Robo-AO and Kepler

Robotic Laser Adaptive Optics Imaging of 715 Kepler Exoplanet Candidates using Robo-AO

Nicholas M. Law, Tim Morton, Christoph Baranec, Reed Riddle, Ganesh Ravichandran, Carl Ziegler, John Asher Johnson, Shriharsh P. Tendulkar, Khanh Bui, Mahesh P. Burse, H. K. Das, Richard G. Dekany, Shrinivas Kulkarni, Sujit Punnadi, and A. N. Ramaprakash

The Astrophysical Journal, 791:35 (18pp), 2014 August 10


High-Efficiency Autonomous Laser Adaptive Optics

Christoph Baranec, Reed Riddle, Nicholas M. Law, A. N. Ramaprakash, Shriharsh Tendulkar, Kristina Hogstrom, Khanh Bui, Mahesh Burse, Pravin Chordia, Hillol Das, Richard Dekany, Shrinivas Kulkarni, and Sujit Punnadi

The Astrophysical Journal Letters, 790:L8 (6pp), 2014 July 20



  • Autonomous laser adaptive optics imaging system
  • Palomar Observatory 60-inch telescope (1.5 m)
  • 200 objects per night

Sloan-like Filters

Detector / AO

44" x 44" fov

0.04" pixels

8.6 fps readout

1.2 kHz control loop

90-100 Hz wavefront control

141-218 nm wavefront error

AO Performance

Before correction


Corrected: 0.12"

Adaptive Optics

Low Overhead

  • 40 s to slew/point
  • 40-42 s for laser acquisition
  • 30-180 s on target
  • Queue-based observing
  • Optimizes schedule based on:

Compare to 5-35 min

  • priority
  • slew time
  • telescope limits
  • prior observing attempts
  • satellite avoidance

200 targets / night


  1. Target selected from queue
  2. Slew, point, acquire target (80 s)
  3. Continuous readout for 30-180 s
  4. Calibrate, then shift each frame based on guide star
  5. Co-add shifted frames

8.6 frames / second

Single, nearly diffraction-limited image

Faint Companions

PSF subtraction of each object to find blended neighbors.

Can detect 1/100 contrast at separations above 0.2".

Stretch to Peak

Stretch to 10%

Subtract PSF

Faint Companions

Airy Disk

What's it useful for?

Doesn't go as faint as Keck

but can target a lot of objects

and is cheap.

Kepler follow-up

Bright targets

and lots of them.


  • > 3500 candidates ("KOIs")

  • < 3% confirmed

  • 10%-15% may be false positives, e.g., blended transiting binaries

Properties of Systems

  • Planet radius, mass, temperature
  • Statistics of planetary systems
  • Planetary systems in binaries different?


AO imaging key

Follow-Up Sample

Robo-AO will eventually target every KOI

Begin with representative sample

Should be constant

Detect Companions

PSF model obtained from 20 KOIs observed under similar conditions on same night.


Only photon noise should remain.

Detection Efficiency

Gold standard: Try to extract simulated companions for every source

Next best: Try to extract simulated companions for representative sample

Three classes of targets, based on PSF quality


53 companions (43 new)

Multiple Systems

Detection Efficiency

High-quality targets

Earlier simulated sensitivity

Transit Dilution

Which star was transited? How deep was the transit for that star?

Transit depth and planet radius:

If planet transits target star,

If planet transits companion star,

Fraction of light from transited star

Determine from magnitude difference

B is in background

Interesting Systems


  • Four planet candidates
  • Jupiter-like candidate with 15.4-day period 
  • Unique in multi-planet systems


  • Five planet candidates
  • Two in 2:1 resonance, separated by third planet
  • Troublesome configuration

Coincident Mulitples

KOI-268: Habitable zone?

  • 1.7 Earth-radii, 110-day orbit, 295 K equilibrium
  • Possibly a triple stellar system
  • Only "habitable" if orbiting largest star

KOI-1845: Likely false positive

  • Two candidates
  • 2nd is 21 Earth radii, with V-shaped transit
  • Faint stellar companion at large separation
  • Likely a background eclipsing binary, not a planet

Statistics of Binaries

Are binary systems different?

Binarity vs. Temperature

Not significant.

Binarity vs. # of Candidates

Might indicate more false positives among single-candidate systems.

Binarity vs. Candidate Period



Short-period giant planets 2-3x more likely to reside in binary systems (98% confidence)

Kozai oscillations?


Kepler Binaries

Interesting Systems

Binary Statistics

Robo-AO and Kepler

By Gregory Green

Robo-AO and Kepler

Journal Club presentation on Robo-AO follow-up of Kepler exoplanet candidates. Reviews Law et al. (2014), doi:10.1088/0004-637X/791/1/35.

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