can small beat the big?

IUCAA

Can small beat the big?

A. N. RamaprakashOn behalf of Robo-AO collaboration partners (IUCAA and Caltech)

BELI

SSIM

A M

eetin

g, B

elgr

ade

Can small beat the big? Transition decade for astronomy

Can small beat the big?

18/09/2012 A. N. Ramaprakash, IUCAA 2

BELI

SSIM

A M

eetin

g, B

elgr

ade

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


BELI

SSIM

A M

eetin

g, B

elgr

ade

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


BELI

SSIM

A M

eetin

g, B

elgr

ade

Mitigation Multiplexing

Wide field, Mosaics Multi-band, MOS, IFU Telescopes

Observing Modes Automation and Queue Schedules Service Observing Adaptive queue schedules Remote observing


BELI

SSIM

A M

eetin

g, B

elgr

ade

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


422

22

)/(D

SNRDFDFStrehlS

bg

star

BELI

SSIM

A M

eetin

g, B

elgr

ade

Most of the light within w=/2d;d=spacing of actuators

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)


S is only 0.23Normalized

BELI

SSIM

A M

eetin

g, B

elgr

ade

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 [Strehl Ratio~exp(-2) ~30%]


BELI

SSIM

A M

eetin

g, B

elgr

ade

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 0.5 μm

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

AO guide star faintness limit


For a given desired Strehl Ratio, r0 and λ definethe faintest star that can be used for AO, irrespective of the telescope size.

BELI

SSIM

A M

eetin

g, B

elgr

ade

Laser Guide Stars

18/09/2012 A. N. Ramaprakash, IUCAA

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 10

BELI

SSIM

A M

eetin

g, B

elgr

ade

Adaptive Optics - Limitations Expensive

Only large telescopes can afford good AO systems

Setting up overheads Large telescopes use AO only

sparingly


BELI

SSIM

A M

eetin

g, B

elgr

ade

Laser Guide Stars - Limitations Cone effect

Light paths from the distant star and the laser guide star are different

Dmax~2.91 θ0 <H> ~8m for sodium

LGS ~3m for Rayleigh

LGS Natural guide stars

for tip-tilt compensation


ROBO-AO

BELI

SSIM

A M

eetin

g, B

elgr

ade

ROBO-AOAdaptive optics for small and medium telescopes


BELI

SSIM

A M

eetin

g, B

elgr

ade

Acknowledgements

Partially funded by the National Science Foundation.

http://www.astro.caltech.edu/Robo-AO/18/09/2012 14A. N. Ramaprakash, IUCAA

BELI

SSIM

A M

eetin

g, B

elgr

ade

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

BELI

SSIM

A M

eetin

g, B

elgr

ade

Robo-AO testbed


BELI

SSIM

A M

eetin

g, B

elgr

ade

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 > 1.2kHZ18/09/2012 A. N. Ramaprakash, IUCAA 17

BELI

SSIM

A M

eetin

g, B

elgr

ade

Science Cameras Andor EMCCD

1k2, 45”x45” FoV, Visible Fast ROI, Nyquist λ=620

InGaAs 320x240, noisy, to

1.7um H2RG detector

2k2, 2’x2’ FoV, 900nm-2.2um

Fast ROI, Nyquist λ=830nm


BELI

SSIM

A M

eetin

g, B

elgr

ade

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


BELI

SSIM

A M

eetin

g, B

elgr

ade

Robo-AO Cassegrain instrument model


BELI

SSIM

A M

eetin

g, B

elgr

ade

UV laser at Palomar 60 inch telescope


BELI

SSIM

A M

eetin

g, B

elgr

ade

Robo-AO on the P60 telescope


Robotic Software

Adaptive Optics system +Science Instruments

RoboticTelescope(P60)

Laser box

BELI

SSIM

A M

eetin

g, B

elgr

ade

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


BELI

SSIM

A M

eetin

g, B

elgr

ade

On-sky wavefront sensor data


BELI

SSIM

A M

eetin

g, B

elgr

ade

Robo-AO in action


BELI

SSIM

A M

eetin

g, B

elgr

ade

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


BELI

SSIM

A M

eetin

g, B

elgr

ade

Power of Robo-AO


Traditional Laser Guide Star

Adaptive Optics

Robo-AORobotic Laser Guide Star AO

Telescope diameter 3-10m 1.5-3m

Lock-on time 5-15 mins / target 0.5-1 minutesTargets per

night Tens Hundreds

Program Length Few nights Weeks+

Targets per program ~100 Thousands

Personnel1 astronomer +

6 spotters + 2 telescope

control

1 astronomer (peacefully sleeping)

BELI

SSIM

A M

eetin

g, B

elgr

ade

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)

Band SNR Compared to

1.5 m

SNR Compared to 4 m

FWHM (1” is typical)

Strehl

J 2.9X 0.4X 0.2” 50%

H 7.1X 0.98X 0.26” 70%

BELI

SSIM

A M

eetin

g, B

elgr

ade

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…18/09/2012 A. N. Ramaprakash, IUCAA 29

BELI

SSIM

A M

eetin

g, B

elgr

ade

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


BELI

SSIM

A M

eetin

g, B

elgr

ade

Robo-AO vision


ROBO-AOROBO-AO

ROBO-AOROBO-AO

ROBO-AO

ROBO-AO

ROBO-AO

BELI

SSIM

A M

eetin

g, B

elgr

ade

Robo-AO vision

18/09/2012 A. N. Ramaprakash, IUCAA32

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

BELI

SSIM

A M

eetin

g, B

elgr

ade

Robo-AO Movies


BELI

SSIM

A M

eetin

g, B

elgr

ade


THANK YOU

BELI

SSIM

A M

eetin

g, B

elgr

ade

Robo-AO error budget


can small beat the big?

Documents

caltechiucaabelissima

normalizedbelissima

iucaa4belissima meeting

iucaa5belissima meeting

iucaa3belissima meeting

iucaa2 belissima meeting

iucaa6 belissima meeting

telescope control system