WIYN Observatory


The NASA Exoplanet Star (and) Speckle Imager, or NESSI, is expected to be available on WIYN beginning in October, 2016. This new instrument utilizes two electron-multiplying CCD cameras to capture speckle images in two colors simultaneously. Speckle observations provide resolutions at or near the diffraction limit of the telescope allowing companion detection and characterization to delta magnitudes of approximately 5. NESSI will have remote controlled filter wheels in each beam, split by the dichroic at 686.4nm.

The EMCCDs can operate with high sensitivity and low noise even at very fast readout rates, providing high time resolution. The maximum rate of imaging with zero-second exposures for the full 1024x1024 pixel image with no binning is 26fps. By using subwindows and binning, the cameras will operate at higher frame rates (details to be determined).

NESSI will also introduce a new "wide-field" mode that will enable the collection of images with fields of >70 arcseconds. Each 6-slot filter wheel will come with two "narrow-band" speckle filters, two standard SDSS filters, and (currently) two empty slots.

Further information on NESSI can be found on these web pages.

NESSI Characteristics

 Wide Field ModeSpeckle Mode
Telescope Focal Plane: 
Telescope f/#: 6.2896.289
Plate Scale: 9.374 arcsec/mm9.374 arsec/mm
Focal Lengths: 
L1 Focal Length: 100mm30mm
L2 Focal Length: 150mm200mm
Optical Path: 
Tel. Focus:0mm = 0in0mm = 0in
L1:100mm = 3.937in30mm = 1.181in
L2:258.4mm = 10.173in278.4mm = 10.961in
Detector:150mm = 5.906200mm = 7.874in
Total Length:508.4mm = 20.016in508.4mm = 20.016in
Detector Image Plane: 
Magnification from Tel. focal plane:1.5x6.67x
Pixel Scale (13 micron pixels):0.0813 arsec/pix0.0182 arsec/pix
Unvignetted Circle Dia.:56 arcsec22 arcsec
Square Detector FOV:83 x 83 arcsec19 x 19 arcsec

NESSI Detectors

 1024 x 1024 pixel electron multiplying CCDs (Andor Ixon Ultra 888's).
 The electron multiplying aspect of EMCCs allows imaging at higher speeds than traditional CCDs because the readnoise is effectively lowered.
 High speeds are also made possible through shutterless operation in a frame transfer mode.

NESSI Filters

Filter Wheel ACenteral λ, bandwidthFilter Wheel BCentral λ, bandwidth
SDSS/u354.3nm, 32.7nm SDSS/i765.4nm, 146.4nm
SDSS/g480nm, 151.1nm SDSS/z943.3nm, 242.7nm
SDSS/r620nm, 143.5nm 716716nm, 51.5nm
467467.1nm, 44nm 832832nm, 40.4nm
562562.3nm, 43.6nm  

NESSI Field Of View

NSF University of Wisconsin Indiana University University of Missouri Purdue University

Last modified: 20-Sep-2016 16:49:01 MST