4.1. Example 1 - Datasets descriptions

4.1.1. Extended source with offset to sky

This is a NIRI imaging observation of an extended source, a galaxy showing as a dense field of stars. The observation sequence uses an offset to a nearby blank portion of the sky to monitor the sky levels since there are no area in the science observation that is not “contaminated” by the galaxy.

The calibrations we use for this example are:

  • BPM. The bad pixel masks are now found in the Gemini Science Archive instead of being packaged with the software. They are associated like the other calibrations. (The date in the name is the “valid from” date.)
  • Darks for the science and sky offset frames.
  • Flats, as a sequence of lamps-on and lamps-off exposures.
  • Short darks to use with the flats to create a bad pixel mask.
  • A set of standard star observations.


The Bad Pixel Masks (BPMs) are now found in the archive rather than packaged with the software. You must get the static BPM from the archive. See Getting Bad Pixel Masks from the archive in Tips and Tricks.

Here is the breakdown of the files. They are included in the tutorial data package. They can also be downloaded from the Gemini Observatory Archive (GOA).

N20160102S0270-274 (on-target)
N20160102S0275-279 (on-sky)
Science darks
N20160102S0423-432 (20 sec, like Science)
N20160102S0373-382 (lamps-on)
N20160102S0363-372 (lamps-off)
Short darks
Standard star

A note about finding the short darks in the GOA. Those darks are used solely to create a fresh bad pixel mask (BPM). In the archive, the calibration association will not find those darks, they need to be searched for explicitly. If you need to find short darks for your program, do as follows:

  • Set a date range around the dates of your science observations.
  • Set Instrument to NIRI.
  • Set Obs.Type to DARK.
  • Set the exposure time to 1 second.