[Paper Review] The All Sky Automated Survey. The Catalog of Variable Stars. IV.18^h - 24^h Quarter of the Southern Hemisphere

G. Pojmański, G. Maciejewski|arXiv (Cornell University)|Dec 28, 2004

Astronomical Observations and Instrumentation20 citations

TL;DR

This paper presents the fourth installment of the All Sky Automated Survey (ASAS) catalog of variable stars in the southern celestial hemisphere, covering right ascension 18h–24h. Using V-band photometry from 2001–2004, the authors identify 10,311 variable stars—1,641 eclipsing, 1,116 pulsating, 938 Mira-type, and 6,616 others—classified via automated algorithms using period, amplitude, Fourier coefficients, 2MASS colors, and IRAS fluxes, with data publicly available online.

ABSTRACT

In this paper we present the fourth part of the photometric data from the 9x9 deg ASAS camera monitoring the whole southern hemisphere in V-band. Preliminary list (based on observations obtained since January 2001) of variable stars located between RA 18^h - 24^h is released. 10311 stars brighter than V=14 were found to be variable (1641 eclipsing, 1116 regularly pulsating, 938 Mira and 6616 other stars). Light curves have been classified using the automated algorithm taking into account periods, amplitudes, fourier coefficients of the light curves, 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 cover the 18h–24h right ascension range in the southern hemisphere.
• To identify and classify variable stars using long-term V-band photometric monitoring from 2001 to 2004.
• To develop and apply an automated classification system integrating photometric variability, light curve morphology, and infrared data (2MASS and IRAS).
• To provide a publicly accessible, high-precision photometric catalog of variable stars for the astronomical community.
• To improve the reliability of variable star classification by combining statistical tests (AOV, variance in bins) with visual inspection and multi-wavelength data.

Proposed method

• Utilized four 9°×9° wide-field CCD cameras at Las Campanas Observatory, monitoring the southern sky in V-band with a limiting magnitude of V ~14.
• Applied a multi-aperture photometry pipeline with astrometric calibration using the ACT catalog and photometric zero-pointing via Tycho stars.
• Identified variable candidates using high magnitude dispersion (top 5%) and statistical tests: Analysis of Variance (AOV), variable-length bin variance, and trend analysis.
• Classified light curves using automated algorithms based on period, amplitude, Fourier coefficients, J–H and H–K colors, and infrared fluxes from 2MASS and IRAS.
• Grouped stars into predefined types (e.g., DSCT, RRC, DCEP, M, MISC) and applied visual inspection to resolve ambiguous cases.
• Assigned a unique ASAS ID (hhmmss–ddmm.m) and provided period, epoch, maximum magnitude, amplitude, and cross-identification with GCVS and 2MASS.

Experimental results

Research questions

• RQ1 What is the distribution and classification of variable stars in the 18h–24h right ascension range of the southern celestial hemisphere?
• RQ2 How effective is the automated classification algorithm in distinguishing between different types of variable stars using photometric and infrared data?
• RQ3 What is the completeness and reliability of variable star detection in this region using three years of ASAS V-band data?
• RQ4 How do infrared colors (J–H, H–K) and fluxes improve the classification of pulsating and irregular variables?
• RQ5 What proportion of variable stars in this region are eclipsing, pulsating, Mira-type, or irregular, and how do their light curve characteristics differ?

Key findings

• A total of 10,311 variable stars were identified in the 18h–24h right ascension range of the southern sky, with 1,641 classified as eclipsing (EC/ESD), 1,116 as pulsating (DSCT, RRC, RRAB, DCEP), 938 as Mira-type, and 6,616 as other types (MISC).
• The automated classification algorithm achieved high consistency, with 861 stars receiving multiple classifications, primarily due to EC/ESD or EC/RRC ambiguities.
• The catalog includes precise photometric parameters: period (P), epoch of maximum/minimum (T₀), peak magnitude (V_max), and amplitude (ΔV) for each variable star.
• Infrared data from 2MASS and IRAS significantly improved classification accuracy, especially for late-type stars and irregular variables.
• The light curve morphology, combined with Fourier coefficients and color indices, enabled reliable distinction between periodic and aperiodic variability.
• The full dataset, including light curves and tables, is publicly accessible via the ASAS website at http://www.astrouw.edu.pl/~gp/asas/asas.html and the Princeton archive.