To facilitate successful observing runs, the LDT supports several methods for preparing and submitting observing target lists and telescope motion pattern requests.
Target List Catalog
Observer Target List Files
The LDT accepts target catalogs through a tool called the Observer Target List. This is an interface that allows the user to send targets directly to the Telescope Control System from one of the observer computers ( dct-obs1 / dct-obs2 ). Your Observer Target List file must be on the observer computer in order to use this UI (you may transfer your catalog via scp, USB drive, carrier pigeon, etc.).
The catalog files should be composed using a basic text editor (e.g. vi or emacs) and saved with the extension .tls. The characters in the files must to be limited to the basic ascii text set (no smart quotes, hidden characters, or characters from an extended character set like ISO-Latin-1). It is recommended that you use our target file validator tool prior to your observing night to ensure proper formatting.
A sample file containing Name, RA, DEC, muRA, muDEC, Magnitude, dRA, and dDec, is shown below. Note that the target name appears in double quotes. The telescope will accept both sidereal and non-sidereal track rates through the use of the dRA and dDec differential tracking rates – non-sidereal track rates should be provided in arcsec hr-1. muRA and muDEC should be in mas/yr where muRA is the angular measurement used by most catalogs (μα×cos(δ)). The coordinates must to be in J2000.0, as there is currently no option for submitting coordinates in other epochs.
#title=true ra=true dec=true epoch=false muRA=true muDec=true magnitude=true dRA=true dDec=true rotatorPA=false rotatorFrame=false # "35671 1am NS" 01:00:09.4 +05:59:47 0.0 0.0 21.4 -2.75 -1.18 "19122 1am" 01:29:15.3 +11:37:16 0.0 0.0 16.2 0.0 0.0 "19122 1am NS" 01:29:15.3 +11:37:16 0.0 0.0 16.2 -28.46 -13.3 "136199 Eris 1am" 01:41:13.9 -03:18:44 0.0 0.0 18.7 0.0 0.0 "136199 Eris 1am NS" 01:41:13.9 -03:18:44 0.0 0.0 18.7 -1.36 -0.31 "120348 1am" 02:44:50.7 -10:01:41 0.0 0.0 20.5 0.0 0.0 "120348 1am NS" 02:44:50.7 -10:01:41 0.0 0.0 20.5 -3.16 -0.92
A full explanation of the functionality of the UI and the list format is given in the Observer Target List User Manual.
Observer Target User Interface Highlights
Once you have loaded in a .tls catalog file, the UI features three computed columns to assist with nighttime observing: current airmass, AZ, and EL – all of which will be recalculated any time you resort your table. You may edit any of the targets in your list from the UI by double clicking on the entry you wish to edit. Furthermore, a "Test" line is provided for entering new targets on the fly, which may be used if you do not have many targets or did not have time to write a file prior to arriving at LDT.
Catalog files cannot be saved from the UI, so any changes made to the catalog list within the UI will be discarded when the UI is closed.
Use Cases
Target vs fixed frames, PA, etc. Bring out subtleties of how powerful these things are.
Cases:
The telescope control system supports several tracking modes:
- Sidereal tracking → The telescope will track at the standard sidereal rate.
- Non-sidereal tracking at a constant offset rate → The telescope will track at a rate that is the sum of the sidereal rate plus a constant offset selected by the observer. This is most useful for tracking things like asteroids moving at slow to moderate rates, typically less than about 30 to 40 arcseconds per hour. Offset rates are typically entered in arcseconds per hour for RA and Dec. The ephemeris tools at the Minor Planet Center and JPL Horizons will both provide rates in this format.
- Ephemeris tracking → The telescope will track using a pre-generated ephemeris for a specific object. This is most useful for objects that have larger non-sidereal motions like Near Earth Objects and comets. Ephemerides need to be pre-generated in a very specific format (see Ephemeris Data below) and the files loaded onto the TCS computer before they can be used. Ephemerides can be generated using the tool embedded in the TCS that queries JPL's Horizons service (this is the most direct method), or a user can construct their own ephemerides and ask the TO to upload them to the TCS computer. If the observer supplies the ephemeris, they MUST indicate whether their ephemeris is in ICRS/J2000 (FK5 on the TCS) or in Topocentric Apparent (APPT on the TCS).
- Ephemeris plus non-sidereal offset rate tracking → This combines the previous two modes. The basic tracking follows an ephemeris and then on top of that an offset rate is added. This can be a useful way to "split the difference" when tracking a moving object against a stellar background. By adding an offset rate, the telescope can be made to track at some apparent fraction of the moving object rate, redistributing the image smearing.
The telescope control system supports two basic frames of reference (this is NOT the same thing as the coordinate system reference frame for RA,Dec etc.):
- Target frame → most common case for imaging. The detector will be kept oriented in the RA/Dec on-sky frame of reference. The zero point of this frame has the line North-South aligned with the instrument fiducial. For an imager, the detector columns are the normal fiducial. Instrument rotation angles will be measured from North through East.
- Fixed frame → Often used for spectroscopic observations of point source objects. The instrument fiducial direction is typically aligned along the slit for a slit spectrograph. The zero point for this frame has the instrument fiducial aligned with the vertical direction. There is a 180degree ambiguity. For example, for the DeVeny spectrograph, setting the frame to Fixed and the instrument angle to 180degrees will align the slit vertically, which is also aligned with the parallactic angle. For guiding, the TO will need to select the guide mode for Fixed frame, which accounts for the lack of instrument rotation compensation.
The system can be used in any combination of the Tracking Mode plus Frame. For example, spectra of a main belt asteroid could be taken with the the telescope tracking using a non-sidereal offset rate and the frame set to Fixed to allow for holding the slit at the parallactic angle.
Ephemeris Data
Using the TCS Horizons Interface
Telescope Motion Pattern Data
- Pattern Data Submission [Set of commands to be executed in order] With dither patterns, guide is supposed to break / reacquire -- but it sometimes breaks.
- Automated Functions
Other Resources
We provide a list of Object Data and Finder Chart Generators