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The Potential of Ground Based Telescopes
Jerry Nelson UC Santa Cruz 5 April 2002


Contents
· · · · ·

Present and Future Telescopes Looking through the atmosphere Adaptive optics Extragalactic astronomy Planet searches

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QuickTimeTM and a Photo - JPEG decompressor are needed to see this picture.


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Desire for larger telescopes
· History shows largest telescope diameter doubles every 31 years
­ 2.5m ­ 5m ­ 10m 1917 1948 1993 Hooker Hale Keck

· 2001 NAS decadal astronomy and astrophysics survey committee (AASC) recommended a 30 - m telescope (GSMT) as its highest ground based priority · Other groups in the US and in Europe are thinking and talking about giant telescopes (up to 100- m) on the ground · Advances in adaptive optics makes this particularly exciting
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California Extremely Large Telescope

· CELT is a study to build a 30 - m telescope · UC and Caltech are partners · Funding is not yet in hand (proposal submitted) · Site is unknown (several candidates)

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Science Potential for CELT

· Increased angular resolution
­ With AO can reach 0.007 arc second resolution (100x improvement) ­ Study morphological details of most distant galaxies (cosmology) ­ Study details for star and planet formation ­ Study stellar evolution in globular clusters ­ Quasars and Active Galactic Nuclei (black holes) ­ Solar system objects

· Increased light gathering power
­ With CELT can collect 9x the energy from an object (over Keck) ­ Spectroscopy of most distant objects known ­ Planet searches and their study

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Scientific Potential

· Seeing limited observations
­ 0.3 - 1.0 µm ­ Scale 2.18 mm/arc second (f/15) ­ Wide field of view available: 20 arcminutes

· Diffraction limited observations
­ 1 - 25µm, mainly 1 - 2.5µm ­ Thermal IR possible, but not most important ­ At 1 µm angular resolution of 7 mas ­ Resolution element size: 15µm (at f/15, 1 µm wavelength) ­ Large field of view: 1 arc minute at 1 µm with multi conjugate AO

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CELT and Stonehenge

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Front view of CELT


Plan view of CELT showing Nasmyth platforms and instruments


CELT basic layout-1080 segments


CELT

Keck



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How a Deformable Mirror Works

BEFORE

AFTER

Incoming Wave with Aberration
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Deformable Mirror
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Corrected Wavefront

Deformable Mirror
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Neptune at 1.65 microns

Without adaptive optics

With adaptive optics

May 24, Hubble Legacy 5apr02 1999

2.3 arc sec

jen

June 28, 1999

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The future of AO in astronomy
· More powerful AO systems
­ More energy concentrated into diffraction limited image ­ Better resolution at shorter wavelength

· Larger diffraction -limited fields of view
­ Multi - conjugate AO systems to cancel aberrations "where they occur" ­ Multiple laser beacons

· Larger telescopes with AO
­ NAS AASC recommended a ground based 30 - m telescope

· California Extremely Large Telescope (CELT)
­ University of California - Caltech partnership ­ 30 - m diameter
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­ Adaptive optics working down to 1 µm ( / D = 0 .007 arcsecond resolution)
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CELT Adaptive Optics Issues
· AO system requirement: wavefront residual 133 nm
­ Strehl= 0.84 at 2 µm ­ Strehl = 0.50 at 1 µm ­ Strehl = 0.24 at 0.7 µm

· Native atmosphere is roughly 2000 nm rms (tilt removed) · System will require ~ 5000 actuators · MCAO will require ~ 3 layers, each with 5000 actuators · Wavefront sensing will require 80x80 lenslet arrays, advanced detectors · Sky coverage will require ~5 Na laser beacons · Computations currently impractical (need better algorithms and computers)
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CELT Plans

· Conceptual design study underway
­ Started September 2000 ­ End March 2002 ­ + fund raising

· Preliminary Design should start end of 2002
­ + fund raising

· Detailed design should start mid 2004 · Construction may begin 2006 · Completion ~ 2012

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Galaxy Evolution

· · ·

When did galaxies form? When did disks stabilize? When and how did bulges form?

· · · ·

When was the Hubble sequence in place? What is the merger rate as a function of time? What caused the sharp decline in star formation since a redshift of 1? What was the Galactic environment at the time of the formation o f the solar system (z~0.4)?


Galaxy Evolution


Field Galaxy Studies


New Sample of >200 galaxies.
PSF Star 5 kpc

1"

z=0.59

Example: 30"x30" Field All Bright objects are galaxies .
PSF Star

z=0.70


"Extreme" Adaptive Optics 1 : ExAO
·Science driver: Direct detection of extrasolar planets ·"Extreme AO": systems powerful enough to control the scattered light halo at large radii

1

R. Dekany , JPL


ExAO System Phase Space
Target stars Young: 1-20 MYr Medium: 0.1-5 GYr Mature 5 GYr Contrast goal 105 @ 0.2" 106 - 107
plus d iffuse dust 9

mr 8-10 5-8 <4

distanc e 30-60 pc <50 pc 4-8 pc

# of stars d 100 100s 10s

subaperture

~30 cm ~20 cm ~5-10 cm

10 @ 1"

·Three areas of phase space: ·Young stars: identified through space motions, X- ray emission, etc.
­ Planets are warm (500 - 1000K) and very bright in the near - IR

·Field stars: detection of massive (2 - 10 M J ) planets around older field stars ·Reflected- light: detection of reflected sunlight at < 1 micron


Young Extrasolar Planets
·Low- mass planets (the most exciting ones) cool and dim extremely rapidly (Burrows et al 1997) ·Planets are most detectable at ages < few 10 7 years ·A (surprisingly?) significant population of stars of appropriate age exists close (50 pc ) to earth (Zuckerman et al, Webb et al) ·Current AO and HST can detect young planets orbiting these stars at wide (50 - 100 AU) separations ·ExAO could probe solar - system- like scales (5 - 20 AU, 0.2 - 0.4")

TWA6 and candidate mH=20 object @ 2.5" separation (=150 AU?)
HST/NICMOS

Keck AO Image Feb 2001 (NIRSPEC/Scam)

2.5

arcsec


Detectable young - planet flux ratios for Keck and CELT


Detection of mature Jovian planets in reflected sunlight
·Performance can be expressed in terms of the distance at which a Jupiter in a solar system like ours could be detected in a four - hour integration ·Performance predictions based on refined version of Angel (1994) scaling laws (more pessimistic than Angel's original paper)

12 10 8 6 4 2 0 1000 10000

ExAO Jovian-sytem detection distance

5-m tel. 8-m tel. 10-m seg. tel. 30-m seg. tel.

100000

1000000 10000000

n actuators


Conclusions

· Large, diffraction limited telescopes are here · Larger, diffraction limited telescopes are coming · AO with good sky coverage and interesting fields of view are coming soon (laser beacons, MCAO) · Jovian planets will be detectable

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