Can small beat the big?

1. Can small beat the big? A. N. Ramaprakash On behalf of Robo-AO collaboration partners (IUCAA and Caltech)

2. Can small beat the big? • Transition decade for astronomy • Can small beat the big? A. N. Ramaprakash, IUCAA

3. Downtime • On-Sky Efficiency • Fraction of the available time which the telescope spends in collecting useful astronomical and calibration data • Factors • Transmission • Weather • Technical downtime • Scheduled Maintenance • Commissioning • Large observatories are expensive to operate • Keck Telescopes – 175 USD per minute • VLTs – 125 Euros per minute • Minimize the above factors • Currently about 70% - 80% efficiency is typical • Often not clear what exactly this means A. N. Ramaprakash, IUCAA

4. Overheads, Mitigation • Overheads • Identification and Acquisition of target and guide star • Instrument and telescope set up time • Readout, pre-processing & quick look • Calibration observations • Mitigation • Ease of acquisition • Ease of use • Stable systems • Observatory calibrations • Pipelines A. N. Ramaprakash, IUCAA

5. Mitigation • Multiplexing • Wide field, Mosaics • Multi-band, MOS, IFU • Telescopes • Observing Modes • Automation and Queue Schedules • Service Observing • Adaptive queue schedules • Remote observing A. N. Ramaprakash, IUCAA

6. Adaptive Optics • Merits • Sensitivity (S) - inverse of the time needed to reach a desired SNR • For faint point sources observed under background limited conditions where D is the telescope diameter • Enhanced angular resolution •   1/D A. N. Ramaprakash, IUCAA

7. How good is your adaptive optics? • Diffraction Limited Performance • Measured FWHM of PSF = FWHM of Airy disk (1.03 /D) • different from Rayleigh criterion for resolving power • Strehl Ratio (S) – ratio of the peak intensity of the measured PSF to the theoretical maximum (< 1 by definition) • FWHM can reach diffraction limit even when Strehl is very small • How good depends on what you want to do: • High resolution - Strehl of 10-15% is often enough; Also for slit spectroscopy • Detect faint objects - Strehl of 40% may not be enough as the central core might contain only a fraction of the total light • Point Source Sensitivity (PSS) Most of the light within w=/2d; d=spacing of actuators S is only 0.23 Normalized A. N. Ramaprakash, IUCAA

8. Simple AO approach - Limitations • Guide star availability • 0 = 0.31 r0 / <V> • Closed loop at 100Hz to 1KHz • Need a R=12-15 star typically • Small isoplanatic angle • θ0 = 0.31 r0/ <h> • 5" -30" for 1rad2 mean square wavefront error [StrehlRatio~exp(-2) ~30%] A. N. Ramaprakash, IUCAA

9. AO guide star faintness limit • Theoretical faint limits • Rlim=17 for Strehl Ratio~30% at K (2.2um) • Rlim=13.1 for Strehl Ratio~30% at R (0.6um) • r0  λ6/5 • r0 at 2μm is 5.9 times what it is at 0.5μm • D(r)=6.88(r/r0)5/3 • Larger phase error at shorter wavelengths demands more photons for correction • Also needs more number of correction subsections (~D/r0)2 For a given desired Strehl Ratio, r0 and λ define the faintest star that can be used for AO, irrespective of the telescope size. A. N. Ramaprakash, IUCAA

10. Laser Guide Stars • R~17 for tip-tilt NGS in LGS systems • Isokinetic angle larger than isoplanatic angle • About 87% of the power is in the lowest two modes, tip and tilt A. N. Ramaprakash, IUCAA

11. Adaptive Optics - Limitations • Expensive • Only large telescopes can afford good AO systems • Setting up overheads • Large telescopes use AO only sparingly A. N. Ramaprakash, IUCAA

12. Laser Guide Stars - Limitations • Cone effect • Light paths from the distant star and the laser guide star are different • Dmax~2.91θ0<H> • ~8m for sodium LGS • ~3m for Rayleigh LGS • Natural guide stars for tip-tilt compensation ROBO-AO A. N. Ramaprakash, IUCAA

13. Adaptive optics for small and medium telescopes ROBO-AO A. N. Ramaprakash, IUCAA

14. Acknowledgements Partially funded by the National Science Foundation. http://www.astro.caltech.edu/Robo-AO/ A. N. Ramaprakash, IUCAA

15. Why Robo-AO • Robotic • high observing efficiency • Adaptive Optics • spatial resolution set by D • sensitivity set by D4 • Laser Guide Star • high sky coverage • Small Telescopes • availability • Rayleigh • economical Unique Science Capabilities A. N. Ramaprakash, IUCAA

16. Robo-AO testbed A. N. Ramaprakash, IUCAA

17. Wavefront correctors • Shack-Hartmann WFS • 11 x 11 • UVCCD39, <5e- noise at <2kHz • Micro-Electro-Mechanical Systems (MEMS) deformable mirror • 12 x 12 actuators • 3.5 μm stroke • PI fast steering mirror • USB electronics on Linux • Loop Rate > 1.2kHZ A. N. Ramaprakash, IUCAA

18. Science Cameras • Andor EMCCD • 1k2, 45”x45” FoV, Visible • Fast ROI, Nyquistλ=620 • InGaAs • 320x240, noisy, to 1.7um • H2RG detector • 2k2, 2’x2’FoV, 900nm-2.2um • Fast ROI, Nyquistλ=830nm A. N. Ramaprakash, IUCAA

19. Robotic Control Software • Fully robotic control system • Subsystems work as daemons • Supervisor controls scheduling, operations • Watchdog processes • Programming intelligence is a challenge • Robots are only as smart as the people that make them! • Error control and exception handling • Safety system for equipment and staff • Laser safety a priority A. N. Ramaprakash, IUCAA

20. Robo-AO Cassegrain instrument model A. N. Ramaprakash, IUCAA

21. UV laser at Palomar 60 inch telescope A. N. Ramaprakash, IUCAA

22. Robo-AO on the P60 telescope Robotic Software Robotic Telescope (P60) Adaptive Optics system + Science Instruments Laser box A. N. Ramaprakash, IUCAA

23. Robo-AO wavefront sensors • Shack-Hartmann • 11 x 11 subapertures • High sensitivity to UV • High-speed optical switch • Image motion (tip/tilt) • From science instruments A. N. Ramaprakash, IUCAA

24. On-sky wavefront sensor data A. N. Ramaprakash, IUCAA

25. Robo-AO in action A. N. Ramaprakash, IUCAA

26. AO Imaging Capabilities – Robo-AO on P60 • Diffraction-limited resolution (mV<17) • ~0.1-0.15” in the visible • ~0.2-0.25” in the near-infrared • 0.5+ Strehl in the near-infrared (30% sky) • Seeing improvement (100% sky) • ~45” to 2’ field of view • General imaging • range of filters, exposure times, observation setups A. N. Ramaprakash, IUCAA

27. Power of Robo-AO A. N. Ramaprakash, IUCAA

28. Signal to Noise Ratio Improvements • Astrometric precision gains in both SNR and FWHM • Prediction: 100μas precision in around 15 minutes • (based on Cameron et al. Keck & Palomar performance) A. N. Ramaprakash, IUCAA

29. Science programs • (Sub)stellar, asteroid companion surveys • Astrometric planet searches • Rapid transient characterization • Efficient discrimination of blended binary false-positive candidates • 1000’s of new lensed quasars • Follow ups • Higher angular resolution • Deeper Images • Spectra • Different bands, periods or cadence • The list goes on and on… A. N. Ramaprakash, IUCAA

30. Robo-AO enables new science • Large single-image surveys • Several thousand targets, all at high-angular resolution • Otherwise extremely time intensive on currently available LGS AO systems • E.g. stellar binarity surveys, searches for lensed quasars, planetary transit follow up • Rapid transient characterization • Diffraction limited images within minutes of detection of transients • Reduction of integration time for infrared photometry • E.g. separation of transient events from host galaxy • Time-domain astronomy • Queue supports recurrent, regularly spaced observations of specific targets • E.g. long-term, high-precision astrometric characterization of sub-stellar companions A. N. Ramaprakash, IUCAA

31. Robo-AO vision ROBO-AO ROBO-AO ROBO-AO ROBO-AO ROBO-AO ROBO-AO ROBO-AO A. N. Ramaprakash, IUCAA

32. Robo-AO vision Deploy and demonstrate a robotic laser adaptive optics and visible/IR science system on a 1.5m telescope Emphasis on robustness Make it affordable Replicate and deploy to the world’s 1-3 m class telescopes A. N. Ramaprakash, IUCAA

33. Robo-AO Movies A. N. Ramaprakash, IUCAA

34. Thank You A. N. Ramaprakash, IUCAA

35. Robo-AO error budget A. N. Ramaprakash, IUCAA