Äîêóìåíò âçÿò èç êýøà ïîèñêîâîé ìàøèíû. Àäðåñ îðèãèíàëüíîãî äîêóìåíòà : http://www.stsci.edu/institute/conference/hsl/Nelson.PDF Äàòà èçìåíåíèÿ: Tue Apr 11 00:25:04 2006 Äàòà èíäåêñèðîâàíèÿ: Sat Dec 22 12:02:55 2007 Êîäèðîâêà: Ïîèñêîâûå ñëîâà: arp 220

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

Hubble Legacy 5apr02

jen

2

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


Hubble Legacy 5apr02

jen

4


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
Hubble Legacy 5apr02 jen 5


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)

Hubble Legacy 5apr02

jen

6



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

Hubble Legacy 5apr02

jen

8


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

Hubble Legacy 5apr02

jen

9


CELT and Stonehenge

Hubble Legacy 5apr02

jen

10






Front view of CELT


Plan view of CELT showing Nasmyth platforms and instruments


CELT basic layout-1080 segments


CELT

Keck



Hubble Legacy 5apr02

jen

20




How a Deformable Mirror Works

BEFORE

AFTER

Incoming Wave with Aberration
Hubble Legacy 5apr02

Deformable Mirror
jen

Corrected Wavefront

Deformable Mirror
23



Hubble Legacy 5apr02

jen

25


Hubble Legacy 5apr02

jen

26


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

27


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
Hubble Legacy 5apr02

­ Adaptive optics working down to 1 µm ( / D = 0 .007 arcsecond resolution)
jen

28


Hubble Legacy 5apr02

jen

29


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)
Hubble Legacy 5apr02 jen 30


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

Hubble Legacy 5apr02

jen

31


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

Hubble Legacy 5apr02

jen

41