Observing Venus (and Mars) with Adaptive Optics Jeremy Bailey (UNSW)
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Transcript of Observing Venus (and Mars) with Adaptive Optics Jeremy Bailey (UNSW)
Observing Venus (and Mars) with Adaptive Optics
Jeremy Bailey (UNSW)
Adaptive Optics• Many large ground-based telescopes are equipped with adaptive optics.
• These allow diffraction limited imaging at near-IR wavelengths.
• At 2 m diffraction limit of a telescope is:
• But currently we are limited by seeing to resolutiond of 0.5–1.0 arcsec (100-200 km).
B
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Aperture Arc sec Km at Venus/Mars
4 m 0.13 32
8 m 0.07 16
32 m 0.016 4
Extremely Large Telescopes
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• Even larger telescopes – known as Extremely Large telescopes (or ELTs) are now being designed.
Thirty Metre Telescope (TMT)Thirty Metre Telescope (TMT)
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Adaptive Optics images
Jupiter with Gemini Telescope and adaptive Jupiter with Gemini Telescope and adaptive optics — image processed by Chris Go.optics — image processed by Chris Go.
Titan with ESO VLTTitan with ESO VLT
Uranus and its rings with Keck telescopeUranus and its rings with Keck telescope
Titan
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NIFS ImagesNIFS Images
Gemini AO ImagesGemini AO Images
Current AO Systems• Require a guide “star” close to
the science object.• With a planet like Mars or
Venus …– Too big to be used as a guide
star itself.– Too bright to allow a nearby star
to be used as a guide star (scattered light).
– e.g. Attempts to use Phobos (mag 10.4) as a guide star for Mars (mag -2.8) have not been successful.
– Laser guide stars don’t help.
VEX VIRTIS-MVEX VIRTIS-M
AAT IRIS2AAT IRIS2
R ~ 200R ~ 200
R ~ 2400R ~ 2400
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Resolution at Mars/VenusResolution at Mars/Venus(Near-IR Imaging Spectrometers)(Near-IR Imaging Spectrometers)
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Resolution at Mars/Venus Resolution at Mars/Venus (Near-IR Imaging Spectrometers)(Near-IR Imaging Spectrometers)
Limb viewing
The resolution of The resolution of GMTIFS at Mars and GMTIFS at Mars and Venus (~3-4km) is Venus (~3-4km) is sufficient to vertically sufficient to vertically resolve the atmosphere in resolve the atmosphere in limb viewing geometry.limb viewing geometry.
Spacecraft can do this, but Spacecraft can do this, but it has never before been it has never before been possible with ground-possible with ground-based telescopes.based telescopes.
Current Performance - UKIRT90km resolution
MGS MOLA data
8m Telescope - DiffractionLimited at 2m - 16km resolution
ELT4km resolution
Solution
• We need an AO wavefront sensor that can work on the extended structure of the image of Mars or Venus (rather than a point source).– For Venus use the 2.3 m cloud structure or 1.27 m
airglow (or perhaps the sunlit crescent in the visible).
– For Mars use the surface albedo features.
• We know this is possible because solar AO systems work on extended structure (e.g. solar granulation).
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Shack-Hartmann Wavefront Sensor
Correlating Shack-Hartmann
Used in solar adaptive Used in solar adaptive optics systems.optics systems.
Measures image shifts Measures image shifts by correlating structure by correlating structure in individual pupil in individual pupil images. images.
Intel processors contain Intel processors contain specific support for rapid specific support for rapid measurements of image measurements of image shifts in their SSE shifts in their SSE instruction sets (as it is instruction sets (as it is important for video important for video compression algorithms)compression algorithms)
Solar AO Example
Data taken with “low cost” Data taken with “low cost” AO system for McMath AO system for McMath Pierce solar telescope.Pierce solar telescope.
Hardware cost US$25,000Hardware cost US$25,000
Keller et al., 2003, SPIE Proc. 4853, Keller et al., 2003, SPIE Proc. 4853, 351.351.
Options• Build a new instrument designed for planetary
AO.
• Retrofit “correlating” capability to an existing AO system.
• Use a solar telescope (that already has this capability) to observe Venus.
• Shoud work very well – these planets are bright sources and should be capable of provding good (high Strehl) AO correction.
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