Calibrations

To properly reduce GPI observations one must download the proper calibrations. This document describes how the user can download all types of calibrations from the Gemini Observatory Archive. The user should read the instructions here on how to access the GOA, these instructions are only details on how to access GPI particular data. 

Depending on the type of observations a program may require different type of calibrations. Calibrations are typically taken weekly or bi-monthly and the PI should search for calibrations taken within a month of the data taken in the program. It is assumed that the PI is logged in and have gone to the Gemini Observatory Archive page.  

• Arcs: Used to allow proper spectral extraction and wavelength calibration
• Astrometric Standard Field: Used to allow proper astrometry correction.
• Darks: For proper dark subtraction.
• Spectral Flats: For proper flat correction
• Distortion map used by the pipeline
• Bad pixel map used by the pipeline
• Polarization Flats: Used to allow proper polarization spot extraction.
• Polarization Standard/Telluric Standard: Used to allow proper polarization calibration and proper spectral calibration. Usually taken in open loop.
• PSF Standard: Not part of the baseline calibrations.

Arcs

These calibrations are typically taken on a biweekly basis. For each target a short arc is taken on the sky position to correct for the flexure of the instrument, and is part of the files available for the program. Deeper arcs are taken biweekly in all bands.  

Follow the steps below to download the deeper baseline arcs, set the fields below: 

• Instrument: GPI
• Obs Type: ARC
• Obs. Class: dayCal
• UTC Date: with "YYYYMMDD - YYYYMMDD" and replace the dates with dates 15 days before your observation and with 15 days after your observation. If the data were taken on 20160416, then the field should be "20160401 - 20160501"
• Filter: [Filter used in your science]
  • IF your filter is K1 or K2 you will also have to download the long H arcs to get the shift from H to K1 or K2
• Click on SEARCH to obtain a list of available ARCs

Astrometric Standard Field

These calibrations are typically taken whenever the instrument is mounted on the telescope, and are used by the pipeline for the astrometric corrections. Currently there is no simple flag but a search has to be done using the exact name of the target: 

Follow the steps below to download the baseline astrometric fields:

• Instrument: GPI
• Target name: 
  • Orion: "Theta1 Ori B"
  • Baades window: "HD165054"
  • Binaries: "HIP 80628", "HIP 44804", "HD 157516"
• UTC Date: with "YYYYMMDD - YYYYMMDD" and replace the dates with dates 2 months before your observation and with 2 months after your observation. If the data were taken on 20160416, then the field should be "20160216 - 20160616"
• Filter: H
• Click on SEARCH to obtain a list of available astrometric fields
• Choose the one closest in time with the science observation 
  • Click on the Datalabel for the observation
  • In this new window clear the target name
  • Click on search to obtain the associated flexure arc and download this arc and the observation

Darks

These calibrations are typically taken on a biweekly basis. User should scale any DARKs using the closest exposure time as only a standard set of DARKs in certain exposure times are taken each week.

Follow the steps below to download the baseline darks:

• Instrument: GPI
• Obs Type: DARK
• Obs. Class: dayCal
• UTC Date: with "YYYYMMDD - YYYYMMDD" and replace the dates with dates 15 days before your observation and with 15 days after your observation. If the data were taken on 20160416, then the field should be "20160401 - 20160501". 
  • Choose the darks taken closest in time to the science
• Filter: [Filter used in your science]
  • IF your filter is K1 or K2 you will also have available the long thermal darks of 300s
• Click on SEARCH to obtain a list of available darks

Distortion Map

The following file is used by the pipeline for proper distortion correction:

S20120121210S0066-distor-150310.fits.gz

The PI can also use the pipeline and the available astrometric fields to create the distortion map. It should be noted that the distorsion has no obvious changes in the last few years.   

Bad Pixel Map

The following file can be used for bad pixel correction:  

S20141213S0323_badpix.fits.gz 

The BPM can also be created by the pipeline by using the available flats.  

Polarization Flats

These calibrations are typically taken on a biweekly basis.

Follow the steps below to download the baseline polarization flats:

• Instrument: GPI
• Obs Type: FLAT
• Obs. Class: dayCal
• UTC Date: with "YYYYMMDD - YYYYMMDD" and replace the dates with dates 15 days before your observation and with 15 days after your observation. If the data were taken on 20160416, then the field should be "20160401 - 20160501"
• Filter: [Filter used in your science]
• Disperser: Wollaston
• Click on SEARCH to obtain a list of available polarization flats. 

Polarization Standard/Telluric Standard

These standards are typically taken in open loop on a bimonthly basis.

Follow the steps below to download the baseline standards:

• Instrument: GPI
• Obs Type: FLAT
• Obs. Class: partnerCal
• UTC Date: with "YYYYMMDD - YYYYMMDD" and replace the dates with dates 2 months before your observation and with 2 months after your observation. If the data were taken on 20160416, then the field should be "20160216 - 20160616", widen the search if no calibrations appear. 
• Filter: [Filter used in your science]
• Disperser: Wollaston for Polarization or Prism for telluric
• Click on SEARCH to obtain a list of available calibrations
• If this is Prism you also need the flexure arc for the spectral extraction. 
  • Choose the one closest in time with the science observation 
    • Click on the Datalabel for the observation
    • Click on search to obtain the associated flexure arc and download this arc and the observation

PSF Standards

PSF standards are not taken as part of the baseline calibrations. Baseline PSF correction should be accomplished by using the satellite spots.