PrismQuickStartGuide

PRISM Quick Start Guide
{toc}
A. Starting LOIS
1.Key
Button labels are written in a Geneva font
Commands you type are written in a Courier font

2.Make sure MOVE is running
MOVE must be running, awake, and not guiding on a star before you start LOIS

3.Make sure the large LN2 storage tank is not connected to camera's dewar
See Perkins QSG for more information

4.Start up ds9 and LOIS
On the Perkins computer in an xterm window type:

telnet hans
Once hans is open, login as obs72 (same password as on perkins) then type:

ds9 &
lois &
The LOIS window, shown below, will appear on the screen.



In the LOIS console window:

click Configure
In the "configlois" window that pops up select (for PRISM):

Telescope Interface-> "perkins"
Camera Interface-> "prism"
Instrument Interface-> "PrismInst"
Display Interface-> "DS9/XP" (not "DS9/Saotng")
enter your name and affiliation for "Observer(s)" and "Affiliation" (once set, these parameters are remembered and you won't need to re-enter them)
click Start


Wait until LOIS finishes loading all windows; generally, it is ready when the "Perkins Telescope Control" window is up and values are filled in from the MOVE computer

To use IRAF type the following into the xgterm window:

ds9 &
cl
If there is no xgterm window available you can press the IRAF button on the taskbar and press the "Launch DS9, IRAF" button. You can change IRAF's current directory with a "cd" command (typically "cd /perkins/data/your_directory"). To display images from IRAF in the ds9 display "cd" into the appropriate directory and type "display [filename]" where [filename] is the filename of the image you want to load in the current directory.

5.Set up data storage in LOIS
In the LOIS console window:

Click the "Storage" buton
In the "store" window that pops up:

Enter the root you want for your files
Enter the starting extension number
Select the directory in which you want your images to be stored. The directory should be named with the date and be in /perkins/data/ (The directory does not have to already exist, LOIS will create it if necessary).
By default a ".fits" extension is added to all files, click Off if you do not want this extension added. Your files will be named: root.extension.fits or root.extension.
Auto-storing of images is On by default, click Off if you do not want to store your images.

6.Load standard PRISM scripts
In the LOIS console window:

Type "source prismstart.tcl"
Click on the "Show User Buttons" button
This will bring up a window with the default scripts relevant to PRISM. To use a default script, fill in the parameters then click the left-most button with the script name.

B.Filters, Masks, Polarimetry, Spectroscopy
1.Filters
When first starting up, click on each of the three "Home Wheel" buttons in the PRISM Control Panel one at a time. Wait until one wheel is finished before starting another wheel. This initializes and homes each wheel since there is only one absolute encoder. Even if you are not using the Polarimetry or Grism wheels you still need to home them so that you know they are in an open position.

If you move the cursor off the home button after you have clicked it you will see the button turn red while it searchs for home, then gray when home is found. The Pos1 button will also turn green. Another indication that the wheel has homed successfully is in the right-hand side of the LOIS Console Window. Look here for "Sending Command HM0\r". Occasionally, the Filter Wheel (top) will fail to find home. The only indication you will have is in the right-hand side of the LOIS Console Window. It will beep and several red error messages will be printed. If the wheel fails to find home click "Home Wheel" again. If a second attempt fails call Brian.

To change to a different filter, click on one of the "Pos#" buttons in the PRISM Control Panel. When the move is complete the new position button will turn green. Also, in the right-hand side of the LOIS Control Window you will see "Delta Position: 0\r" followed by "Sending Command RP5\r".

The names of the filters in the Filter Wheel are kept up to date. If the U filter is to be inserted, it goes in position2, not 1. Position 2 is also where the VR filter (used for KBO observations) goes.

2.Masks
All of these commands are issued in the "LOIS console window" (normally the window across the bottom of the screen).

Note that these commands are temporary until the GUI in the PRISM Control Panel is fixed. Until then, there is no graphical feedback about when these commands have finished.

Before putting in a new mask, make sure that all masks are already out of the way. Any mask-in command will automatically issue a home command, but please be careful to avoid a collision. You can run the home command yourself by typing "mask mask=0" into the LOIS System Console.

To check the status of the masks observe the commands in the right-hand side of the LOIS Console Window. You will see commands go by that are checking each mask to see if the home switch has been activated. This command is complete when you see four "Sending Command HM0\r" lines in the window (depending on which mask is in, these commands may be scattered before and after the Delta Position commands).

To move a mask (1-4) into place type "mask mask=#" into the console where # is the number of the mask. In the right-hand side of the LOIS Console Window the "Delta Position" values will change. These numbers will ramp up, pause, then ramp down. When you see "Delta Position: 0\r", the mask is in place.

Engineering command*: To move a mask to a specific position type "mask mask=1 abspos=
{html}
<posval>
{html}
" where the posval is some value between 0 and 89100. Any value outside this range will return an error. Observers should not need to use this command.
As of 17 February 2004, mask 1 is a Hartmann-type mask, and mask 2 is Ken Janes's M67 mask, mask 3 is empty, and mask 4 is Ted's test pattern transparency.

When moving a mask in it takes 5 seconds to check each mask is at home and 55 seconds to move mask in.

When moving a mask out it takes 52 seconds to move the mask out and 5 sec to check all other masks are at home.

Note: mask 3 is not working properly, there may be some motor slippage (it claims to take only 15-30 sec to move back out). Do not use mask 3 until further notice.

3.Polarimetry
The PRISM polarimetry wheel (filter wheel #2) provides use of six positions. Currently (30 August 2005), there are three polarid filters in the wheel (Pol1, Pol2, Pol3). The polaroid filters are all the same, but differ slightly in their orientation angle. Therefore, you are advised to choose one "Pol" position and stick with it throughout an observing run to avoid obtaining inconsistent data.

The polarimetry wheel provides 360 degrees of angular coverage. There are 1600 steps per full rotation, therefore a position angle can be specified using the following conversion:

{anchor:}
steps =(1600 steps / 360 deg)*(position angle in deg)

For example, 0 degrees corresponds to polar position offset 0, 90 degrees to polar position offset 400, and so on. Note that the absolute polarimetry angle has not yet been calculated for any of the polarimetry elements.

In the LOIS console, the following PRISM polarimetry commands may be executed:

polar home
polar step=[int]
The home command sends the polarimetry wheel to the "home" position (polar position offset 0). The step command specifies the relative number of steps (positive or negative) to move from the current position. It does not specify the absolute number of steps to move from the home position. Therefore, the observer will need to keep track of the current polarimetry position angle as it is moved.

Since the readout time for unbinned PRISM images is 45 seconds (or 15 seconds for 2x2 binning), you may want to consider sub-framed images to maximize the quality of your polarimetry data. Sub-frame imaging can significantly reduce image readout time, decreasing the likelihood of sky conditions changing over a set of measurements taken at different position angles. To take a sub-frame, see "Sub-frame readout" (Section C.2).

Furthermore, if high spatial resolution is not a concern, 2x2 binning can also be used to reduce image readout time. To change the bining see "Binning pixels" (Section C.3).

For examples of PRISM polarimetry scripts written in the Tcl scripting language, see "prism_pol_cal.tcl" and "prism_UQ_loop.tcl" on hans in /hans/home/obs72/tcl.scripts. [This machine is not accessible from outside Lowell. Email brian.taylor@lowell.edu if you are outside Lowell and would like to see the scripts.]

4.Spectroscopy
To obtain spectroscopy images:

Go to your field
Take a full frame image
Identify your target and place it at position x=1044 y=1064 (for 1x1 binning) or x=522 y=532 (for 2x2 binning). You can either do this manually or you can use the tcl script "recenter"
To use the "recenter" script type the following into the LOIS System Console:

source recenter.tcl
recenter [from_x] from_y_ [to_x] to_y [platescale]
Note that for the recenter script, you need to first figure out where your target is now (use the cursor in ds9), these are the

{html}
<from_x>
{html}
and

{html}
<from_y>
{html}
. Platescale is 0.39 for 1x1 binning, and 0.78 for 2x2 binning. If you omit the [to_x] and [to_y] options it automatically assumes x=1099 and y=1053 (from 1x1 binning).

For 1x1 binning:

recenter

{html}
<from_x>
{html}


{html}
<from_y>
{html}
1062 1053 0.39

For 2x2 binning:

recenter

{html}
<from_x>
{html}


{html}
<from_y>
{html}
531 527 0.78

Put in the slit mask. This will be mask #1, with 5 slits across the field. You will be putting your star into the middle slit. Type "mask mask=1" into the LOIS System Console. The little slits are about 6 pixels wide (in y, or declination) and 37 pixels long (in x, or right ascension). Note that you still should not have the VPH grism in. If necessary, tweak your source position (using recenter or by hand) so that your source is centered in the middle slit.

Now, put in the VPH grism. To do this, click on the "VPH Grism position" button in the filter control window.

Choose an exposure time and take images. Lower row numbers are shorter wavelengths. You can use atmospheric lines for wavelength calibrations. An argon comparison lamp has been installed and may be used at the user's discretion. Beware, there is some fringing on the red end of the spectrum.

When done with spectroscopy please take the mask back out by typing "mask mask=0"

C.Taking Data
1. Taking an image
In the camera control window:

Enter the desired exposure time and number of exposures (boxes at top of window)
Choose the frame type: Object, Flat, Dark, or Bias (buttons at bottom of window)
Click "Go" to take an image that will be saved to an unique filename
Click "Test" to take an image that will be saved to "test.fits" (this image will be overwritten the next time you click Test).
2. Sub-frame readout
1. Take a full frame image and identify the region of interest for sub-frame readout.
1. In the DS9 window select a subframe region with the cursor around your target.
1. Type "save_sub" in the LOIS console window.
1. Take a test image and verify that your subframing is correct.
1. To turn off subframing and return to full frames type "subframe sub=0" in the LOIS console window.
3.Binning pixels
If spatial resolution is not a concern, 2x2 binning can be used. Binning increases the pixel size and decreases the array readout time.
Binning    Pixel scale (arcsec/pixel)    Full-frame readout time (sec)
1x1    0.4    45
2x2    0.8    14
The default binning on LOIS startup is 1x1. To change the binning, click on the "CCD Config" menu in the "PRISM Camera Control" GUI and select the desired binning option. Note that there are also 3x3 and 4x4 binning options, but these have not been tested yet.

4.Focussing
1. Take a full-field test frame
1. Identify a suitable focus star and get its coordinates from the DS9 display.
1. Type "source kajfocus.tcl" (if you have not already typed "source prismstart.tcl" at startup).
1. Then do "kajfocus xc yc expt focstart focstep nsteps", where:

xc - x coordinate of the focus star from step 2
yc - y coordinate of the star
expt - exposure time for focus frames
focstart - starting focus value
focstep - focus step size
nsteps - number of focus steps to take
This program will make a subframe around the star, take focus exposures, and run the phot routine. The results are put into a file called focus.dat located in the current image directory. You will see the subframes on the image display as the program proceeds. When complete, the program sets the image format back to the full frame (make sure to take a test image to verify that full framing has been activated). One can determine the best focus by examining the focus.dat file and picking the minimum of a parabolic fit through the FWHM values. Subsequent focus runs are appended to the existing file. The most recent focusing run is at the bottom of the file.

An example of entries in a focus.dat file.:

04:45:28.01 48.86 47.54 3.14 16.48 0.060 2403.25
04:45:49.02 48.32 47.88 3.26 16.44 0.063 2396.46
04:46:10.01 48.75 48.18 2.70 16.49 0.059 2410.10
The values in the file are:

UT
image center x (pix in subframe)
image center y (pix in subframe)
FWHM (pix)
rough magnitude estimate
magnitude error
background level (DN)
The recommended procedure has moderately large steps of 50 focus units with 9 steps to go +/- about 200 steps from the expected focus value. For example, if you expect the focus to be around 3800 you might start out:

kajfocus xc yc 15 3600 50 9
Then examine the focus.dat file in your data directory and determine the optimal focus. You can iterate the process with a finer focus step

5.Focus vs. Filter
PRISM filters are not parfocal, so you will need to adjust the focus during the course of the night. This process will be automated in the future, but for now you will need to change focus manually. We recommend focusing in the R filter. The offsets from each filter from the R filter are given in the table below. For each filter, the relative focus change from the R filter is given and an example is given (from the night of 25 September 2005, 8pm MST).

Filter    Relative focus change    Sample focus
B    R-40    3740
V    R-20    3760
R    R    3780
I    R+120    3900
Note that B, V, and R focus readings are fairly close together. If you are only using these filters and focusing is not as critical and you can leave the focus set at the V band focus.

D.Image Analysis via IRAF
Start an xgterm window by doing either:

In any existing terminal type "xgterm &"
or
Click on Applications in the upper left hand corner of the display
drag down to CDE Menu
drag over to Lowell
drag over to xgterm
Then in the new xgterm that pops up:

type "cd /perkins/home/obs72/iraf"
type "ds9 &" to start a new dedicated ds9 window
type "cl" to start iraf
type "cd /perkins/data/pcdata/
{html}
<your data directory>
{html}
"
In iraf, imexam is used to display information about fits images. To use imexam, type "imexam" at the IRAF command line. Move the cursor to a point of interest on the image. Then press one of the following keys for its associated output:

r - radial profile
e - contour plot
c - column plot
l - line plot
h - histogram
a - circular aperture photometry (prints to xgterm rather than graphics window)
j - line 1D gaussian fit
k - column 1D gaussian fit
s - 3D surface plot
u,v - vector plot
q - quit
When you run a radial profile in imexam additional information is printed on the bottom of the window. The output consists of:
the final radius used for the photometry and fitting
magnitude
flux
mean background
peak value of the profile fit
e
pa (in degrees between -90 and +90 with 0 along the x axis)
the Moffat beta value if a Moffat profile is fit
three diferent measures of the FWHM.
The FWHM values are, in order, the profile fit to the enclosed flux, the profile fit to the individual pixels, and the direct measurement from the derivative of the enclosed flux profile. Note that except for the direct method, the other estimates are not really measurements of the FWHM but are quantities which give the correct FWHM for the specified profile type. [From iraf help files.]

E.Scripting
1.tcl scripts
Create a file in the tcl scriptdirectory on hans (/hans/home/obs72/tcl.scripts). Most of the syntax can be figured out by noticing what is displayed in the console window when you execute a command, or by looking at other tcl scripts.

More documentation coming soon

2.Creating a clickable button for a tcl script
After you have created a tcl file as directed above, in the console window:

Type "source
{html}
<file>
{html}
.tcl"
Type "cbutton proc=
{html}
<name>
{html}
"
Click User Buttons
In the User Buttons window that appears:
Enter the parameter values (if available)
Click the button labeled with your function name to execute your script
F.Special Commands
To automatically move the telescope a small distance between exposures (useful when taking sky flats):
type "flat_dither on"
To turn this off:
type "flat_dither off"
Note that the throw is hardwired at 120 arcseconds to the west.
G.Other Notes
1.If LOIS dies, please do this:
Sometimes LOIS goes into a state where you can still click on buttons but it will not take an image. If this occurs, go to your hans window and in the obs72 home directory run "lois.snap." This will create a file called lois.snapcore_x.xxx where the x are numbers. If LOIS goes into a state where you are unable to do anything please run this script. Include the snapcore filename in your failure report.

2.Please Report Problems!
Please report any problems you may have experienced during your observing, even if it was resolved by a telephone call to someone. To report a problem, send an email to:

mailto.72statusatlowell.edu

Note that the mailto."atlowell.edu" part is necessary even when sending from the observer account. Problems that are not time-critical enough to warrant a telephone call can be reported to this email address.

3.Create an automatic electronic log of your night's data
In any perkins terminal window (not hans), cd to your data directory and type "autolog". This is an iraf script and will take a few minutes to complete (depending on how many files you have). If your data files are named "base.nnn.fits" it will create a file "base.LOG" in your data directory. The current version of the script requires that the "*.fits" extension be used.

Instructions for printing this file are included within the file, on the first line. It is printed in landscape mode with no borders to allow the maximum printable space on the page.

4.Get an email log of your night's data
This log is less extensive than the electronic log (above). To get this email, at the end of your night (or whenever you want the log), in any perkins terminal window type "obs_report prism

{html}
<your full email address>
{html}
".

These logs are generated automatically from a mysql database. The database query runs immediately, and only for the current (UT) date.

5.Updates
Please send requests for additional information, corrections, updates, etc. to: mailto.Brian.Tayloratlowell.edu. Or you can leave a marked-up copy in my mailbox in the PRC at Lowell.

-- Main.BrianWTaylor - 27 Dec 2006

-- Main.MikePavel - 18 Sep 2007