These pages contain information on the functionality of the IRIS2 Infrared Imager and Spectrograph. Local project information can be found at the Local IRIS2 Project Page (AAO Local access only). Pages maintained by Chris Tinney and Stuart Ryder.
On only its second observing run, IRIS2 has helped play a major role in monitoring the fading afterglow of a Gamma Ray Burst (GRB). On what was scheduled to be a Director's commissioning night for IRIS2, the observers (Stuart Ryder and Jeremy Bailey, assisted by Frank Freeman) were contacted by Paul Price from Caltech, on behalf of the Caltech-NRAO-CARA collaboration, who wished to trigger their pre-approved ATAC override program to obtain Ks imaging of a newly-discovered Gamma Ray Burst source, GRB011121. Undeterred by the fact that the source coordinates of (11h 34m, -76o) meant that it would have to be observed below the pole, the observers swung into action, and within a short period of time, had obtained confirmation images of the afterglow. This was further complicated by:
Nevertheless, we were able to follow it for almost 7 hours (the Director having given over the rest of his night for this important event) as the source got higher in the sky, but noticeably fainter. Unfortunately, the GRB was already too faint in the J and H bands to permit an Italian collaboration to trigger their own IRIS2 spectroscopic override, but the opportunity to provide extended photometric coverage of a still fairly unique class of object shows that IRIS2 is well on the way to making a significant international scientific impact.
- the source being at a zenith distance of 74 degrees, so that
- it was partly vignetted by the windscreen, and
- a bug in the new telescope control system meant that offsets for dithering had to be fed in by hand!
GRB011121, as seen in the Ks band with IRIS2 on the night of Nov 22 2001 UT.
Final integration testing of IRIS2 revealed poor imaging performance over at least half the field of view. As a result only about one quarter of the array was available for imaging during the first (Oct/Nov 2001) commissioning run. Analysis of the images indicated the likely source of the problem was the field flattener mount. So Roger Haynes, Greg Smith, Urs Klauser and Dwight Horiuchi set too between two IRIS2 runs to redesign, re-install and test a new mount. Amazingly, despite an incredibly tight schedule, this all worked to plan (well done guys!). Image quality of 1 pixel can now be achieved at a focus value of 150 over the entire field. Further iterations on detector alignment when the science device is installed for the next (March 2002) run should deliver slight additional improvements.
Other exciting news is that the 'hot pixel' problem we thought we had with the IRIS2 science-grade device turns out to be a recently discovered effect in recently produced HAWAII arrays. No-one (including Rockwell, the manufacturer) knows why, but when you power up the detector as you cool, you get lots of hot pixels. If you don't power-up when cooling, the detector is clean! (In fact, on the last engineering device cycle when we did this the 1/f-noise-injecting super hotspot was not present, so for the Nov/Dec IRIS2 run, three-quarters of the array should be perfectly usable). The science device will be installed for the March 2002 IRIS2 run, along with the last of the sapphire grisms (the S-J) and hopefully the rest of the IRIS2 filters.
On Wednesday October 24, 2001 IRIS2 arrived at the AAT for its first commissioning and scheduled observing time. Thanks to the heroic efforts from both Site staff, and the members of the IRIS2 team, we were able to get the instrument on the telescope, and on sky by about 9pm on Friday October 25. Commissioning observations then began and proceeded in parallel with Shared Risks Service Observing until the first scheduled observer began work on October 30. For more information see "October 2001 Commissioning".
First Light! - images of the Tarantula Nebula (30 Doradus) in the Large Magellanic Cloud were the first pictures taken (after pupil alignment and focus) in the Ks passband at 2.2um. On the following night, this image of the Orion Nebula was acquired in a narrowband filter which selects out the molecular H2 nu=1-0 transitions.
The IRIS2 infrared imager and spectrograph has been the AAO's major in house instrumentation project for the last 3 years. It is expected to provide the AAO with an infrared facility with an extended lifetime. The primary scientific requirements IRIS2 was designed to address are
with secondary goals of
It is constructed around a 1024x1024 HAWAII HgCdTe infrared detector, and is essentially a f/8 to f/2.2 focal reducer in design. Spectroscopy is achieved by the implementation of an aperture wheel allowing the insertion of 1" and 5" long slits (and a matrix mask for calibration), and a wheel in the collimated space containing grisms. These grisms use ~50mm 45 degree prisms of silica and sapphire to deviate the beam and feed replica transmission gratings applied to their surfaces.
The spatial scale of IRIS2 is 0.45"/pixel, giving a field of view of 7.68' x 7.68'. The 1" slit for spectroscopy corresponds to limiting spectroscopic resolution of 2.2 pixels on the detector. At this resolution the dispersion of the silica grisms provides R~1400 and of the sapphire grisms provide R~2300.
- Imaging sensitivities & S/N calculator
Broadband Imaging Figures of Merit. Filter JHK Zeropoint
1 ADU/s at 1 airmass
Flux for JHK=0
5-sigma limiting magnitude
in 1 hr (on sky)
1.4" seeing, 3" aperture.
J 22.48 9.8e8 15.9 21.2 H 22.54 1.0e9 14.1 20.4 Ks * (22.13) (7.1e8) 13.4 19.8 K 22.13 7.1e8 13.1 19.6 * For the purposes of proposal preparation and S/N calculations we temporarily adopt the catalogued K magnitude as the Ks magnitude
for the standards to get these numbers (and do the reverse to calibrate the available deep imaging which is currently only at Ks).
- Imaging overheads
The major imaging overhead for broad band filters is the detector readtime. This is currently 1.5s with the engineering grade array, but should be faster with the science grade array.
For the current engineering array readout time of 1.5s, there is an overhead of 2s on every DRM read.
So, for example, for K-band imaging where you might be exposing for 10s in thirty cycles (before nodding the telescope to the next position), the overheads are 20% for readout. Please note that windowing is not currently possible.
You should assume an overhead of roughly 3s for a typical telescope offset when dithering or nodding to slit. If nodding the entire detector to sky (i.e. nodding by 8') then overheads will be more like 9s per offset.
- Spectroscopic sensitivities & S/N calculator
Providing a single S/N estimate for a given magnitude object in a given passband is clearly only ever going to be approximate. Sky brightnesses and atmospheric throughput in the infrared can vary by factors of up to ten, even within an atmospheric window.
- In the following calculations we have used median sky brightnesses per pixel, and median object brightnesses per pixel. This means that in a given spectrum half the pixels will have S/N better than that listed below and half will be worse. However, the these estimates should be adequate for most proposals.
- S/N estimates below are for 1.2" which should be assumed for proposal purposes for IRIS2.
- Only S/N estimates for the R~2400 saphire grisms are provided. Throughput with the silica grisms is very poor, and their use is not recommended at present.
- Nodding along the slit is assumed. If the target object is nodded to blank sky, then your S/N will be a factor of sqrt(2) worse in a given exposuire time than that provided below.
- These estimates are based on observations acquired in October 2001. Sky brightnesses in J and H will vary from night to night. In summer the sky brightness at K may be worse by up to a factor of two, and in winter, a factor of two better. These estimates should be used for proposals, but please be aware that actual performance on your run may be different.
J-band Spectroscopy : S-K grism (Saphire 240 l/mm) + J filter. See below for wavelength coverage.
H-band Spectroscopy : S-H grism (Saphire 316 l/mm) + H filter. See below for wavelength coverage.
Nodding: Exposures of 600s in MRM mode (read noise ~10e-) have sky counts > 5*read noise in 80% of pixels, and sky counts > 2.5*read noise in 90% of pixels. Recommended timescales for nodding are therefore 600s or greater.
Sky brightness per pixel distribution:
Percentile 95% 83% 69% 50% 29% 18% Sky brightness per pixel in 600s less than 1040e 520e 291e 146e 72e 52
Signal to noise per 2-pixels (ie per wavelength resolution element), In 1.2" seeing for J=17 object in 1h, nodding target along slit, object extracted from three pixels (1.35") along slit.
SKY Subtraction Noise
=sqrt(2) * sqrt(SKY)
S/N in 1h for 2-pixels 5240 102 2053 20.1
Nodding: Exposures of 300s in MRM mode (read noise ~10e-) have sky counts > 5*read noise in 90% of pixels, and sky counts > 2.5*read noise in 96% of pixels. Recommended timescales for nodding are therefore 300s or greater.
Sky brightness per pixel distribution:
Percentile 83% 60% 50% 29% 10% Sky brightness per pixel in 300s less than 1040e 416e 208e 104e 52e
Signal to noise per 2-pixels (ie per wavelength resolution element), In 1.2" seeing for H=16 object in 1h, nodding target along slit, object extracted from three pixels (1.35") along slit.
SKY Subtraction Noise
=sqrt(2) * sqrt(SKY)
S/N in 1h for 2-pixels 7272 173 2260 13.1
K-band Spectroscopy : S-K grism (Saphire 240 l/mm) + K or Ks filter. See below for wavelength coverage.
Nodding: Exposures in MRM mode are completely sky limited in even 100s exposures.
Sky brightness per pixel distribution:
Thermal radiation dominates the background at K (unlike J and H where OH emission dominates), so the background has an essentially continuum spectrum rising from 1560 e/pix/300s to 6760 e/pix/300s in a more-or-less linear slope.
Percentile 50% Sky brightness per pixel in 300s less than 3848e
Signal to noise per 2-pixels (ie per wavelength resolution element), In 1.2" seeing for K=15 object in 1h, nodding target along slit, object extracted from three pixels (1.35") along slit.
SKY Subtraction Noise
=sqrt(2) * sqrt(SKY)
S/N in 1h for 2-pixels 136800 739 2952 4.0
- Spectroscopic overheads.
The major overheads for spectroscopy are acquisition and flushing of the acquisition image residual dark current.
Readout overheads for most spectroscopy exposures (which are acquired in MRM mode) are small. There is a slight delay (1-2s) at the end of an exposure as the least-squares fit is re-done a final time and a 2s readout over the length of the whole exposure.Telescope
So, for example, for K-band spectroscopy where you might be exposing for 300s with 60 non-destructive reads (before nodding the telescope to sky), the overheads are (2s+2s)/300s or 1.3% for the exposure time.
You should assume an overhead of roughly 3s for a typical telescope offset when dithering or nodding along the slit.
Acquisition is the major overhead for spectroscopy. You will acquire your target using short imaging exposures. You should be able to get away with acquisition using 4-5 such images to put your object down the slit. If your target is faint (or hard to identify) this can easily take up to 15 minutes. The night assistant will also need to acquire a guide star. This is usually done in parallel to getting the target close to the slit, but can add an extra overhead of a few minutes.
Flushing acquisition residual images.
MRM mode exposures after an acquisition image can suffer from increased noise due to the the residual image left from the acquisition process. It is suggested that you should expect to add up to one minute taking a dark after your acquisition image, before you start a long MRM.
This guide is currently under development. We are providing information here as we learn it, so please bear with us if the particular factoid you need is not here just at the moment.
The InstrumentIRIS2 is a fairly straightforward all-transmissive collimator-camera focal reducer (from f/8 to f/2.2). The optical train contains 10 elements ( a window + 4 element collimator + 5 element camera). All elements were specified to the manufacturer to be coated to better than 2% reflectivity. In order to maintain simplicity, scale changes are achieved by changing top-ends. So changes can be made between, but not during, nights.
The figure shows the general IRIS2 layout.
It is available in several forms.
Top end Pixel scale Field of view f/8 0.449+-0.002"/pixel
7.7'x7.7' f/15 0.24"/pixel
4.1'x4.1' f/36 0.10"/pixel
Cryogenics & LayoutThe instrument is kept cold by two Cryodyne closed-cycle refrigerators. In order to ensure minimal thermal cycling of the fragile (and valuable) detector, the instrument has two dewars. The main dewar contains all the collimator-camera optics, the detector and the pupil, filter and grism wheels. This dewar has a long cycle time, and it is hoped that once commissioned, this dewar would be kept cold and untouched permanently. It also has an auxiliary liquid nitrogen cooling system which is used to accelerate cool down.
The fore-dewar contains the aperture wheel, and room for future expansions to include a multi-slit juke-box, IFU elements and polarimetry analysers. It will be able to be cycled on a one day time-scale, so user provided filters, masks etc., will go here.
WheelsThe IRIS2 wheels are self explanatory. The aperture wheel or slit wheel has: fully clear and fully opaque apertures; 1" and 5" long slits for spectroscopy at f/8.
The 12 position coldstop wheel sits at the re-imaged telescope pupil, and is loaded with cold stops for use in applications where thermal background is critical. This wheel is also used for narrow band filters at short wavelengths, where the instrument can be used without a cold stop.
The 12 position filter wheel contains filters for use with the cold stop.
The 8 position grism wheel contains up to five locations for mounting spectroscopic prisms, as well as an opaque position for obtaining detector darks.
FiltersThe current filter complement is listed below. All filters are 60mm in diameter, which is required for unvignetted operation at f/8. These filters were purchased as part of the GEMINI IR Filter Consortium. The dates listed under Acquired? are the dates when NDC Infrared Engineering (the supplier) has said they will provide these filters - these have obviously not been accurate in the past. The filters labeled yes have all been installed as at October 2001.
Filter Name Cut-on Wavelength
Acquired? Broadband J 1.164 1.325 yes H 1.485 1.781 yes Ks 1.982 2.306 yes K 2.028 2.364 yes Z 0.996 1.069 Allegedly July 2001 Narrowband He I 1.075 1.091 Allegedly August 2001 J continuum 1.198 1.216 yes but not yet installed Pa Beta 1.272 1.292 yes H continuum 1.558 1.582 yes [Fe II] 1.632 1.656 yes Methane Offband (CH4_s) 1.53 1.63 yes but not yet installed Methane Onband (CH4_l) 1.64 1.74 yes but not yet installed H2 nu=1-0 S(1) 2.106 2.138 yes Br Gamma 2.150 2.182 yes H2 nu=2-1 S(1) 2.231 2.265 yes K continuum 2.253 2.287 yes CO(2-0) band head 2.278 2.312 yes
Instrument throughputs, countries and formats
Instrument throughput for imaging
IRIS2 Imaging Filter Start
for JHK=15 star
Approximate* Sky Counts
Comments J 1.164 1.325 1.245 161 5105 870 80 H 1.485 1.781 1.633 296 5395 4900 14 Ks 1.982 2.306 2.144 324 3988 4870 14 K 2.028 2.364 2.196 336 (3698) 6420 10 Z 0.996 1.069 1.033 73 - - He I 1.075 1.091 1.083 16 - - not delivered yet J cont 1.198 1.216 1.207 18 - - not installed yet Pa beta 1.272 1.292 1.282 20 240 280 H cont 1.558 1.582 1.570 24 349 190 [Fe II] 1.632 1.656 1.644 24 458 750 Methane off 1.53 1.63 1.58 100 - - not installed yet Methane on 1.64 1.74 1.69 100 - - not delivered yet H2 nu=1-0 S(1) 2.106 2.138 2.122 32 355 190 Br gamma 2.150 2.182 2.166 32 397 175 H2nu=2-1 S(1) 2.231 2.265 2.248 34 376 193 K cont 2.253 2.287 2.270 34 472 140 CO(2-0) bhead 2.278 2.312 2.295 34 370 190 * Reported values measured in October 2001. These can be expected to be higher at wavelengths longward of 2um in summer, and lower in winter.
Wavelength ranges and Count rates for spectroscopyThe following table summarizes the IRIS2 grism wavelength coverage and throughput as measured at October 2001 Commissioning.
These measurements were made with the 5" slit in 1-1.5" seeing and photometric conditions using the Carter & Meadows (1995, MNRAS, 276, 734) standard star HD38150 at Airmass=1.24. The numbers reported below have been scaled for exposure time and detector gain, but not airmass.
IRIS2 Grisms Grism Filter
Comments Sapphire Grisms (R~2400) S-K
2450 2.04 2.38 0.45 158 40 (at 2.04,2.38um) Short wavelengths cut-off by K bandpass
Long wavelengths cut-off by K bandpass
2400 1.155 1.278 0.25 340 280 (at 1.155um,1.278um) Short wavelengths cut-off by J bandpass
Long wavelengths cut-off by detector format
2500 1.575 1.80 0.33 152 76 (at 1.80um)
11 (at 1.82um)
Short wavelengths cut-off by detector format
Long wavelengths cut-off by H bandpass
~2400 Delivered, but not yet installed or tested. S-J
~2400 Delivered, but not yet installed or tested. Silica Grisms (R~1200 - not recommended at present) KH
~1600 ? 2.37 ~0.74 133 17 (at blue end) Short wavelengths cut-off by poor blaze
Long wavelengths cut-off by K bandpass
1600 1.54 1.80 0.51 212 15 (at 1.54um) Short wavelengths cut-off by poor blaze
Long wavelengths cut-off by H bandpass
1500 1.60 1.80 0.57 76 15 (at 1.64um) Short wavelengths cut-off by poor blaze
Long wavelengths cut-off by H bandpass
1500 1.17 1.32 0.39 140 10 (at 1.17um)
40 (at 1.24um)
Short wavelengths cut-off by poor blaze
Long wavelengths cut-off by J bandpass
Note that the countrates for the Sapphire grisms are currently better per wavelength unit than for the Silica grisms. Until we get the Silica grisms tilted to optimise their blaze's to lie inside the atmospheric windows, the sapphire grisms are probably to be preferred, especially as they will permit much better sky subtraction - the only case in which this might not be true is the Sil94+H vs Sap316+H comparison.
Please also note that the KH and HJ grisms can observe K or H, and H or J, not K and H or H and J simultaneously.
Gain - Engineering array
5.2 e/adu for the engineering array.Readnoise - Engineering array
15 e for the engineering array, in the absence of the 1/f noise. Probably more like twice that with the 1/f noise present, which (sad to say) is all the time.Quantum Efficiency
The 1/f noise produced by the hotspot in the engineering array appears as a "horizontal banding" on every readout. Experiments with spectroscopic data show that if you have a blank area of the array available, you can median 200-300 columns of the detector to produce a "1/f spectrum" for each image. Subtracting this from every column seems to remove this 1/f noise very effectively, and deliver near the 14-15e- performance the engineering device delivers in the absence of the hot spot. Depending on your science application, it may be worth playing with your data to see if this works for you.
Has not been measured yet. Here's the standard Rockwell curve they claim to meet.
Full Well / Linearity - Engineering array
Linearity tests show that quadrant 1 (the lower right quadrant) really sucks. Its full well is a strong function of x locations and is at best about 10,000 adu at the left edge, and falls to 2000adu or less at the right edge of the quadrant. Forget about trying to get useful data out of this quadrant.Residual Images - Engineering array
Quadrants 2-4 seem to behave well up to 28000 adu per pixel. All three quadrants show the same non-linearity behaviour. Non-linearity is less than 1% over the range 0-28000 adu.
Tests made with the slit in place illuminated by a flat field lamp, and then followed by darks, seem to indicate residual images are present at the 0.01% level. That is if you illuminate the slit with light at a rate of about 6667adu/s (ie 10000 adu in a 1.5s exposure), and then follow this with a 30s dark, you will get a residual image at a level of about 15adu (or 0.5adu/s). Clearing these residual images seems to be a matter of both taking lots of resets and reads of the detector, and just physically waiting a while.
So you have to remember that the residual image appears as a dark count. Short exposures on bright sources followed by long exposures on faint sources may show residual images, even though the 0.01% of the HAWAII arrays is quite good. This seems to mainly be a problem when you take acquisition images for spectroscopy, followed by a long MRM exposure. Experience with this is being gained, but the current recommendation is
Cross Talk between Quadrants - Engineering array
- Acquire your object in a passband with the lowest sky counts possible. This will usually be J.
- Before you start a long spectroscopy sequence, take a dark 1.5s x 30cycle DUMMY. Experiments show this will reduce residual image contamination by a factor of about 5. If your target is faint enough to need long MRM exposures, this overhead is worth it.
- Be aware that the first spectrum you take after acquisition may still have slightly higher noise.
Small (but not zero).
Image ScaleImage scale was measured using telescope offsets to be = 0.449+-0.002"/pixel.
Note that this is the average over a large fraction of the field. There is astrometric distortion in the IRIS2 optics, which results in the image scale at the far corners of the array being about 1.4% different from that in the array centre.
Detector OrientationThe information provided here is current for the October 2001 commissioning run. The detector may be re-aligned precisely with NW by either the November run or the next run in Semester 2002A.
The detector orientation as it appears on the SKYCAT display (and in FITS files) is North to the bottom, W to the left, when IRIS2 is used in its default Cassegrain rotator=90 orientation (instrument rotation is not currently possible).
On the October commissioning run, the detector was slightly misaligned, with North rotated away from the array column direction by 80'+-5' in the sense N through E. This should be corrected by Semester 2002A.
A postscript copy of this graphic is available here.
Slit Orientation on Detector and on SkyThe slit was observed to be oriented N-S on the sky to within 5' (or 0.08 degrees) on the October 2001 commissioning run. This is the sort of uncertainty within which the Cass rotator can be positioned. The table below shows the measured slit location in (x,y) and FWHM along the slit. The 'widening' away from the field centre is almost certainly due to the optical image quality problems seen in October 2001 commissioning. The slit itself is very close to 150um in width along its entire length.
150um (1") slit alignment an FWHM (on detector)
October 2001 Commissioning run.
536.90 44 2.32 532.61 238 2.12 530.44 336 2.03 525.64 551 1.99 523.36 652 2.06 521.09 752 2.28 515.62 995 3.28
Slit re-positioning accuracyTests of slit re-positioning show that the slit seems to re-position with no backlash to <0.1 pixel when the instrument is nearly upright.
At large angles to the West (~5h west where tests have been done), the slit seems to re-position to < 0.1 pixel as long as it always moves in the same direction. That is, going Open->150um slit repositions to < 0.1 pixel. Going Blank-> 150um slit also re-positions to < 0.1 pixel, but shifted by ~1 pixel from the position obtained going in the direction Open->150um.
So, currently it appears that normal acquisition (switching between the Open and 150um slit) will re-position the slit to <0.1 pixel.
CalibrationRecommended calibration procedures are in a state of flux, as we gain experience. Here's what we know
The dome flat patch on the windscreen can be illuminated using lamps mounted at the Prime Focus access area. There are two lamps, which can be plugged into a socket, the voltage for which can be controlled from the control room. The two lamps are a desk lamp, and a much brighter flood lamp.
If the telescope is not positioned for dome flats, ask the night assistant, support astronomer or afternoon technician to put it there. (Dome=0deg, Windscreen=21deg)
Night-time - Photometric StandardsThe Carter & Meadows standards and CIT/CTIO standards are generally too bright to be observed in the shortest integration time (1.5s with the engineering grade array). The UKIRT Faint Standards, particularly FS1-FS35, are well-suited to 3-10 sec exposures (for more information on these standards see Hawarden et al. at 2001, astro-ph/0102287). Other standards in common use include the LCO Red stars, the HST/NICMOS Faint Standards, and the Hunt standards. As usual, it is recommended that standard stars be observed over a range of airmasses similar to that of your targets.
Transformations from the IRIS2 system to other systems will be provided once enough stars spanning a wide range in colour have been observed. In the meantime, fussy observers should observe a suitable range of standards to calibrate their own data.
Night-time - Smooth Spectrum StarsFinding standard (i.e. smooth spectrum stars of your favourite type) can be easily done with the Gemini Search Tool included in the NIRI spectroscopic proposal preparation information. This Gemini list includes A,F,G and K dwarfs.Night-time - Spectro-photometric Standards
You can also look at the ESO VLT Spectroscopic Standard information. Their list also contains O and B stars as well.
There aren't any!
In the optical, one uses spectrophotometric standards that have tabulated fluxes and wavelengths. In the IR, there are no such standards. There are some pseudo-standards, in the sense that tables of flux versus wavelength do exist for some stars. However the fluxes are either derived from models (for DA white dwarfs) or from a scaled version of the solar spectrum (for solar analogs). These standards are for space based missions and are not particularly useful in calibrating ground based data.
So the usual procedure is to use 'smooth spectrum' standards (see below) to remove the effects of terrestrial absorption on your spectra. Then you can use the same standard (if its photospheric temperature and magnitude is known), or another standard (with known photospheric temperature and magnitude) to create an absolute flux scale.
Dome flats - J,H,K,KsWe currently expect the best procedure will be to take 'lamp on'-'lamp off' sequences with the telescope pointed at the white patch on the dome .
Change the lamp at Prime Focus access to the desk lamp. Adjust the dome flat lamp intensity (from the knob in the control room) to get ~9000 adu with the lamp on at Ks in 1.5s. Then check that with the lamp off, there is a difference in recorded counts from the lamp on of at least 4000 adu/pixel (this may get hard to achieve in summer, especially for K band flats - in this case you'll just have to take more flats to beat down noise).
Recommended exposure times are Ks=1.5s, H=3s, J=4s, (and do about 30 cycles). Then for each filter repeat with the lamp off.
There is a sequence to do this. Set up the lamp to get the right counts in Ks (above) in 1.5s. Then start dome_broad_on.tcl. Then turn off the dome flat lamp, and start dome_broad_off.tcl. Each sequence takes about 7 minutes to run.
Dome flats - Narrowband filters
For narrow band filters change the desk lamp at prime focus for the large lamp. Turn it right down the control room dial to its minimal setting. You should get 8-9000adu in a 1.5s exposure with the H2v=2-1. Then the following table indicates rough count levels for all the filters in 1.5s.
Filter Time Desk Lamp on full
Desk Lamp off
H2v=1-0 1.5 11000 Br gamma 1.5 10000 300 H2v=2-1 1.5 9500 500 K cont 1.5 10000 1000 CO 2-0 1.5 7000 800 Pa beta 1.5 6000 H cont 1.5 8000 Fe II 1.5 12000
There are sequences to take all these. Set up the main lamp (as dim as it will go) to get the right counts in K2v=2-1 (as above) in 1.5s. Then start dome_narrow_on.tcl. Then turn off the dome flat lamp, and start dome_narrow_off.tcl. Each sequence takes about 10 minutes to run.
Spectroscopic flatsCan be done from the dome patch as above, but you'll need to swap the desk lamp at Prime Focus for the large lamp. Once again use a 'lamp on'-'lamp off' sequence. Currently we expect that dome flats should be taken in the same read mode as your object observations (i.e. MRM observations would need MRM dome flats, and DRM observations would need DRM dome flats). For MRM observations/flats you may probably want to have roughly the same number of reads in both dome flats and observations.
Use the main lamp at PF access, and turn it all the way up. If you've just taken arcs, take a 1.5sx30 dark to flush any residual images.
- S-K + K, S-K+Ks - 20s x n. NBTake a 'lamp off' exposure BEFORE the lamp on exposure.
- S-K + J - 20s x n
- S-H + H - 20s x n
Arcs / Wavelength CalibrationFor detailed information on arc calibration, and useful archive data see the Wavelength Calibration page.
Unfortunately the current arc lamp system does not produce a large number of lines in all the band-passes. You can try to use the OH emission night-sky lines in your spectra, but experience seems to indicate these only work well in the H band. In the J-band the contrast in these lines is not as good as in H, while in the K-band you will run out of lines at the red end of the spectrum.
The overheads in taking arcs for every exposure will also be large. At present we therefore suggest you see wavelength calibration as a two step process.
Obtain arcs at the start or end of your night, for the purposes of dispersion correcting your data (ie putting all the rows of the detector onto a linear wavelength scale). If wavelengths shift during the night they are most likely to do so in small shifts - not changes to the overall dispersion curve. So data at the start or end of the night should be adequate to dispersion correct all your data. Use the night sky lines to correct for small shifts in wavelength zero-point during the night, if this is critical to your program.
Arc lamps are mounted
in the AAT chimney (and can be observed by lowering the diffuser flap on the calibration box, and turning on the lamps you want). Only the CuAr and FeAr lamps here are useful, and only in the J band. and on the back of the TV mirror carriage in the Acquisition and Guiding Unit (AGU).. A Xe lamp has been mounted here. To use it, ask the night assistant to switch to Aux Focus, then switch the lamp on using the remote switch next to aatssf (select FULL POWER).
Arc J window H window K window Comments CuAr + FeAr 60sx2 Only 2 lines Nothing Only useful in J CuHe Nothing Nothing Only 2 lines Ne 60sx2 Nothing Nothing Several lines in J window, but only few
hundred adu in 30s against a bright background
Xe 5sx10 30sx2 20sx4 Many good lines in J. Eight good lines in H
A dedicated Cassegrain calibration unit including an integrating sphere, and an automatically controlled set of lamps (arcs and incandescent) is in preparation.
IRIS2 can run from two accounts: "aatobs" or "iris2tes" (passwords are available from your support astronomer). Use the "aatobs" account for actual observing - it will try to connect with the telescope system running on aatssz. You should use the "iris2tes" account for testing the system, as it will not connect to the telescope system, and so can't interfere with actual observing. You can run a simulation of the telescope if you want.
CommandsThere are three different commands available from both accounts:
iris2 - runs the full system controlling both dewar mechanisms and detector.
iris2dsim - run with the dewar mechanism control in simulation but using the detector.
iris2sim - run with both dewar and detector simulated. This runs entirely on the solaris system and needs no other hardware.
To run the PTCS telescope system
This needs to be running before IRIS2 is started up.
- Make sure the correct disks are in the CCS labeled:
- RTOS-X (in C6)
- AATCS 2000 (for use with RTOS-X) (in D6)
- Initialise the CCS if it is not already running.
- Reset the VME system (black RESET button at top) in the bottom of the CCS rack (this machine is ccsgate), and wait about a minute for it to complete its reboot
- Log into aatssz as "aatobs"
- Type the commands:dits_netstarttelThe telescope control interface should now come up and connect with the CCS. This may take 10-30 seconds and the display will start updating. If this does not happen, type cleanup in the window from which it was started (better yet, do it twice!), then go back to step 2 above. You can reinitialise the CCS at any time and the system should reconnect to it and continue running. To shut down the PTCS, use the cleanup command as above.
Full startup procedureThis describes the complete sequence from scratch. Currently it is probably best to reset everything each afternoon, or if you need to recover from a crash or hang at night. Given all the steps involved, it is best to get an AAO staff member to do this.
- Reset the following:
- The IRIS2 VME system (aatvme6) behind the partition in the control room, using the black button at the bottom of the unit. This just resets aatvme6 and the fibre optic link to the controller (not the Solaris system aatvme10). When it has come up fully, the two lowest red lights should be on (indicating there is a carrier to and from the controller), and the uppermost of the green lights in the adjacent panel should flicker (indicating the Sparc and the VME are talking to each other).
- The controller (on the side of the dewar) using the switch labeled RST (one of a group of three switches on the end module S/N 12 in the unit). Don't hit the one marked POWER in the adjacent module!!!!
- The dewar VME system (aatvme7) in the Cass rack using the red button marked RESET.
- Power cycle the dewar electronics - the top unit in the rack above aatvme7. The switch is on the back, so be careful reaching for it.
N.B. - you don't need to reset the dewar system if you are going to use the iris2dsim command, and you don't need to do any of these resets if you are using iris2sim.
- telnet to aatvme6 from a window on any machine. It will take about 5 minutes from reset before it is ready. When you connect it will start outputting messages on the terminal. Type through these to log in:username: vw16xpassword: 16xtarget
Then type the following commands:td t1(this will stop those annoying messages coming out)cd "/instsoft/drama/local/dct/r0_3/vw68k"<vxdctload
Note - the following instructions set up the system to run with the user interface on the aatssx console and the image display on the aatvme10 console. However it can be run from any X terminal or console by logging in to aatvme10.
Log in to aatssx using any account.
On a terminal window type:
xhost aatvme10then telnet to aatvme10 and log in as "aatobs". Type the following commands:(only if you want to run a telescope simulation - omit this if you are connecting to the actual telescope)dits_netstarttel(or iris2sim, or iris2dsim)iris2
This will bring up the system on aatssx. If the startup has completed successfully, you will be greeted with a "System Configuration" window (shown below), which selects the data/dummy directories and file root name by default, and allows you to specify the first run number (generally you should not attempt to overwrite existing files) as well as the names of the Observers. You can then exit from the skycat window here. Log in as "aatobs" again on the aatvme10 console and type skycat. In this way you get the IRIS2 GUI and skycat (image display) on two different screens.
If for some reason the system does not come up properly, the best solution is to type cleanup in the aatvme10 window from which IRIS2 was started (not the aatssz window from which the PTCS was started!), and once more for luck. Then try dits_netstart and iris2 again. If this still doesn't work, you may have to go back to the very beginning. Keep trying, and you should be rewarded eventually!
To close down IRIS2Go to the original terminal window you typed the iris2 command in, and typecleanupThis will shut down everything except skycat. You can leave skycat running if you want to restart. You will just have to go to the "Detector" menu and select "Reset Server Connection..." after the IRIS2 system has restarted.
Once IRIS2 is up and running, you should have four displays visible on various terminals:
The Portable Telescope Control System (PTCS) duplicates much of the functionality of the telescope control console and night assistant's terminal. It allows the observer to switch between the Reference axis "R" (which is the default whenever a slew occurs) and the pre-defined apertures "A" and "B". To command a specific offset, or slew to a new coordinate, the observer must first click on the green "Control OFF" button, which will then change to "Control ON" highlighted in yellow. From the "Commands" menu, select "New Target¨ and enter the RA, Dec, Epoch, proper motion, etc., then hit "Slew" to send the coordinates to the Control Computer System (CCS); this may take a few seconds - watch the CCS terminal, which should load the new coordinates and commence the slew. To offset the telescope slightly, select "Offsets..." from the "Commands" menu and enter the offsets in arcseconds. Note that for RA, the offsets are in arcseconds on the sky, not arcseconds of polar axis rotation as they are on the night assistant's console. To go back to the Base position, enter offsets of (0,0), not the negative of the previous offsets entered. Note also that switching Control ON (which can also be commanded from an Observing Sequence) makes the current telescope position the new Base position. If the PTCS window freezes (as can happen if an Xterminal runs out of memory), then it is best not to kill it, as this will require bringing up the whole PTCS and IRIS2 system from scratch. The PTCS process should still be running, so all that is necessary to re-connect to it is to start up a new PTCS window from the original Xterm by typing tel2 (if this one also freezes, another can be started as tel3, etc.). However, ultimately you may still need to reboot the Xterminal and start all over again anyway.
This shows the status of various IRIS2 sub-systems (e.g. the SPECTRO task which controls the instrument configuration, the DRT task which takes and records the observations, etc.), which will (hopefully) all be green. Below this is a Messages sub-window which will alert you to any problems during startup (e.g. a wheel might have failed to home properly) by highlighting them in red. There is an "Exit" option in the "File" menu, but in practice the only safe way to shut down IRIS2 is to use the cleanup command as described above. The "Reset" option under "Commands" will do a soft reset of all tasks, and bring up the System Configuration window again, but experience suggests it is best to run the system down at the end of each night. It is possible to send low-level TCL commands to move the wheels to non-standard positions using the "TCL Command" option under the "Commands" menu.
IRIS2 User InterfaceThis is the main configuration and control system for IRIS2. It is divided up into 6 sections:
Instrument Configuration: is a schematic representation of the light path through the instrument as currently configured. If the light path is blocked at any point by a blank in one of the wheels, the light rays will be coloured red. Once light reaches the detector, the light rays change to blue. In imaging mode, the light rays should all come to one focus at the detector; whenever a grism is in use, dispersion is indicated by two separate light rays/wavelengths coming to two separate foci on the detector.
Whenever the observer selects a new instrument configuration from the Spectrograph section, the outline of the dewar changes from black to red; only when the observer has done a "Configure", and all the wheels/translator have arrived at their desired positions, does the outline change back to black again. Whenever a wheel or the array translator is moving, its status will change to "Moving" in this display, and the grey circle at lower right will blink red. The "Dewar Status" display underneath should show green; if not, the dewar temperature or pressure which is out of range can be identified by selecting the "Dewar Status..." option from the "Commands" menu.
Spectrograph: allows the observer to manually reconfigure IRIS2, though mostly this will be done as part of an Observing Sequence. There are three tabs: "Image", "Spectra", and "All" to allow changes specific to that mode only. Pull-down menus to the right of each wheel location allows the observer to select the appropriate filter, grism, cold-stop, or slit. However, only after pressing the "Configure" button underneath will all the requested changes take place in sequence. Similarly, entering a new array translator focus value has no effect until the "Configure" button has been pressed. The "Auto" option next to "Focus" will allow automatic compensation for the change in camera focus with wavelength/filter (this function is not yet implemented, so has been disabled). The four buttons marked "J", "H", "K" and "Ks" are accelerators, in that they not only select the designated filter, but also set Grsim to OPEN_TUBE, select the appropriate coldstop based on the current top end, and then do an immediate "Configure". The "Edit" button will (at some stage in the future) permit the observer to store particular configurations, for later recall as part of an Observing Sequence.
Detector: allows the observer to set up and record a single image. The observation number of the next run to be recorded (that is not a dummy or a glance) is shown at the top. Currently, only one readout speed ("Normal") is available, with a minimum exposure time of 1.5 sec. "Time Series" mode can be used to save a series of exposures as a 3-D datacube (select "Keep cube"), or more commonly, is used in a `movie mode' to monitor changes in object position, focus, etc. in real time. Simply select "Time Series", "DRM", and "Glance", set the time for a single exposure, and set "Cycles" so that the sequence will run for long enough to accomplish what you wish to do (unfortunately, time-series readouts cannot be aborted once started).
There are three choices for readout mode of the array:
- DRM stands for "Double Read Mode", which consists of one read at the start of the exposure, and one read at the end of the exposure. Only the difference between these two is saved in a file. This is the optimum readout mode for broadband imaging, since it has the lowest overheads, and the data is always sky noise-limited rather than detector noise-limited. The value of "Time" is the interval between the two reads, and "N of Reads" is set to 2 by default. To cut down on disk space usage, a number "Cycles" of exposures can be averaged before being written as a single file. Further iteration is possible by setting the number of "Repeats", but for most purposes, the need to dither or the use of time-series mode (see above) makes this fairly redundant.
- MRM stands for "Multiple Read Mode" (also known as "Up-the-ramp" sampling), in which the array is read non-destructively at several equally-spaced intervals (referred to here as the "Period"), and a fit is made to the samples at each pixel. This method is robust to cosmic rays, and yields the lowest read noise (so is preferred for spectroscopy), but has the highest overheads. The Period is set by the value of "Time", and the number of sampling periods will be one less than "N of Reads", i.e. if "Time" is 10 seconds, and "N of Reads" is 11, then the total integration time will be 100 seconds. Again, multiple "Cycles" can be averaged before writing to disk.
- Fowler stands for "Fowler sampling", which is similar to MRM except that the array is read more often near the beginning and near the end of an exposure. This mode is not yet implemented with IRIS2.
There are also three types of observation:The object name to be saved with a single exposure can be entered here (or during an exposure, if the integration is long enough). The "Run" button initiates an observation of the specified type. The "Dark", "Flat" and "Arc" buttons don't actually set up for any particular type of exposure, but do set the OBSTYPE keyword in the header, so that they will be archived as calibration, rather than science exposures.
- Normal: the final image is displayed in Skycat, and written to disk in the iris2_data/ area with the root name and file number specified. These files will be archived.
- Dummy: the final image is displayed in Skycat, and written to disk in the iris2_dummy/ area with the name "a.fits", then "b.fits", etc. until "z.fits", after which "a.fits" is renamed to "a.fits.old" and a new "a.fits" is created. None of these files are archived, but they can be used for "bias" subtraction in SkyCat.
- Glance: the final image is displayed in Skycat, but not written to disk. These images cannot be used for "bias" subtraction in skycat, nor do they have the WCS (World Coordinate System) defined.
The "Save as..." button allows the observer to set the parameters for a particular type of exposure, and then recall these in an Observation Sequence by use of the DETECTOR config <config_name> command. Be careful however - if observation type "Glance" or "Dummy" is selected and saved with the config, then the images taken as part of the sequence may not be archived, or saved to disk at all!Observe Pop-Up: This pop-up window will appear once an exposure or a sequence has been initiated, and shows the current status, and time remaining (including readout overheads).
Messages: displays the system responses to various commands, and the progress of Observing Sequences. Also shown here are the names of the data and dummy files as they are written to disk, and the amount of disk space remaining.
Window: When sub-window (individual quadrant) readouts become available, this section will allow the observer to specify which quadrant they want. Since all quadrants are read out in parallel, the use of sub-windows does not save any time in reading out, but will cut file sizes by 75%.
Sequences: allows the observer to edit and initiate Observing Sequences, which make observing much more efficient. There are two tabs: Standard and User. Standard sequences are supplied by AAO staff astronomers, and cannot be modified by visiting observers (currently Standard and User point to the same directory, so it IS possible for a visiting observer to unwittingly overwrite a Standard sequence); they can however be copied into the User area, and modified from there. As the name implies, Standard sequences are useful for routine observing, such as photometry of standards, nodding along the slit, etc. User sequences can be defined for more elaborate types of observations. Full details on the command syntax for Observing Sequences can be found in Jeremy Bailey's overview document, or by examining those sequences already supplied. To edit or run a sequence, simply highlight it with the mouse and select "Edit" (only if a User sequence) or "Run".
It allows the observer the chance to set or modify the object name ("Set Object..."), or add a comment to the FITS header ("Add Comment..."). The "Stop" button will cause a sequence to pause after the end of a current exposure (this button then changes to "Continue...", allowing the sequence to be resumed). Currently, it is not possible to abort an exposure in progress, so pressing "Abort" will have no effect, and one must wait for the exposure to finish. When a sequence is executing, this window will have two extra options: "Hold" and "Continue", which enable the sequence to be paused, and then re-started without exiting.
For reasons which are still not understood, window sometimes does not vanish at the end of an exposure as it is meant to. If this happens, it can be dismissed with the window manager (click on the top-left corner and select "Close"). You will then need to select "Clear Interlocks" under "File" in the IRIS2 User Interface main window to re-enable the main functions and commence a new exposure.
Skycat Image Display
The image display for IRIS2 is built upon the ESO Skycat tool, with some extra capabilities added to enable interaction between IRIS2 and the telescope. The display is updated in "real time", that is after each read of the array. Both Normal and Dummy runs come with full World Coordinate System (WCS) information in the FITS header, so that astrometry is possible. While the absolute coordinates are only as good as the last pointing ("SNAFU") star that was measured, the relative coordinates should be quite accurate.
When Skycat is first started, it will not be connected to the display server process. To establish the connection, start a Glance observation with the IRIS2 User Interface, then from the "Detector" menu of Skycat, select "IRIS_PROC". The display should now start updating with the latest readout of the array. When viewing old images or DSS images while taking new data, you may wish to temporarily suspend the real-time display. You can do this by selecting "Disconnect" from the "Detector" menu, then "IRIS_PROC" when you are ready to resume the real-time display. If the IRIS2 User Interface needs to be restarted for any reason, then the display server connection can be re-established by selecting "Reset Server Connection..." under "Detector".
Some information on the main features of Skycat can be found on the ESO Skycat Web pages. We will only describe here the features particular to IRIS2.
- Bias image: Quite often in infrared astronomy, the sky signal swamps that from the source, and it is only by subtracting an image of the blank sky (or any region of sky offset from the object of interest) that the source starts to become visible. To assist this process, Skycat allows the user to define an image (referred to here as the bias, but could be any type of image) which is to be subtracted from all subsequent images before they are displayed. To enable this process, select "Bias Image..." under the "File" menu. This brings up another window from which up to five different bias images can be pre-loaded. To load the first bias image, click on the "Load" button in line 1, which brings up a file browser. Select the image you wish to subtract, then click "OK". To turn on bias subtraction, select "Subtract". Alternatively, whatever image is currently shown in the Skycat display can be set to be a bias image by clicking "Copy image -> bias". You will most likely have to do an "Auto Set Cut Levels", or set the Low and High cut levels manually to scale the bias-subtracted result. To disable bias subtraction, simply de-select "Subtract" in this window.
- Reference Pixel: Currently, the WCS in the FITS header is defined relative to a reference pixel at (460,460), i.e. near the top-right corner of quadrant 2. At the start of each night, the night assistant will use the APOFF program in the CCS to define Aperture A by positioning a pointing standard in this pixel. The better the current pointing model, and the closer the target to the last pointing standard, the better will be the absolute astrometry. The location of the reference pixel can be shown by selecting "Mark Reference Pixel" under "Detector" (or hidden using "Clear Reference Pixel Mark"). To place the object of interest at the Reference Pixel, position the cursor over it, then hold down the Shift key while left-clicking the mouse. This will bring up a list of options, the first of which is "Move object to reference pixel (460,460)". Selecting this option will cause Skycat to pass the necessary offsets to the PTCS (using the WCS), which will then offset the telescope accordingly.
- Marks: Besides the Reference Pixel, there are two additional Marks that can be set by the user. Holding down the Shift key while pressing the left mouse button will bring up a list of options, including "Set mark 1 here" and "Set mark 2 here". Once one or both marks have been set, it is possible to have the telescope move any other object in the field to that pixel, by Shift+left-clicking on that object, and selecting "Move object to mark 1" or "Move object to mark 2". The confirmation dialog that comes up whenever a telescope move is requested will specify not just the RA and Dec to move to, but also the offsets in arcseconds, and (for the benefit of the night assistant), the equivalent guide probe offsets which would achieve the same result. This is the preferred option when acquiring an object for spectroscopy; coarse alignment is done by moving close to a mark on the slit axis, a guide star is acquired, and fine-tuning is done by offsetting the guide probe. The marks can be temporarily hidden by selecting "Hide Marks" under "Telescope", or restored with "Show Marks". In addition, the offset between them (in arcseconds of RA and Dec) can be called up with "Show Offset between Marks".
- Slew to Catalog Object: By calling up the coordinates of an object from a database like NED or SIMBAD using the "Data Servers" menu, then highlighting that object in the list of sources found, the coordinates of that object can be passed direct to the CCS and the telescope slewed there by selecting "Slew to Selected Object" from the "Telescope" menu.
We plan to implement the ORAC-DR data processing pipeline for IRIS2 for imaging.
- Flat fielding
Experience with the engineering grade device used to date indicates there are pixel-to-pixel sensitivity variations of up to +-20% present. So flat fielding of your data is essential.
- Sky Subtraction
Sky subtraction is the single most important aspect of infrared data processing. In the optical, you can usually just flat field your data, and then extract a spectrum from regions of the slit adjacent to your object, and then subtract that as your sky (call this "subtraction along slit"). In the infrared the night sky is so bright, that residual flat fielding errors (ie incorrect match of slit illumination function, variation in spectrograph sensitivity along slit, spatial vriation in OH emission, etc) at the 0.1-1% level can mean that residual errors from this process can be significant.
So the procedure in the infrared used is to nod your target along the spectrograph slit (or for extended objects to nod the telescope to blank sky) so that you can perform sky subtraction directly (call this "direct sky subtraction"). This adds sqrt(2) more photon noise to your data, but usually results in greatly reduced systematic errors, because you observe with exactly the same instrumental set-up and through exactly the same optics and pixels for both object and sky. Unfortunately, because you don't observe the sky and object simultaneously, variations in the OH emission as a function of time may mean that you still get residual errors in the sky subtraction. However these can be readily removed by applying a subtraction along slit subtraction step after doing the direct sky subtraction step.
Object extraction works almost idetically to the techniques typically used in the optical. There are lots of ways to do this.
o You can assume your object is straight on the detector and just extract a fixed number of rows.
o You can 'straighten' you spectra (recommended for IRIS2 data taken in October and December 2001, or taken away from the central rows of the detector) , and then extract a fixed number of rows.
o You can apply any number of 'optimal extraction' algorithms which will weight the flux extracted from each row by the brightness of the object in that row.
Which you do, and how much effort you spend, will depend on your application.
- Wavelength Calibration
See the Wavelength Calibration page, which includes arc line lists, sample arcs and crude calibrations you can apply to your data.
Like all grism systems in focal reducers, there is signficant curvature of the IRIS2 spectral format. If your data is taken in just one or two locations along the slit, you can derive wavelength calibrations for just these locations. If you objects are scattered along the slit, you'll need to either do a full 2-D wavelength calibration, or do a calibration for the location along the slit of each observation.
This is where we'll put technical information, appendices, the sorts of stuff observers will need to know only occasionally.
To reboot aatvme10From the "aatobs" account in an xterm logged in to aatvme10, typeaatvme10_reboot
aatvme6 188.8.131.52 aatvme7 184.108.40.206 aatvme10 220.127.116.11
To put a wheel into simulation mode
Login to aatssy as a member of the "drama" group. Thencd /instsoft/drama/local/spectro/r0_8rm GRISM.simto allow grism movement, ortouch GRISM.simto disable grism movement (including homing on runup), etc. Then telnet to aatvme10, and login as "iris2tes" (or "aatobs"). Do asysgodits_netstartiris2eng
to bring up the wheel engineering GUI. To move the slit wheel opposite to the usual direction of travel, use negative steps, e.g. to go to posn. 6 from the home posn., enterSLIT STEP -22400or multiples thereof to get to other positions - note that BLANK3 is halfway between the 1" slit in posn. 2, and the 5" slit in posn. 3.
The same commands can be sent from the IRIS2 Observing GUI by going to the System Loader window, selecting the "TCL command" option from the "Commands" menu, and then enteringobey SPECTRO@aatvme7 SLIT [args STEP -22400]and click "Apply". Note that to get to the Matrix Mask in posn. 5, you will generally have to go there via posn. 7 (-22400) then posn. 6 (-44800).
IRIS2's October 2001 Commissioning
Why are we Building IRIS2 ?- A Guide for the non-astronomer.
Antony Dunk's IRIS2 development image pages
IRIS2 Goes to the AAT!
You can view a visual record of the progress, or read Bridget Dawson's Diary.
IRIS2's First Pump Down
Have a look in Anthony Dunk's image gallery to see IRIS2's dewar bolted together for the first time and undergoing vacuum tests. It got down to 0.5 mTorr in an hour!
First Light for IRIS2 Optics
This image shows the results of warm tests of the IRIS2 Optics, as provided by Graseby Specac Inc (UK). When tested warm, the optical elements do not lie in their optimal locations, so the results provide more of a "sanity check" than stringent results. But they do indicate that we seem to be sane so far. The image is 350um on a side and each pixel is 0.7um in size. For reference the IRIS2 pixels will be 18.5um in size. There's a radial plot available also (Note that the pixels here are the 0.7um optical detector pixels, not the 18.5um pixels that IRIS2 will eventually use.
Low-res Grisms Delivered.
Rendering of IRIS2 at the Cassegrain focus
These pages contain information on the functionality of the IRIS2 Infrared Imager and Spectrograph. Local project information can be found at the Local IRIS2 Project Page (AAO Local access only). Pages maintained by Chris Tinney and Stuart Ryder.
Last modified Dec 5, 2001 by Stuart Ryder.