Summary of OSCIR Quickstart Run: November - December 2000

The Gemini North OSCIR Quickstart program was conducted during a single observing run between November 20 and December 10, 2000. The following is a summary of the run which will be useful to PIs and Co-Is reducing OSCIR data. These descriptions are not intended to be exhaustive and do not cover all the issues that may arise when reducing OSCIR data; please contact the Gemini Contact Scientist assigned to your program for further assistance.

FITS Files

The "raw" data files in the OSCIR Quickstart distribution are the exact files written by the instrument computer during the observations, except for modifications to a few header records made by Gemini personnel during post-processing to indicate data quality. The files are 6-dimensional FITS format (see a detailed description of the OSCIR data format). Gemini has developed an IRAF package for basic manipulation of the files; an alternative IDL package is also available from the University of Florida.

FITS Headers

The OSCIR FITS headers list many observing parameters for the instrument (filter, integration time, etc.), telescope (pointing data), and observation (Program ID, Observing conditions, Data Quality). Processors should familiarize themselves with the information.

All the instrument parameters were written automatically by the OSCIR software based on the instrument settings at the moment of the observation. Telescope pointing data was also written automatically after being read by the OSCIR computer from the telescope control system (TCS) through a special interface. Therefore, the values of these parameters are reliable (within the uncertainties of the telescope pointing, etc.)

Some header records, such as the object name, the observing conditions, and the data quality, were set manually either during or after the observation. We have endeavored to verify that these header records are correct, but they may be in error and caution should be exercised. To verify an OBJECT keyword value of "Alpha CMa", for example, you can check that the automatically-written RA_TEL and DEC_TEL records actually contain the coordinates for Alpha CMa.

A Note on Data Quality

For each Quickstart observing program, we have included in the distribution all data taken for that program that appeared to be a valid observation. We have excluded files for which there were significant instrument- or telescope-related problems (e.g. the detector was saturated, or a large pointing error was evident). However, we have not excluded files with problems such as poor image quality, higher than usual noise due to detector problems or cirrus clouds, and so forth. Such problems are noted in the observing log and FITS headers. It is important for a data processor to understand the quality of the data and judge its scientific value carefully.

Pipeline-Reduced Data

For good-quality OSCIR data, Gemini has supplied pipeline-reduced files. The pipeline reduction produces a single 2-D image, usually representing the average of all the chop & nod differences computed from the file. The file was generated using the IDL/UF routine F6GET.

In some cases, when one or more savesets in an integration were noted to be bad during the observations (e.g. due to clouds or a temporary instrument problem), the bad savesets were omitted from the average. Details on the omitted bad nod and savesets are contained in the BNOD and BSET parameters in the headers of the pipeline-reduced files.

PLEASE NOTE: The pipeline reduction is only a first attempt by Gemini personnel to provide an approximate reduced image. Better results are likely to be obtained by more careful analysis of the raw data to delete bad savesets, shift-and-add individual savesets, etc. It is the responsibility of the PI to reduce the raw data in the best possible way, although Gemini Contact Scientists and Instrument Specialists can provide assistance upon request.

Other Files included in the Distribution

Supplemental files are described in the GNQSdata_readme.txt file included with the data distribution. Here are a few additional notes on these files.

Background Plots: For each pipeline-reduced file there is a GIF file showing the signal level in the "reference" (off-source) frames throughout the integration (generated using the IDL/UF routine f6bstat). The "square-wave" steps visible in these plots occur when the telescope nods and the reference switches between chop beams A and B; they illustrate the so-called "radiative offset" between beams A and B. You may also be able to see smaller steps between individual savesets.

At Gemini, the radiative offset is usually less than one percent of the background signal. If it is larger than normal, one of the chop beams may have been partially on the dome. If the "square-wave" pattern is lost in very large random variations, there may have been clouds.

Issues Related to Quickstart Observing

Processors of OSCIR data should be aware of the following issues pertaining to the December Quickstart run. Again, please consult the Gemini Contact Scientist assigned to your program for details.

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In original form; Tom Hayward
Last update February 6, 2001; Phil Puxley