Robo-AO Overview:System, capabilities, performance
Christoph Baranec (PI)
Why Robo-AO?
Robotic – high efficiency observing
Laser Guide Star – high sky coverage
Adaptive Optics – spatial resolution set by D
Small Telescopes – lots of available time
Robo-AO at the P60
Robotic
Reed Riddle (software lead) to fill in details
following this presentation…
Laser guide star
• Rayleigh LGS (e.g. Starfire, Mt. Wilson, MMT, WHT, SOAR, LBT?)
– Range gated – 650 m at 10 km – mV~9
– On/off operation
– More robust operation in presence of clouds/haze
• Waived by FAA – no human spotters required
• Interface with USSTRATCOM– Send them target list 3-4 days prior to lasing
– Will receive list of ‘open windows’ for each target
AO system
• High order wavefront will be measured by laser and corrected by deformable mirror
• Stellar image motion captured by one of the science cameras and used to drive tip/tilt corrector
• Single atmospheric dispersion corrector for both science instruments (not UV)
Visible science instrument
• Andor iXonEM+ DU-888
• Electron Multiplying CCD
• 1024 x 1024 pixels
• 44” x 44” square FoV• 0.043” pixels (Nyquist at λ = 620 nm)
• Full frame rate: 9 Hz
• Sub frame rate: ~200 Hz
Baseline NIR camera: InGaAs
• InGaAs – (Xenics: Xeva)– Delivery in 8 weeks from order– 0.9-1.7 μm sensitivity– 180 e- read noise– 7000 e-/s dark current– ~200k e- full well– 320 x 256 pixels (0.062”/pixel Nyquist λ = 900 nm)– ~20 x 16 arc sec field
Xeva-1.7-320
Ideal (future?) NIR camera
• HgCdTe – (Teledyne: H2RG)+ 2’ FoV, 0.062” pixels (Nyquist at λ = 900 nm)
+ Excellent noise
+ Flexible readout – integrating while T/T guiding
- Cost – no $$ yet…- Development time
Likely initial observing modes
• Infrared Science:– Tip/tilt sensing with visible, integrate on IR
camera
• Visible Science:– Fast readout of visible camera - Lucky
imaging/post facto shift and add
• H2RG will give additional capability
AO capabilities – quick answer
• ~Diffraction-limited resolution visible
• 0.5+ Strehl in the NIR
• General imaging
Range of: filters, exposure times, camera setup
Error budget
Assuming mV=17 T/T star
Performance – H-Strehl
• mV < 15 dominated seeing, HO errors. mV > 19 dominated T/T errors• Greater than 40% Strehl with mV = 19 T/T in median conditions
• FWHM at H < 0.26” in even 75% worst seeing conditions
*At Zenith