A
thermal and mid-infrared imager and spectrograph for the E-ELT
Two Mid-infrared instrumentation studies for the next
generation telescope E-ELT have been performed by a consortium consisting of
the MPIA, the
MIDIR is a combined imager and spectrograph for
the 42m European Extremely Large Telescope, E-ELT. It will cover the wavelength
range from 3 to 20mm with a goal to extend the wavelength coverage to 27mm if the
atmospheric properties of the site are sufficiently good. Because of the
naturally high thermal background from telescope and atmosphere the main applications
for MIDIR will be imaging and spectroscopy at highest angular resolution and
high spectral resolution. In these areas MIDIR will be complementary or even
superior to future space facilities like JWST-MIRI. Additional capabilities of
MIDIR include quick response times to targets of opportunity and high time
resolution (order of milli-seconds). To reach its maximum resolution and
sensitivity, MIDIR will require an adaptive optics (AO) system. Due to the
thermal emission from additional warm surfaces in the optical train MIDIR
requires an IR-optimized and cooled AO system.
The combination of an E-ELT at a good site with a
dedicated mid-IR instrument enables compelling science cases in numerous areas
from the conditions in the early Solar system to Gamma-ray bursts at very high
redshift. Including the formation and evolution of proto-planetary disks and
the luminous centers of active galaxies MIDIR is best suited to study the
origins of life in the Universe and the evolution of galaxies. Because of the instrument’s
flexibility, the discovery space of MIDIR does not crucially depend on the
projection of current science “killer applications” 15 years into the future.
MIDIR is one of eight instruments currently being
studied for the E-ELT. This report summarizes the results from a nine months
long instrument “Small Study”, which has been partially funded by the EU.
Table 1 lists the main instrument/AO parameters and
requirements on the telescope. Our study shows that a first-rate mid-IR
instrument on the E-ELT is scientifically recommended and technically feasible.
The guaranteed scientific return and the reduced demands on the wavefront
quality (with respect to optical/near-IR instruments) suggest MIDIR as a
first-light E-ELT instrument. MIDIR does not require developments of
fundamentally new technologies, but extends certain technologies beyond the
current state-of-art. However, several issues need to be addressed in more
detail in future studies.
Table 1: Summary of instrument, telescope and AO requirements and parameters.
Parameter |
Value |
|
|
Instrument parameters |
|
Wavelength range |
3.5 – 20mm (goal: 3.5 – 27mm) |
|
Instrument modes |
·
broad/narrow-band
imaging ·
low
resolution, long slit spectroscopy (R~300) ·
medium
resolution IFU spectroscopy (R~3000) ·
high
resolution IFU spectroscopy (R~50,000) |
|
Field of view |
~ 40² ´ 40² (imaging) ~1² ´ 1²
(IFU spectroscopy) |
|
Image quality |
diffraction limited at all
wavelengths and field positions |
|
Entrance window |
~150 – 250 mm Æ |
|
Mass |
4700 kg (incl. electronics) |
|
Size |
3 ´ 2.3 m3 + 1.4 m3 (without AO) |
|
|
Telescope requirements |
|
Acceptable telescope f/# |
4.5 – 15 |
|
Minimum scientific field size |
1.5' ´ 1.5' |
|
Straylight baffling |
no warm baffles |
|
Thermal emission |
optimized for low thermal
background and minimum number of surfaces |
|
Maximum zenith angle |
60 degrees (limited by AO
performance) |
|
Focal station |
Cassegrain or Nasmyth |
|
Back focal distance |
³ 500 mm |
|
Instrument attachment |
off-line image de-rotation in
software, fixed pupil |
|
Chopping |
no requirements |
|
Pointing/tracking accuracy |
~1² (1-s) |
|
Telescope site |
as high (h ³ 4000m) and dry (PWV << 1mm) as possible |
|
|
AO requirements |
|
Principle |
single-conjugate system,
specific to MIDIR |
|
Operation |
encapsulated and cooled to
TBD Kelvin (mid-IR optimized) |
|
Performance |
³ 50% SR at
L&M, 80% SR at N&Q |
|
Correctable FOV |
³ 40² ´ 40² |
|
ADC |
intern, if required at all
(TBD) |
Responsible: Rainer Lenzen
Last modification:
18.07.2007