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GPI Phase II Checks

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The purpose of these page is to give quick guidelines to both Contact Scientists, NGO's and PI's to make sure that the defined observations in the OT are correctly defined. 


The Phase II check point of view GPI consists of 4 components as these are driving the Phase II checking.


  1. OIWFS (The Adaptive Optics, AOWFS), a high order, fast (1KHz) AO system that corrects for the atmospheric turbulence. Sets the limit on allowed brightness in I-band.  
  2. LOWFS (The CAL unit), low order, slow AO (0.1Hz) system that is designed to keep the object on the mask. Sets the limit on allowed brightness in H-band.  
  3. The IFS, Hawaii 2 NRG chip, field of view 2.7”x2.7”, minimum exposure time 1.49s, maximum exposure time 999s. Sets the limit on allowed brightness in the science band and the maximum field of view. 
  4. Coronographic Mask or Direct. Sets the limit on Inner Working distance and brightness. 


Main webpage for performance information is found at The following checks and details are taken from the document GPI-Feasibility-P2-Checks.pdf


The first simple check is to check warnings and errors in the OT. The warnings have been defined to catch all if not most typical issues. A properly defined observation sequence should have no errors or warnings. Note that not all issues are caught and thus the need for the checklist below. 

1. Check the I and H magnitudes for the target component that they are within the defined limits. Any targets fainter with magnitudes outside the aforementioned limits are not supported in queue mode. 


 Maximum BrightnessB

 Minimum BrightnessB

I-band (OIWFS) 



H-band (LOWFS)A





A. Only valid in Coronographic mode, in the Direct mode there is no LOWFS and thus no constraint imposed by the LOWFS.

B. Subject to modification due to weather constraints, see table below.

 Observing Conditions

Decrease of faintness limit [in magnitudes]C 

IQ70 CC70


IQ70 CC80 3.5

IQ85 CC50


IQ85 CC70


IQ85 CC80 5.0



C: Note that the decrease in magnitudes is ONLY applied to the faint end, it does not mean that brighter than normal targets can be observed. This is to make operations safe and avoiding locking on noise in the control loops.  


2. Check the science wavelenth magnitude in the target against the table below. There is only a brightest limit, for which the shortest exposure time (1.5s) will saturate the detector in the brightest pixels. 

Observing Mode   Maximum brightness


Y...K2]-coro  0.4
[Y...K2]-coro-pol   2.4
[Y...K2]-direct  7.4
[Y...K2]-direct-pol  9.4

3. Check that there is an associated acquisition for every target and mode. This means that a change from H to K1 requires a new acquisition.

4. Check that there is a calibration for every hour of observation, if the sequence is longer than ~1h then a new acquisition is needed.

5. Are there notes from the PI for any particular observing sequences, calibrations, saturation issues or any non-standard observations.

6. Is the Observing constraint set? Normally either Airmass (<1.5) or "Hour Angle" is used.

7. Is the exposure time set correctly (note that some PI's may want to saturate the pixels next to the Coronograph? Check page for details.

8. Check the target component that the target has defined:

A. Magnitudes for I, H and the science wavelength

B. Proper motions are defined, most if not all GPI targets have significant proper motions. 

C. Correct coordinates are critical, PI should use the OT search function to get the proper coordinates.  

9. Exposure times for each observe should be less than 60s (in some cases 90s, depending on sky rotation) to avoid rotational smearing during the exposure.

10. In K1 and K2 bands should have a proper set of skies defined. A rule of thumb is 1/5th of the science time spent taking skies. Skies are charged to the program. 

11. Check the elevation plot of the target. GPI performance is only guaranteed up to a Zenith angle of 45 degrees, any lower elevation has no guarantee for the performance. Contact the PI to make sure that the PI is aware that the data quality assessment for lower elevations is not based on contrast but just the external constraints i.e. it is IQ70 and CC50.  

12. The throughput of the K2 is significantly worse than the K1 (see for details) we strongly suggest that unless the science goals can't be achieved in K1 that the PI is contacted about a switch from K2 to K1.


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