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Untwinkling the Stars
Improving Our View of
the Universe with
Adaptive Optics
26 August 2011
Elinor Gates
UCO/Lick Observatory
Center for Adaptive Optics
Lick Observatory, Mount Hamilton, CA
9 Telescopes ranging in size from 0.5 m to 3 m
"Observing stars through the Earth's atmosphere is like
bird watching from the bottom of a swimming pool."
-Remington P. S. Stone
Why do stars twinkle?
Robert Hooke suggested that stars twinkle because there are
"small moving regions of the atmosphere having different refracting
powers which act like lenses." (1665)
Newton wrote that his telescope observations were limited by the fact that
"the air through which we look is in perpetual Tremor... The only
remedy is a most serene and quiet air, such as may perhaps be found
on the tops of the highest mountains above the grosser clouds."
Astronomer Horace Babcock, in 1953, proposed using a deformable optical
element together with a wavefront sensor to compensate for atmospheric
distortions.
Only in the last 15 years has technology matured enough to make this possible.
Slide Courtesy Claire Max
Turbulence in the atmosphere limits the
performance of astronomical telescopes
• Turbulence is the reason why
stars twinkle
• More important for astronomy,
turbulence spreads out the
light from a star; makes it a
blob rather than a point
Even the largest ground-based astronomical telescopes
have no better resolution than an 8" backyard telescope!
Slide Courtesy Claire Max
Turbulence arises in several places
stratosphere
tropopause
10-12 km
wind flow over dome
boundary layer
~ 1 km
Heat sources w/in dome
Slide Courtesy Claire Max
Images of a bright star, Arcturus
Lick Observatory, 1 m telescope
Long exposure
image
Short exposure
image
“Perfect” image:
diffraction limit
of telescope
Distant stars should resemble “points,”
if it weren’t for turbulence in Earth’s atmosphere
Slide Courtesy Claire Max
There are Three ways to eliminate blurring
due to the atmosphere
1. Get above the turbulence by going into space (Hubble Space Telescope)
2. Use computer post-processing of ground-based images:
Speckle Imaging. Limited to relatively bright objects.
3. Use Adaptive Optics to compensate for turbulence using hardware:
- Measure the blurring due to turbulence (up to 1000 times per second)
- Then correct for effects of turbulence by changing the shape of a
special "deformable mirror" behind the primary mirror of the
telescope
- Needs a reference star nearby to measure turbulence.
Slide Courtesy Claire Max
Space vs. Ground Based Telescopes
Telescope:
HST
Shane
Mirror Diameter:
2.4 m
3.0 m
Resolution at 2.2 microns: 0.23 arcseconds
0.18 arcseconds
Lick Observatory's Shane 3m telescope can see smaller structures than
the Hubble Space Telescope when using Adaptive Optics.
Space vs. Ground Based Telescopes
Telescope:
Keck
JWST
Mirror Diameter:
10 m
6.5 m
Resolution at 2.2 microns: 0.055 arcseconds
0.085 arcseconds
Keck Observatory's 10m telescope can see smaller structures than
the planned James Webb Space Telescope when using Adaptive Optics.
Schematic of adaptive optics system
Feedback loop:
next cycle
corrects the
(small) errors
of the last cycle
Slide Courtesy Claire Max
Most deformable mirrors today have thin
glass face-sheets
Glass face-sheet
Cables leading to
mirror’s power supply
(where voltage is
applied)
PZT or PMN actuators:
get longer and shorter as
voltage is changed
Reflective coating (e.g. Aluminum)
Slide Courtesy Claire Max
Deformable mirrors come in many
shapes and sizes
Today: mirrors from Xinetics. From 13 to 900 actuators (degrees of
freedom); 3 - 15 inches in diameter.
Xinetics Inc.Devens, MA
Future: very small mirrors (MEMS, LCDs); very large mirrors
(replace secondary mirror of the telescope)
Slide Courtesy Claire Max
Adaptive optics system is usually
behind main telescope mirror
Example: AO system at Lick Observatory’s 3 m telescope
Support for main
telescope mirror
Adaptive optics package
under main mirror
Slide Courtesy Claire Max
What does a “real” adaptive optics system look like?
Light from telescope
Wavefront
sensor
Tip/Tilt
Mirror
Deformable
mirror
Infra-red
camera
Gemini North Adaptive Optics Animation
QuickTime™ and a
Sorenson Video decompressor
are needed to see this picture.
Adaptive optics in action
Lick Observatory Adaptive Optics System
Adaptive optics on 10-m Keck II Telescope:
Factor of 10 increase in spatial resolution
9th magnitude star imaged in
infrared light (1.6 mm)
Without AO
width = 0.34 arc sec
With AO
width = 0.039 arc sec
Slide courtesy of Claire Max
Often no bright star where you really need one!
Reference Star
Science
Object
Turbulence
h
Common
Atmospheric
Path
Telescope
Slide courtesy of Claire Max
If there is no nearby star, make
your own “star” using a laser
Implementation
Concept
Lick Obs.
Courtesy Laurie Hatch
Slide courtesy of Claire Max
How does a Sodium Laser make an Artificial Star?
60 miles up is a layer in the mesosphere containing metals,
sodium, potassium, calcium.
These metals are deposited by meteors burning up in the
Earth’s atmosphere.
Tune laser to emit 589 nm wavelength light.
Sodium atoms absorb and are excited by laser.
The atoms quickly de-excite, re-emitting the light, and
create an artificial star wherever you need one.
Slide courtesy of Claire Max
Sodium Laser Guide Star at Keck II
Science observations started in 2005.
Image of sodium light taken from telescope
very close to main telescope
Light from Na layer
at ~ 90 km
Max. altitude of
Rayleigh ~ 35 km
Rayleigh scattered light
Slide courtesy of Claire Max
87 Sylvia with Moonlets Romulus and Remus
Franck Marchis, UC-Berkeley
Discovery Image, ESO 8.2m VLT
2004 Aug 9
Aug-Sept 2004
Vesta
Keck Observatory AO
K-band Pyroxene narrow-band filter (1.99 micron wavelength)
QuickTime™ and a
YUV420 codec decompressor
are needed to see this picture.
Movie shows rotation over
about 20 minutes
Image 1.1 x 1.1 arcseconds
Jupiter
Imke de Pater, UC-Berkeley
Left: False Color IR Composite Image (1.29, 1.58 , and 1.65 microns)
Right: 5 micron detail of the Great Red Spot and Red Spot Jr.
(Keck Observatory)
Images of Io
UL: Keck, 2.2 microns
LL: Keck, 3.5 microns
UR: Galileo space
orbiter, Visible Light
LR: Keck, No AO
correction
Titan Occultation
Titan - Saturn’s largest moon
Antonin Bouchez et al. 20 Dec 2001
QuickTime™ and a
YUV420 codec decompressor
are needed to see this picture.
QuickTime™ and a
YUV420 codec decompressor
are needed to see this picture.
Uranus with 3 Moons
17 October 2003, NGS, r0 ~ 18cm
Uranus - New Ring
Imke de Pater - UC Berkeley
Discovered with HST, but imaging from Earth possible with Keck AO!
Neptune in Infrared Light
With Keck adaptive optics
2.3 arc sec
Without adaptive optics
May 24, 1999
June 27, 1999
l = 1.65 microns
Slide courtesy of Claire Max
Lick Ha 225
Laser Guide Star Polarimetry of Herbig Ae/Be Stars
Marshall Perrin, James Graham UC-Berkeley
Planetary
Nebula
BD+303639
AO Images
from Gemini
North
June 1999
Campbell’s
Hydrogen Star
Discovered
1893 by W. W.
Campbell at
Lick
Observatory
M13 - Globular Cluster
Gemini North, 5”x5” view
Left: Visible Light Image, No AO Correction
Right: 2.2 micron, AO Corrected (940 second exposure)
Galactic Center at 2.2 microns
Andrea Ghez, UCLA
Galactic Center
Andrea Ghez, UCLA
Galactic Center - Andrea Ghez, UCLA
Quasar Structure
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
Quasar Host Galaxy: SDSS2323+0040
Elinor Gates, UCO/Lick
Mark Lacy, Spitzer Science Center
NGS, 120 min, H Band
Host Galaxy Luminosity:
MV = -21.8  0.15
Host Galaxy r1/2:
0.4  0.1" ~ 3.1  0.5 kpc
MBH(Host) = 2.9x108 MO
MBH(BLR) = 4.0x107 M
L/LE = 0.14-1.0
z = 0.76
1"
Companion Galaxy
Quasar Host Galaxy:
SDSS0244+0028
LGS, 125 min, H Band
Host Galaxy Luminosity:
MV = -22.7  0.1
Host Galaxy r1/2:
1.3  0.4" ~ 10.7  3.3 kpc
MBH(Host) = 1.3x109 MO
MBH(BLR) = 3.4x108 M
z = 0.84
New developments:
tiny deformable mirrors
Potential for less cost per degree of freedom
Liquid crystal devices
Voltage applied to back of each pixel changes index of
refraction locally
MEMS devices (micro-electro-mechanical systems)
Ele ctrostati cal ly
Me mbrane
actuate d
Attachm e nt mi rror
diaphragm
post
Conti nuous mirror
Mirror surface map
Slide Courtesy Claire Max
ViLLaGEs - Visible Light Laser Guide Star Experiment
Shane AO Upgrade
Uses two
deformable mirrors:
Woofer - Tweeter
System
Tweeter is a MEMS
device
Upgraded Near-IR
detector and optics
in IRCAL
TMT size compared to AT&T Park
TMT
AO - Coming to a large telescope
near you!
AO’s potential for expanding our understanding of
the Universe is clear!
All large telescopes have Adaptive Optics or plans
to build an AO system in the near future.
More large telescopes are installing Sodium Laser
systems now that Lick Observatory has proved
real science can be done with this technology.
Giant telescopes (30 m diameter or more) of the
future require AO and Lasers to realize their full
potential.