This section describes recipes for a variety of procedures you may need to perform. A more complete description of the hardware and software commands can be found in the sections about hardware and software.
It should only be necessary to down-load the LSI-11/23 software at the beginning of an observing run or after a power failure. To down-load the LSI-11/23 software type:
DOWN_LOAD
This takes about two minutes, and when successfully completed will print the following on the terminal window:
PASDBG V02.4
%PASDBG-I-NODSM No DSM - target not yet loaded
PASDBG>
%PASDBG-I-BOOT1 Loading Bootstrap
%PASDBG-I-BOOT2 Loading User Image. Please Wait.
PASDBG V02.4
Target stopped at physical (00002056), virtual (002056): JMP @#2422
Executing KERNAL code
No process set, physical mapping in effect
PASDBG>
If it does not print this, the LSI-11/23 was probably already running
and you have just bombed it! Don't panic, just type DOWN_LOAD
again.
The SBRC Array Control Electronics (ACE2) drive electronics for the detector array contains a timing generator with EEPROM resident firmware. It should not be necessary to down-load this code from the VAX. However, if circumstances conspire to make this necessary, first load the Logic Chip Array code by typing:
CASPIR/LCA
When this completes (after a couple of minutes) load the ACE2 timing program by typing:
CASPIR/TIMING=IR_CASPIR:SBRC256
This loads the timing program and two data banks through an RS-232 line and takes several minutes to complete.
If you have problems try pressing the reset button on the front panel of the ACE2 unit, wait until the green light starts flashing again, and repeat the above procedure.
The CASPIR Status Display normally used by observers is the MAIN display. Two other Status Displays are also available. One is the VOLTAGES Status Display which shows the operating voltages and other parameters associated with the detector array. The other is the MISC Status Display which contains miscellaneous information such as the current grey scale ranges used in the Idle and Run image displays etc.
These display can be selected by typing any of:
CASPIR/DISPLAY CASPIR/DISPLAY=VOLT CASPIR/DISPLAY=MISC
The dewar should be adjusted so that the telescope exit pupil is matched to the internal cold stop. The positioning of the dewar is expected to be accurately reproducible in normal operation, so visual confirmation that the pupil image is unvignetted should be all that usually is required.
Acquire a bright star and drive the telescope out of focus so that you can clearly see the image of the telescope primary mirror. This is best done by zooming in on the image of the star in the Idle Display (see FIGDISP ). The dewar should be tipped so that the image of the primary mirror is unvignetted. This can be done using either the normal direct imaging cold stop in position 2 of the Utility Wheel, or the alignment mask in position 1 of the Utility Wheel (see Table ). Using the former, you see the full primary mirror aperture and must gauge whether the image is circular. Using the latter, you see the image through four small holes located at the periphery of the pupil mask and must gauge whether the four images have equal brightness. If the image ofthe primary mirror is vignetted, you will have to align the dewar. Switch MOPRA's console video to the monitor on the Cassegrain Access Platform by connecting the appropriate BNC cable to the BNC `T' on one of the RGB inputs at the rear of MOPRA's monitor. Disable the console terminal screen saver from the Session Manager menu. Stop the instrument rotator and position CASPIR towards the Cassegrain Access Platform by typing:
ROTATOR/REFERENCE=STATIONARY
ROTATOR 0
Then go to the Cassegrain focus and tip the dewar using the three adjustments on the mount to the IMB until the out-of-focus image is circular. To do this, loosen the Allen bolt slightly, loosen the inner locking nut, and adjust the outer nut. When completed, retighten the Allen bolt, and the inner lock nut.
Return the Cassegrain instrument rotator to position angle mode by typing, e.g.:
ROTATOR/REFERENCE=POSITION_ANGLE
ROTATOR 179.5
>p>
The CASPIR detector array is actively maintained at a temperature of 32 +/- 0.1 K. The dewar body must be cold enough so that thermal emission from the camera does not rival the electrically generated dark current. In practice, the dewar body is cooled to about 60 K, but somewhat higher temperatures can be tolerated without significant performance degradation.
Temperature control is through the TEMPERATURE DCL command (see Temperature Control ). The Temperature Status Display is selected by typing:
TEMPERATURE/DISPLAY
The array operating temperature and tolerance should be set by the technical staff using the commands:
TEMPERATURE/SET_POINT=32.0 TEMPERATURE/TOLERANCE=0.1
The tolerance is the threshold level permitted before a ``Temperature-Out-Of-Range'' error is reported.
The array and camera temperatures are continuously monitored while the infrared control software is running. These temperatures are recorded on disk and can be plotted at any time to see a history of the temperature fluctuations. The interval between temperature samples should be set by the technical staff using the command:
TEMPERATURE/INTERVAL=2.0
The time value is specified in minutes.
To plot the temperature fluctuation history on the workstation screen type:
TEMPERATURE/PLOT
This uses the values of XMINIMUM, XMAXIMUM, XAUTOSCALE, YMINIMUM, YMAXIMUM, and YAUTOSCALE listed in the Temperature Status Display. These values can be changed with the corresponding TEMPERATURE command.
A hardcopy of the temperature plot can be made by typing:
TEMPERATURE/HARDCOPY
Old temperature data in the disk file can be cleared by typing:
TEMPERATURE/CLEAR
The temperature controller can be reset by typing:
TEMPERATURE/RESET
The performance of the array can be checked at the telescope by recording calibration frames. The read noise and dark current are determined by setting all wheels to their blank position. For the read noise measurement first record an average dark frame by typing:
CASPIR/DARK/TIME=0.3/CYCLES=100/METHOD=2
then record another dark frame with only one cycle:
CASPIR/DARK/TIME=0.3/CYCLES=1/METHOD=2,
subtract the average dark frame from this frame and determine the standard deviation of the pixel values. This is the read noise for two reads of the array (a difference of the end of the integration ramp and the reset voltage). The single-read read noise is the standard deviation of this frame divided by square-root of 2 and multipled by 9 e-/ADU. Values of about 40 e- are expected.
The dark current measurement is complicated by the long settling time (a few seconds) of the array after resetting. This means that it is not meaningful to subtract a short exposure dark frame from a long exposure dark frame to determine the dark current. To measure the dark current, record two long exposure dark frames of different duration with one cycle each, e.g.:
CASPIR/DARK/TIME=100/CYCLES=1/METHOD=2
CASPIR/DARK/TIME=50/CYCLES=1/METHOD=2,
subtract the two frames and determine the mean pixel value. The dark current is the mean pixel value divided by the integration time difference between the frames and multipled by 9 e-/ADU. Mean values of about 13 e-/s/pixel are expected from this measurement, but significant numbers of pixels have dark currents in excess of 50 e-/s/pixel, as shown in the Figure . For the 5 s integration time used in imaging observations, the average dark current is about 30 e-/s/pixel. For the longer integration times typical of spectroscopic observations, this value corresponds to the 90th percentile of the cummulative dark current distribution.
Figure: Dark current as a function of time since pixel reset. The
plotted points are average dark current measurements formed by
differencing dark exposures with durations indicated by the extent
of the horizontal error bars. The vertical error bars indicate the
standard deviation of dark current values across the array. The
solid line is the 90th percentile of the cummulative dark current
distribution for each measurement (i.e., 90% of pixels have a dark
current lower than this value).
The signal strength can be checked by recording images of the standard
stars listed in Photometric Standards.
Measure the total sky-subtracted signal in the stellar image and convert
to instrumental
magnitudes using 
. Correct for
extinction using the mean extinction corrections listed in
Extinction Data
and form the zenith zero point offsets for each
filter, defined to be 
. These can be compared
with the typical values listed in C.
Typical sky brightness figures are also listed in Appendix C. These can be checked using a dark-subtracted sky frame and the zero point offsets determined above, or the zero point offsets listed in Appendix C.
Focus the telescope using the image of a standard star in the Idle
Display. Make sure that the display is not saturated using the
CASPIR/IZMAX=... command, and use the F19 key in that display
to measure the FWHM of the stellar image. 
due the pixel sampling. Increments of 5
focus numbers usually produce satisfactory results. Smaller
increments are required in very good seeing.
Alternatively, you can use any of the three focussing masks installed
in the dewar: 1) When using the fast camera, use the focussing mask in
position 5 of the Utility Wheel (see Table 18).
This places two small holes at the pupil position. A prism over one
hole displaces its image by 
10 
on the array.
The result is two separated images of the star which move in the
direction perpendicular to their separation (i.e., vertically on the
Idle Display) as the telescope focus is adjusted. Correct focus
corresponds to the minimum separation of these images (i.e., the two
images lie in the same image row). 2) When using the fast camera, it
is also possible to use the focussing mask in position 4 of the
Utility Wheel (see Table 18). This is identical
to the position 5 mask, but does not use a displacing prism. Correct
focus is obtained by measuring the separation of the two images for at
least two different focus values, and calculating the focus value
corresponding to zero separation of the images. This mask is
primarily used to calibrate the position 5 mask. 3) The Utility Wheel
masks cannot be used with the slow camera which is also located in the
Utility Wheel. To focus the slow camera, use the focus mask in
position 16 of the Upper Filter Wheel (see Table
17). This is a two hole mask without
displacing prism, like the second mask just described.
CASPIR has been designed so that usually there should be no need to adjust the focus for different filters. However, filters in the lower filter wheel operate in a converging beam when using the slow camera, so some refocussing may be needed. Any focus offset will be small.
The telescope focus is known to change with internal air temperature. Figure 2 shows the measured variation in manual/automatic focus numbers with inside air temperature. The fitted line is
Small deviations from the fitted line may arise because of small
mounting differencesfor the dewar, but relative focus changes can be
accurately tracked using the fitted slope of 3.24 focus numbers per
C for temperatures above at least 
C.
Figure 2: Temperature variation of telescope focus. The solid symbols
are current measurements made since the Tip-Tilt system was
installed. The open symbols are pre-Tip-Tilt measurements and have
been offset by a constant in focus value to bring them into
approximate agreement with the post-Tip-Tilt values. The solid line
is a fit to the post-Tip-Tilt points only. The change in slope
below C may not be real.
In principle, the temperature dependence of the telescope focus can be removed by operating the focus control in compensated mode. This is achieved by typing the following command into the telescope console terminal:
CONFIGURE/FOCUS_CONTROL=COMPENSATED
or including its equivalent in your telescope startup procedure. In practice, 2.3 m telescope focus mechanism tends to lock-up when operated in this way, so its use is not recommended.
Dome flats are normally recorded through each filter with the flatfield lamp on and then off. The difference of these two is taken to be the response of the system to illumination through the telescope. Dome flats are recorded with the telescope at the zenith by illuminating the upper windscreen with incandescent lamps on the telescope top-end ring. Move the telescope to the zenith by typing:
ZENITH
into the telescope console terminal.
The upper windscreen is moved over the telescope by typing:
CONFIGURE WINDSCREEN_CONTROL CLOSED
into the telescope console terminal. The primary mirror cover must be open, and the dome lights off. The incandescent lamps are is controlled through the VAX commands:
SWITCH FLATFIELD_ILLUMINATION ON SWITCH FLATFIELD_ILLUMINATION OFF
typed into the telescope console terminal. These can be equated
with the DCL symbols LON and LOFF by typing:
LON :== SWITCH FLATFIELD_ILLUMINATION ON LOFF :== SWITCH FLATFIELD_ILLUMINATION OFF
into the telescope console terminal or including this in your
telescope STARTUP.COM file. Wait until the lamp cools, i.e.,
the mean count level stabilizes, before recording the lamp off frame.
The lamp intensity is set by adjusting the flatfield illumination
control on the telescope console. There is also a switch on the
top-end ring for enabling 4 or 8 of the lamps. Settings of
20% illumination (4 lamps) for broad band filters and 100%
illumination (4 lamps) for narrowband filters work well for the
0.5''/pixel scale with an integration time of 0.4 sec. Use 40%
illumination (4 lamps) for the 0.25''/pixel scale with broad band
filters.
Return the upper windscreen to normal operation by typing:
CONFIGURE WINDSCREEN_CONTROL VERTICAL_ONLY_TRACKING
into the telescope console terminal.
Dome flats give better photometric accuracy than sky flats because a
significant contribution to sky flats is due to thermal emission from
the telescope at the longer wavelengths which is unrelated to the
relative response of the array to light. A photometric performance
comparison between dome flats and sky flats for the Kn filter is
shown in Fig. 4. Despite their better photometric
performance, there is still a residual sensitivity gradient vertically
on the array of 0.05 mag amplitude. Horizontal gradients are
generally 
0.03 mag, as shown by the scatter in each cluster of
filled circles. Better performance may be obtained by averaging dome
flats taken with the instrument rotated by 180 .
Figure 4: Sensitivity variation versus detector row number for Kn
data reduced using a dome flat (filled circles) and a sky flat
derived from the data (crosses). The data were obtained by
recording images of a single star placed at different positions on
the array in a 
grid. Each cluster of points corresponds
to measurements with the star at different column positions.
Two focal plane scales are available for direct imaging ; the fast camera with 0.5''/pixel, and the slow camera
with 0.25''/pixel. The instrument can be configured for either of
these by typing the commands FAST or SLOW. Direct
imaging in the 3-4 
m window must be done with the 0.25''/pixel
scale to avoid saturation on the background flux. Images can also be
obtained at M using the 0.25''/pixel scale and the red leak in the
P 
narrow band filter to reduce the background intensity to a
manageable level. Broad band filters are background noise limited at
both scales, while some of the narrowest narrow band filters are
marginally dark current/read noise limited.
Direct imaging is performed using the Direct_Imaging observing mode which is set by typing:
CASPIR/MODE=DIRECT_IMAGING
The preferred readout method for direct imaging is method 2. This method forms a difference between the end of the integration ramp and the reset level (see §4.3.2), so is immune to DC voltage drifts. However, the reset pedestal pattern is imprinted on the data in these method. It is essential to record dark and bias frames to permit linearization and remove the pedestal pattern.
It is often necessary to use readout method 1 for direct imaging in
the 3-4 m band and at M. This is the fastest readout method
where the data are referenced directly to electrical ground (see
§4.3.1). Method 1 is susceptible to DC voltage
drifts because it does not perform a voltage difference. This is
manifest as a column striping with a four column period which changes
from frame to frame. The pattern can be characterized in clear sky
regions and subtracted during data reduction, but a better alternative
is to use readout method 2 when background levels permit.
Readout method 3 differences the signal level at the end and beginning of the integration ramp (see §4.3.3). Reset pedestal is not imprinted on the data in this method, but it is susceptible to DC drifts between the beginning and end of the integration interval. This is removed in readout method 4 (see §4.3.4) by additional samples of the reset level at the beginning and end of the integration period. Further performance characterisation of these methods is required.
In reducing your data (§6, §8, and §9), you will need bias frames and dark frames recorded with the same exposure time as each object frame and with the same readout method. These can be obtained by typing, e.g.:
CASPIR/DARK/TIME=5.0/CYCLES=10/METHOD=2
The minimum integration times in each readout method are listed in §4.3 (0.2 sec in method 1, 0.3 sec in method 2, 0.4 sec in method 3).
Three broad band K filters are available (see Table 19 and Appendix K). Kn is the preferred broad band K filter to use from SSO. Its short wavelength edge is similar to the original K filter, but its long wavelength edge is tailored to exclude much of the thermal emission in the long wavelength end of the original K band. K' was designed with the same goal for observation at Mauna Kea Observatory (Wainscoat & Cowie 1992, AJ, 103, 332). It extends to short wavelengths with poor transmission from SSO, so in practice it has a similar band pass to Kn from SSO, but the short wavelength edge is defined by vagaries of atmospheric transmission rather than the known properties of the filter. The K filter is the original broad band K filter. It is less sensitive than Kn due to the thermal contribution to the measured background flux, and should only be used when it is necessary to accurately reproduce data on the original broad band K system. The following transformation between K and Kn has been determined from model stellar atmosphere energy distributions and measured filter transmission curves:
It is not possible to use the broad band L filter without saturating
on the thermal background at the shortest integration times and
smallest pixel scale. The 3.6 m continuum filter is used as a
narrow band L filter substitute and is referred to below as nbL.
The red leak in the P narrow band filter requires it to be used
with a PK50 glass blocker. This is not mounted with the P
filter so that it can be used as an attentuator with the M filter.
If the P filter is selected by typing:
CASPIR/FILTER=PBETA
the PK50 blocker in the Lower Filter Wheel is automatically selected.
If the P filter is selected by an explicit upper filter wheel
command, this will not be the case.
The AAO [Fe II] filter is centered slightly redward of the standard [Fe II] filter (see Appendix K). It should also be used with a PK50 blocker that is automatically selected if the filter is requested by typing:
CASPIR/FILTER=AAOFEII
Standard stars for direct imaging are listed in Appendix
F. The IRIS standards in Table
21 are recommended for JHK imaging. The
standard values are listed on the Carter SAAO system. Care should be
exercised in selecting these standards as many of them may saturate
the array in good seeing using the 0.5''/pixel scale. Fainter
equatorial JHK standards can be found in the UKIRT list (Table
22). The original MSSSO standards (McGregor
1994, PASP, 106, 508) are listed in Table 23.
These are recommended for the 3-4 m region and at M.
Sky subtraction is most demanding in the 3-4 m band and at M.
Since most of the background is thermal emission from the telescope,
it is advisable to perform these observations away from the zenith
where field rotation is slower. This is so that the view of the
telescope structure seen by CASPIR changes only slowly during the
observation sequence.
Direct imaging is usually performed as a dithered mosaic using the
CASPIR/DO=filespec command (see §5.2). The
actions performed during the execution of a DO file are controlled by
two parameters, the TIPTILT parameter and the STAGE_OFFSET parameter.
The values of both parameters are displayed in the MISC Status Display
selected by typing:
CASPIR/DISPLAY=MISC
The value of the TIPTILT parameter is set by the
CASPIR/TIPTILT=... command and the value of the STAGE_OFFSET
parameter is set by the CASPIR/STAGE_OFFSET=... command (see
§5.2).
If the TIPTILT parameter is set, the Tip-Tilt image correction system is operated during the execution of the DO file or in NOD mode. DO file parameters specify the type of correction to be used. If the STAGE_OFFSET parameter is set, the IMB X-Y stage is moved in response to each telescope offset to bring the specified reference star onto the Tip-Tilt sensor. The default action is to leave the correction subframe fixed with respect to the Tip-Tilt sensor. The geometry of the offset pattern is then set by the accuracy of the IMB X-Y stage settings, rather than the offsetting ability of the 2.3 m telescope which is the case if the Tip-Tilt system is not used. If the STAGE_OFFSET parameter is not set, the IMB X-Y stage is not moved in response to telescope offsets but the correction subframe is moved with respect to the Tip-Tilt sensor to reacquire the reference star. The former mode is suited to mosaics using large offsets. The latter may be preferred where more accurate offsets of small amplitude about the science object are required, since it is not subject to IMB X-Y stage setting errors. The operation of the Tip-Tilt system is more fully described in §3.13.
Before using the Tip-Tilt system in this way, it is necessary to calibrate the scale of the X-Y stage motions. Center a star in the CASPIR array and move the X-Y stage to center the same star in the Tip-Tilt sensor display by typing:
IMB/XY_INCREMENT
and using the keypad cursor keys to move the X-Y stage. Exit from
this by typing a Q. Then zero the X-Y stage offsets at this
position by typing:
IMB/XY_ZERO
Move the X-Y stage 20 mm East by typing:
IMB/Y=-20.0
and drive the telescope west to recenter the star in the Tip-Tilt sensor display. Record the position of the star in the CASPIR Idle Display. Repeat the procedure with the X-Y stage at Y=20.0 mm and determine the X-Y stage scale by adopting the nominal value for the CASPIR image scale (0.5''/pixel or 0.25''/pixel). Determine the appropriate correction factor to the nominal X-Y stage scale (5.0''/mm) by dividing by 5.0, and input this correction factor by typing:
CASPIR/XY_SCALE_FACTOR=factor
The X-Y stage scale factor is normally about 1.055. The X-Y stage should now accurately define the requested mosaic pattern, and it should be possible to register the data frames using the adopted array pixel scale and the OFFRA and OFFDEC offsets recorded in the FITS file headers.
Tip-Tilt DO file commands are described in §5.2. In the simplest application, it is necessary to enable tip-tilt correction on object frames and disable tip-tilt correction when measuring sky frames. This is done by adding a tiptilt or notiptilt DO file command to each DO file line; tiptilt enables tip-tilt correction and notiptilt disables it. The type of Tip-Tilt correction must be specified at least in the first run of the DO file using the tt_mode command (typically tt_mode=correct).
Guide star acquisition procedures are described more fully in §3.13 and the guide star acquisition hardware are described in §4.5.
A grism , or Carpenter prism, is a
transmission grating mounted on a prism that has its angle chosen in
such a way that the desired order of the grating passes through the
grism undeviated. Figure 5 shows a schematic
grism and the optical light path through it. We define 
to be
the prism angle, to be the grating groove angle which is also
the grating blaze angle in its reflection mode, 
to be the
deflection angle, 
to be the refractive index of the prism
material, and d to be the grating groove spacing.
In the simplest case for a grism 
. Then consideration
of the phase lag between adjacent facets of the grating in the prism
material and external to the prism shows that the undeviated
wavelength ( 
0) is given by:
where N is the order of the grating.
For deviated rays the grating equation becomes:
Geometrical ray trace shows that a ray with normal incidence passes
undeviated ( 0) when . That puts the
grating blaze at 0. For different from or
different from the refractive index of the replicating resin
used to produce the grating, the blaze is at a different wavelength,
but the above grating equations remain valid.
Figure 5: Optical diagram of a simple grism.
Thus the grating groove spacing and the prism angle for a given prism material define the location of the spectrum on the detector, and the grating groove angle and resin index define the grating blaze function.
The long slit J, H, and K grisms in CASPIR provide two pixel
resolving powers of 500 over each of the respective photometric
passbands through a 1 
128'' slit. Wider long slits in
the Aperture Wheel can be used at the expense of spectral resolution.
Grism spectra should be recorded at two positions along the slit in an
ABBA sequence. This permits better sky subtraction than procedures
which require interpolation of the sky flux. The object can be nodded
between these two positions either by manually moving the telescope or
by acquiring data in Nod mode. Nod mode has the advantages that
nodding is performed automatically, the nod positions are defined as
telescope apertures so are unaffected by changes in the instrument
rotator angle, and the cumulative sum of the AB differences can be
viewed in the Run Display. The longest possible integration time is
required to overcome read noise. In practice, this means using an
integration time of 180 sec in method 2.
To use the grisms, first configure CASPIR for direct imaging with the
fast camera (0.5''/pixel scale) by typing FAST, and obtain an
image of a star in the Idle Display. Select your long slit by
typing, e.g.:
CASPIR/APERTURE=LSLIT1
Note the pixel positions of the center of the slit and the two desired nod positions, and then return to imaging the whole field by typing:
CASPIR/APERTURE=FASTCLR
Center the star on the slit-center pixel and redefine aperture A by typing:
APERTURE/HERE A
into the telescope console terminal. Manually move the star to the first nod position or offset the telescope EW by typing, e.g.:
OFFSET/SCALE 10.0 0.0
into the telescope console terminal and then define aperture N1 by typing:
APERTURE/HERE N1
into the telescope console terminal. Repeat this at the second nod position for aperture N2. Return the star to slit-center by typing:
APERTURE A
into the telescope console terminal and select Nod mode by typing:
CASPIR/MODE=NOD
into the CASPIR command terminal.
Spectroscopic observations are best performed using the Tip-Tilt system in either guide or correct mode. Operation of the Tip-Tilt system with CASPIR is more fully described in §3.13 and in the Tip-Tilt manual. To use the Tip-Tilt system for spectroscopic observations, roughly center the object on the slit-center pixel, then offset the IMB X-Y stage to the location of a suitable reference star by typing into the telescope console terminal, e.g.:
TIPTILT/OFFSET/SCALE -26.5 +10.5
if you know the reference star RA and Dec. offsets in arcsec on the sky, or
TIPTILT/COORD 12 26 25.9 -17 18 42 J2000
if you know the reference star coordinates, or
TIPTILT BS2015
if the reference star coordinates are in a telescope coordinate file, or
TIPTILT/TRACK
if you can use the optical image of the infrared object as the reference star, or
TIPTILT/HERE
if there is a suitable reference star within the Tip-Tilt acquire frame and you wish to drive the reference star to the correct subframe, or
TIPTILT/FIND
if there is a suitable reference star within the Tip-Tilt acquire frame and you wish to move the correct subframe to the pixel location of the reference star. Start correcting by typing:
TIPTILT/CORRECT
The Tip-Tilt system will pull the reference star to the center of the correct subframe, and hence may move the object out of the slit slightly. Recenter the object on the slit-center pixel by moving the Tip-Tilt sensor X-Y stage incrementally (using the above TIPTILT/OFFSET... commands) until the correct box center coincides with the slit-center pixel on the CASPIR array.
For small offsets ( 
) between the slit center and the N1
and N2 slit positions, it may be preferable to leave the IMB X-Y stage
fixed and move the correction subframe on the Tip-Tilt sensor during
each telescope offset. This is achieved by setting the TIPTILT
parameter and unsetting the STAGE_OFFSET parameter by typing:
CASPIR/TIPTILT/NOSTAGE_OFFSET
Larger offsets with the long-slit grisms will require IMB X-Y stage motions:
CASPIR/TIPTILT/STAGE_OFFSET
Now select the appropriate slit, grism, and the fast camera lens, and place the filter wheels in clear positions by typing, e.g.:
CASPIR/APERTURE=LSLIT1/UTILITY=K_GRISM/UFILTER=CLEAR/LFILTER=CLEAR/LENS=FAST
or
KGRISM
The Idle Display image will change to a spectrum and you can begin taking data.
Grism data can be obtained in either the Direct_Imaging observing
mode or the Nod observing mode. In Direct_Imaging mode, data frames
are obtained singly with one frame recorded for each REPEAT requested.
In Nod mode, successive exposures are obtained in an ABBA pattern at
two positions on the sky defined by telescope focal plane
apertures named N1 and N2. This permits accurate sky-subtraction
by differencing the images. The number of AB pairs obtained is set by
the REPEATS parameter which can be changed during data acquisition.
If a CASPIR/SHOW=CURRENT command has been given, the current
A-B difference is displayed in the Run Display. If the SHOW parameter
has been set to MEAN with a CASPIR/SHOW=MEAN command, the
average of the accummulated difference images is displayed in the Run
Display. This allows the observer to assess the quality of the full
dataset.
Data acquisition is started in Direct_Imaging or Nod mode by typing:
CASPIR/RUN
In Nod mode, each ``repeat'' consists of two runs (i.e., two recorded files) taken with the object at the N1,N2 or N2,N1 aperture positions. Set the ``repeats'' value to a large number initially, and reduce it to end the run.
The expected spectral images for common astronomical lines as well as Xenon and Argon arcs with each grism are shown in Figures 6 to 11. Tables of Xenon and Argon arc line wavelengths and OH airglow wavelengths (Oliva & Origlia 1992, A&A, 254, 466) can be found in Appendix J, as well as plots of extracted Xenon and Argon arcs for each grism. Xenon and Argon calibration lamps as well as an incandescent lamp are available in the calibration lamp module of the IMB. These are activated by typing any of:
IMB/CALIBRATION=XENON IMB/CALIBRATION=ARGON IMB/CALIBRATION=INCANDESCENT
It is recommended that lamp-on and lamp-off frames be obtained for the calibration lamps. The lamps can be switched off, without moving other components of the calibration lamp module but typing, e.g.:
IMB/XENON=OFF
The calibration lamps are switched off and the lamp select mirrors removed from the telescope beam by typing:
IMB/CALIBRATION=OFF
or just:
IMB/CALIBRATION
Wavelength calibration can also be achieved by measuring the compact planetary nebulae listed in Table 29 of Appendix J, or by recording mercury spectra of the fluorescent room lights.
Grism spectra are flat fielded using the incandescent lamp in the calibration lamp module. Record pairs of lamp on and lamp off frames, without moving the flip mirror between these frames. This can be done by typing:
IMB/CALIBRATION=INCANDESCENT
to turn the lamp on, and:
IMB/INCANDESCENT=OFF
to switch it off without moving the mirror, or by typing the DCL
symbols LON and LOFF into MOPRA. Note that these
abbreviations have a different effect to the same symbols typed into
the telescope console terminal.
A flat spectrum object must be measured to remove terrestrial
atmospheric absorption features from an object spectrum. A flux
standard must also be measured to flux calibrate the object spectrum.
Stars earlier in spectral type than F are preferred as calibrators for
the grism spectra because they have few intrinsic spectral features,
and the H 
ion bump around 1.6 m is less pronounced than in G
dwarfs. However, it is necessary to also record a spectrum of a K or
M star in order to measure and remove the hydrogen absorption lines in
the early-type star spectrum. Lists of suitable stars can be found in
Appendix G. Plots of terrestrial atmospheric
absorption can be found in Appendix M.
Figure 6: Predicted astronomical (top) and airglow (bottom) spectra
for the J grism.
Figure 7: Predicted Xenon (top) and Argon (bottom) lamp spectra for
the J grism.
Figure 8: Predicted astronomical (top) and airglow (bottom) spectra
for the H grism.
Figure 9: Predicted Xenon (top) and Argon (bottom) lamp spectra for
the H grism.
Figure 10: Predicted astronomical (top) and airglow (bottom) spectra
for the K grism.
Figure 11: Predicted Xenon (top) and Argon (bottom) lamp spectra for
the K grism.
The observing procedure for the short slit grisms is similar to the
long slit grisms. More care is required in the placement of the two
object positions along the short slit to avoid light loss at the slit
ends while accurately measuring the sky flux at the other slit
position. In practice, this means measuring spectra at two position
displaced along the slit by 
from its center.
The expected spectral images for common astronomical lines, airglow, Xenon and Argon arcs, with each grism are shown in Figures 12 to 17. Plots of extracted Xenon and Argon arc spectra for each order of each cross-dispersed grism are shown in Appendix J.
Figure 12: Predicted astronomical (top) and airglow (bottom) spectra
for the IJ grism.
Figure 13: Predicted Xenon (top) and Argon (bottom) lamp spectra for
the IJ grism.
Figure 14: Predicted astronomical (top) and airglow (bottom) spectra
for the JH grism.
Figure 15: Predicted Xenon (top) and Argon (bottom) lamp spectra for
the JH grism.
Figure 16: Predicted astronomical (top) and airglow (bottom) spectra
for the HK grism.
Figure 17: Predicted Xenon (top) and Argon (bottom) lamp spectra for
the HK grism.
The coronograph mode in CASPIR is used to image faint emission near brighter objects with sizes comparable to the seeing disk. The coronograph does two things; first, it occults the direct light of the bright object over a region of the sky comparable to the seeing disk, and secondly, it blocks light from the bright object which is diffracted around the telescope secondary support structure.
This is achieved in CASPIR by selecting either the 2'' or 5'' diameter occulting disk in the Aperture Wheel (see Table 16), and selecting the pupil plane mask in the Utility Wheel (see Table 18). This means that the CASPIR coronograph can only be used with the fast camera (0.5''/pixel scale), as the slow camera is also located in the Utility Wheel. The size of the occulting disk is based on the expected extent of the faint emission being measured and the seeing, and is selected by typing, e.g.:
CASPIR/APERTURE=DISK2
Only one pupil plane mask is available. This is selected by typing:
CASPIR/UTILITY=MASK
Use of the coronograph masks in CASPIR is complicated by the alt-az
nature of the 2.3 m telescope. Because the 2.3 m telescope has an
alt-az mount, CASPIR is continuously rotated to maintain a fixed
orientation with respect to the sky. The image of the secondary
support structure then rotates in the pupil plane. The pupil
plane mask is a Maltese Cross shaped baffle with each section of the
cross having a half-angle of 15 . The mask has a fixed
orientation with respect to the dewar. In using the coronograph pupil
plane mask, it is desirable to set the instrument rotator position
angle so that the secondary support structure remains vignetted for
the longest time. If the parallactic angle is increasing set
the instrument rotator position angle to the parallactic angle
plus 15 . If the parallactic angle is decreasing
set the instrument rotator position angle to the parallactic angle
minus 15 . The secondary support structure will then
be behind the pupil plane mask, but will move as the telescope tracks.
The rate of motion depends on position on the sky. Consult Figure 9.9
in the 2.3 m Telescope Observer's Manual to estimate this speed.
Field rotation at the Cassegrain focus is not monotonic and changes
most rapidly near the zenith. Consequently, coronograph observations
are best done away from the zenith.
Operation of the Tip-Tilt system is fully described in the Tip-Tilt manual. Factors relevant to its operation with CASPIR are summarised below.
Give the Tip-Tilt system access to the telescope by typing:
ENLIST TT CONFIGURE EFFECTIVE_WAVELENGTH 2000 CONFIGURE GUIDER_WAVELENGTH 700
into the telescope console terminal.
The Tip-Tilt software is run on MISTY under X Windows from any user account (your own or ``user23''). Start the system by typing:
tiptilt &
After the initialization sequence completes, click on the ``operate'' button to select acquire mode. Correct and acquire integration times should be set to something less than 100 mS. When a suitable guide star is in the image display, select it by pressing ``Shift'' and clicking on the star with the left mouse button. The correct box is moved to this object, and tip-tilt correction is commenced by clicking on the ``correct'' button.
After the telescope and CASPIR have been properly configured, type:
CALIBRATE STAGE
into the telescope console terminal and follow the instructions. This procedure defines the IMB X-Y stage zero point and Tip-Tilt correct subframe to the telescope system.
Now enable use of the Tip-Tilt system and IMB X-Y stage motion from CASPIR DO files and in NOD mode by typing:
CASPIR/TIPTILT/STAGE_OFFSET
into the CASPIR command terminal.
Normally, the CASPIR array and the Tip-Tilt CCD will remain cofocal and
no adjustment of the Tip-Tilt focus should be required. If
focus adjustment is required, focus the telescope on the infrared
array, then adjust the focus of the optical image in the Tip-Tilt
display using the IMB/FOCUS command. Use the up and down arrows
to change the focus of the acquistion unit focal reducer, and type Q
to quit. Do not move the telescope focus to focus the optical image.
The Tip-Tilt sensor can be used in acquire mode for normal object
acquisition. With the instrument rotator at a position angle of
180 , North is up and East to the right on the Tip-Tilt display,
as shown schematically in Figure 1
To guide on an offset guide star, it is first necessary to offset the IMB X-Y stage to the location of a suitable star. The small size of the Tip-Tilt CCD field of view relative to the offset guide field makes it essential to pre-select suitable reference stars from charts of your fields. Procedures for doing this is described in §3.14. The Tip-Tilt systems allows the observer to specify reference stars to the telescope system by their coordinates, e.g.:
TIPTILT/COORD 12 34 46.5 -15 34 23 J2000
or from a telescope coordinate file, e.g., :
TIPTILT BS2015
or by their offsets in arcseconds on the sky, e.g.:
TIPTILT/OFFSET/SCALE 12.0 -3.4
or by typing:
TIPTILT/TRACK
if the object at the tracking coordinate (the infrared object) can be used as the reference star, or by typing:
TIPTILT/HERE
if there is a suitable reference star in the Tip-Tilt acquire frame and you wish to drive the reference star to the correct subframe, or
TIPTILT/FIND
if there is a suitable reference star in the Tip-Tilt acquire frame and you wish to move the correct subframe to the pixel location of the reference star.
When the Tip-Tilt system is correcting, the position of an object on
the CASPIR array can be adjusted by translating the IMB X-Y stage
using telescope TIPTILT/OFFSET command so that the object is
dragged, by the Tip-Tilt system, to the desired infrared position.
Measure the desired offset in arcseconds from pixel locations on the
CASPIR array and apply this correction to the specified reference star
offsets.
The Tip-Tilt system can also be controlled through the DO file used to acquire CASPIR data. The DO file commands controlling Tip-Tilt are:
tiptilt - Turns on Tip-Tilt operation. notiptilt - Turns off Tip-Tilt operation. stage_offset - Enables IMB X-Y stage motion. nostage_offset - Disables IMB X-Y stage motion. track_coord - Track on a new object coordinate (i.e., RA, Dec.). guide_coord - Defines a new guide star coordinate (i.e., RA, Dec.). gra_offset - Defines guide star RA offset in arcsec on sky. gdec_offset - Defines guide star Dec. offset in arcsec on sky. ttx - X coordinate of Tip-Tilt correct subframe center. tty - Y coordinate of Tip-Tilt correct subframe center. ttdx - X size of Tip-Tilt correct subframe. ttdy - Y size of Tip-Tilt correct subframe. acqx - X coordinate of Tip-Tilt acquire subframe center. acqy - Y coordinate of Tip-Tilt acquire subframe center. acqdx - X size of Tip-Tilt acquire subframe. acqdy - Y size of Tip-Tilt acquire subframe. tt_mode=correct - Operates Tip-Tilt in correct mode. tt_mode=guide - Operates Tip-Tilt in guide mode. tt_mode=acquire - Operates Tip-Tilt in acquire mode. tt_mode=recalibrate - Operates Tip-Tilt in recalibrate mode. tt_atime - Sets acquire mode integration time (ms). tt_gtime - Sets guide mode integration time (ms). tt_ctime - Sets correct mode integration time (ms). tt_find - Enables Auto-Acquire mode. nott_find - Disables Auto-Acquire mode. tt_error - Do not abort on Tip-Tilt error. nott_error - Abort DO file if Tip-Tilt errors encountered.
Generally, it is advisable to leave the infrared system running at the
end of a night. This allows array temperature logging to continue.
The dewar should be left blanked off to avoid prelonged exposure to
saturated light levels. Use the STARTNEWNIGHT command at the
beginning of a new night to create a new dated data subdirectory and
reset the run number.
To fully shut down the infrared system, type:
IR_SHUTDOWN
When all processes have stopped, and all but the command entry window
have been removed from the workstation screen, click on the Session
Manager (key) icon and select Quit in the Session menu.
This logs the INFRARED process out of MOPRA.
CASPIR data files are written to the MOPRA data disk as FITS files. These files are accessible from MISTY in dated subdirectories of the directory /data/mopra/. Data files can be copied from MOPRA to MISTY by typing the following into MISTY, e.g.:
cp /data/mopra/10oct94/ir*.fits .
chmod -x *
Data are archived from MISTY to exabyte tape on drive ex0 (left drive)
or ex1 (right drive). It is the responsibility of observers to
provide their own exabyte tapes. Typically 100 Mbytes of data
are produced in a single night of direct imaging, so data from several
nights can fit on one exabyte tape. Data files on MISTY can be
archived in TAR format to an exabyte tape already containing data
using the following example procedure:
allocate ex0 (Allocate drive and insert tape in right drive.) mt eom (Position tape at end-of-medium.) mt nbsf 1 (Backspace over one file.) tar t (Read last TAR saveset on tape.) tar t (Move over one end-of-file marker.) cd /data/misty/... (Go to your top level data directory.) tar cv 10oct94/raw (Archive data in subdirectory 10oct94/raw.) mt nbsf 1 (Backspace over the saveset.) tar t (Check saveset written correctly.) mt rewind (Rewind tape.) deallocate ex0 (Deallocate and remove tape.)
An instrument history file exists for logging alterations to the instrument and for user comments. CASPIR users are encouraged to record their experiences in this file for the benefit of others. These comments will be incorporated into this manual where appropriate. To access the file, either to read it or add your comments to it, type:
HISTORY
This uses the VMS EDT editor in screen mode. To exit, type
<cntrl>Z and then EXIT to update the file, or
QUIT to leave the file unchanged. The file can also be
accessed through the MSSSO WWW home page.
Convenient charts for identifying offset guide stars for CASPIR observations of southern objects can be obtained using the COSMOS database at the AAO, or the southern Digitised Sky Survey.
To access the COSMOS database, telnet to the COSMOS machine at Epping by typing:
telnet cosmos.aao.gov.au username: cosmos password: UKSTcosmos
Enter your object coordinates into a text file one object per line in free-format, e.g.,
cat > input.dat 08 06 30.24 -10 18 50.0 21 52 58.01 -69 55 40.4 <cnrtl>d
Start the COSMOS program and take the defaults on all the questions except for those listed below:
cosmos >> Change default parameters (n)? y >> Min, Max BJ magnitude (0.00 25.00): 0.0 20.0 >> No. plots across, down page (1 1): 5 3 >> Please select an output device: 1 (postscript) >> Filename => output.ps >> Text output filename (<CR> for none): output.dat >> Input coordinate file (<CR> for none): input.dat (coordinate file) >> Equinox (J2000.0): B1950.0 >> Diameter of charts (6.0 arcmin): <CR> (good size) ... >> More plots (y)?: n
Now ftp the results (output.ps and output.dat) back to your home machine and print them. The COSMOS charts are contained in the file output.ps (e.g., Figure 18). The output.dat file is a text listing of source positions, brightnesses, etc. These can be used to calculate offsets to suitable guide stars in arcsec on the sky. The users guide for the COSMOS program can be found in the file /cosmos/disk1/doc/Userguide.tex. Contact Michael Drinkwater at the UKSTU for further information (mjd@aaocbn3.aao.gov.au).
Figure 18: Typical COSMOS charts for 
regions of sky.
The southern Digitised Sky Survey is best accessed via CDROM. The World Wide Web SkyView Basic (http://skyview.gsfc.nasa.gov/skyview.html) or STScI (http://stdatu.stsci.edu/dss/dss_form.html) nodes can also be used, but these can be slow and the file headers differ from those of the CDROM versions. Convenient lists of stars from the Hubble Guide Star Catalog within a specified radius of an object (specified by name or coordinate) can be obtained from the ESO web site (http://archive.eso.org/gsc/gsc). SkyView Advanced (http://skyview.gsfc.nasa.gov/cgi-bin/v3.0/skyview_advanced.pl) can also be used to select Digitized Sky Survey images by specifying object names, overlay HST Guide Star Catalog stars as well as many other cataloged objects, and print the image and coordinates of overlayed objects in one streamlined, but slow, process.
To extract a Digitized Sky Survey image from CDROM type
getimage and follow the instructions for loading the relevant
CDROM disk.
When all the FITS files have been obtained, enter the filenames into a text file one per line, e.g.:
cat > files.dat 3c195.fits 2152-699.fits <cntrl>d
Then form a postscript mosaic of these images using DSSPLOT (e.g., Figure 19) by typing:
dssplot files.dat
DSSPLOT is part of the CASPIR IRAF package. Refer to §6 for information on how to obtain copies of this package. Print the mosaic by typing, e.g.:
lpr -s -Plaser_d dssplot.ps
Figure 19: Typical southern Digitised Sky Survey charts formatted with DSSPLOT.
Positions of objects in the image can be obtained using IRAF. Load the STSDAS and GASP packages, then first form the RA/DEC world coordinate system for file image.fits by typing:
makewcs image
Then display the image and measure positions with the image cursor by typing:
display image 1 rimcursor wcs=world wxformat=%12.2H wyformat=%12.2h
Alternatively, if the (x,y) coordinates of the object are known, convert these to RA and DEC by typing:
xy2rd image x y