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Editing and Prioritizing

This page contains instructions on editing slit and object properties and assigning priorities to objects. Go directly to:



The colored symbols overlaid on top of the image represent the priority levels of the objects listed in the catalog window. Single clicking on an object in the Skycat display will highlight that object in the object table display, and vice versa. 

The objects in the Object Table need to be prioritized. There are five priority levels: Priority 0 (Acquisition Object), Priority 1, 2, 3 and Ignore Object (X).

Acquisition Objects are used to align the mask on the sky. Priority 1 objects are ones that you wish to observe. Priority 2 and 3 objects are potentially interesting objects, however at this time slits for this object are less important (`Priority 3' objects are less important than `Priority 2' objects). Objects that you want to keep in the Object Table but not have considered at this point may be labeled `Ignore Object'. You may want to use these objects later to fill unused space in a mask designed to contain as many as you important objects as possible.

Each of these priority levels corresponds to a different symbol as follows:

  • Acquisition (guide) Object = Cyan diamond
  • Priority 1 = Blue triangle
  • Priority 2 = Green square
  • Priority 3 = White circle
  • Ignore Object = Yellow cross
  • [Prioritized objects]

    In the catalog window:

    1. Single or multiple rows may be flagged at once. To change the priority of a single object, simply highlight (click) on the object and click on the appropriate priority button: "Acq. Object, P0", "Priority 1", "Priority 2", "Priority 3".
    2. To change the priority of multiple objects, either press "Shift-Click" for a block of successive objects in the catalog listing, or press "Ctrl-Click" for non-successive objects. Then click on the appropriate priority button.
    3. To change the priority of every object in the catalog, it is often easier to use IRAF. This is outlined below.
    4. To cancel a flagged object, select it and click on "Ignore Object". It will then be marked with a yellow cross on the image display.

    Only objects that appear in the catalog table (i.e. are represented on the image by some symbol) may be selected and therefore included in mask designs.

    NOTE: A minimum of two acquisition objects are required for the mask alignment. A maximum of 10 are allowed. It is recommended to use 2-4 acquisition objects.Make sure none of these are in the gaps between the CCDs. You can show the gaps by clicking "Plot GMOS gaps" on the catalog window.

    Slit sizes and tilts

    To adjust the size and position of the slits, simply:

    1. Click on the required object(s).
    2. Enter the new parameter in the boxes adjacent to the parameter listings, e.g. Slit Size Y, etc.
    3. Either hit "Enter", or click on "Update Row" and the value for the object will be changed. Note that it does take a couple of seconds to update the row. Thus if multiple parameters are being changed, it's easier to enter all the values in the boxes and then click "Update Row", rather than pressing "Enter" after each individual parameter value is altered.
    Editing object parameters with the catalog window.


    Note that by default the slit width (Slit Size X), slit tilt, and X and Y slit positions are not included in the Object Table if you use stsdas2objt to create the table. If the slitsize_x column is not present then a width of 1 arcsecond is assumed. These columns can be added to the FITS Object Table using the IRAF task tcalc (see Using IRAF to edit the object table below).

    It is possible to have tilted slits if your FITS Object Table must contain the slittilt column before you load it into the mask design software (see Using IRAF to edit the object table below). To tilt a slit for a particular object:

    1. Click on the required object(s).
    2. Click on the "Tilted Slits" button. A pop-up window will appear (see right).
    3. Enter the required angle of the slit (between -45 and 45 degrees). A positive angle rotates the slit counter-clockwise with respect to the vertical, a negative angle rotates the slit in the clockwise direction.
    4. To un-tilt the slit for an object, click on the "Tilted Slits" button and chose an angle of 0.


    Editing an object

    To edit any column values for an object:

    1. Select the object.
    2. From the menu, select "Edit - Edit Object".
    3. In the pop-up window that appears, all columns including ID number, RA and Dec may be changed from the boxes adjacent to the column name. Once the value is changed hit "Enter" or click on the "Enter" button. It will then ask you to confirm the change.
    4. Once the appropriate values have been edited, close this window.
    [Edit column window]

    Using IRAF to edit the Object Table

    It is easiest to use IRAF when creating the Object Table, or when you wish to add a column or change a certain column value for the whole Object Table.

    To print the table in IRAF, type tprint mask_OT.fits . You can also use tread mask_OT.fits. Using tread, you can scroll across to see all columns, however, you can not alter values using this tool. To exit tread, hit Ctrl,D then type quit. For help, hit Ctrl,D and then type help. The task tedit can be used to interactively edit tables and is useful for editing a few rows.

    To only list the column names of the Object Table, use the task tlcol, e.g. tlcol mask_OT.fits will list the names of the columns for that FITS file.

    The task tcalc performs arithmetic operations on table columns. Using this, you can add columns, or alter a column and output the result into new column.For more information about the table editing tools contained in IRAF, type help ttools. Most of the tools in this package may be useful in editing or creating new Object Tables. Some useful examples are:

    tcalc mask_OT.fits "slitsize_x" 0.75 colfmt="f6.2" colunit="arcsec"
    tcalc mask_OT.fits "slitsize_y" 5.0 colfmt="f6.1" colunit="arcsec"
    tcalc mask_OT.fits "slittilt" 0.0 colfmt="f6.1" colunit=""
    tcalc mask_OT.fits "slitpos_y" 0.0 colfmt="f6.2" colunit="arcsec"
    tcalc mask_OT.fits "slitpos_x" 0.0 colfmt="f6.2" colunit="arcsec"

    Last update May 27, 2013; Mischa Schirmer and Bryan Miller
    In original form February 10, 2003; Dione Scheltus

    Gemini Observatory Participants