Building the Evryscope: Hardware Design and Performance

Abstract

The Evryscope is a telescope array designed to open a new parameter space in optical astronomy, detecting short timescale events across extremely large sky areas simultaneously. The system consists of a 780 MPix 22-camera array with an 8150 sq. deg. field of view, 13" per pixel sampling, and the ability to detect objects down to m g 16 in each 2 minute dark-sky exposure. The Evryscope, covering 18,400 sq.deg. with hours of high-cadence exposure time each night, is designed to find the rare events that require all-sky monitoring, including transiting exoplanets around exotic stars like white dwarfs and hot subdwarfs, stellar activity of all types within our galaxy, nearby supernovae, and other transient events such as gamma ray bursts and gravitational-wave electromagnetic counterparts. The system averages 5000 images per night with ∼300,000 sources per image, and to date has taken over 3.0M images, totalling 250TB of raw data. The resulting light curve database has light curves for 9.3M targets, averaging 32,600 epochs per target through 2018. This paper summarizes the hardware and performance of the Evryscope, including the lessons learned during telescope design, electronics design, a procedure for the precision polar alignment of mounts for Evryscope-like systems, robotic control and operations, and safety and performance-optimization systems. We measure the on-sky performance of the Evryscope, discuss its data-analysis pipelines, and present some example variable star and eclipsing binary discoveries from the telescope. We also discuss new discoveries of very rare objects including 2 hot subdwarf eclipsing binaries with late M-dwarf secondaries (HW Vir systems), 2 white dwarf / hot subdwarf short-period binaries, and 4 hot subdwarf reflection binaries. We conclude with the status of our transit surveys, M-dwarf flare survey, and transient detection.

Evryscope and K2 Constraints on TRAPPIST-1 Superflare Occurrence and Planetary Habitability

“…From its location at Cerro-Tololo Inter-American Observatory (CTIO), the Evryscope images its 8520 square degree field of view every two minutes. The system takes images in the g' band with a typical dark-sky limiting magnitude of g' = 16 and a resolution of 13" per pixel (Ratzloff et al 2019). Each night, the Evryscope tracks the sky continuously for two hours as it takes images, then ratchets back to its original position and resumes tracking for another two hours, repeating throughout the night.…”

EvryFlare. I. Long-term Evryscope Monitoring of Flares from the Cool Stars across Half the Southern Sky

“…The Evryscope is designed to observe the entire Southern sky down to an airmass of two and at a resolution of 13 pixel −1 . To achieve ∼6 hours of continuous monitoring each night on each part of the sky, the Evryscope tracks the sky for 2 hours at a time before ratcheting back and continuing observations (Ratzloff et al 2019).…”

“…Careful background modeling and subtraction is performed before raw photometry is extracted with forced-apertures at known source positions in a reference catalog. Light curves are then generated for approximately 9.3 million sources across the Southern sky by differential photometry in small sky regions using carefully-selected reference stars and across several apertures (Ratzloff et al 2019). Any remaining systematics are removed using two iterations of the Sys-Rem detrending algorithm (Tamuz et al 2005).…”

Hot Subdwarf All Southern Sky Fast Transit Survey with the Evryscope

“…The wide-seeing Evryscope is optimized to find rare, fast transit objects. It is a robotic 22 camera (each with 29MPix) array mounted into a 6 ft-diameter hemisphere which tracks the sky (Law et al 2015;Ratzloff et al 2019a). The instrument is located at CTIO in Chile and observes continuously, covering 8150 sq.…”

“…Here we only briefly describe the calibration, reduction, and extraction of light curves from the Evryscope; a detailed description can be found in the Evryscope instrumentation paper (Ratzloff et al 2019a). Raw images are filtered with a quality check, calibrated with master flats and master darks, and have large-scale backgrounds removed using the custom Evryscope pipeline.…”