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Observation preparation

, Updated

Phase II observations should be set up using the Template Observations included in your program. These will be filled in with the targets and observing conditions from the Phase I proposal and will include blank observations for the point source standards for speckle observations.

Observing Strategies

Speckle:

In speckle mode 'Alopeke and Zorro typically take 1-minute integrations comprised of 1000 images of 60 msec each using a 256x256 pixel (2.5") subarray which closely matches the isoplanatic patch size. Under good conditions it is possible to achieve diffraction-limited resolution (0.016" FWHM at 500nm and 0.025" at 800nm) with this configuration. Larger subarrays may be used for extended objects, but the performance will depend on the stability of the atmosphere.

Speckle observations of bright targets (V<12) may be obtained with seeing better than 1 arcsecond (IQ85), through thin clouds (CC70), and without constraints on the background (BG-any) or water vapor (WV-any). However, fainter targets (V>12) will require better seeing (IQ70) and clear skies (CC50). CC50 is required for photometry.

Wide-Field:

In wide-field mode 'Alopeke and Zorro typically read out the full frame using the conventional amplifier at 1MHz. It is also possible to bin, read out a subarray, or use the EMCCD amplifier for faster readout, or read more slowly (0.1 MHz) for lower read noise. See the EMCCD page for the full list of readout options.

Overheads

Each target must include an acquisition, and every group of speckle targets within 15 degrees and/or every hour must include a point source standard. A photometric standard must be included once/night when doing photometry.

Acquisition overheads associated with setting up on each new target include time for slewing the telescope, configuring the guiding, and centering the target. These sum to ~5 minutes for targets with V<12 and ~6 minutes for targets with V>12.

Point source standards (bright stars known to be single) will be observed at each sky location with a minimum of one per hour. These take ~10 minutes (including acquisition overheads) and must be included in time requests. Groups of science targets closer than ~15 degrees may share point source standards.

Programs wishing to do photometry must include 10 minutes (including acquisition overheads) per night per photometric calibrator (wide binaries).

Filter changes add ~1 minute of overhead.

Observation Overheads
Action Overhead (min)
Acquisition (V<12) 5
Acquisition (V>12) 6
Point Source Standard 10
Photometric Standard 10

Readout and file-write overheads are 6-8% when using the 256 or 512 ROI in speckle mode, and a single set of 60ms x 1000 images (1 minute of open-shutter) will take 64-65 seconds to complete.

Speckle Readout Overheads
ROI Integration Overhead Total Time
256 x 256 1000 x 60ms 6% 64s
512 x 512 8% 65s

Wide-field (full-frame) overheads depend on how many images are saved in each FITS file. Saving 100 full-frame images per file incurs an overhead of ~0.03s / image and saving 500 full-frame images per file (the maximum for full-frame, producing a 1GB file) incurs an overhead of ~0.02s / image.

`Alopeke and Zorro OT Details

This page explains how to configure the Gemini "Visitor Instrument" component for use with 'Alopeke and Zorro

Name

The Visitor Instrument name should be set to "Alopeke" in the case of 'Alopeke, and "Zorro" for Zorro

Exposure Time

The "Exp Time" field should be filled in with the total desired integration time for each target.

Position Angle

The "Pos Angle" field sets the position angle of the instrument on the sky (degrees East of North). It is not expected that this field will be used with 'Alopeke given the circular field of view.

Wavelength

The "Wavelength" field is used by the TCS to calculate the relative atmospheric dispersion with respect to the guide wavelength, and should be set midway between the two filters, typically ~0.66um.

Phase II Checklist

Instrument Configuration

  • The Instrument Name should be "Alopeke" for GN and "Zorro" for GS
  • The Observing Tool has no mechanism to specify the instrument configuration (dichroic & filters), so please include a note with this information.
  • The "Exp Time" should be the total desired integration time
  • The Wavelength should be between the two imaging filters, typically ~0.66um

Target Coordinates

  • Must be accurate to better than 1 arcsecond
  • Must include proper motions

Guiding

  • 'Alopeke and Zorro observations must be guided using PWFS2
  • The OT will attempt to find a guide star automatically. If this fails the "Auto" guide star group will be empty, in which case you should use the "Manual GS" button to search for another which will not vignette the science target. Please email your Contact Scientist if you have any questions.

Standards and Calibrations

Finder Charts

  • Include a point source standard for each sky location, with a minimum of one per hour.
  • Include a photometric calibrator if photometry is required.
    • If the field centering will not be obvious please include a finder chart showing the desired position.