ArgusSpec, a fully autonomous low-resolution rapid follow-up spectrograph, has been optimized for stellar flare follow-up by prioritizing high speed follow-up, optical efficiency, and wavelength coverage. Stellar flares are challenging transients to follow-up at a large scale due to their spacial and temporal unpredictability and their sub-minute rise in flux followed by an exponential decay. We present performance data from commissioning along with results from operations with a real-time transient alert stream from Argus Pathfinder, located at the Pisgah Astronomical Research Institute in western North Carolina alongside ArgusSpec, and Evryscope North, housed at Mount Laguna Observatory.
Wide-field telescopes like the Evryscope enable all-sky searches for fast optical transient events such as kilonovae, optical counterparts to fast-radio-bursts and other exotic events. To further understand these phenomena, we need infrastructure with the capability to monitor and quickly analyze these events. The Evryscopes are an allsky system with a total field of view of 16,512 sq. deg. that, coupled with the Evryscope Fast Transient Engine (EFTE), can catalogue fast optical transients down to g=16. In the past two years, EFTE has seen millions of transients across the sky including hundreds of flaring events from cool stars and a population of millisecond glints produced by Earth-orbiting objects that appear morphologically similar to transient astrophysical phenomena. In order to further characterize these events, the Evryscope and other all-sky optical surveys, such as the upcoming Argus Pathfinder and Argus Optical Array, require a framework to discriminate between this fog of imposter transients and real astrophysics. EFTE-Rocks is an automated orbit determination pipeline that takes short-duration transients from EFTE and associates them into tracklets based on an initial trajectory. Here we present a framework to characterize which orbital debris produce glints seen by fast, wide-field telescopes; lessons learned; and future software improvements. We also discuss its applications to upcoming surveys that are capable of probing for fainter objects at faster cadences.
The Argus Optical Array is a synoptic survey observatory, currently in development, that will have a total collecting area equivalent to a 5-meter monolithic telescope and an all-sky field of view, multiplexed from 900 commercial off-the-shelf telescopes. The Array will observe 7916 deg2 every second during high-speed operations (mg ≤ 16.1) and every 30 seconds at base cadence (mg ≤ 19.1), producing 4.3 PB and 145 TB respectively of data per night with its 55-gigapixel mosaic of cameras. The Argus Array Hierarchical Data Processing System (Argus-HDPS) is the instrument control and analysis pipeline for the Argus Array project, able to create fullyreduced data products in real time. We pair sub-arrays of cameras with co-located compute nodes, responsible for distilling the raw 11 Tbps data rate into transient alerts, full-resolution image segments around selected targets at 30-second cadence, and full-resolution coadds of the entire field of view at 15+-min cadences. Production of long-term light curves and transient discovery in deep coadds out to 5-day cadence (mg ≤ 24.0) will be scheduled for daytime operations. In this paper, we describe the data reduction strategy for the Argus Optical Array and demonstrate image segmentation, coaddition, and difference image analysis using the GPU-enabled Argus-HDPS pipelines on representative data from the Argus Array Technology Demonstrator.
The Argus Optical Array is an all-sky telescope composed of 900 0.2-m off-the-shelf, wide-field telescopes that covers 20% of the entire sky in each exposure. Using low-noise CMOS detectors, the array reaches g=19.6 in minute-long exposures, while deep coadds will reach g=23.6 every five nights. By observing the entire accessible sky simultaneously, Argus is sensitive to timescales orders of magnitude faster than most time-domain surveys, whose cadence is fixed by the time between visits to the same field. All 900 telescopes are mounted on a single platform that rotates about an axle; thus, operating a complex array telescope is reduced to smoothly tracking using this one axle. This requires few-arcminutes pointing of the system’s rotation axis, as it is impossible to make a conventional pointing model for an all-sky telescope. The Argus polar alignment system, first demonstrated on the 8-ft-diameter Argus Array Technology Demonstrator, consists of custom software that controls two off-the-shelf high-load-capacity linear actuators attached to one end of the pointing axle of the Argus Optical Array. The Argus tracking system is a closed feedback loop that consists of an encoder and custom linear actuator, which leverages the large lever arm of the system to easily rotate our telescope platform. This approach was tested on the Argus Array Technology Demonstrator. Here we detail both motion control systems, our automated polar alignment routine, and performance on polar alignment and tracked image quality.
Recent advancements in low-cost astronomy equipment, including high-quality medium-aperture telescopes and low-noise CMOS detectors, have made the deployment of large optical telescope arrays both financially feasible and scientifically interesting. The Argus Optical Array is one such system, composed of 900 eight-inch telescopes, which is planned to cover the entire night sky in each exposure and is capable of being the deepest and fastest Northern Hemisphere sky survey. With this new class of telescope comes new challenges: determining optimal individual telescope pointings to achieve required sky coverage and overlaps for large numbers of telescopes, and realizing those pointings using either individual mounts, larger mounting structures containing telescope subarrays, or the full array on a single mount. In this paper, we describe a method for creating a pointing pattern, and an algorithm for rapidly evaluating sky coverage and overlaps given that pattern, and apply it to the Argus Array. Using this pattern, telescopes are placed into a hemispherical arrangement, which can be mounted as a single monolithic array or split into several smaller subarrays. These methods can be applied to other large arrays where sky packing is challenging and evenly spaced array subdivisions are necessary for mounting.
The Argus Optical Array will be the first all-sky, arcsecond-resolution, 5-m class telescope. The 55 GPix Array, currently being prototyped, will consist of 900 telescopes with 61 MPix very-low-noise CMOS detectors enabling sub-second cadences. Argus will observe every part of the northern sky for 6-12 hours per night, achieving a simultaneously high-cadence and deep-sky survey. The array will build a two-color, million-epoch movie, reaching dark-sky depths of mg=19.6 each minute and mg=23.6 each week over 47% of the entire sky, enabling the most-sensitive-yet searches for high-speed transients, gravitational-wave counterparts, exoplanet microlensing events, and a host of other phenomena. In this paper we present our newly-developed array arrangement, which mounts all telescopes into the inside of a hemispherical bowl (turning the original dome design inside-out). The telescopes’ beams thus converge at a single “pseudofocal” point. When placed along the telescope’s polar axis, this point does not move as the telescope tracks, allowing every telescope to simultaneously look through a single, unmoving window in a fixed enclosure. This telescope bowl is suspended from a simple free-swinging pivot (turning the usual telescope mounting support upside-down), with polar alignment afforded by the creation of a virtual polar axis defined by a second mounting pivot. This new design, currently being prototyped with the 38-telescope Argus Pathfinder, eliminates the need for a movable external dome and thus greatly reduces the cost and complexity of the full Argus Array. Coupled with careful software scope control and the use of existing software pipelines, the Argus Array could thus become one of the deepest and fastest sky surveys, within a midscale-level budget.
The Argus Optical Array is a synoptic survey instrument that will use 900 commercial off-the-shelf telescopes to cover a composite all-sky of view with a total collecting area equivalent to a 5-meter telescope. We are currently carrying out a staged development process, leading up to the construction of the 38-telescope Argus Pathfinder system, which will observe the entire Northern sky between −20◦ < δ < 72◦ each night for 15 minutes per field. Argus Pathfinder is currently scheduled for a Q3 2022 deployment to the Pisgah Astronomical Research Institute in Rosman, NC. The Argus Array Technology Demonstrator (A2TD) is the first in this series of prototype instruments, and consists of 9-telescopes in a fiberglass enclosure on a tracking platform. The A2TD is a tool for rapid development, testing, and performance validation of the essential subsystems of the Argus Array design, including a custom-developed tracking drive and polar alignment system, thermal environment control, optical windows, and observatory control. The A2TD is also used for on-sky validation of telescope and camera pairs that have been bench-aligned, and for development of observatory automation and control software that are either directly transferable or scalable to later development stages, including the Argus Pathfinder. In this paper, we present the development process and design of the Argus Technology Demonstrator, and highlight early results from on-sky testing with the instrument.
As technological improvements continue to lower manufacturing costs, astrographic telescopes and cameras are becoming cheaper and more accessible to a wider community. The Argus Optical Array (AOA) capitalizes on these advances to create an all-sky, high-cadence telescope array with arcsecond-resolution and a cost in the $20M range. The completed array will have a 5-m class collecting area consisting of over 900 individual telescopes observing the entire Northern sky simultaneously at a 1-minute cadence (and capable of observing at second-timescales). The Argus Array Technology Demonstrator (A2TD) enables the investigation of the performance of telescopes, cameras, climate control, precision tracking and pointing systems for inclusion in the completed AOA. It consists of nine 8-inch telescopes under a hemispherical enclosure mounted onto the Hercules Mount, a semi-fixed, equatorial mount. The mount adjusts its polar axis alignment via two high-precision linear actuators while supporting a load of over 180 kg including counterweights. The dome is decoupled from the platform containing the telescopes to minimize the effect of windshake during observations. Sidereal tracking is performed by two linear actuators which connect to the outer dome and the telescope platform separately and track synchronously at arcsecond precision. The Hercules mount was constructed from a combination of low-cost commodity materials, with only three key components requiring precision CNC machining. Systems tested on the Hercules Mount will scale or transfer directly to the next instrument in the Argus series of prototypes: Argus Pathfinder. Here we present on-sky results of the Hercules Mount and our plans for the next generation of Argus prototypes.
ArgusSpec will be a fast-response, low-resolution spectroscopic follow-up system. Built almost entirely from off-the-shelf components, including a medium-aperture (16-in.) Ritchey-Chretien telescope, a very-low-noise CMOS detector, a low-resolution (R~100) spectrograph, and a fast-slew (50 deg/s) mount, ArgusSpec will begin observations of bright transient events (mV ≤ 13) within tens of seconds of detection. ArgusSpec will use all-sky transient alerts from the Evryscope, the Argus Pathfinder, and the planned full Argus Array; the latter two systems giving the fastest alerts for optical transients to date. Until now, the high-cadence sky has been largely inaccessible for spectroscopy. For example, large flares from active stars have dramatic impacts on orbiting exoplanets, but are difficult targets for spectroscopic follow-up due to their short-timescale evolution. Planets in the active stars’ habitable zones will be impacted by flares and superflares (energies ≥ 1033 erg), and associated high-energy particle emissions, which could strip the planet of its atmosphere and impart massive amounts of ultraviolet flux; this could be devastating to any life on the planet’s surface. There has not been a systematic spectroscopic survey of energetic flaring events across a wide range of stellar masses; almost all large flares observed spectroscopically have been from a small sample of active mid-M stars through staring campaigns. For the first time, ArgusSpec will build a library of superflare spectra from across the night sky, allowing for statistical constraints to be placed on their blackbody evolution and morphology. Here we present the design, project status, and science drivers of ArgusSpec.
Wide-field surveys using small-aperture, mass-produced telescopes have the potential to lower instrument hardware costs by orders of magnitude. The Argus Array series of instruments will open new pathways into the study of optical transients via high-cadence, all-sky imaging. The first prototype, the nine-telescope Argus Technology Demonstrator, is already onsky and validates novel concepts in tracking and high-speed data reduction. Next, the fully funded Argus Pathfinder consists of 38 telescopes on a single mount, and will observe the sky between -20° and +72° declination over the course of each night. The project is planned to culminate with the Argus Optical Array observing 20% of the entire sky simultaneously with 900 telescopes at cadences as fast as 1 second. As the number of telescopes increases, so do the maintenance requirements. For a standard open-air array on many mounts, this could result in operations costs far in excess of those of an equivalent monolithic telescope and lead to inconsistent sky coverage while parts of the array are offline. To limit wear and the need for cleaning, re-alignment and focusing, we seal our telescopes in a filtered and air-conditioned environment. This enclosure will be heavily insulated and maintained within a temperature range small enough to prevent measurable changes in telescope focus. Cameras and other power sources in the enclosure are water-cooled and the heat is removed to an isolated service module containing the array’s HVAC and support equipment. From there, the system temperature is maintained at a few seasonally changed set-points. This paper presents the design of the Pathfinder enclosure and environmental control system.
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