Hubble Space Telescope Coronagraphs John Krist Space Telescope Science Institute

Hubble Space Telescope Coronagraphs John Krist Space Telescope Science Institute

Hubble Space Telescope Coronagraphs John Krist Space Telescope Science Institute

Ayers, Steve, Local News Reporter has reference to this Academic Journal, PHwiki organized this Journal Hubble Space Telescope Coronagraphs John Krist Space Telescope Science Institute Why Use HST High resolution with wide field of view anywhere in the sky Wavelength coverage from l = 0.2 – 2.2 mm Its stability allows significant PSF subtraction High Contrast Imaging Techniques Used on HST Direct observation with PSF subtraction Coronagraphic observation with PSF subtraction Spatial filtering Spectral+spatial filtering

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Choice of Cameras as long as High Contrast Imaging Direct imagers: WFPC2: 160” x 160”, l = 0.2-1.0 mm STIS: 52” x 52”, l = 0.2-1.0 mm ACS Wide Field Camera: 200” x 200”, l = 0.4-1.0 mm ACS High Res Camera: 26” x 29”, l = 0.2-1.0 mm NICMOS: 11” x 11” to 51” x 51”, l = 0.9–2.2 mm Coronagraphs: ACS High Res Camera STIS NICMOS Camera 2: 19” x 19” Components of the HST PSF Diffraction from obscurations Rings, spikes Scatter from optical surface errors Stray light & ghosts Diffraction from occulter (coronagraph) Electronic & detector artifacts CCD red scatter, detector blooming Diffraction from Obscurations V b in addition to (no aberrations) Model PSF HST Entrance Pupil

Scatter from Optical Surface Errors V b in addition to (ACS/HRC) Observed 18 nm RMS wavefront error Krist & Burrows (1995) Midfrequency Error Map Phase retrieval derived PSF ACS Surface Brightness Plots Observed PSF Model PSF No surface errors ACS V b in addition to (F606W) Electronic & Detector Artifacts WFPC2 NICMOS No Halo (model) Observed (I b in addition to ) Electronic b in addition to ing CCD Red Halo ACS/HRC shown. Also in STIS in addition to WFPC2 F1042M

Stray Light & Ghosts NICMOS (direct) F110W “Grot” PSF Subtraction Stability of HST allows diffracted in addition to scattered light to be subtracted Beta Pictoris Alpha Pic Beta – Alpha Pic ACS coronagraph ACS Science Team (work in progress) WFPC2 WFPC2 Science Team (Unpublished) Reference PSF Subtraction Roll Subtraction Sources of PSF Mismatches Focus changes caused by thermal variations “Breathing” = 3-5 mm primary-secondary separation change within an orbit = 1/18-1/30 wave RMS change Attitude changes (0 – 1/9 wave change) Internal changes in camera Color differences Field position variations (WFPC2) Star-to-occulter alignment (coronagraphs) Lyot stop shifting (NICMOS) Jitter

Direct Observation with PSF Subtraction Primarily used as long as WFPC2, but also ACS in addition to NICMOS on occasion PSF is subtracted using an image of another star (or roll self-subtraction) Deep exposures saturate the detector, but bleeding is confined to columns ( as long as CCDs) or just the saturated pixels (NICMOS) Direct Observations – WFPC2 GG Tauri Circumbinary Disk Science results in Krist, Stapelfeldt, & Watson (2002) V b in addition to I b in addition to – PSFs Unsubtracted Log stretch Disk around binary T Tauri system Inner region cleared by tidal as long as ces Integrated ring flux = 1% of stellar flux @ I b in addition to Direct Observations – ACS/HRC HD 141569 – PSF Reference PSF HD 141569 7” ACS Science Team observations (unpublished) Disk around a Herbig Be star at d = 99 pc Disk flux = ~0.02% of stellar flux

Using a Coronagraph Suppresses the perfect diffraction structure Does not suppress scatter from surface errors prior to occulter Reduces sensitivity to PSF mismatches caused by focus changes & color differences Occulting spot prevents detector saturation, ghosts, in addition to scattering by subsequent surfaces Deeper exposures possible NICMOS Coronagraph 0.076” pixels, l = 0.9 – 2.2 mm Spot in addition to Lyot stop always in-place Occulting spot is r = 0.3” hole drilled in mirror Contains 2nd dark Airy ring at l=1.6 mm (spot diameter = 4.3l/D, 83% of light) Rough edge scatters some light (“glint”) Useful inner radius ~0.5” Spot in corner of field 0.6” NICMOS Coronagraph Pupil Models Pupil after spot With an Aligned Lyot Stop

Effects of NICMOS Lyot Stop Misalignment Aligned Lyot Stop Model Misaligned Lyot Stop Model Observed F110W (~J b in addition to ) Misalignment results in 2x more light in the wings + spikes NICMOS PSF Mean Brightness Profiles (F110W) Normal PSF Coronagraph Coronagraph – PSF (Roll subtraction) NICMOS Image of HD 141569 F110W (~J b in addition to ) Science results in Weinberger et al. (1999) HD 141569 Reference Star Image1 – PSF1 Image1 – PSF2 Image2 – PSF1 Image2 – PSF2

NICMOS Coronagraph Advantages Only HST camera to cover near-IR Small spot allows imaging fairly close to star Lower background compared to ground-based telescopes NICMOS Coronagraph Problems Poorly matched spot/Lyot stop sizes result in low diffracted light suppression Small spot results in sensitivity to offsets & focus changes Lyot stop position “wiggles” over time Numerous electronic artifacts in addition to blocked pixels (“grot”) STIS Coronagraph Primarily a spectrograph CCD, 0.05” pixels, PSF FWHM = 50 mas, 52” x 52” field Unfiltered imaging: l = 0.2 – 1.0 mm Occulters are crossed wedges: r = 0.5”-2.8” (21l/D – 110l/D @ V) Lyot stop always in the beam “Incomplete” Lyot stop

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STIS Occulters STIS Coronagraph Pupil Models After Occulter, Be as long as e Lyot Stop After Lyot Stop STIS PSF Mean Brightness Profiles Direct Coronagraph Coronagraph – PSF (Roll subtraction) Wings high due to red halo, UV scatter

STIS Image of HD 141569 HD 141569 Reference Star HD 141569 – Reference Star 7” Science results in Mouillet et al. (2001) STIS Coronagraph Advantages Smallest wedge widths allow imaging to within ~0.5” of central source Occulter largely eliminates CCD red halo in addition to ghosts seen in direct STIS images STIS Coronagraph Problems Incomplete Lyot stop results in low diffracted light supression Unfiltered imaging Wedge position not constant

CODEX Azimuthal profile plot The Future of HST High Contrast Imaging WFC3(): UV-Vis & near-IR cameras No coronagraphs or occulters WFPC2: Cumulative radiation damage taking its toll (WFPC2 would be replaced by WFC3) STIS & ACS: Can continue as long as years NICMOS: Can continue, but may need to be turned off if power system (battery) begins to deteriorate Gyroscope failure: Would result in increased jitter (3 mas now, perhaps up to 30 mas on 2 gyros) NICMOS & small-diameter STIS coronagraphic observations probably discontinued ACS coronagraph might possibly continue, but depends on jitter repeatability

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