MAX-AT Workshop
Madison, Wisconsin, 27 - 29 August
Maximum Aperture Telescope Workshop
Organized by AURA
Chaired by Jay Gallagher
MAX-AT Workshop
Madison, Wisconsin, 27 - 29 August
Basic Ideas for Very Large Aperture
Telescopes
the case for continuing groundbased astronomy
Matt Mountain
Gemini Telescopes
August 1998
Basic Ideas for Very Large
Aperture Telescopes
the case for continuing groundbased astronomy
 Goals

Establish a framework for discussing the science case for a
Very or Extremely Large Aperture Telescope

Examine the challenges for 8m - 10m groundbased
telescopes in an “NGST era”

Look at how a 21st Century groundbased telescope could
extend and compliment the capabilities of an 8m NGST

Highlight some of the very real technical and cost-benefit
challenges that have to be overcome
 Make the case, that in an NGST era, with our current
science interests, a groundbased 30m - 50m telescope is the
necessary (if somewhat daunting) “next step”
Science
What is the case for a new groundbased
facility?
?
“Observing and understanding the origins
and evolution of stars and planetary systems,
Gemini N Gemini S
of galaxies, and
of the Universe itself.”
- Gemini Science Requirements, 1990
Keck 1
WHT
Keck 2
ORM
HET
Large collecting area
Palomar
Magellan 1
LBT 2
VLT 2
VLT 4
and
quality MMT
LBT 1imageSubaru
Magellan 2
VLT 1
VLT 3 superb
and
optimized IR performance
UKIRT CFHT
WIYN
ARC
TNG
MPA
KPNO
IRTF
NTT
CTIO
AAT
ESO
Framework for a Science Case
Where are our current science interests
taking us?
-
Lets be presumptuous….
21st Century astronomers should be
uniquely positioned to study “the
evolution of the universe in order to
relate causally
the
physical conditions
 Dynamics,
abundances’
requires
- spectral
resolutions
> 5,000
during
the Big
Bang to
the development
 Isolating
individual
objects or
phenomena 1997)
requires
of RNA
and DNA”
(Giacconi,
- high spatial resolution
 Imaging spectroscopy at high spectral and spatial
resolution requires
- collecting area
Adapted from Science, vol. 274, pg. 912
Challenging 8m - 10m telescopes -
Imaging Spectroscopy of the majority of objects in
the HDF
10”
4 mag.’s
Current Keck
spectroscopy limit
HDF Differential Number counts from Williams et al 1996
“Deconstructing High z Galaxies”
Integral field
observations of a
z = 1.355 irregular
HDF galaxy
(Ellis et al)
“Starformation histories
of physically distinct
components apparently
vary - dynamical data is
essential”
Going beyond Gemini
SN in Arp 220 (VLBI
Harding et al 1998)
0.2”
0.4”
2”
~ 0.01”
“milliarcsecond scale
emission is common,
perhaps universal in
LIG’s”
“Deconstructing the M16 Pillars
with Gemini”
Beyond surveying M16
“pillars” for forming stars,
closer inspection with NIRI
reveals bipolar outflow
Integral field
spectroscopy reveals
outflow dynamics
Embedded forming stars
Approximate field of view of
Gemini Mid Infrared Imager
Coronagraph
reveals faint low
mass companion
AO+NIRS spectroscopy
shows spectrum of
a forming “super-Jupiter”
Going beyond Gemini
Solar System @ 10 pc
500 mas
x 30
Gilmozzi et al (1998)
Gemini
10 s, t = 10,000s
R = 1800
l (mm)
Models for 1 MJ Planets at 10 pc from Burrows et al 1997
Jupiter
How we will be competitive from the
ground
 The “Next Generation” Space Telescope (NGST)
will probably launch 2006 - 2010

an 6m - 8m telescope in space
 NGST will be extremely competitive for:


deep infrared imaging,
spectroscopy at wavelengths longer than 3 microns
 Groundbased telescopes can still compete in the
optical and near-infrared

moderate to high resolution spectroscopy
 Groundbased facilities can also exploit large
baselines

high angular resolution observations
Sensitivity gains for a 21st
Century telescope
For background or sky noise limited observations:
S
N

(Effective Collecting Area)1/2 .
Delivered Image Diameter 
For background or sky noise limited spectroscopy:
S
N

S/N x (106)1/2
Equivalent Telescope Diameter .
Effective Aperture Width

 To meet these scientific challenges:
S/N  30 x S/N of a 8m ~ 10 m Telescope
The gains of NGST compared to
a groundbased 8m telescope




Assumptions (Gillett & Mountain 1998)
SNR = Is . t /N(t): t is restricted to 1,000s for NGST
Assume moderate AO to calculate Is
N(t) = (Is . t + Ibg. t + n . Idc + n . Nr2)1/2
Source noise
background
dark-current read-noise

For spectroscopy in J, H & K assume
“spectroscopic OH suppression”

When R < 5,000
SNR(R) = SNR(5000).(5000/R)1/2
and 10% of the pixels are lost
Relative Signal to Noise (SNR) of NGST/Gemini
-- assuming a detected S/N of 10 for NGST on a point source, with 4000s integration
Photon-limited performance averaging OH lines
Intermediate cases
determined by
detection noise
2
Photon-limited performance between OH lines
2
10
10
Relative Signal to Noise (SNR) of NGST/Gemini
-- assuming a detected S/N of 10 for NGST on a point source, with 4000s integration
Spectroscopy between
the OH lines
2
2
Telescopes can still be competitive
from the ground
The
for be
groundbased
“Maximum Aperture
Telescope” must
 science
NGSTcase
will
very competitive
for:
exploitthe
observational
requirements for imaging spectroscopy,
deep
infrared imaging,
requiring:
 spectroscopy at wavelengths longer than 3 microns
Groundbased
telescopes
can still
compete
in the
1. 
High
spatial resolution
to isolate individual
objects
or
phenomena
optical and near-infrared
moderate to high resolution spectroscopy
2. Moderate to high spectral resolution spectroscopy for

Groundbased
facilities
can also exploit large
dynamics
and abundance
measurements

baselines
3. An effective
telescoperesolution
diameter ofobservations
~ 50m to complement
 high angular
NGST (and the MMA)
10 milliarcsecond imaging spectroscopy to 28 - 30 magnitudes
“its resolution stupid..”
Facility




Gemini 8-M
CHARA
Keck 1 & 2 +
VLTI +
Baseline
(m)
8
354
165
200
Collecting Area
(m2)
2 x 50
5.5
157 + 11
201 + 20
“its resolution stupid..”
Facility





Gemini 8-M
CHARA
Keck 1 & 2 +
VLTI +
VLIA
Baseline
(m)
8
354
165
200
~ 1000
Collecting Area
(m2)
2 x 50
5.5
157 + 11
201 + 20
800 (16 x 8m)
Goal: 0.001 arcsecond images at 2.2 microns
signal/noise gains ~ 10 compared to 8m telescopes
sensitivity gains ~ 102 over Gemini for point like sources
“its collecting area stupid..”
Facility




Gemini 8-M
CHARA
Keck 1 & 2 +
VLTI +
Baseline
(m)
8
354
165
200
Collecting Area
(m2)
2 x 50
5.5
157 + 11
201 + 20
“its collecting area stupid..”
Facility






Gemini 8-M
CHARA
Keck 1 & 2 +
VLTI +
20 m
50-M Telescope
Baseline
(m)
8
354
165
200
20
50
Collecting Area
(m2)
2 x 50
5.5
157 + 11
201 + 20
316
1963
Goal: 0.01 arcsecond images at 2.2 microns
signal/noise gains ~ 30 compared to an 8m
sensitivity gains ~ 103 over Gemini for point like sources
Modeled characteristics of 20m and
50m telescope
Assumed point source size (mas)
20M
(mas)
1.2mm 1.6mm 2.2mm 3.8mm 4.9mm 12mm 20mm
50M
(mas)
1.2mm 1.6mm 2.2mm 3.8mm 4.9mm 12mm 20mm

20
20
26
41
58
142
10
10
10
17
23
57
70%
70%
50%
50%
50%
50%
240
94
50%
Assumed detector characteristics
mm < l < 5.5mm
Id
0.02 e/s
5.5mm < l < 5mm
Nr
qe
Id
4e
80%
10 e/s
Nr
qe
30e
40%
Relative Signal to Noise Gain of groundbased
20m and 50m telescopes compared to NGST
-- assuming a detected S/N of 10 for NGST on a point
source, with 4x1000s integration
1
100
100
50M R=5
50m R=10,000
20m R=5
10
S/N Gain
20m R=10,000
10
10
1
0.01
0.01
1E-3
1E-3
10
W avelength ( m m )
1
0.1
0.1
1
10
1
1
0.1
10
100
0.1
0.01
0.01
1E-3
1E-3
1
10
W avelength ( m m )
Groundbased
advantage
10
NGST advantage
1
100
Relative Signal to Noise Gain of groundbased
20m and 50m telescopes compared to NGST
-- assuming a detected S/N of 10 for NGST on a point
source, with 4x1000s integration
1
100
10
100
100
50m R=30000
50m R=1000
20m R=1,000
10
10
S/N Gain
1
1
0.1
0.1
20m R=30,000 10
10
1
1
0.1
0.1
0.01
0.01
0.01
0.01
1E-3
1E-3
1E-3
1E-3
1
10
W avelength ( m m )
Groundbased
advantage
10
1
10
W avelength ( m m )
NGST advantage
1
100
“its sensitivity and resolution ..”
Facility






Gemini 8-M
CHARA
Keck 1 & 2 +
VLTI +
20 m
50-M Telescope
Baseline
(m)
Collecting Area
(m2)
8
354
165
200
20
50
2 x 50
5.5
157 + 11
201 + 20
316
1963
Goal: 0.01 arcsecond images at 2.2 microns
signal/noise gains ~ 30 - 60 over Gemini
sensitivity gains ~ 103 over Gemini for point like sources
50m Point Source Sensitivities
10 s 10,000s
10
6
10
5
R=10000
Flux density (nJy)
R=1000
10
4
10
3
10
2
10
1
10
0
1
R=5
10
Wavelength ( m m)
Magnitudes
50m Point Source Sensitivities
10 s 10,000s
10
10
20
20
R=10,000
R=1,000
30
30
R=5
1
10
Wavelength ( m m)
Adaptive Optics will be essential
- and still a lot to understand
Image profiles
are Lorenzian
16 consecutive nights of
adaptive optics the CFHT
AO performance on a 50m
Telescope
Strehl
1k actuator AOS on 50-m (10% Seeing)
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
1.2 micron
1.6 micron
2.2 micron
3.8 micron
4.9 micron
12 micron
20 micron
0
10
20
30
40
Field Angle (arcsec)
Chun, 1998
50
60
AO performance on a 50m
Telescope
Strehl
5k actuator AOS on 50-m (Median Seeing)
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
1.2 micron
1.6 micron
2.2 micron
3.8 micron
4.9 micron
12 micron
20 micron
0
10
20
30
40
50
60
Field
Angle (arcsec)
 Diffraction limited
imaging
constrained to small field of view
Chun, 1998
The Challenge - Multiple Laser Beacons
- still a lot of technologies to develop
*
*
*
*
*
SRFA ~ 0.75 requires NBeacons
1.2mm
1.6mm
2.2mm
3.8mm
4.9mm
12.0mm
20.0mm
75
40
20
5
3
<=1
<=1
Adaptive Optics will be
essential
Diffraction limited imaging will be constrained
to small field of view
How does this constrain the science?
Imaging of the Universe at High Redshift
with 10 milli-arcsecond resolution
 Simulated NGST
K band image
8K x 8K array (3mas pixels)




Blue for z = 0 - 3
Green for z = 3 - 5
Red for z = 5 - 10
 = 0.1
Isoplanatic patch at
2.2 microns for 10mas
imaging
48 arcseconds
Going beyond Gemini
SN Remnants in Arp 220
(VLBI Harding et al 1998)
0.2”
0.4”
2”
~ 0.01”
“milliarcsecond scale
emission is common,
perhaps universal in
LIG’s”
Observation scale lengths
Observations at z = 2 - 5
100 AU
Accretion Disks
Protoplanetary
Disks
0.1 pc
Molecular
Cloud
Cores
Jets/HH
10 pc
Mol. Outflows
1 AU
1R
1 - 10 milliarcseconds
AGN
Planets
Spectroscopy

Imaging
10 AU
Galactic observations out to
1kpc at 10 mas resolution
Stellar
Clusters
100 pc
GMC
Spectroscopic Imaging at 10 milliarcsecond resolution
- using NGST as “finder scope”
 Simulated NGST K
band image
 Blue for z = 0 - 3
 Green for z = 3 - 5
 Red for z = 5 - 10
  = 0.1
2K x 2K
IFU
0.005” pixels
48 arcseconds
l
OWL
OverWhelmingly Large
100-m diameter f/6.4
3 arc minutes FOV
Spherical primary &
secondary mirrors
57
.
126
20
83
.
100
50 Meter Telescope Concept
50 m
2m diameter adaptive
secondary producing
collimated beam, with
1 arcmin. FOV
(Oschmann 1996)
F/1 50m diameter
parabolic primary
50 m Design Performance
Concept:
Parabolic segmented
primary to simplify
polishing and testing
Primary mirror wind
buffeting corrected by
small 2m diameter
adaptive secondary
Collimated beam used to
relay focus to 2m
“telescopes” at both
Nasmyth foci
Diffraction limited
performance across ~
0.6 arcmin. FOV at l =
2.2 microns
Technology and “cost-benefit”
challenges
 Developing multi-laser beacon, high order adaptive
optics or investigate atmospheric “tomography”

near-diffraction limited performance is at the heart of the
MAX-AT science case
 Choosing the most effective aperture


A 50m requires producing and polishing over 1,900 square
meters of “glass”
equivalent to 39 Gemini’s or 25 Keck’s or over 20 HET’s
 Deciding on which site or hemisphere…..
“What can it cost?”
50m Telescope










costs (1997$)
Primary mirror assembly
Telescope structure & components
Secondary mirror assembly
Mauna Kea Site
Enclosures
Controls, software & communications
Facility instrumentation (A&G, AO)
Coating & cleaning facilities
Handling equipment
Project office
Total
$622M
$190M
Scaled costs
$11M
$78M
$70M
$26M
$35M Constrained
costs
$9M
$5M
$40M
$1,086M
S (Keck + Gemini + ESO-VLT + Subaru) = $1,560M
OverWhelmingly Large
OWL
Just to put things into perspective...
The next step ?
Cumulative Area (m 2 )
A 400 year legacy of groundbased telescopes
1400
900
400
0
-100
1600
1700
1800
Year
1900
2000
50m telescope
Basic Ideas for Very Large
Aperture Telescopes
the case for continuing groundbased astronomy
 Goals - recap

Establish a framework for discussing the science case for a
Very or Extremely Large Aperture Telescope

Examine the challenges for 8m - 10m groundbased
telescopes in an “NGST era”

Look at how a 21st Century groundbased telescope could
extend and compliment the capabilities of an 8m NGST

Highlight some of the very real technical and cost-benefit
challenges that have to be overcome
 Make the case, that in an NGST era, with our current
science interests, a groundbased 30m - 50m telescope is the
necessary (if somewhat daunting) “next step”
Workshop Summary (preliminary)
 In view of the large number of science projects
identified, there is sufficient scientific interest in
building a 30-50m telescope observatory.
 Moreover, there was consensus already at the end
of the first day of the meeting that MAX-AT should
be maximized to do science based on high
resolution imaging and spectroscopy.

10 milli-arcsecond imaging spectroscopy at 28 - 30
magnitude
 This Observatory should extend and complement
the capabilities of NGST and the MMA
Workshop Science Cases
(preliminary)
 Planet formation
 Formation of stars and planetary systems (disks)
 Planet Formation
 Imaging of planets around nearby stars
 Cepheids out to redshifts z~0.1 (measure H_0)
 measure  matter and H_o in far fields
 Measure t_o (age of stars)
 radioactive decay of Thorium in old giants below RGB
tip.
 Geometry of the Universe via Supernovae at z~3 (q_0)
 Main goal is to break degeneracy of omega matter and
omega lambda.