[Paper Review] The All Sky Automated Survey. The Catalog of Variable Stars. III. 12h - 18h Quarter of the Southern Hemisphere

G. Pojmański, G. Maciejewski|arXiv (Cornell University)|Jun 10, 2004

Astronomical Observations and Instrumentation10 citations

TL;DR

This paper presents the third installment of the All Sky Automated Survey (ASAS) catalog of variable stars, focusing on the 12h–18h right ascension region in the southern hemisphere. Using V-band photometry from 2001–2004, the authors identify 10,453 variable stars via an automated algorithm enhanced with 2MASS colors and IRAS fluxes, classifying them into eclipsing binaries, pulsating stars, Mira variables, and other types, with full data available online.

ABSTRACT

This paper describes the third part of the photometric data from the 9 x 9 deg ASAS camera monitoring the whole southern hemisphere in V-band. Preliminary list of variable stars based on observations obtained since January 2001 is presented. Over 3,200,000 stars brighter than V=15 on 18,000 frames were analyzed and 10453 were found to be variable (1718 eclipsing, 731 regularly pulsating, 849 Mira and 7155 other stars). Light curves have been classified using the improved automated algorithm, which now takes into account 2MASS colors and IRAS infrared fluxes. Basic photometric properties are presented in the tables and some examples of thumbnail light curves are printed for reference. All photometric data are available over the INTERNET at http://www.astrouw.edu.pl/~gp/asas/asas.html or http://archive.princeton.edu/~asas

Motivation & Objective

• To extend the All Sky Automated Survey (ASAS) catalog of variable stars to the 12h–18h right ascension region in the southern celestial hemisphere.
• To identify and classify variable stars using long-term V-band photometric monitoring from 2001 to 2004.
• To improve variability detection and classification by incorporating 2MASS infrared colors and IRAS fluxes into the automated algorithm.
• To make the full photometric data and light curves publicly accessible via the internet for the astronomical community.
• To provide a reliable, large-scale sample of variable stars for future studies of stellar variability and population characteristics.

Proposed method

• Utilized the ASAS system at Las Campanas Observatory, employing four wide-field (9°×9°) cameras with f/2.8 telephoto lenses and 2K×2K CCDs to monitor stars in the V-band nightly.
• Applied a multi-aperture photometry pipeline with simultaneous flux extraction from apertures of 2–6 pixels, minimizing blending effects and improving accuracy.
• Calibrated photometry using Tycho-2 stars and astrometry based on the ACT catalog, achieving sub-arcsecond positional accuracy.
• Implemented a two-stage variability detection: initial screening using magnitude dispersion and AOV statistics (threshold >10), followed by variance and trend analysis in variable-length bins.
• Employed an enhanced automated classification algorithm that integrates 2MASS J–H and H–K colors and IRAS infrared fluxes to improve separation of variable star types.
• Conducted final classification through visual inspection of light curves, with results grouped into 11 classes including eclipsing binaries, RR Lyrae, Cepheids, Mira stars, and miscellaneous types.

Experimental results

Research questions

• RQ1 What is the distribution and population of variable stars in the 12h–18h right ascension region of the southern sky?
• RQ2 How effective is the integration of 2MASS and IRAS data in improving the classification accuracy of variable stars in the ASAS survey?
• RQ3 What is the completeness and reliability of the automated variability detection pipeline in identifying stars with diverse light curve morphologies?
• RQ4 How do the photometric properties (period, amplitude, color) of variable stars in this region compare with known stellar populations?
• RQ5 To what extent can the automated classification algorithm distinguish between eclipsing binaries, pulsating stars, and Mira variables using multi-band photometric data?

Key findings

• A total of 10,453 variable stars were identified in the 12h–18h right ascension region of the southern sky, based on three years of V-band photometry from January 2001 to December 2003.
• The sample includes 1,718 eclipsing binaries, 731 regularly pulsating stars (including RR Lyrae and Cepheids), 849 Mira variables, and 7,155 stars classified as miscellaneous or irregular variables.
• The inclusion of 2MASS J–H and H–K colors significantly improved the separation of variable star types, particularly in distinguishing Mira stars and pulsating variables from other classes.
• The automated classification algorithm achieved high reliability, with 39,000 candidates passing initial screening and 10,500 undergoing final visual inspection, resulting in a final catalog of 10,453 confirmed variables.
• The survey achieved a photometric precision of 0.01 mag for bright stars and sub-arcsecond astrometric accuracy, with systematic errors minimized through Tycho-2 calibration.
• All photometric data, light curves, and classification tables are publicly available at http://www.astrouw.edu.pl/~gp/asas/ and http://archive.princeton.edu/~asas, enabling broad community access and follow-up studies.