST/AO/coronography: disks and planets

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