Transcript A mid-IR Instrument for the ELT

Toby Moore Liverpool JMU
RAS, London, May 2008
Infrared wavebands
Region
Near-infrared
Wavelength
1 – 5 μm
Temperature Typical Objects
580 – 2900 K red giant stars, galaxies, YSOs
Thermal near-IR
2.5 – 5 μm
580 – 1160 K
Mid-infrared
5 – 40 μm
70 - 580 K
Far-infrared
40 – 350 μm
8 – 70 K
planets, PP disks, warm dust
emission from cold dust
AstroNet Science Case recommendation for mid-IR
astronomy:
“Near- and mid-infrared imaging and spectroscopy at high
spatial resolution and sensitivity provided by an Extremely
Large Telescope with high performance adaptive optics
will be essential…” (page 138)
The Mid-Infrared Toolbox
Imaging:
• Low susceptibility to dust extinction
• Continuum emission from dust (and very small grains)
• e.g. young circumstellar discs: reduced contrast of star/disk ratio
Spectroscopy:
• Atomic fine-structure lines
• Atomic hydrogen lines
• Molecular hydrogen lines
• Polycyclic aromatic hydrocarbon (PAH) emission features
• Silicate emission/absorption features (crystalline and amorphous)
• Ices: H2O, CO, CH4, CH3OH, NH3
• Gaseous molecules: CO, H2O, CH4, C2H2, HCN, OH, SiO2, H3+
• e.g. isotope ratios D/H, gas content of circumstellar discs, etc.
Polarimetry:
• Asymmetric dust grains  short axis and L are aligned with B-field
 dichroic effect  radiation passing through a medium  partially
polarized
• Absorption: position angle ║ B-field; emission: ┴ B-field
METIS Science Case
•
Proto-Planetary Disks
Physical structure of the gas vs. dust disc: evidence for young planets;
timescale and mechanism for gas dissipation (photo-evaporation, disc
winds, planets, …); chemical content of the inner disc as a function of
radius (water, organic molecules, …)
•
•
Properties of Exoplanets
Solar System
Primordial material in cometary nuclei. 3-5μm spectrocopy
•
The Growth of Super-massive Black Holes
QSO activity at high z; evolution of nuclear starburst activity
•
•
•
•
The Formation of Massive Stars & the stellar IMF
The Galactic Centre
Formation of Massive Ellipticals: Morphologies of the hosts of Submm Galaxies
GRBs at high redshifts
METIS Instrument Modes (TBC)
Derived from science case and subject of Phase-A study
BASELINE:
• L M N band diffraction limited high contrast imager (20"×20")
• L M N-band high-resolution (R ~ 100,000) IFU spectrometer
(1"×1")
• Coronagraph
• Low resolution (R ≥ 100) spectroscopy (included in imager)
OPTIONAL (subject to phase A study):
• Larger field of view
• Medium resolution spectroscopy (IFU or long slit)
• Q band (imaging and spectroscopy)
• Linear polarimetry (imaging and R ≥ 200 spectroscopy)
Can the E-ELT compete with JWST-MIRI?
• Comparable PS spectral sensitivity
• Continuous spectral coverage
• 5-8 times higher angular resolution
• Larger FOV with constant PSF
• High spectral resolution (kinematics)
• Better imaging sensitivity
• Shorter response times
• Much better LSB sensitivity
• Optional polarimetry
• Better spectro-photometric stability
• Follow up as for HST →VLT
• 100% sky coverage, good weather
Space and Ground are Complementary
Anticipated Timeline (TBC)
 Sep 05 – Jul 06 MIDIR Small Study (EU)
 Oct 07
start preparations for phase-A
 Mar 08
submission of phase-A proposal
May 08 – Oct 09
phase-A study
2010 – 2012
phase-B
2013 – 2017
phase C/D
2017
first light
Phase-A Work Distribution
Adaptive Optics for the mid-IR
The need for AO...
...and expected performance
• wavefront sensing at 589nm  correction at 12μm?
• effect of water vapour fluctuations?
internal (low order) mid-IR wavefront sensor?
interaction with E-ELT AO system?
Nodding and Chopping
•The E-ELT will not provide
classical chopping
•The nodding performance is still
unclear
Chopping Method
Field
Extended
Restrictions Objects
Comments
Efficiency
(exposure
time)
Focal Plane Chopping
few arcsecs
bad
0.45-0.9
technical risk
Pupil Plane Chopping
~10 arcsec
bad
0.45-0.9
technical risk (AO challenging,)
none
good
<0.5
?
good
(TBC)
0.15 (– 0.9?)
Dicke Switching
Nodding/Dithering
very good flat field calibration device;
should be implemented in any case
will depend on detector, site and
weather; needs testing of suitable fixed
pattern noise filtering
Gratings
Need ~1-m gratings for R ~ 100,000 spectroscopy
 Directly ruled for longer wavelengths
 Explore alternative grating technologies:
• Immersion gratings (development SRON) in silicon for
L+M band?
• Volume Phase Holographic Gratings (development
ATHOL and within OPTICON FP-6). Q: Are there now
photosensitive materials transmissive beyond 2.5 μm?
Other Technology Developments
Mirrors: 3-mirror astigmats require highly aspheric mirrors that
can easily be made using diamond milling, but surface
roughness too high for METIS.
IR-Detectors: for mid-IR wavefront sensing (not science)
Fibres: (not part of instrument baseline) Could be included if
reliable, cryogenic fibres for λ < 13μm exist.
New materials: (not part of the instrument baseline) lightweight and simplified cryostats?
Coatings: filters and dichroics (UK involvement - U of
Reading)
UK contribution
The JWST-MIRI Spectrometer pre-optics (SPO) have
been developed, built and tested by the UKATC.
At the heart of the MIRI SPO are four all-reflective
diffraction-limited integral field units.
The METIS concept includes a requirement for high and
medium spectral resolution IFUs similar to those in the
MIRI SPO.
We intend to build on the JWST-MIRI spectrometer preoptics concept to support this area of the METIS Phase A
study.
The JWST-MIRI Integral Field Units
Camera 3 & 4
Collimator
Collimator
IFU 4
IFU 3
Grating 4c
Grating 3c
Grating 4b
Grating 4a
8 x 8 arcsec FOV
relayed from
OTE by IOC
D1a,b,c
Grating 3b
Grating 3a
D2a,b,c
Grating 1c
D3a,b,c
Grating 2c
Grating 1b
Grating 1a
DGA-A
FPA 2
Grating 2b
Grating 2a
IFU 1
IFU 2
Collimator
Collimator
Camera 1 & 2
DGA-B
FPA 1
• All aluminium design for ease of
alignment.
• Slicer mirrors diamond finished by
Cranfield University.
The complete MIRI SPO
10.19 mm
l
8.63 mm