Hectospec Run Preparation

Detailed information about hectospec can be found at the CfA hectospec page, at Doug Mink's hectospec page. The published description of the instrument by Fabricant et al. can be found at ADS

Catalogue issues

Running xfitfibs

The code used to place fibers is downloaded from the hectospec assignments page. Follow instructions on that page to download the code and making it executable. Some information on how to prepare data is available on the assignments page. The xfitfibs manual itself is only accessible by running xfitfibs.
  1. First of all find out the dates of observation and times when the field transits. Since hectospec is operated on queue scheduling, any time while the field is below 1.5 airmasses is valid. However, note that since the MMT has an alt-az mounting, fields that go close to the zenith cannot be observed while transiting because of the very quick change in instrument rotation.

  2. Create the field catalogue which will be used to determine the field coordinates. These must be in the "starbase" format where columns are separated by tabs, not blanks. See the example perl scripts for the field center and the object catalog . Make sure the field (*.fld) and catalogue (*.cat) have the same name. Notice that the test field name has an '.orig' appended. It must be copied as '.fld' so xfitfibs recognizes it. The 'fld' file will be overwritten by xfitfibs. If the field and catalogue do not follow the convention above (2 line header etc), xfitfibs will not run . The times that were found in item 1 are placed in the fld file under variable '$start'.

  3. Using a catalogue with the guide stars only, use the default parameters under the parameters tab of xfitfibs (the radio boxes with red colors). These specify the parameters used by xfitfibs to classify the guide stars, interacting directly with the Guide Star Catalogue and DSS (at the CfA presumably).

  4. Press the "Fit Guides" tab. If the radio box just before the RA column is red, this means that the field position may be tweaked, using the grid specified in the tab (default 2 arc minutes at 0.25 arc minutes intervals) and the final result written to the "fld" file. The grid parameters can be changed ad libitum. Often it is easier to tweak by hand, toggling the guide stars and guide annuli, placing the mouse on the ring representing the hectospec field of view and moving it. Before doing this, unset the red button next to the field RA column so that changes will not affect the "fld" file. Move the field around examining when stars fall inside the guide annuli. The boxes with r0, r1, r2 show the rotation angle for beginning, middle and end of exposures and should be green. If any box is yellow or red, the field may need to be rotated so all three boxes are green. To do this toggle on the guide annuli and place the mouse on the red circle at the ends.

  5. Once candidate stars are selected, they can be inspected with ds9. They must also be classified by pressing the "Classify Candidate Guide Stars" button. This will retrieve and analyse DSS images, deciding if the candidates are worthy enough to iluminate the guide probes. Stars that are in legal positions have blue colors in the field plot, while stars that will be monitored by the guide probes have green colors. The last box in the field table will show how many guide stars are available. If it is red that is bad news - a new position has to be searched for. The bottom line is that there must be at least two probes which can access stars.

  6. To make life easier configure guide stars for one field at a time (i.e., a separate file for each configuration. xfitfibs updates these files.

  7. The ensemble of configured files can then be "glued" together:
    head -2 egs_field_01.fld > egs_final.fld ; grep '14:' egs_field_*.fld >> egs_final.fld

  8. Edit the rank file (in this case junk.rnk) writing the minimum and maximum number of objects of a given rank should appear in each configuration. In order to have 6 spec-ph stars, write 6 in both the minfield and maxfield columns.

  9. Now that the ensemble of field centers are ready run xfitfibs again. If the configurations were done correctly for the individual fields, fitting guide stars and classifying them will be quick and easy.

  10. In the parameters tab set the minimum and maximum number of sky fibers and how they will be chosen.These numbers refer to the sky positions "calculated" (somehow) by xfitfibs, not those indicated in the catalogue file by the user.

  11. Press the "Fit Fibers" tab, set the number of rank levels ("depth") set the rank button (it becomes red) and press "begin fit". This will fit all configurations and place sky fibers at the end. Depending on the number of ranks this is a long process. Unfortunately the present incarnation of xfitfibs does not tell you which rank it is fitting. I have found out that if there are too many rank levels (I tried 10) it crashes with "segmentation volation". This was solved by limiting the number of ranks to 6 or 7. Of course this need further checking. Once all ranks are exhausted, xfitfibs will place the sky fibers at sky positions it calculates.

  12. xfitfibs outputs the final configurations in a '*.cfg' file. This will contain the fiber number, RA, DEC, plate X, plate Y position, catalogue number and rank. If the number is -1, this is a sky position chosen by xfitfibs. A zero means that the fiber is parked (unused); otherwise it corresponds to the entry number in the input catalogue. The sky Ra and Dec seem bogus.

  13. Once finished press the "Send" tab, pickout the project number. If it is not there, let the hectospec team know so they can update the code. After pressing send several tests will be carried out. If there are no problems the files are shipped to the CfA.

Viewing configured objects

To check that all is sane, I wrote a perl script that reads the input and configuration files, generating regions files that can be fed to DS9 for each instrumental setup.This also calculates correct sky fiber coordinates. In order for this to work the following csh script setting IRAF up must be edited and made executable.
Last modified: Fri Apr 27 16:27:28 MST 2007