Hectospec/chelle Fiber Assignments

 February 17, 2005

(last modified, Sept 20, 06)
     Here is the current operation mode for Hecto observing runs.

(1) The PI makes a catalog of objects, which may be ranked in preference. The catalog must also include guide stars on the same coordinate system. Guiding is done at the edge of the Hectospec field, not on the surface where the object fibers are positioned. Thus, there are very stringent requirements on guide stars by the small area of sky available and the limited range of magnitudes allowed by the TV cameras.

The 2mass and GSC II catalogs can be used where an  observer catalog is minimal in stars. In that case, the program tmcguidestars should be used. This program searches the 2mass catalog for coincidences with the observer catalog, and computes a coordinate transformation. 2mass and GSC II stars are selected in the field, transformed to the observers' catalog coordinate system, and added to the catalog.  Note: the target catalog must have some stars in common with the 2mass catalogs.  You might need to add stars to insure that, even if you don't intend on observing them.  Bad News tmcguidestars is not yet ready for export. It does run on CfA computers, in a command line mode. External projects should contact instrument scientists if they need help with guide star selection.

(2) The PI downloads the configuration program from CfA,
and  runs the config program for approximate dates of observation.  In this process, guide stars are checked for suitability using a number of criteria (magnitude range, not a galaxy, no neighbors, etc).

(3) xfitfibs requires information such as date and length of observation, number of exposures, ranking of config, and for Chelle observations, the filter and binning needed, all which will be used in scheduling. The output of the program is a number of files which would now be sent to a CfA computer for human checking, via the button Submit

(4) The configuration file is modified a few minutes before the observation takes place, in order to update positions, rotation angles, random sky selections, and guide stars.

Please submit your configuration files at least 10 days before the run starts.

  Brief Instructions on Running Xfitfibs


   Here, I describe the basics of obtaining a fiber assignment file from a catalog.  The xfitfibs program itself contains many pages of help for particular items, and after going through these steps, one should consult those pages for detailed help.   The observers manual, which duplicates this section is at cfa-www.harvard.edu/oir/MMT/MMTI/hectospec.html  (it tends to be updated later than this page, however).

I. Make a catalog

The catalog should be in starbase format (Tab delimited) with at least these columns:

ra             dec           type

but it's probably better to have more:

ra             dec            object        rank    type mag

A sample catalog would look like:
ra             dec            object        rank    type
-----------    -----------    ----------    ----    ----
0:40:30.289    41:16:08.73    008-060       1    TARGET
0:40:31.566    41:14:22.54    010-062       1    TARGET
0:54:58.594    43:05:22.298            guide
0:54:59.146    39:03:36.815            guide

Note the row with dashes (also tab delimited). "guide" indicates the guide stars, located at the end of the file.  In this case, the guide stars have no rank or object name (but the tabs are there).  The starbase suite of programs may be downloaded at
The command  check is useful top run on your catalog to see that the format is valid (type "check < mycatalog"; no message means that the catalog is valid).  The command  fldtotable will convert an ascii table to starbase (see the help pages).

It is nothing short of essential that the targets and guide stars be on the same coordinate system.

The coordinate transformation program is
but will have difficulty running if the field is dense in stars because of the web interface time out limit.

II. Run Xfitfibs

II.1 Load catalog and select field centers

  1. Start up program. this brings up the drawing window and the field window
  2. Load a file with pull down menu. This will draw the objects  and a 1d circle centered on the objects' centroid, and also make 1 target center in the fld window.
  3. In the latter window, enter the start time in UT, e.g.:  March 3 03:00:00 2005
  4. Enter an exptime in minutes and nexp (e.g., 15 and 3). (Leave pa, minutes, r0, r1 and r2 alone)
  5. For each entry in the field table, enter a priority which will be used in the schedule.
  6. If you need sky offsets, please enter the number and  time  in minutes per exposure.   Offsets will typically be 5 arcs; successive exposures will be in different locations with the same offset value.
  1. for Chelle observations, select the on-chip binning, either 1x1 or 2x3. Spec projects leave this and the filter blank.
  2. for Chelle observations, select the filter.  Choices are Ca19, OB21, OB24, OB25, OB26, Na28, RV31, OB32, OB33, OB37, Ca41, iodine, and dumiodine.  OB25 is the Halpha filter. See http://cfa-www.harvard.edu/cfa/oir/MMT/MMTI/hectospec/Filter_Specs_a.pdf
  3. for Spec observations, select the grating: 270 or 600.  Then select the centralwave(length). For the 270, this is always 6500. For the 600gpm grating, you have a choice of 4800, 5300, 5800, 6300, 6800, 7300, 7800, 8300.  Errors will occur upon submission if you enter invalid numbers.
    1. Click on the box next to the config number (beginning of line), it should turn red indicating it is being operated on.
    2. In the drawing window you may now move the circle to where you want it by clicking and dragging, or enter new coords by hand. You may add fields by using the table pull down menu. When you are through moving things around, you should turn those buttons off. 
    3. Click on parameters in the field table window, and set the # of sky fibers.  Once you are happy with your field centers, we need to...

II.2 select candidate guide stars

Click on Fit Guides  tab,
then begin fit.

The number of guide stars will appear at the far right of the fld table row. A red background means too few stars available. You may have to move the circle center or change the mag limit on the guide stars (at the peril of them not being seen at the telescope).

It may also be the case that the rotator angles are red, even though there are enough guide stars.  In this case you can change those angles by clicking on "toggle guide annuli", going to the drawing window clicking on the (faint) red circle at the ends of any of the 3 annuli and dragging the annuli around until r0,r1 and r3 are green.

Next you need to classify the  guide stars to remove double stars, stars that are too faint, and plain old galaxies.  Click on

"classify candidate..."

After a while a message will come back with the results. Some stars may be rejected. Click on ok to rerun the guide  star selection.

You can view the guide stars by bringing up the  "Guide" window. Use view to elect each config in turn.
Clicking on show,  will start up ds9 and display all the guide stars in different frames. Nixed stars may also be seen by using view.  If you are left with no guide stars, you may try to lower the faint mag limit in the parameters menu, but please advise us that you have done so, and expect some trouble at the telescope.

II.3 Fit fibers.

Click on fit fibers, if your objects have a ranking system, then select rank, otherwise don't click on it. Make depth=7. If you are configuring for Chelle, click on that as well. Now, begin fit.  

Note that all the field centers you have entered in the fld table are fit at once, such that no target is assigned more than once.  If you create two different output files from the same catalog, by running xfitfibs at different times with different field centers, then you may have duplicates.

Check to see that you have fit the number of targets you expected, otherwise, change your sky fiber numbers in parameters.  Ranking of targets may be changed by using the rank window.  See the details in the help page.

II.4 Submit

Now you ready to submit:

Click on the Send tab.
Pick the current trimester (e.g., 2005a)
Pick the PI number,
Click on send
You may get a warning about changed parameters in the field table, which I think can be ignored.  A number of files are then sent to CfA, where they are checked again before being sent out to Mt Hopkins.  Note that sending a config file (the one actually used at the telescope) directly to Mt Hopkins is discouraged, since such a file would not have the Program number identified, that being added during the "send" process.

Send will fail if you did not classify the guide stars. Go back and classify them, and then run Fit fibers again.

Send will fail if you did not enter a valid filter or binning for Chelle observations, or valid grating and centralwave(length) for Spec. Correct those, and press Fit fibers again. Now submit

Now you can submit.

Questions should be addressed to
hectospec at cfa.harvard.edu
hectochelle at cfa.harvard.edu