THESE PAGES ARE OBSOLETE. PLEASE USE THE NEW IRIS2 PAGES INSTEAD.


IRIS2
The AAO Infrared Imager & Spectrograph
The images above show the Orion Nebula as imaged by IRIS2 in the H2 v=1-0 molecular line during commissioning in October 2001, and IRIS2 itself mounted at the Cassegrain focus of the 3.92-m Anglo-Australian Telescope.

Contents

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.

News

IRIS2 Catches the Afterglow of a Gamma Ray Burst!  (Nov 23, 2001)

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.

GRB011121, as seen in the Ks band with IRIS2 on the night of Nov 22 2001 UT.


IRIS2 Gets Improved Optical Mounts  (Nov 20, 2001)

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.

IRIS2 Goes to the AAT (Oct 30, 2001)

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.

Past News


IRIS2 Functionality in Brief

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

IRIS2 Proposers Guide

IRIS2 Users Guide

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 Instrument

IRIS2 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.
 
IRIS2 Layout 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
(measured)
7.7'x7.7'
f/15 0.24"/pixel
(estimated)
4.1'x4.1'
f/36 0.10"/pixel
(estimated)
1.7'x1.7'

Cryogenics & Layout

The 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.
 

Wheels

The 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.

Filters

The 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
(µm)
Cut-off Wavelength
(µm)
Acquired?
Broadband 
1.164 1.325  yes
1.485  1.781 yes
Ks 1.982  2.306  yes
2.028  2.364  yes
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
(um)
End
(um)
Cen
(um)
Width
(nm)
Count Rate
(e/s)
for JHK=15 star
Approximate* Sky Counts
(e/s/pix)
Max Exp
(s)
(<14000adu/pix)
Plot
(gif)
Plot
(ps)
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 spectroscopy

The 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
(order)
R Start
(um)
End
(um)
Dispersion
(nm/pixel)
Peak Rate
e-/pix/s for
JHK=10 star
Minimal Rate
e-/pix/s for
JHK=10 star
Plot
(gif)
Plot
(ps)
Comments
Sapphire Grisms (R~2400)
S-K
Sap240
K
(m=1)
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
S-K
Sap240
J
(m=2)
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
S-H
Sap316
H
(m=1)
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
S-J
Sap150
H
(m=2)
~2400 Delivered, but not yet installed or tested.
S-J
Sap150
J
(m=3)
~2400 Delivered, but not yet installed or tested.
Silica Grisms (R~1200 - not recommended at present)
KH
Sil72
K
(m=2)
~1600
?
2.37
~0.74
133
17 (at blue end)
Short wavelengths cut-off by poor blaze
Long wavelengths cut-off by K bandpass
KH
Sil72
H
(m=3)
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
HJ
Sil94
H
(m=2)
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
HJ
Sil94
J
(m=3)
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.
 


Detector

Image Scale

Image 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 Orientation

The 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 Sky

The 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.
Detector X
(pixels)
+-0.05
Detector Y
(pixels)
+-0.5
FWHM
(pixels)
+-0.005
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 accuracy

Tests 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.
 

Calibration

Recommended 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 Standards

The 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 Stars

Finding 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.

You can also look at the ESO VLT Spectroscopic Standard information. Their list also contains O and B stars as well.
 

Night-time - Spectro-photometric Standards
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,Ks

We 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
ADU/pixel
Desk Lamp off
ADU/pixel
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 flats

Can 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 Calibration

For 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.
     
     
     
     

     

    Starting up IRIS2

    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.
     

    Commands

    There 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.
      1. Make sure the correct disks are in the CCS labeled:
      RTOS-X                                         (in C6)
      AATCS 2000 (for use with RTOS-X)  (in D6)
      1. Initialise the CCS if it is not already running.
      2. 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
      3. Log into aatssz as "aatobs"
      4. Type the commands:
           dits_netstart
           tel
      The 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 procedure

    This 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.
    then telnet to aatvme10 and log in as "aatobs". Type the following commands:
    dits_netstart
    tel
    (only if you want to run a telescope simulation - omit this if you are connecting to the actual telescope)
    iris2
    (or iris2sim, or iris2dsim)

    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 IRIS2

    Go to the original terminal window you typed the iris2 command in, and type
    cleanup
    This 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.

     

    Observing with IRIS2

    Once IRIS2 is up and running, you should have four displays visible on various terminals:

    PTCS

     
    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.

    System Loader

     
    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 Interface

    This 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:

    • 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 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.

    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!


    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".


    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).
    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.
     

    Data Processing Guide

    Imaging


    We plan to implement the  ORAC-DR data processing pipeline for IRIS2 for imaging.
     

    Spectroscopy


    Technical Information

    This is where we'll put technical information, appendices, the sorts of stuff observers will need to know only occasionally.

    To reboot aatvme10

    From the "aatobs" account in an xterm logged in to aatvme10, type
    aatvme10_reboot

    IP numbers

    aatvme6  192.231.166.242
    aatvme7  192.231.166.243
    aatvme10 192.231.166.244

    To put a wheel into simulation mode

    Login to aatssy as a member of the "drama" group. Then
    cd /instsoft/drama/local/spectro/r0_8
    rm GRISM.sim
    to allow grism movement, or
    touch GRISM.sim
    to disable grism movement (including homing on runup), etc. Then telnet to aatvme10, and login as "iris2tes" (or "aatobs"). Do a
    sysgo
    dits_netstart
    iris2eng


    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., enter

    SLIT STEP -22400
    or 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 entering

    obey 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).

    Stuff

    IRIS2's October 2001 Commissioning

    Why are we Building IRIS2 ?- A Guide for the non-astronomer.

    Antony Dunk's IRIS2 development image pages

    Past News Items