University of Florida

CIRCE Observing Features

Below we provide a brief description of CIRCE's observing features, relevant for astronomers planning observations:


  • Detector: engineering grade HAWAII-2RG (1-2.5 micron)
  • Format: 2048x2048-pixel array with 18-micron pitch
  • Pixel size: 0.1 arcsec/pixel
  • Field of View: 3.4x3.4 arcmin (204x204 arcsec)
  • Instrumental image quality: <0.3-arcsec FWHM
  • Current filters: J, H, Ks, plus "Dark"
  • Remaining filter capacity: 8 available slots
  • Minimum full-frame exposure: 3 seconds
  • Read noise: 30-45 e- RMS (channel dependent);
    Background-limited in minimum exposure time in H, Ks;
    background-limited in <12s in J.
  • Dark Current + In-dewar Background: <0.01*sky flux in all bands

Fast Photometry:

CIRCE's fast photometry is offered as a "guest mode" for the instrument. In order to apply for fast photometry observations with CIRCE, observers must do so through collaboration with the CIRCE science team at the University of Florida, which must be arranged BEFORE submitting an observing proposal. The CIRCE team will assist the proposer in developing the experimental design, including readout modes, time sampling, dither strategies, field of view, etc. Since this will likely have a STRONG impact on the proposal itself, we recommend establshing contact at least 2 weeks before the proposal deadline.

The CIRCE HAWAII-2RG detector has 32 amplifiers, each of which reads out a 2048x64-pixel strip of the detector. These are clocked in parallel, and the base clock speed is 100 kHz (100,000 pixels per second per amplifier). This enables a fast photometry mode where a "band" of pixels 2048 pixels wide can be read out in 64*10 microsecond = 0.64-milliseconds. Thus, for a sampling time that is N*0.64 milliseconds, the effective field of view is 200-arcsec wide by N/10 arcsec high.

Both up-the-ramp and CDS readout modes are possible, with differing duty cycles, reset impacts, and saturation issues. For details, contact the CIRCE PI Stephen Eikenberry (eiken at ufl dot edu).

Imaging Polarimetry:

  • Field of View: 12x12 arcsec through focal plane mask
  • Retarder: custom Bernhard Halle super-achromatic half-wave plate
  • Modulator: Rotating HWP mechanism just inside entrance window
  • Analyzer: Wedged Double Wollaston (WeDoWo) prism
  • Instantaneous images: "o", "e", "o-45", "e-45" (allows full linear Stokes measurement in a single exposure)


  • Coming soon! (Planned for install in early 2015)