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GPI OT Details

This page describes the steps to properly configure the instrument using the OT. Generally the user should use the skeleton templates that are created in Phase II and apply them to obtain the proper sequences. Instructions on for the general use of the OT can be found on the OT page and related links, as this page describes particular details for using OT with GPI. There is a GS-GPI-library available that contains complete examples of various modes and setups. Use the OT and select "libraries" and the program can be downloaded. 

The GPI in the OT can be broken down into the following components: 

The GPI Observing conditions

 

The GPI baseline observing conditions are IQ70 and CC50, changes to the requested conditions will affect the performance and the magnitude limits of GPI as shown on Observing Constraints page. The most common change for GPI is to adjust the Elevation Constraint. This can be done either by selecting Airmass in the pulldown menu next to Elevation Constraint or more frequently by choosing Hour Angle as a constraint. An example of the Hour Angle constraint is shown in the image to the right (click to enlarge). By seeting min to -1.5 and max to 1.5 the observation is constrained to have the science started no earlier than 1.5h before transit to ending no later than 1.5h after transit.

 

 

The GPI Main Component

The GPI main component is used to configure the instrument to set the Observing ModeDisperserastrometric field flagADC usage and the exposure times and coadds used in the observations. The exposure time and the coadds can be modified later in the GPI Iterator. The layout of the component is shown in the thumbnail figure to the right, click on the thumbnail for a larger image. 

 

This main GPI component can be broken into the following fields:  Observing ModeDisperserastrometric field flagADC usage and the exposure times and coadds. Each is described in detail below.    

Astrometric field selection

By default this is set to FALSE (unselected) as this is only used for calibration observations to trigger astrometric field selection in the pipeline. The only case for a standard observer is the PI requests "Nighttime Program Calibrations" of a specific field as defined in the observations. This field is highlighted in green in the thumbnail figure to the right, click on the thumbnail for a larger image. 

 

Observing Mode pulldown menu

As seen in the image below the PI can choose the specific "Observation Mode" for the observation. This can't be changed and is then fixed for the whole defined observation. An example of the pulldown menu is shown in the thumbnail figure to the right, click on the thumbnail for a larger image. 

 

Disperser pulldown menu

In this menu the PI can choose the disperser to be either Spectroscopy or Wollaston for polarimetric measurements. This can't be changed and is then fixed for the whole defined observation. An example of the pulldown menu is shown in the thumbnail figure to the right, click on the thumbnail for a larger image. 

 

Usage of ADC

By default this is set to IN, the PI is not recommended to change this default. This can't be changed and is then fixed for the whole defined observation. An example of the pulldown menu is shown in the thumbnail figure to the right, click on the thumbnail for a larger image. 

 

Exposure Time and Coadds field

Here the PI can set the exposure time and coadds for the sequences. It is possible to change this later in the iterator component. The relevant boxes are highlighted in green in the image below. The exposure time and coadds should ideally be configured to yield a total observation time of 60s or less for each image to avoid image smearing due to sky rotation, see more details on page Exposure Times. These two boxes are is highlighted in green in the thumbnail figure to the right, click on the thumbnail for a larger image. 

 

GPI Target Component

The target component for GPI is identical to the target component for most other instruments. The main differences are:

  • No AOWFS or OIWFS is defined. The science target is always the OIWFS/AOWFS target, this means that there is no possibility to observe without closed loops, with the exception of photometric or polarimetric standards that are taken in open loop with the Direct mode. 

  • The PI must define the I, Y, J, H, and, K band magnitudes. These are used to set the proper configurations and checks. In particular the  I-band and H-band are critical as they are used by the AOWFS and LOWFS configuration. 

Below each of the sections of the GPI target component (Base, search functioncoordinatesmagnitudes and proper motions are described in detail.

Target Component 

To the right a thumbnail is shown of the general tab, click on the thumbnail for a larger image. As seen there is only Base target defined, no other targets should be defined. 

 

Search function 

Highlighted in the thumbnail to the right (click on thumbnail for a larger image) is the search or look-up button (a spyglass). By clicking on the button a query will be used based on the supplied target name to obtain the coordinates and proper motions. At the moment the magnitudes are not obtained automatically and must be typed in manually. 

 

Coordinates 

Highlighted in the thumbnail to the right (click on thumbnail for a larger image) is the coordinates fields. The PI must give:

  • Target Name (used in the search function)

  • Right Ascension

  • Declination

  • Target type (Sidereal or Non-Sidereal)

 

Magnitudes 

Highlighted in the thumbnail to the right (click on thumbnail for a larger image) is the magnitudes fields. The PI must give:

  • Magnitudes for all the Y, J, H, and K bands. 

 

Proper Motions 

Highlighted in the thumbnail to the right (click on thumbnail for a larger image) is the proper motion fields, if the search function has been used then they are filled in automatically, if not they must be supplied with an accuracy of 10mas/year. PI must fill in the fields for: 

  • Proper motion in Ra in mas/year

  • Proper motion in Dec in mas/year

  • Epoch

 

GPI Sequence Component

The GPI Sequence component contains the actual observation sequences. The general functionality is identical to other instruments but there are some minor differences. There are three subcomponents:

Standard Sequence iterator

In the case of no changes in exposure times nor polarization then this is used with an nested observe under the iterator. The number of observe can be changed so that the total observing time reaches the desired time.  

The observe is the field in the middle of the right hand panel in the thumbnail image to the right. 

 

Sky observations

The SKY observations are used in the case of K1 or K2 observations to obtain open loop observations. In the image thumbnail to the right the sky sequences are highlighted in green (click on the thumbnail for a larger image).  

How to take polarization images is shown at the end of this section.  

 

Offset Iterator/On Target

In the image thumbnail to the right the ON target  sequences are highlighted in green (click on the thumbnail for a larger image). Highlighted in blue is the two Offset sequences under the Standard Sequence highlighted. 

The first of the two offset sequences is the ON target Offset sequence with 0,0 offsets and with guiding ON. The on-target sequences are of the CLASS SCIENCE and thus charged to the PI. 

Typically 80% of the frames should be ON target and the remainder OFF target (SKY).  

 

Offset Iterator/Off Target (skies)

In the image thumbnail to the right the off target (sky)  sequences are highlighted in green (click on the thumbnail for a larger image). 

The second of the two offset sequences is the OFF target Offset sequence with 0,20 offsets and with guiding OFF. The OFF target sequences are of the CLASS NIGHTTIME PROGRAM CALIBRATION and thus charged to the PI. 

Typically 20% of the frames should be OFF target  (SKY), but the PI is free to choose a suitable number of frames as they are charged to the Program.   

 

Setting the CLASS 

The CLASS of the Observation is visible by selecting the Observe. The CLASS menu is highlighted in green in the thumbnail image to the right.  

 

The GPI Iterator

This iterator allows the change of exposure time, number of coadds, and halfwave plate rotation. There is actually the option to change the disperser and the filter but this must not be used as that will break the observing sequence. The options are visible in the grey field in the thumbnail image to the right.

 

Half Wave Plate (HWP) rotation angle

By choosing the Half Wave Plate as the option in the GPI Sequence iterator one can add the desired values for the HWP. The values are in degrees and standard values for each GPI Sequence is 0.0, 22.5, 45.0 and 67.5

How to add more loops over the HWP is shown in the step below.  

 

Additional HWP observations

With a standard spectroscopy observation one would increase the observes, but in the case of polarization this is not recommended. If one increase the observes it means that one would repeat each HWP step multiplied by the number of observe i.e with observe=3 then the sequence would be  0.0, 0.0, 0.0, 22.5, 22.5, 22.5, 45.0, 45.0, 45.0, 45.0 and finally  67.5, 67.5, 67.5 

To achieve that additional loops over the HWP is done the PI must copy the GPI Iterator step and paste it below the first. In the thumbnail image to the right there are 3 GPI Iterators (highlighted in green) that yields the sequence as shown in the right hand panel of the image.  

 

Mixing skies and HWP changes

In the case of polarization observations in K1 or K2 it is necessary to combine HWP changes with SKY observations. The pertinent structure is shown in the image to the right. 

The ON target observations are shown highlighted in red in the sequence tab and corresponds to steps 1 to 16, the OFF target (SKY) sequence steps are highlighted in blue and corresponds to steps 17 to 20 in the sequence.