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MIR Baseline Calibrations

For all queue observations, a set of "baseline" calibrations is required to ensure the long-term utility of data in the archive. The baseline calibration set will vary with mode (and sometimes instrument) but includes all the observations deemed necessary to produce scientifically useful data. PIs are free to request additional calibrations beyond the baseline set. However, while baseline calibrations are not charged to the program, additional calibrations are charged to the program and time to observe them must be included in the original proposal. All calibrations, baseline or additional, must be specified by the PI in the Phase II definition. Calibrations that are and are not included in the baseline set for all Gemini mid-infrared observations are described in the table below.

Baseline calibration data have no proprietary period and are publicly available in the archive as soon as they are uploaded. Time used to obtain baseline calibrations between nautical evening twilight and nautical morning twilight is charged to the partner country associated with the program or programs (this is why the observe class in the OT must be set to "Nighttime Partner Calibration"); between morning and evening twilight, no time is charged (observe class set to "Daytime Calibration"). Any time required for additional calibrations requested by the PI is charged to the program ("Nighttime Program Calibration"). To help us with proper time accounting, please ensure that the observe class is set correctly on all calibration observations. Examples of baseline calibration observations are available in the OT libraries for each instrument.



Imaging and Michelle Imaging Polarimetry Spectroscopy
Bad pixel mask Not included as part of the baseline calibration set.
Flat Fields Not included as part of the baseline calibration set. We have not been able to find a satisfactory way of flatfielded Michelle and T-ReCS imaging observations, and the detector response is rather flat in any case. Included for Michelle (not T-ReCS) spectroscopy observations and must be defined at phase II. See the OT library for examples.
Darks Not included; the chopped and/or nodded nature of all T-ReCS and Michelle observations means that darks are not needed to reduce data.
Wavelength calibration Not applicable. Transmission information is available for Michelle and T-ReCS filters. Derived from telluric absorption lines in the spectrum of the calibration star, or from telluric emission lines in the raw science data. For more information, see here.
Telluric standard Not applicable The PI must specify two telluric standards in the Phase II Science Program, one that would match the airmass of the science target if observed prior to it, and one that would match the airmass of the science target if observed after it. If the time on the target is short (less than about 30 minutes), then only one telluric standard at a similar airmass to the science target need be defined. For observations taking longer than about 2 hours, both standards will be observed. Either stars or bright asteroids may be used as telluric standards, depending on which resolution is being used. More information and lists of mid-infrared telluric standards are available.
Flux standard A Cohen (or similar) standard will be observed for each science observation. PIs must define two photometric standards for each science target in the Phase II science program, one that would match the airmass of the target if observed before it and one that would match it if observed after. If the time on the target is short (less than about 30 minutes), then only one photometric standard at a similar airmass to the science target need be defined. For observations taking longer than about 2 hours, both standards will be observed. Photometric accuracy is limited to ~10% by the uncertainty in the airmass correction and in the fluxes of the standards themselves. More information and lists of mid-infrared photometric standards are available. Not part of the baseline calibration set. Absolute flux calibration through narrow slits is very unreliable and many stars commonly used as mid-IR telluric standards do not have well-known fluxes. Please include imaging observations at a similar wavelength in your proposal if absolute flux calibration is important.
Unpolarised standard Michelle imaging polarimetry only: A Cohen standard will be observed for each science observation (see discussion here). As for flux standards, the PI must specify two such standards for each target in the Phase II program. For observations lasting longer than about 1 hour, both standards may be observed. Not applicable
Polarised standard Michelle imaging polarimetry only: Not included in the baseline calibration set. Polarised standards will be observed periodically and will be available in the archive, but as a rule will not be observed for each imaging polarimetry programme. Not applicable
Atmospheric extinction Not part of the baseline calibration set, but choosing a photometric standard at an airmass matching the science target will minimise problems. Please include specific flux standard observations in your proposal if extinction corrections to better than ~10% are required. Not part of the baseline calibration set. A good choice of telluric standard will minimise problems.
Point Spread Function Not part of the baseline calibration set. The flux standard should provide an approximate measurement of the PSF, but if dedicated PSF star observations are required, they must be included in the time request. Not applicable.
World coordinate system Automatically included in the headers. The default accuracy is 1-2 arcsec. Please consider (and request extra time for) a special astrometric setup if higher accuracy is required. Not applicable
Focal plane mask image Not applicable Focal plane mask images are not included as part of the baseline calibration set but will be taken periodically for engineering purposes.