Observing Strategies (Phase I Set-up)

For questions about `Alopeke and/or Zorro, contact the support team. For questions about PIT or the proposal process in general, please file an helpdesk ticket.

This page is a guide for setting up Phase I observations.  Currently, the focus is more on speckle observations than wide-field imaging.  For wide-field and more specific question about setting up proposals, please contact the support team.  To get an estimate for what to expect using `Alopeke and Zorro for wide-field imaging, we encourage PIs to use the GMOS ITC.

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.

In general, speckle observations are taken in blocks during the semester by the NASA speckle team.  For normal speckle observations, multiple 1-minute integrations are taken of each target depending on the conditions.  In most cases, PIs can expect the following number of integrations per target:

PIs can always request a certain number of frames for their targets.  These numbers are meant as a guide for PIs in determining the amount of time to ask for in proposals.

Wide-Field Imaging:

Under Construction...  For help with estimating exposure times, see the GMOS ITC.  For additional support, please contact the support team who will be more than happy to help.

Overheads

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 most targets.

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.

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.  In most cases, the separation between the point source standard and the target should have a difference in distance and time as small as possible.  PIs may choose to assign their own standards or the NASA speckle team will assign one for them.  Regardless, the time for standards should be included in the proposal.

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.

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.

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.