to initialize ING specific packages (includes routines for checking focus, rotation and tilt of the detectors).
If you plan to reduce your data on-the-fly please don't work directly on the
images stored in the /obsdata/whta/"date" directory (which is cross-mounted
). Instead, copy the images
to a directory in the /scratch filesystem, e.g. /scratch/whta/20120814, and
run your analyses on the duplicated data.
(introduce the GG495 blocking filter)
Select slit mode to observe (remove the comparison mirror in case it
Select comparison mode to take lamps (introduce a mirror in the beam
to drive the light from the lamps into the spectrograph)
ISIS mechanisms from the GUI
The ISIS mechanisms can also
be controlled from a
the new ISIS Control System and the A&G Control
System explaining how to use the GUIs can be found here
The use of the GUI is very simple. A number of icons buttons are used
throughout the GUI in order to perform specific tasks.
The GUI has several windows, those relevant for the ISIS user are here.
Back to the top
Note that UltraDAS commands
run under Linux ("WHTICS"
), and therfore they can be
executed in background mode (by appending &
at the end of the command
line). This enables one to take images simultaneously with both red and blue
arms, for example run red 900 & run blue 900
takes a 900s exposure in
each arm, and returns the command-line prompt when the blue-arm
completes. Note that the red-arm exposure (in this example) won't necessarily be complete
when the prompt is returned; don't e.g., turn on calibration lamps until exposures
in both arms are complete.
Furthermore, UltraDAS commands can be combined with
ISIS commands to create scripts to execute observing sequences. A complete list and description
commands can be found in the
command dictionary of the UltraDas Software manual. A summary of
the most commonly used commands is given here for a quick reference:
Data acquisition commands
Some of the most important commands related to data acquisition are
listed below (arguments are denoted by <>):
The arguments above stand for
- run <camera> <int time> <"title">
Takes a run and saves it in: rxxxxxxx.fit.
E.g. run blue 600 "N157 B", takes a 600s exposure
with the blue arm and stores it in the output file (e.g. r1826342.fit).
The title of the fits file is set to "N157 B". If you do not specify a
title, the name in a header will be the same as in your catalogue.
- multrun <camera> <m> <int time>
Same as run but repeats the run sequence m times and
generates m output files.
- flat <camera> <int time> <"title">
Takes a run and set the OBSTYPE header parameter to FLAT.
- multflat <camera> <m> <int time>
Same as flat but repeats the run sequence m times and
generates m output files.
- arc <camera> <int time> <"title">
Takes a run and set the OBSTYPE header parameter to ARC.
- multarc <camera> <m> <int time>
Same as arc but repeats the run sequence m times and
generates m output files.
- bias <camera> <"title">
Takes a run and set the OBSTYPE header parameter to BIAS.
- multbias <camera> <m> <"title">
Same as run but repeats the bias sequence m times and
generates m output files.
- glance <camera> <int time>
Takes an exposure and saves it in s1.fit.
This file is overwritten when a new glance is taken. If you want to have
a permanent copy of a given glance image, type promote s1.fit.
- scratch <camera> <k> < int time>
Takes a run and saves it in: sk.fit. k is an integer
within the range 1-99. The scratch file sk.fit
is overwritten when a new scratch<k> is taken.
- abort <camera>
Aborts an exposure which is running in the backgroud. The data are not saved to disk.
- finish <camera>
Terminates an exposure which is running in the background, and saves the data to disk.
- newtime <camera> <int time>
Changes the length of an exposure which is running in the background (e.g. newtime red 900 for
the red arm)
- Ctrl_z followed by bg
suspends the current process which is running in the foreground and starts it running in the background. Therefore if you executed a pair of integrations as run red 900 & run blue 900; bell, so that the red integration is running in the background and the blue integration is running in the foreground (with an audio alarm queued to sound when the blue-arm integration completes in this instance), typing Ctrl_z then bg would cause the blue integration to also run in the background, making the command line prompt available to issue, e.g., a pair of finish commands. Note that the bell command would execute immediately on typing Ctrl_z in this example.
which CCD you want to use, the red
or blue one. Enter red or blue.
time> Integration time in seconds.
< "title"> Title
of the exposure recorded in the image header (optional argument).
Back to the top
5. Afternoon settings and calibrations
CCDs from the observing system (WHTICS)
Before starting the calibration images
in the afternoon you should set the readout speed and the
windowing of the CCD camera.
- Set the detector readout speed to
slow or fast (as desired) by typing for example:
SYS@taurus> rspeed <camera> slow
Have a look at the blue-arm
and red-arm pages
for details on the operational characteristics for each readout
speed. Normal observations are usually using the slow readout speed. Be careful as
the default read speed on e.g., resetting the controllers is fast, so you
should check that it is in slow mode before
to take your calibrations in the afternoon (if you plan to observe in slow read mode).
- Windowing the CCDs. Note that the
ISIS detectors cover more than 4 arcminutes in the spatial direction.
is therefore desirable to window each CCD to an appropriate length
by defining an effective slit length.
SYS@taurus> window red 1 "[555:1520,1:4200]"
(3.5 arcminutes for red arm+REDPLUS)
SYS@taurus> window blue 1 "[585:1550,1:4200]" (3.2 arcminutes for blue arm+EEV12).
- Binning the CCDs.
SYS@taurus> bin red 1 2
will bin x2 in the dispersion direction.
Currently, it is not recommended to use 4x1 or 4x2 binning
while windowing, because the CCD controller times out and/or the observing system hangs
for a short time, one or other of which occurs for more than 50% of the time. All images are read-out and saved correctly, but it is not possible to take multiple (multrun) exposures.
This problem occurs for both red and blue CCDs, and slow and fast read-out
speeds. The current workaround is not to use the combination of binning 4x1 or
4x2 with windowing. This problem is caused by a controller internal error.
Once the CCD windows have been defined, the system will automatically create and save two files, one for each CCD, which contain the window, bin and readout speed parameters. The default file names are udas_REDPLUS.cfg and udas_EEV12.cfg. Different names can be used with:
SYS@taurus> saveccd <camera> <filename>
To load the CCD parameters use:
SYS@taurus> setccd <camera> <filename>
To load the default CCD configuration files just omit the field <filename>.
The setccd command is especially useful after issuing a dasreset. This command resets the software and hardware of a CCD camera (e.g. when one camera stops working):
SYS@taurus> dasreset <camera>
After a dasreset, binning, windows and readout speed revert to
their defaults, 1x1, no window and fast respectively.
5.2 Taking arcs
SYS@taurus> complamps cuar+cune
and take a test exposure:
SYS@taurus> arc red 5 test
allow you to compute the exposure time to obtain a reasonably intense
Follow the same procedure with the blue arm. Take into account that
usually long exposure times of > 40 s are needed in the blue.
5.3 Taking lamp flats
flats turn off all the dome lights and close the curtains in the
SYS@taurus> complamps w
and take a test exposure:
SYS@taurus> flat red 1 test
allow you to compute the exposure time to obtain a reasonable intense
flat. Flats should not be brighter than 42000 ADUs. When using low
resolution gratings in the red arm, the use of a
neutral density filter is needed. ND filters can be put in place with e.g.
SYS@taurus> compnd 0.8
To remove the ND filters type
SYS@taurus> compnd 0
Once the proper neutral density filter and exposure
time is set, do a multflat:
SYS@taurus> multflat red 11 5 "good flat"&
5.4 Taking biases
Before taking bias frames turn off all the dome
lights and close the blinds in the control room. It's also
good practice to configure the comparison mirror in the beam. As
an example, to take 11 bias frames in the red and blue arms
SYS@taurus> complamps off
SYS@taurus> multbias red 11 & multbias blue
In principle, one can also take biases on ACAM simultaneously with those in the ISIS red and blue arms (by simply concatenating multbias acam 11 & to the above line). However, it's been noted that taking biases simultaneously on ACAM and the ISIS red arm causes additional noise in the form of horizontal lines on ACAM and the ISIS red arm,
which are not present if biases are taken separately. Taking biases on ACAM and ISIS simultaneously is therefore discouraged.
5.5 Taking sky flats
We suggest that observers take twilight sky flats in order to determine the slit
illumination function. Knowledge of this is desirable
when observing extended targets or two (or more) targets simultaneously in the
slit, and is useful for accurate sky subtraction.
The internal-lamp flats, being free of lines, are of course used for
determining the CCD's pixel-to-pixel response.
To take sky flats with ISIS leave the
telescope at Zenith in engineering mode (i.e. no tracking). No offsets between
individual flats are needed.
For the higher resolution gratings (R1200R, R1200B, H2400B), you
should start 10-15 minutes before a sunset. For lower resolution gratings
start around a sunset.
take a test exposure to decide the exposure time:
SYS@taurus> sky red 1 test
Once the counts level is good, take sky flats with the following command
SYS@taurus>sky red <exp_time> & sky blue
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6.1 Target acquisition
Acquisition of targets in the slit will be carried out by the telescope operator.
Briefly, the slit is polished and aluminised, and is inclined to the optical axis of the telescope at an angle of 7.5 degrees to allow the reflected image of the sky
to be viewed by the A&G box TV camera, currently ag4. To configure the A&G box for acquisition and observing, issue the command
The default orientation of the slit will be set to the parallalctic angle
at the mid-point of your integration by the OSA, but inform the telescope
operator if you prefer a different angle, for example, in order to place multiple targets in the slit. If you want to save an acquisition image, ask the telescope
operator to stop ag4 running in TV framing mode and execute the command
SYS@taurus> run ag4 <exp> <"comment">
Remember to ask the telecope operator to switch ag4 back to TV framing mode, so that the centering in the slit can be monitored throughout your subsequent
6.2 Focusing the telescope
To focus the telescope point to a bright star (V=9-11), it can be one of your
standards) at low airmass.
Use fast readout speed and take a test image with one of the arms (usually red,
because the seeing is better in red than in blue).
SYS@taurus>rspeed red fast
SYS@taurus>glance red 10 &
Exposure times of ~10s should be used to adequately sample the
seeing. Look at the image to check that the spectrum isn't saturated and has SNR of at least ∼50 per pixel, and then execute the focusrun script:
SYS@taurus>focusrun <camera> <num_exp>
<exp_time> <focus_start> <focus_increment>
Typical values are
SYS@taurus>focusrun red 9 10 97.7 0.05
This will take 9 images of 10s each, changing the focus of the
telescope from 97.7 mm in increments of 0.05 mm between the images.
All images are saved and you can determine the best focus by analyzing "manually" the
spatial profile in each image, or running the iraf focus script in the
directory where your data are being written (/obsdata/whta/"date"):
ecl> ! isis_focus
Note that usage of an exclamation mark at the beginning of this command is necessary.
The script prompts for the run number of the first image
and number of images taken in the focus sequence. The run number should
be given without the "fit" extension, and with r at the beginning (e.g. r1234567).
The first image will be opened in ds9 and you can now position the cursor on the spectrum and press any key on the keyboard
to measure the spatial profile at that position. All images are displayed
one by one and a spatial-profile fit is
shown for each image in the sequence. Eventually, a window opens showing measured
values of FWHM versus the telescope focus, with a parabolic fit
over-plotted. At the same time, the best empirical and fitted telescope
focus values are printed in the iraf terminal. Closing the opened graphical
window will give you a prompt back in iraf session.
Once the value of the focus is determined
(e.g. 97.85) set the value of the focus by
SYS@taurus> focus 97.85
NB Don't forget to change the readout speed back to slow.
Warning: If changes are made to the configuration of ACAM when ISIS is the selected instrument the corresponding focus offset for the ACAM optical element configured will be applied to the telescope. An ISIS focus run performed with a focus offset applied will compensate for it. However, if the telescope focus is set to the ISIS nominal focus with a focus offset applied, but an explicit focus run isn't performed (e.g. due to time constraints), the telescope will be defocused by an amount commensurate with the offset. In this case, if you notice that the dF parameter in the TCS window is non-zero, ask the TO to remove it. Check at the start of the night that a focus offset isn't applied, and never change the configuration of ACAM while observing with ISIS.
SYS@taurus>rspeed red slow
6.3 Taking spectra of an object
First select the slit mode and slit width
SYS@taurus> slitarc 1.0
Ask the OSA to point to your target (you
can provide a
targets with the coordinates of the targets you
plan to observe during your run). Also state the position angle you
want for the slit. If you will observe with the slit at parallactic angle
(i.e. oriented in the vertical direction) to minimise differential slit losses
sue to differential chromatic refraction), it's advisable to adjust this at least every 1.5-2 hours because
the slit doesn't actively track the parallactic angle. The change
of parallactic angle with time can be determined using the
(select Option=Parallactic Angle). Note that it's as important to adjust the
slit orientation every ~1.5-2 hours near zenith as it is at higher air mass;
although differential chromatic refraction is smaller near zenith, the rate
of change of parallactic angle is higher. These two effects combine to
make the relative movement of blue and red images across the slit only
weakly dependent on air mass.
If you change the slit PA to better track the vertical, always check the acquisition, and re-centre as necessary.
In the case of a target acquired in a blind offset, repeat the blind offset acquisition if you
change the slit orientation.
The OSA will take an image of the slit with the TV
camera and will use it to centre your object in slit. If your objects
are faint (V>20) it is a good practice to acquire a brighter object
the field close to the target (less than 20 arcminutes, but preferably less than
2 arcminutes) and do a blind offset to your target.
In bright time and/or when the seeing
is not good then you'll likely need to use blind offset stars for brighter
In such cases prepare blind
offset stars in advance to save time. For accurate blind
offsets, both target and offset star should be in the same coordinate system
and have at least two decimal places
in seconds of RA and one decimal place in arcseconds of Dec. Always check if the offset
star has an appreciable proper motion.
Once your object is in the slit do
SYS@taurus> run red <exp_time> "<comment>" &
run blue <exp_time> "<comments>"; bell
An audio alarm will sound when the blue-arm exposure completes,.
6.3.1 Blind offset acquisition
In the blind offset procedure, the accumulated
handset corrections applied to locate the reference object in the slit
from its initial "gocat" location
to tangent-plane coordinates, and these are added to the pointing model's
collimation terms in elevation and azimuth. This creates a localised,
correction to the pointing model, and this localised pointing model is adopted
in the blind offset procedure to position the faint target in the slit once
the reference target has been acquired accurately.
However, closing the loop on the reference star discards
this localised pointing model, and if the loop is subsquently opened and
a blind_offset applied, the rms offset accuracy will be degraded to at least 0.5-arcsec.
A blind offset should not be executed if the loop has been closed
on the reference object. For example, if a bright target in a galaxy or cluster is observed
closed-loop, followed immediately by a blind offset to a faint target
in the same galaxy or cluster, the acquisition of the faint target will be compromised.
The correct procedure for a blind offset acquisition is
(i) gocat "target" and identify a suitable guide star
(ii) gocat "reference"
(iii) centre the reference object
(iv) quickly apply blind_offset "target"
(v) close the loop quickly
The rms accuracy of this procedure is <~0.2-arcsec. Open-loop
tracking error (~0.1-arcsec/minute) in the acquisition is minimised by
a guide star in advance of the blind offset, allowing the loop to be
closed quickly after the blind offset to the target completes, and of
course by quickly applying the blind offset once the reference target
has been centred in the slit.
6.4 Night calibrations
If you need arcs of lamp
flats during the night proceed as in section
6.5 Observing bright targets
If you need to observe bright targets you can use the main neutral density
filters in the light path, common for both red and blue arm. Take into
account that these neutral density filters are not uniform, mostly outside the
useful area of the chip. The table below indicates the area of the chip in pixels
where the filters were observed to be "gray".
In addition to the non-uniformity all these filters have small-scale structures,
difficult to be removed by flat-field correction. If there is a need to use these
filters, flat-fields should be taken to mask regions with small-scale structures out.
To insert the main neutral density filter, use the command:
SYS@taurus> mainfiltnd 2
to insert 0.3 neutral density filter (see the table below).
The available options are the following:
|| useful window
6.6 Quick-look spectrum extraction
Run the ISIS quick-look script at IRAF with e.g.:
isis> isis_ql r1234567 252
where the image name is given without the '.fit' extension, and the last
number on the line is the approximate x position of the spectrum on the CCD.
The script carries out an optimal extraction
(takes ~ 1 sec) and displays the spectrum in the iraf graphics window using
splot, so all the usual keystrokes are available. No wavelength calibration
is provided. We strongly recommend that to use the isis_ql package you first copy the required data to a scratch area, e.g. /scratch/whta/"directory".
Note that if the detector is binned, e.g., x2, in the dispersion direction, isis_ql still plots the extracted spectrum in unbinned pixels. Therefore a line expected to fall e.g., 300 binned pixels redward of the central pixel will fall 600 plotted pixels redward of the central pixel.
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You can copy your data to your laptop or an external disk when connected to the ingext
- rsync -avuz email@example.com:/obsdata/whta/yyyymmdd/ .
you can copy the data to the FTP area, and subsequently retrieve it over the Internet:
- follow these
Or, you can
write your data to a DVD (~4 GB capacity)
- get a DVD from your SA or OSA and
put the DVD in the DVD burner (located in the computer room)
- follow the instructions here