NESSI, the NN-Explore Exoplanet Stellar Speckle Imager

NESSI with the top lid removed.


NESSI is a new instrument at WIYN (first light was in Oct. 2016) built and designed by Nic Scott and Steve Howell (NASA/Ames) and Elliott Horch (Southern Connecticut State University) with funding from the NASA-NSF Exoplanet Observational Research partnership, NN-Explore.

A description of NESSI is published by Scott et al. 2018

NESSI is an optical imaging system ideally suited for speckle interferometry, high-speed photometry, and imaging with sampling at small plate scales. It employs two state-of-the-art Andor iXon Ultra 888 electron multiplying CCDs (EMCCDs), which operate simultaneously in blue and red channels with 1024x1024 active pixels.

In NESSI, the telescope beam is collimated and then split by a dichroic into blue and red components at 686nm. The beams may be filtered through the current choice of SDSS ugriz filters and narrower-band speckle filters with central wavelengths of 467, 562, 716 and 832 nanometers. NESSI can image at two different fields-of-view and plate scales by switching on the fly between a choice of collimating and re-imaging optics (0.018 arcsec/pixel over an 19x19 arcsec FOV or 0.08 arcsec/pixel over a 83x83 arcsec FOV).

The Andor cameras can operate at high speeds with shutterless exposures by using a frame-transfer mode, wherein charge is quickly shifted from the exposed "active area" pixels vertically into an identical 1024x1024 array of shielded pixels from which readout commences. While fast readout produces high readnoise, this is overcome by passing the collected charge through an electron multiplying register, which amplifies the electrons to produce an effectively much lower readnoise. The cameras can also be operated as conventional CCDs or without the frame transfer function and with a mechanical shutter.


Proposals to use NESSI are solicited through the NN-Explore program proposal process at NSF's OIR Lab (a program aimed at exoplanet science). University partners may also choose to submit some proposals. To date, most of the NESSI observations have been conducted as part of a queue observing program at WIYN. Observers using NESSI for speckle imaging submit target lists to the queue and receive reduced data products. For information on speckle imaging with NESSI, read the speckle imaging description. For inquiries about NESSI you may contact the support scientist, Mark Everett (

Using and Acknowledging NESSI data

A request for acknowledgement is made of authors using NESSI data in publications.

NESSI data products produced by certain exoplanet science programs are being archived by IPAC at the ExoFOP archive through the support of PI's who wish to promote collaborative use of the data by the astronomical community.

See WIYN's NESSI webpage for more overview of the instrument.