NOAO Web Observing Proposal

Targets and Guide Stars

Information requested in target tables

The fields in the non-Gemini target tables include:

  Object ID            queue: specify a unique 3-digit number for each target
  Object               20 characters maximum
  RA                   e.g., xx:xx:xx.x
  DEC                  e.g., +-xx:xx:xx.x
  Epoch                e.g., 1950.3
  Magnitude 
  Filter 
  Exposure time        in seconds PER EXPOSURE
  Number of exposures
  Days from new moon   use a number 0-14
  Sky condition        use "spec" or "phot"
  Seeing               max allowable PSF FWHM (arcsecs)
  Comment              20 characters maximum

  Object ID        unique 4-digit number assigned automatically
  Object           20 characters maximum
  RA               e.g., xx:xx:xx.x
  DEC              e.g., +-xx:xx:xx.x
  Epoch            all targets must be B1950 or J2000
  Magnitude
  Observation time total exposure time and overhead in minutes for all filters
  Image quality    these next 4 parameters are given as percentages as described at
  Cloud cover       http://www.us-gemini.noao.edu/sciops/ObsProcess/obsConstraints/obsConstraints.html
  Water vapor        
  Sky background
  Guidestars       P=PWFS, 0=OIWFS, A=AOWFS, lower case=marginal selection
  Comment          20 characters maximum

Entering targets

Each target table generated through the Web form is restricted to 50 targets, but each run can have multiple target tables.

Targets can be typed directly into the target table or a list of targets can be uploaded through the Web form using an ASCII-formatted file. The uploaded file contains the target name (20 characters max.), epoch (only B1950 or J2000 allowed for Gemini), and the RA and DEC (+-xx:xx:xx.x) in a tab-separated list. For example:

NGC 4151	B1950	12:08:01.1	39:41:02
NGC 7027	B1950	21:05:09	42:02:03
L183	B1950	15:51:35.7	-02:40:54

Guide stars for Gemini

The column "WFS stars" in the Gemini target table indicates what and how many guide stars were found for each target where P=PWFS (peripheral), O=OIWFS (on-instrument), and A=AOWFS (adaptive optics) - a lower case letter is used for guide stars found outside the primary limits but still within the general criteria set by Gemini (see the table below). For example, Pa would indicate 1 PWFS star and 1 AOWFS star were found for a NIRI + Altair run, but the AOWFS star was between R=11-15 mag. and would provide only a partial correction.

The following table summarizes the criteria used for finding the various guide stars for the instruments currently available with Gemini.

NIRI:

  1-2 PWFS stars are needed
    Annulus centered on target:  ~5-7 arcmin (~6-7 arcmin for f/6 camera)
    Magnitude range of stars:  R = 6 - 15, otherwise R < 16 

  OIWFS stars:
    f/6   	none
    f/14  	annulus of 61-168 arcseconds   	
    f/32  	annulus of 28-168 arcseconds   		
    f/32+Altair	annulus of 28-120 arcseconds
    magnitude range: H < ~17 

  AOWFS star:
    When observations with the Altair AO system are specified, the
    algorithm searches for one guide star within 25 arcseconds of 
    the target.  Full correction for R < 11, otherwise R < 18 for
    partial correction.



GMOS:

  For imaging, an OIWFS star is required:
	radius 4.8 arcmin, V < 16.

  The Web form will also search for PWFS stars for all targets, 
  though they can be used only in slit-spectroscopy mode.  




GNIRS, Phoenix, Michelle, T-ReCS, and AcqCam:

  The form searches for 1-2 PWFS stars in the 5-7 arcmin annulus.

The guide stars are found using an IRAF task called gstars. We use the USNO-A2.0 catalog for the search. For each target in the user list, gstars converts the user target coordinates from the user coordinate system to the catalog coordinate system, extracts all the catalog stars within the maximum search radius, and computes radii and position angles for the extracted stars. For each guide star type, i.e., PWFS, OIWFS, or AOWFS, candidate guide stars satisfying the radial distance constraints and magnitude constraint are selected and ranked according to magnitude and distance from the center of the annulus. Bright stars and stars that are not too near the edge of the annulus are ranked the mostly highly. The ranked candidate guide stars are searched for stars in the preferred magnitude range. For guide stars other than the first, preference is given to objects more than 90 degrees from the first selected objects. If fewer than the requested number of guide stars are selected the position angle and preferred magnitude contraints are lifted.

For Gemini, the observing time should be the total wall-clock time (in minutes) needed to observe your target. This must include the sum of all exposure times in all filters plus overhead. Do not simply enter the time returned from an exposure time calculator as this will not include overhead for target and guide star acquisition, which will typically be an additional 15-30 minutes per pointing. Offsetting for sky exposures and dithering will also add to the total observation time. In most cases, summing the observation times for all targets should very nearly equal the total time request from the front page of your proposal. It can be very helpful to reviewers if you include a specific breakdown of your time request in the body of your technical description.

The Gemini Observatory website provides information on the performance of these instruments which can be used to estimate integration times and overhead. This can be found in the "Performance and Use" sections of the following documents.

For details on the specific conditions associated with percentiles for each condition, see the Gemini observatory web page at