[Paper Review] The All Sky Automated Survey

G. Pojmański|arXiv (Cornell University)|Dec 11, 1997

Astronomical Observations and InstrumentationEngineering95 citations

TL;DR

The All Sky Automated Survey (ASAS) proposes a low-cost, fully automated photometric monitoring system using small, off-the-shelf telescopes to survey the sky for variable stars and transient objects. Using a prototype instrument at Las Campanas Observatory, the team achieved differential photometry accurate to 0.02 mag for bright stars, detecting over 70 new periodic variables, including several W UMa and Algol-type stars, with a 12–13 mag magnitude limit over 150 square degrees.

ABSTRACT

Technical description of the new project called All Sky Automated Survey and results of the tests of our prototype instrument are presented. The ultimate goal of this project is photometric monitoring of the large area of the sky with fully automated, low cost instruments. Possible applications of the project are indicated and future prospects discussed. At present over hundred square degrees is observed 5-10 times each night in I-band, alowing us to monitor over 30 000 stars brighter than 12-13 magnitude. Full description, pictures and current status of the project can be found at http://sirius.astrouw.edu.pl/~gp/asas/asas.html .

Motivation & Objective

• To develop a fully automated, low-cost photometric survey system for monitoring large areas of the sky.
• To detect and characterize photometric variability in stars, including periodic variables, comets, asteroids, and transient events.
• To enable long-term, high-cadence monitoring of bright stars (down to 12–13 mag) across a wide sky area.
• To minimize human intervention through remote data processing and automated data reduction pipelines.
• To scale the system by deploying multiple identical instruments at multiple observing sites with multi-filter capabilities.

Proposed method

• The prototype uses a 135/1.8 telephoto lens with a 512×768 pixel CCD (Meade Pictor 416) on an equatorial mount with stepper motor drives for right ascension and declination.
• The system employs a custom serial driver to control the CCD camera at 110 kbaud, overcoming a data transfer bottleneck.
• Photometry is performed using differential aperture photometry on stars in the 14.2 arcsec/pixel field of view.
• Variable stars are detected via automated phase dispersion minimization (PDM) analysis on light curves with a 3-sigma threshold.
• Data are reduced and calibrated using a common photometric system, with future upgrades to 2k×2k CCDs to increase data throughput.
• The system is designed for remote operation with minimal human intervention, using self-contained enclosures and automated weather protection.

Experimental results

Research questions

• RQ1 Can a low-cost, automated photometric survey system achieve sufficient photometric precision to detect variable stars in the 12–13 mag range?
• RQ2 What is the performance of a prototype robotic telescope system in detecting known and new periodic variables in a dense stellar field?
• RQ3 How accurate is differential photometry using a commercial CCD and telephoto lens in a sky-limited environment?
• RQ4 Can automated data reduction and variable detection algorithms (e.g., PDM) reliably identify periodic variables in large datasets?
• RQ5 What are the scalability and long-term operational prospects of deploying multiple identical instruments across multiple sites?

Key findings

• The ASAS prototype successfully monitored over 150 square degrees of the sky, with more than 30,000 stars observed over 50 times each during the test run.
• Differential photometry achieved an accuracy of approximately 0.02 mag for the brightest stars, though absolute calibration remained limited to ±0.05 mag.
• The system detected 70+ periodic variables with periods under 10 days, 50 of which were not listed in the General Catalog of Variable Stars.
• Four new periodic variables were confirmed: one W UMa-type (P = 0.9444 d), one Algol-type (P = 1.3164 d), and two additional W UMa-type stars.
• The prototype demonstrated that a sky-limited system using a fast telephoto lens and commercial CCD could achieve reliable photometry with minimal infrastructure.
• The project plans to upgrade to 2k×2k CCDs to increase data throughput by 10× and enable monitoring of 6,000 square degrees per night with a single instrument.