Technical considerations to prepare SITELLE observations


This page will provide information of interest to the observer preparing SITELLE observations. Like Megacam, WIRCam, and ESPaDOnS, SITELLE is operated in Queued Service Observing mode. Classical observing is not offered to observers. Observers will receive their SITELLE data after pre-processing (and astrometric and photometric calibration) by the CFHT ORBS analysis system, though they may request raw data if necessary.

Observing Constraints

Hereafter we list some of the constraints that PIs should keep in mind when writing a proposal for SITELLE, and when entering their PH2. The critical idea here is to keep OGs as short as what is allowed by the scientific goals of your proposal.

  • Limits in distance to zenith were derived, using a model installed at Cass, from clearance measurements, relative to the telescope's mount itself. Observations are thus limited to 45 degrees North of Zenith, and 53 degrees South of Zenith. (see memo on internal CFHT webpage)

  • Flexure may become a limiting factor when the instrument is far from Zenith, at very high spectral resolution. At a distance of 45 degrees from Zenith, it has been estimated, and it will be verified, when SITELLE will be at CFHT, that the flexure requirement goal of less than 2 pixels is met. (see slide 55 of the Critical Design Review presentation on internal CFHT webpage)

  • The limits on the distance to Zenith imply limits on the time spent on a given observation, which depends on the Declination of the source. At about -20 degrees and +63 degrees, no more than 2 hours can be spent on a given target, while 4 hours are available if the Declination is between -10 degrees and +60 degrees.

    Left: lines of equal Zenith distance plot. Right: maximum time on target as a function of Declination.

  • While technically observations of more than 4 hours are possible for a significant range of Declinations, a limit at 4 hours will be implemented at CFHT in order to increase the probability of such observations being scheduled on any given night. While it should be possible to split a longer than 4 hours observations on multiple nights (see item 3.2.3 of the Science Requirements Document on internal CFHT webpage), PIs are strongly encouraged to favor short observations as often as possible.