ATLAS: A High-Cadence All-Sky Survey System (1802.00879v2)

Abstract: Technology has advanced to the point that it is possible to image the entire sky every night and process the data in real time. The sky is hardly static: many interesting phenomena occur, including variable stationary objects such as stars or QSOs, transient stationary objects such as supernovae or M dwarf flares, and moving objects such as asteroids and the stars themselves. Funded by NASA, we have designed and built a sky survey system for the purpose of finding dangerous near-Earth asteroids (NEAs). This system, the "Asteroid Terrestrial-impact Last Alert System" (ATLAS), has been optimized to produce the best survey capability per unit cost, and therefore is an efficient and competitive system for finding potentially hazardous asteroids (PHAs) but also for tracking variables and finding transients. While carrying out its NASA mission, ATLAS now discovers more bright ($m < 19$) supernovae candidates than any ground based survey, frequently detecting very young explosions due to its 2 day cadence. ATLAS discovered the afterglow of a gamma-ray burst independent of the high energy trigger and has released a variable star catalogue of 5$\times10^{6}$ sources. This, the first of a series of articles describing ATLAS, is devoted to the design and performance of the ATLAS system. Subsequent articles will describe in more detail the software, the survey strategy, ATLAS-derived NEA population statistics, transient detections, and the first data release of variable stars and transient lightcurves.

• The paper introduces ATLAS as a cost-effective, high-cadence survey using twin 0.5-meter Schmidt telescopes with a 2-day cadence to detect near-Earth objects.
• The paper demonstrates ATLAS’s capability by reporting 1,175 candidate supernovae and generating light curves for 240 million stars, enhancing transient and variable star studies.
• The paper highlights ATLAS’s multidisciplinary impact, including gravitational wave follow-ups and improved planetary defense through timely detection of hazardous asteroids.

Summary of ATLAS: A High-Cadence All-Sky Survey System

The "Asteroid Terrestrial-impact Last Alert System" (ATLAS) represents a significant contribution to the field of astronomical surveys, particularly in its application toward detecting potentially hazardous near-Earth asteroids (NEAs). This paper provides a comprehensive overview of ATLAS, detailing its design, hardware components, and performance metrics, as well as its contributions to various branches of astronomical research.

ATLAS was engineered with an emphasis on cost-effectiveness while maintaining high survey capability. Operating with two units located in Hawaii, it achieves a 2-day cadence, allowing it to cover the entire visible sky efficiently. This design enables the detection of moving objects, transients, and variables with high cadence, addressing both the primary objective of detecting dangerous asteroids and a broader spectrum of astronomical phenomena. Each ATLAS unit consists of a Schmidt telescope with a 0.5-meter aperture and a field of view of 28.9 square degrees, offering a limiting magnitude of approximately 19.7 in optimal conditions.

Key Outcomes and Contributions

1. NEA and PHA Detection: ATLAS has demonstrated significant efficacy in detecting asteroids, particularly near-Earth objects (NEOs) and potentially hazardous asteroids (PHAs), superior to most other surveys when considering objects passing within 0.01 AU of Earth.
2. Transient Discovery: With its rapid sky coverage, ATLAS has become one of the leading surveys in identifying bright supernovae. It contributes extensively to the cataloging and paper of transient events, with 1,175 candidate supernovae reported by the end of 2017.
3. Data Release and Variable Star Catalog: The survey has produced light curves for approximately 240 million stars, with variability detected in 5 million of these objects. These data are intended for release through the Mikulski Archive for Space Telescopes (MAST).
4. Comprehensive Impact Assessment: By providing consistent coverage and fast reporting, ATLAS plays a critical role in the assessment of asteroid impact risks. Its capability to detect asteroids during close Earth encounters ensures a robust last-alert system.
5. Gravitational Wave Source Search: ATLAS has actively participated in the search for optical counterparts to gravitational wave events from LIGO-Virgo, showcasing its multi-disciplinary applicability.

Implications and Future Directions

The implications of ATLAS extend beyond asteroid impact detection. The system's variable star catalogs and transient discoveries enrich the understanding of cosmic phenomena. The ATLAS survey's ability to perform its NASA mission while yielding diverse scientific insights exemplifies the potential of high-cadence, all-sky survey systems.

Future developments could include expanding the ATLAS network to the Southern Hemisphere to achieve full-sky coverage and a further reduction in survey cadence. Such an expansion would not only enhance NEO detection but also provide more timely data for transient phenomena, addressing the gap left by current targeting or scheduling limitations.

In summary, ATLAS exemplifies the integration of efficient engineering with scientific inquiry, contributing significantly to both planetary defense and astronomical research. As the network potentially expands, its contributions are expected to proliferate, continuing to refine our observation capabilities and understanding of the dynamic universe.