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Design of GPI Coronagraph Masks

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GPI Observing ModesΒΆ

The GPI instrument control software uses observing modes (FITS keyword OBSMODE) to specify sets of instrument optical masks that work together. Each obsmode consists of a unique set of 4 elements: {Filter, Apodizer, Focal plane mask, Lyot Mask}. Obsmodes come in several basic flavors:

  • Coronagraphic observations, most common for GPI.
  • Direct observations, with no coronagraphic masks in use.
  • Unblocked (unocculted) observations, which use the coronagraphic Apodizer and Lyot mask but not the focal plane masks. These are occasionally used, mostly for certain types of calibration observation
  • NRM modes for non-redundant mask interferometry
  • and a single Dark mode for detector calibrations.

The defined Obsmodes are as follows. See Design of GPI Coronagraph Masks for details on the individual elements.

Obsmode Filter Apodizer FPM Lyot Mask
Y_coron Y APOD_Y FPM_Y 080m12_03
J_coron J APOD_J FPM_J 080m12_04
H_coron H APOD_H FPM_H 080m12_04
K1_coron K1 APOD_K1 FPM_K1 080m12_06_03
K2_coron K2 APOD_K2 FPM_K1 080m12_07
H_starcor H APOD_star FPM_H 080m12_03
H_LIWAcor H APOD_HL FPM_K1 080m12_04
Y_direct Y CLEAR SCIENCE Open
J_direct J CLEAR SCIENCE Open
H_direct H CLEAR SCIENCE Open
K1_direct K1 CLEAR SCIENCE Open
K2_direct K2 CLEAR SCIENCE Open
Y_unblocked Y APOD_Y SCIENCE 080m12_03
J_unblocked J APOD_J SCIENCE 080m12_04
H_unblocked H APOD_H SCIENCE 080m12_04
K1_unblocked K1 APOD_K1 SCIENCE 080m12_06_03
K2_unblocked K2 APOD_K1 SCIENCE 080m12_07
H_starunb H APOD_star SCIENCE 080m12_03
H_LIWAunb H APOD_HL SCIENCE 080m12_04
NRM_Y Y NRM SCIENCE Open
NRM_J J NRM SCIENCE Open
NRM_H H NRM SCIENCE Open
NRM_K1 K1 NRM SCIENCE Open
NRM_K2 K2 NRM SCIENCE Open
DARK H APOD_H FPM_H Blank

Note that there are some “experimental” modes which are rarely, if ever, used. These are

  • The “H Large Inner Working Angle” mode, which pairs the H band filter with the K1 focal plane mask and a specially optimized apodizer; in essence trading off worse inner working angle for (possibly) better starlight suppression.
  • The “H Star” mode, which uses a shaped pupil binary apodization which is theoretically equivalent to the regular H_coron apodization.

These modes are essentially uncommissioned and are not recommended for general use.

See also the Gemini page on GPI observing modes.