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Target Component Editor

The detailed component editor containing the target list for an observation is accessed in the usual manner, by selecting the target component in your science program, and is shown below: 

target component editor

In normal circumstances, the target name, co-ordinates and system corresponding to the base pointing position of the telescope will have been extracted from the Phase I proposal and shown in the top panel. The coordinates can be refined by editing the RA/Dec boxes in the Target Environment panel or by dragging the base position in the position editor graphical display.

The target name should contain alphanumeric symbols and blank spaces only, as some other symbols (e.g., brackets) can be interpreted as commands by the observing system.

If the observation is of a new target, the observation element is created with an empty telescope targets component and the science program viewer displays a placeholder (RA: 00:00:00.00 Dec:00:00:00.0 HMS Deg (J2000)) until an object name is given. When online, target coordinates, including proper motions, can be obtained by querying either the Simbad or NED databases. Select the query from the menu indicated with the "down" arrow (see figure above), enter the catalog name of the target in the Name box, and then either press Return or click on the Resolve (magnifying glass) button.

Target brightness information is entered in the middle panel. In Observing Tools prior to 2010B (June 2010), target brightness information was entered into a text box to the right of the coordinate boxes. Any information entered in the old format is shown at the bottom of the window. This information can be deleted by clicking the red X to the left of the string. Starting with the 2012B OT the target brightnesses are entered as value:bandpass:system triples (see figure above). To manually enter a new brightness, select the bandpass from the pulldown menu to the right of the box labeled "Select" and then enter a value into the box. Additional entries to the table can be added by clicking on the green + below the list. An entry can be deleted by clicking on the appropriate red X. The Brightness table is automatically sorted by wavelength.

Adjustments to the pointing position, e.g. for proper motion and tracking at specific wavelengths, can also be made in the middle panel. The default is to track at a wavelength defined by the filter or specified dispersing element in the instrument with no proper motion corrections. Proper motions in milli-arcsec/year can be entered into the boxes. These are also filled in automatically after some Simbad and guide star searches.

Additional information that affects the tracking can be entered in the Tracking Details tab. Click on the "Tracking Details" button on the right edge of the middle panel to open and close this tab. In the vast majority of cases these settings should be left at their default values.

The upper panel displays the target list. Each position has a tag associating it with the base (telescope) or one of the wavefront sensors (WFSs). The specific WFS tags are associated with telescope offset positions using the offset iterator. The User tag is not associated with a WFS and is normally used to give the coordinates of stars to be used for peak-up before blind-offsetting to a faint target.  If you wish to change the tag type for a particular position, select the item in the target list and choose the new tag type from the pull-down list in the middle panel. The distance between the base position and the other targets is listed in arcminutes, and all of the known magnitudes are listed for each target.

Caution! Note: the only supported sidereal coordinate system is J2000!

You can add or remove items in the target list (except the base position) using the add/remove/duplicate buttons. Pausing the cursor over one of the buttons will reveal adescription of the button's function. A summary of the buttons is given below.

Add button Add new empty target or magnitude
Remove button Remove selected target or magnitude
copy button Copy selected target to buffer
Paste button Paste target buffer into selected target
Duplicate button Duplicate selected target
Select guide star button Select guide star

Targets can be copy/pasted between target components in different observations, including observations in different programs.

The Duplicate button will copy the information of the selected target and copy it toa new line in the table.  If the base position is duplicated then the new target has a User tag. If another type of target is duplicated then the new target has the same kind of tag as the original but therunning number is incremented. For example, if target PWFS2 (1) is duplicated then the new target has the tag PWFS2 (2).

Duplication is especially useful for preparing AO observations in which the AO correction is calculated from the science target.  In these cases the target and guide star must have the same name and coordinates.Therefore, one can simply duplicate the target and then set the tag for the appropriate type of wavefront sensor. If using Altair then the guide star tag should be AOWFS while if using NICI then the guide star tag is OIWFS.

The Image... button opens the position editor. With an image ofthe field displayed in the position editor you can reset the base position to the central position in the image using the Set Base from Image button. This is useful if you've dragged the base position and you want to return the base position to the original position.

The Manual GS button will open the position editor (if it is not already open) and then open the Guide Star Selection dialog for doing guide star searches from the standard online catalogs.

The Auto GS button will perform an automatic search for the brightest guide star which is reachable by the guider at all currently defined offset positions.

The Auto GS WFS Selector button is used to change the default WFS used by the automatic guide star algorithm.

The Save button accepts the latest changes and stores theprogram to the local database.

The Close button closes the science program editor (saving any changes to the local database). 

Non-Sidereal Tracking

Non-sidereal objects can be specified in a number of ways, depending on the object of interest and whether non-sidereal tracking is required. Although the guidelines below should cover most cases, PIs of non-sidereal objects are encouraged to contact their National Gemini Office (NGO) representative and their Contact Scientist (CS) early in the Phase II process to discuss the best way to support their observations.  In all cases, the minimum non-sidereal target definition should include dummy coordinates for the object midway through the semester for queue planning purposes as well as an entry for the guide probe of interest.  Upon observation, the observer will update the object coordinates and choose a guide star based on the current coordinates.  Nearly all non-sidereal objects can be supported --- we have observed Near-Earth Asteroids closer than a moon radius to the earth.

If observations of non-sidereal objects are desired with tracking at the sidereal rate, then the target component should be set up as a standard J2000 sidereal target.  An ephemeris for the target should be included in a note to the observer including UT date/time, J2000 RA, Declination and any other information relevant to the observer (for instance magnitude for objects with large flux variations).  The observer will use this note to determine the object position and select a guide star at the time of observation.  In addition, if the object is recognized by Horizons, then a dummy target may be created for the observer using the "Horizons-Recognized Objects" procedure.

Horizons-Recognized Objects

Non-sidereal objects with orbital elements supplied by Horizons can be automatically queried by the OT through an interface with JPL/Horizons if an internet connection is active.  Examples of such targets would be numbered asteroids or un-numbered Kuiper Belt Objects with provisional designations. Note that objects should be referred by name rather than number if possible. This reduces the chance of improper number input (causing observation of the wrong target) and reduces query tool confusion with low-numbered objects such as (1), which can alternately describe both Ceres and Mercury. PIs should also update the RA and Dec to a position near the middle of the semester for queue planning purposes.

To define a non-sidereal target, select "Nonsidereal" in the "System" pull-down menu (which defaults to "J2000" for sidereal tracking). Enter the target name or number into the "Name" field and hit or click the magnifying glass to query the JPL/Horizons database. This will return orbital elements and the coordinates of the target at the specified date and time. It is up to the PI to double-check any orbital elements retrieved by the query tool and to ensure the object's ephemeris is sufficiently well known for observation. Tracking will occur at the non-sidereal rate, although please be sure to look below for non-sidereal tracking details for your guide probe, particulary issues with the GMOS OIWFS. An example of non-sidereal tracking of a numbered object appears below for the asteroid Ceres using the JPL minor planet format:

non-sidereal target information 

Non-Sidereal Objects Not in the Horizons System or Moons

Objects not yet cataloged by JPL/Horizons, or objects not in Heliocentric orbit are currently not supported by the above query tool.  Sidereal tracking (see above) is the favored method for observing these objects if that is scientifically viable.  If non-sidereal tracking is required, then the object will be set up to use a machine-readable ephemeris.  This ephemeris needs to be produced in a very specific format and should be tested by the observatory prior to observation.  This method requires additional operational resources for testing so please contact your NGO and CS if you suspect that you will need this functionality, as it is a mode not supported by the OT.  We prefer the use of the machine-readable ephemeris to user-computed orbital elements because we do not have the ability to test third-party fitting methods nor the ability to translate between different orbital element formats (such as Barycentric versus Heliocentric).  In addition, the machine-readable format allows the tracking of any object path on the sky.

Peripheral wavefront sensor guiding with non-sidereal tracking

For non-sidereal tracking and guiding with the peripheral wavefront sensors, orbital elements for the target should be specified via the JPL/Horizons query tool or the machine-readable ephemeris method as discussed above. PIs should make sure that the RA and Dec are updated for a point in the middle of the semester prior to submission. In the example pictured above, the RA and Dec position was computed by the JPL/Horizons query tool. A "dummy" guide star should be chosen which will be updated by the observer when the object is actually observed. At the time of observation, the actual guide star will be selected.  When using the peripheral wavefront sensors with GMOS, it is likely that some portion of the field will be vignetted by the probe arm.  Thus, the user should also specify in a note to the observer the clear aperture required.

Altair guiding with non-sidereal tracking

Altair can understand orbital elements or the machine-readable ephemeris and track at any non-sidereal rate. For guiding on a non-sidereal object with Altair, define the Base and the AOWFS as the same non-sidereal target.  These coordinates can be computed using the JPL/Horizons query tool for numbered targets. As with all non-sidereal objects, PIs should include a note with an ephemeris for the target for the entire semester so the observer can verify the telescope position is correct.

GMOS OIWFS guiding with non-sidereal tracking 

The GMOS OIWFS has severe limitations for tracking non-sidereal objects, and its use is not appropriate for fast-moving objects. Electronic non-sidereal tracking with the GMOS OIWFS can be performed for only 1 arcsecond of total motion on the sky, so science exposures (including readout) must be chosen to complete within this range of motion. Following each exposure, a dither must be performed using the offset iterator in order to "reset" the OIWFS star to the center of the OIWFS field of view. This should be done with the offset iterator. If this 1 arcsecond of motion is not sufficient due to the high rate of motion of the object or the use of long exposure times, then one of the peripheral wavefront sensors should be used instead.