Transcript Observing with Ground-Layer Adaptive Optics Christoph Baranec (Caltech) M. Hart (PI; UA), M.

Observing with
Ground-Layer Adaptive Optics
Christoph Baranec (Caltech)
M. Hart (PI; UA), M. Milton (UA), T. Stalcup (W. M. Keck Obs.),
K. Powell (UA), M. Snyder (Dept. Army),
V. Vaitheeswaran (UA), D. McCarthy (UA) & C. Kulesa (UA).
Photo credit: T. Stalcup
Observing with Ground-layer Adaptive Optics
What is Ground-layer Adaptive Optics (GLAO)?
Benefits of GLAO to astronomy.
Description of MMT multiple-laser AO system.
Review of recent GLAO results.
Landscape of GLAO systems around the world.
Traditional single guide star adaptive optics
Natural Guide Star
Natural Star
Science Object
Laser Spot
Telescope
Pupils
Telescope
Credit: T. Stalcup, 2006
Single natural guide star (NGS) AO –
Single laser guide star (LGS) AO –
Unless using science target as guide
source (mV<13), suffer from angular
anisoplanatism. Non-uniform correction
over a field.
Suffer from focal anisoplanatism in
science direction with fall off of
correction with increasing field.
Multiple guide star adaptive optics
Natural Star
Laser Spots
Turbulence
Telescope
Credit: T. Stalcup, 2006
With multiple guide stars (NGS and/or LGS) can obtain three-dimensional
estimate of atmospheric turbulence above telescope. Can then implement
many types of correction: multi-conjugate, tomographic, multi-object, groundlayer, producing differing levels of correction over different fields at cost.
Ground-layer adaptive optics (GLAO)
•First detailed by F. Rigaut (Proc. ESO; 2002) as a way to
improve wide-field imaging on large telescopes.
•Wave front measurements from guide stars located far
from each other (2’ to 10’+) are averaged to estimate the
turbulence close to the telescope aperture.
•Correction applied to a single deformable mirror
conjugate to ground-layer.
•Because ground-layer turbulence is common to entire
field, a partially corrected field is produced over roughly
the guide star constellation.
Benefits of GLAO
Within the guide star constellation:
GLAO
• Decreased image FWHM
• Higher resolution
• 0.1”-0.2” in NIR for 5-10 m class telescopes
• Diffraction limit in MIR
Seeing
GLAO
• Increased signal-to-noise
• Increased energy concentration
• θ50: 0.25”(SL) to 0.13”(GLAO) in K-band
(Lloyd-Hart et al. SPIE 2006)
• Reduces size necessary for spectrograph
instrumentation
Seeing
• Higher precision astrometry
(Lloyd-Hart et al. Opt. Exp. 2006; Baranec et al. ApJ 2009)
Studies of GLAO
• Studies of the Cn2 profile at a number of different
observing sites indicate that typically 0.5 to 0.67 of
the total atmospheric turbulence is in the groundlayer.
(Andersen et al. PASP 2006; Avila et al. PASP 2004; Egner et al. SPIE 2006; Tokovinin & Travouillon MNRAS 2006; Tokovinin et al. PASP 2005;
Baranec et al. ApJ 2007; Velur et al. SPIE 2006; Verin et al. Gemini Rpt. 2000)
• Performance prediction of GLAO by many
simulations.
(Rigaut Proc. ESO 2002; Andersen et al. PASP 2006; Le Louran & Hubin MNRAS 2006; Tokovinin PASP 2004)
• Open-loop predictions of GLAO (comparing
multiple reconstructed wavefronts)
(Athey SPIE 2006;Lloyd-Hart et al. ApJ 2005, Op. Exp. 2006; Baranec et al. ApJ 2007)
First demonstration of GLAO with VLT-MAD
•GLAO using 3 NGSs on 1.5’ diameter at VLT in 2007
•Approximately diffraction-limited
resolution (56 mas): high level of
wavefront correction due to use of
NGS in small constellation.
•Non-uniform Strehl with field due
to upper atmosphere correlations.
•Science targets limited
because there are very
few suitably bright
NGS constellations.
Strehl map at 2.2 µm.
NGSs indicated by triangles.
(E. Marchetti et al. The Messenger 2007)
Why do GLAO with LGS instead of NGS?
High sky coverage.
•Not limited by finding many bright stars near science object.
•Still requires a faint, mv ≤ 18, guide star to be nearby for tip-tilt-focus
sensing. (Rayleigh LGS only need tip-tilt sensing.)
More uniform correction.
•Less affected by correlations in upper-altitude turbulence. A time when
focal anisoplanatism is beneficial!
Multi-LGS AO at the 6.5-m MMT
• Proof of concept for ground-layer adaptive optics and
tomographic adaptive optics using laser guide stars.
• Develop a competitive LGS AO system at the MMT which
can support the current and future suite of AO
instruments.
• Lessons from experiments support the design of adaptive
optics for the 2 x 8.4 m Large Binocular Telescope and
the 25 m Giant Magellan Telescope. (And many others
hopefully…)
MMT LGS AO system components
•Adaptive Secondary Mirror
Brusa-Zappellini et al. SPIE 1998, Wildi et al. SPIE 2003.
•Multiple Rayleigh laser beacons
Stalcup Ph. D Thesis 2006.
•Cassegrain mounted wavefront sensor instrument
Stalcup Ph. D Thesis 2006, Baranec Ph. D Thesis 2007.
•PC-based real-time
reconstructor
Vaitheeswaran et al. SPIE 2008
•MMT F/15 AO instrument suite
RLGS Beam Projector at the MMT
• Two commercially available 15 W doubled
Nd:YAG lasers at 532 nm pulsed at 5 kHz.
• Mounted on side of telescope.
• The laser beams are combined with a polarizing
beam splitter.
• A computer generated hologram creates the five
beacons, 2 arc min diameter on-sky.
Projection
optics
Fast steering
mirror
• Fast steering mirror controls beam jitter.
• Projection optics mounted on the telescope axis
behind the secondary mirror.
• Photometry Return:
• April ’06: 1.4x105 photoelectrons/m2/J
• Equivalent to five mV ≤ 9.6 stars
Laser box on side of telescope
Photo credit: T. Stalcup
Facility WFS Instrument
Facility Wavefront Sensor Instrument mounts to MMT Cassegrain focus (beneath
primary mirror cell). Mounts all current and future AO instruments to underside of WFS
instrument in the same way as with the MMT’s NGS AO system.
RLGS WFS:
•Multi-beacon 60 subaperture
Shack-Hartmann WFS on single
shuttered CCID18 detector
NGS WFS:
•108 subaperture S-H WFS
•2 arc minute searchable field
Single Star Tilt Sensor:
•Electron Multiplying CCD
•Variable beam splitter between
NGS WFS and Tilt Sensor
•Limiting magnitude mV<17 at
200 fps
Facility WFS Instrument
WFS on the MMT
LGS WFS
460 fps single
frame from
LGS WFS
Range gate:
20-29 km
Integration of
11 laser pulses
MMT AO science capability
LGS AO system can mount same instruments as NGS
AO system:
PISCES – HAWAII 1K×1K J, H, K imager. Selectable 30”
or 2’ field (27 or 107 mas pixels.) Currently, main science
camera used with GLAO. McCarthy et al. PASP 2001
PISCES
Clio – L and M band optimized diffraction-limited narrow
field imager. Expect 30-40% SR with GLAO. Freed et al. SPIE 2004
Clio
ARIES – NIR imager and Eschelle spectrograph. GLAO
will increase energy concentration on targets with no
bright NGS. McCarthy et al. PASP 1998
BLINC/MIRAC3 – MIR imager and nulling interferometer.
Hinz et al. SPIE 2000
Closing the AO loop on 5 LGSs
Slopes measured from each LGS WFS and the tilt star
Slopes from corresponding LGS subapertures are averaged (reduces
necessary computation)
A non-common path centroid offset (measured previously from NGS
WFS on bright star) added to signal
Reconstructor PC calculates actuator delta commands
Commands sent to adaptive secondary mirror
PISCES used for wide field imaging. Typical data sets include 60 1s
images (14 images/minute) derotated and stacked.
Overview of comissioning campaign
July 2007 – 4 useable hours over 4 nights, first GLAO focus w/lasers 200 Hz.
October 2007 – 4 nights lost to weather.
February 2008 – 3 of 5 clear nights – First full high order LGS GLAO
correction of a mV ~9 star.
May 2008 – 2.5 of 4 clear nights – First wide field LGS GLAO correction.
Problems with telescope elevation drive and network hindered performance.
October 2008 – 2 of 4 clear nights – GLAO correction to < 200 mas in Ks.
March 2009 – 1 of 4 clear nights – New system operators, limited by noncommon path errors.
First results – Feb 2008
•mV ~ 9, used as own tip-tilt reference
•Seeing limit at λ = 2.14 µm: 0.70”
•With GLAO correction: FWHM 0.33” and 2.3× greater peak intensity
•Stable PSF morphology, limited by non-common path errors
First results – Feb 2008
Relative to the
cumulative seeing
statistics at the MMT
for λ = 2.14 µm, GLAO
takes a 58th percentile
night and corrects it to
the level of a 4th
percentile night.
May
2008
First wide field
correction with
LGS GLAO:
λ = 2.14 µm
Mean seeing
width: 0.72”
Mean GLAO
width: 0.58”
May 2008 – Power Spectra
•Correction in May affected by elevation drive resonances, tilt control
loop network dropout (improper DNS server!)
•High-order loop from LGSs working properly (at low gain.)
October
2008 – M34
110” FOV Seeing
Image of M34
Ks
Log stretch
Seeing Ks: 0.57”
October
2008 – M34
110” FOV GLAO
Image of M34
J, H, Ks
False color
Log stretch
Seeing Ks: 0.57”
GLAO Ks: 0.19”
Oct 2008 – M34 magnified
Central tip-tilt star - Ks – log stretch
Seeing:
0.57”
GLAO:
0.20”
4.8”
Edge field stars - Ks – linear stretch
M34 with GLAO – Ks FWHM with field
Seeing FWHM:
0.57” ± 0.04”
(37th percentile seeing)
GLAO FWHM:
0.19” ± 0.01”
(N/A percentile)
M34 GLAO correction by band
Band
FWHMtilt FWHMavg Peak I tilt Peak I avg EE(0.2”)tilt EE(0.2”)avg
Ks – seeing
0.571”
0.568”
1
1
8.5%
9.2%
Ks – GLAO
0.205”
0.193”
4.6
5.4
33.1%
38.6%
H – GLAO
0.323”
0.330”
J – GLAO
0.294”
0.296”
Comparison of imaging metrics for central star used for tilt sensing and average
of 10 and 23 brightest sources for seeing limited and GLAO respectively.
October 2008 – M36 at Ks
Mean seeing limited: 0.86”
Mean GLAO: 0.27”
Mean increase in peak
intensity: 5.3
Plans for MMT LGS AO
Finish commissioning of GLAO system –
Ensure system stability
Measure GLAO correction as function of tilt star magnitude and location
Narrow field PSF characterization in thermal IR with Clio
Tomographic correction – (diffraction limit in single direction)
Verify reconstructor matrix multiply (602 slopes × 336 actuators)
Confirm tomographic geometry (LGS and NGS locations, WFS pupil)
Test on sky (MAD with NGS)
System upgrades –
Variable beacon diameter to optimize for tomography and GLAO
Individual WFS for each beacon
New GLAO instrumentation (4’-5’ FOV, NIR imager, MOS) Baranec et al. SPIE 2007
Global landscape of GLAO systems
Telescope Guide star
Instruments
Capability
Operations
P60
1 RLGS
VIS / NIR
2’ FOV
Late 2010
WHT
1 RLGS
NIR
1.5’ FOV
2008
SOAR
1 RLGS
NIR
3’ FOV
2009?
MMT
5 RLGS
PISCES
2’ FOV, <0.2” resolution
2008
Gemini N
4 SLGS
-
-
Study only
Gemini S
5 SLGS
MCAO
2’ Diffraction Limited
2010?
VLT
4 SLGS
HAWK-I + GRAAL
10' FOV, 2 x EE in 0.1''
2012
VLT
4 SLGS
MUSE (24 VIS
IFUs) + GALACSI
1' FOV; 2 x EE in 0.2”
at 750nm
2012
LBT
2× 3 RLGS
ARGOS+LUCIFER 4’ FOV, 0.1” resolution
GMT
6 SLGS
TBD
TMT
-
-
EELT
6-9 SLGS
TBD
-
2011?
-
‘Modest’ end of the spectrum
4.2 m William Herschel Telescope with GLAS, 1.5’
partially compensated field
Martin et al. SPIE 2008
4.1 m Southern
Astrophysical
Research Telescope
with low altitude
Rayleigh, 3’ partially
compensated field
Tokovinin et al. SPIE 2008
1.5 m P60 Telescope at
Palomar with CAMERA
UV LGS AO system
Britton et al. SPIE 2008
Gemini North / Gemini South
Proposed GLAO system with 4
Sodium LGS for Gemini North with
no current support
Andersen et al. PASP 2006
Deploying multi-conjugate adaptive
optics system at Gemini South:
•Uses 5 Sodium LGS
•Uses 3 Deformable Mirrors
•Correct to diffraction limit over 2’
•FLAMINGOS-2 – imaging and MOS
•GSAOI - imager
Credit: Gemini Observatory
Very Large Telescope
Credit: N. Hubin
2 x 8.4m Large Binocular Telescope
•Passed PDR of GLAO system in
February of 2009
•Uses 3 RLGS per aperture
•Adaptive secondary mirrors
•Upgrade path towards using SLGS
•Science instrument: LUCIFER
•4’ FOV
•Imager and MOS with cold slit mask
changer
Credit: S. Rabien
25 m Giant Magellan Telescope
•Relies heavily on MMT experience
•Multi-Sodium LGS
•High-order adaptive secondary
•Tomographic and GLAO correction
with clean thermal background
•2nd generation ExAO and MOAO
30 m Thirty Meter Telescope
No GLAO
2 Seeing limited instruments
with 20” and ~10’ fields
Credit: L. Simard
3rd generation MCAO
instrument WIRC
42 m European Extremely Large Telescope
The E-ELT is designed with a deformable
M4 and a tip-tilt M5.
GLAO correction with 3 NGS + 4 LGS
Current GLAO instrument studies:
• CODEX, high resolution, ultrastable visual
spectrograph using GLAO or seeing-limited
• HARMONI, single-field, wide-band spectrograph,
using GLAO, posibly MCAO/LTAO
• METIS, mid-infrared imager and spectrograph, using
GLAO, possibly LTAO
• OPTIMOS, wide-field visual multi-object spectrograph,
using GLAO, possibly MCAO
• SIMPLE, high-resolution NIR spectrograph, using
GLAO, possibly LTAO
Credit: Fernando Comerón
Credit: N. Hubin
Conclusions
Ground-layer adaptive optics has been demonstrated
with multiple NGSs and LGSs
On the verge of GLAO assisted science observations
Large and Extremely Large Telescopes around the
world are developing this capability
LASER AO TEAM
MMT LGS AO TEAM
PI: Michael Hart
Christoph Baranec
Tom Stalcup
Mark Milton
Miguel Snyder
Keith Powell
Vidhya Vaitheeswaran
Matt Rademacher
Ground-layer AO with NGSs
Open-loop GLAO wavefront
sensing and estimation with
NGSs in 2003
•GLAO - Average of
wavefront from 3 stars used
to correct 4th star
•1.6 m aperture telescope
•d = 30 cm
•d/r0 = 1.3 (at λ = 1.25 µm)
DSS archive image
WFS image
Ground-layer AO with NGSs
•Created synthetic
PSFs with additional
high order unsensed
modes
Predicted GLAO PSFs from open-loop data
• Calculated FWHM
and encircled energy
improvement
1
4
3
2
3 surrounding
stars used to
correct central star