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Comparative Performance of a 30m Groundbased GSMT and a 6'5m and 4m NGST NAS Committee of Astronomy

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Gemini Observatory/AURA NIO. 2. Overview. Science Drivers for a GSMT. Performance Assumptions ... 9 Sodium laser constellation. 4 tip/tilt stars (1 x 17, 3 x 20 Rmag) ... – PowerPoint PPT presentation

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Title: Comparative Performance of a 30m Groundbased GSMT and a 6'5m and 4m NGST NAS Committee of Astronomy


1
Comparative Performance of a 30m Groundbased GSMT
and a 6.5m (and 4m) NGST NAS Committee of
Astronomy Astrophysics9th April 2001Matt
MountainGemini Observatory/AURA NIO
2
Overview
  • Science Drivers for a GSMT
  • Performance Assumptions
  • Backgrounds, Adaptive Optics and Detectors
  • Results
  • Imaging and Spectroscopy
  • compared to a 6.5m 4m NGST
  • A special case,
  • high S/N, R100,000 spectroscopy
  • Conclusions

3
GSMT Science CaseThe Origin of Structure in the
Universe
Najita et al (2000,2001)
  • From the Big Bang to clusters, galaxies, stars
    and planets

4
Mass Tomography of the Universe
100Mpc (5Ox5O), 27AB mag (L z9), dense
sampling GSMT 1.5 yr Gemini 50 yr NGST 140 yr
5
Tomography of Individual Galaxies out to z 3
  • Determine the gas and mass dynamics within
  • individual Galaxies
  • Local variations in starformation rate
  • Multiple IFU spectroscopy
  • R 5,000 10,000

GSMT 3 hour, 3s limit at R5,000 0.1x0.1 IFU
pixel (sub-kpc scale structures) J H
K 26.5 25.5 24.0
6
Probing Planet Formation with High Resolution
Infrared Spectroscopy
  • Planet formation studies in the infrared
    (5-30µm)
  • Planets forming at small distances (lt few AU) in
    warm region of the disk
  • Spectroscopic studies
  • Residual gas in cleared region emissions
  • Rotation separates disk radii in velocity
  • High spectral resolution high spatial
    resolution

S/N100, R100,000, ?gt4?m Gemini out to
0.2pc sample 10s GSMT
1.5kpc 100s NGST
X
  • 8-10m telescopes with high resolution (R100,000)
    spectrographs can detect the formation of
    Jupiter-mass planets in disks around nearby stars
    (d100pc).

7
30m Giant Segmented Mirror Telescope concept
GEMINI
30m F/1 primary, 2m adaptive secondary
8
GSMT Control Concept
LGSs provide full sky coverage
Deformable M2 First stage MCAO, wide field
seeing improvement and M1 shape control
  • M2 rather slow, large stroke DM to compensate
    ground layer and telescope figure,
  • or to use as single DM at ?gt3 ?m. (8000
    actuators)
  • Dedicated, small field (1-2) MCAO system
    (4-6DMs).

Active M1 (0.1 1Hz) 619 segments on 91 rafts
10-20 field at 0.2-0.3 seeing
1-2 field fed to the MCAO module
Focal plane
9
GSMT Implementation concept- wide field (1 of 2)
Barden et al (2001)
10
GSMT Implementation concept- wide field (2 of 2)
  • 20 arc minute MOS
  • on a 30m GSMT
  • 800 0.75 fibers
  • R1,000 350nm 650nm
  • R5,000
  • 470nm 530nm
  • Detects 13 - 23
  • photons hitting 30m
  • primary

1m
Barden et al (2001)
11
Spot Diagrams for Spectrograph
On-axis
R1000 case with 540 l/mm grating.
Circle is 85 microns equal to size of imaged
fiber.
On-axis
R5000 case with 2250 l/mm grating.
Barden et al (2001)
12
GSMT Implementation concept- MCAO/AO foci and
instruments
Oschmann et al (2001)
MCAO opticsmoves with telescope
elevation axis
MCAO Imager at vertical Nasmyth
4m
Narrow field AO or narrow field seeing limited
port
13
Spot diagrams for MCAO Imager
Diffraction limited performance for 1.2mm 2.2
mm can be achieved
14
MCAO Optimized Spectrometer
  • Baseline design stems from current GIRMOS d-IFU
    tech study occurring at ATC and AAO
  • 2 arcmin deployment field
  • 1 - 2.5 µm coverage using 6 detectors
  • IFUs
  • 12 IFUs total 0.3x0.3 field
  • 0.01 spatial sampling R 6000 (spectroscopic
    OH suppression)

15
Quantifying the gains of NGST compared to a
groundbased telescope
  • Assumptions (Gillett Mountain 1998)
  • SNR Is . t /N(t) t is restricted to
    1,000s for NGST
  • Assume moderate AO to calculate Is , Ibg
  • N(t) (Is . t Ibg. t n . Idc .t
    n . Nr2)1/2
  • For spectroscopy in J, H K assume
    spectroscopic OH suppression
  • When R lt 5,000 SNR(R)
    SNR(5000).(5000/R)1/2
    and 10 of the pixels are
    lost

Source noise background dark-current
read-noise
16
Space verses the Ground
Takamiya (2001)
17
Adaptive Optics enables groundbased telescopes to
be competitive
For background or sky noise limited
observations S ?? Telescope
Diameter . ???? N
Delivered Image Diameter B???
Where ? is the product of the system throughput
and detector QE B is the
instantaneous background flux
18
Adaptive Optics works well
19
Modeling verses Data
GEMINI AO Data
2.5 arc min.
Model Results
M15 PSF variations and stability
measured as predicted
20
Quantitative AO Corrected Data
  • AO performance can be well modeled
  • Quantitative predictions confirmed by
    observations
  • AO is now a valuable
  • scientific tool
  • predicted S/N gains now being realized
  • measured
  • photometric errors in crowded fields 2

Rigaut et al 2001
21
Multi-Conjugate Adaptive Optics
2.5 arc min.
Model results
  • Tomographic calculations correctly
  • estimated the measured atmospheric phase
  • errors to an accuracy of 92
  • better than classical AO
  • MCAO can be made to work

MCAO
22
AO Technology constraints (50m telescope)
r0(550 nm)
10cm No. of Computer CCD
pixel Actuator pitch S(550nm)
S(1.65mm) actuators power
rate/sensor
(Gflops) (M pixel/s)
10cm 74
97 200,000 9 x 105
800
25cm 25 86
30,000 2 x 104 125
50cm 2 61
8,000 1,500 31
SOR (achieved)
789 2 4 x 4.5
Early 21st Century technology will keep AO
confined to l gt 1.0 mm for telescopes with D
30m 50m
23
MCAO on a 30m summary
  • MCAO on 30m telescopes should be used l gt 1.25 mm
  • Field of View should be lt 3.0 arcminutes,
  • Assumes the telescope residual errors 100 nm
    rms
  • Assumes instrument residual errors 70 nm
    rms
  • Equivalent Strehl from focal plane to
    detector/slit/IFU gt 0.8 _at_ 1 micron
  • Instruments must have
  • very high optical quality
  • very low internal flexure

Rigaut Ellerbroek (2000)
l(mm) Delivered Strehl 1.25 0.2
0.4 1.65 0.4 0.6 2.20
0.6 0.8
9 Sodium laser constellation 4 tip/tilt stars (1
x 17, 3 x 20 Rmag)PSF variations lt 1 across
FOV
24
Modeled characteristics of a 30m GSMT with MCAO
(AO only, lgt3mm) and a 6.5m NGST
Assumed encircled-energy diameter (mas)
containing energy fraction h 30M 1.2mm
1.6mm 2.2mm 3.8mm 5.0mm 10mm 17mm
20mm (mas) 23 29 41 34
45 90 154 181 h
34 47 61 50 54
56 57 58 NGST 1.2mm 1.6mm
2.2mm 3.8mm 5.0mm 10mm 17mm 20mm
(mas) 100 100 82 138
182 363 617 726 h 70
70 50 50 50 50
50 50
Assumed detector characteristics 1mm lt l lt
5.5mm 5.5mm lt l
lt 25mm Id Nr qe
Id
Nr qe 0.01 e/s 4e 80
10 e/s 30e
40
25
Comparative performance of a 30m GSMT with a 6.5m
NGST
Assuming a detected S/N of 10 for NGST on a
point source, with 4x1000s integration
GSMT advantage
NGST advantage
26
Comparative performance of a 30m GSMT with a 4m
NGST
Assuming a detected S/N of 10 for NGST on a
point source, with 4x1000s integration
GSMT advantage
NGST advantage
27
Observations with high Signal/Noise, Rgt30,000 is
a new regime- source flux shot noise becomes
significant
28
High resolution, high Signal/Noise observations
Detecting the molecular gas from gaps swept out
by a Jupiter mass protoplanet, 1 AU from a 1 MO
young star in Orion (500pc) (Carr Najita 1998)

GSMT observation 40 mins (30 mas beam)
29
Conclusions

NGST advantage
NGST
GSMT advantage X

X

NGST Instrument

X
X

X
X
High S/N, R100,000 spectroscopy WF MOS
Spectroscopy l lt 2.5mm
X
X
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