GPI Observing Modes¶
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.