[Paper Review] Pulsating stars in the ASAS-3 database. I. Beta Cephei stars

A. Pigulski|arXiv (Cornell University)|Jun 14, 2005

Stellar, planetary, and galactic studies10 citations

TL;DR

This study identifies 14 new β Cephei stars from ASAS-3 photometric data, confirming their classification through periodogram analysis of light curves and cross-referencing with spectral types and cluster membership. The new stars exhibit large-amplitude pulsations (35–80 mmag), are predominantly located in the Sagittarius-Carina spiral arm, and are associated with young open clusters, highlighting the ASAS-3 survey's effectiveness in detecting bright, multiperiodic pulsators.

ABSTRACT

We present results of an analysis of the ASAS-3 data for short-period variables from the recently published catalogue of over 38 000 stars. Using the data available in the literature we verify the results of the automatic classification related to $β$ Cephei pulsators. In particular, we find that 14 stars in the catalogue can be classified unambiguously as new $β$ Cephei stars. By means of periodogram analysis we derive the frequencies and amplitudes of the excited modes. The main modes in the new $β$ Cephei stars have large semi-amplitudes, between 35 and 80 mmag. Up to four modes were found in some stars. Two (maybe three) new $β$ Cephei stars are members of southern young open clusters: ASAS 164409-4719.1 belongs to NGC 6200, ASAS 164630-4701.2 is a member of Hogg 22, and ASAS 164939-4431.7 could be a member of NGC 6216. We also analyze the photometry of four known $β$ Cephei stars in the ASAS-3 catalogue, namely IL Vel, NSV 24078, V1449 Aql and SY Equ. Finally, we discuss the distribution of $β$ Cephei stars in the Galaxy.

Motivation & Objective

• To validate and refine the automatic classification of β Cephei stars in the ASAS-3 catalogue using photometric and literature data.
• To identify new β Cephei stars among the 38,000 variable stars in the ASAS-3 database by analyzing light curves and periodograms.
• To determine the pulsation frequencies, amplitudes, and multiperiodic behavior of newly identified β Cephei stars.
• To investigate the spatial distribution of β Cephei stars in the Galaxy, particularly their association with spiral arms and young open clusters.
• To assess the detection efficiency of the ASAS-3 survey for low-amplitude versus large-amplitude pulsators, especially in crowded fields.

Proposed method

• Periodogram analysis of ASAS-3 V-band light curves to extract dominant pulsation frequencies and amplitudes for candidate stars.
• Prewhitening of Fourier frequency spectra to isolate individual pulsation modes and confirm multiperiodic behavior.
• Cross-referencing with literature for spectral types, cluster membership, and prior classifications to validate β Cephei status.
• Use of (U-B) and (B-V) color indices, dereddened using infrared photometry (IRAS, 2MASS), to estimate absolute magnitudes and distances.
• Projection of stars onto the Galactic plane using galactic coordinates and estimated distances to map spatial distribution.
• Comparison of detection thresholds (5–10 mmag, up to 14 mmag in clusters) to assess selection effects in identifying large-amplitude stars.

Experimental results

Research questions

• RQ1 How many new β Cephei stars can be reliably identified in the ASAS-3 database using periodogram analysis and cross-verification with literature?
• RQ2 What is the distribution of pulsation amplitudes and periods among the newly identified β Cephei stars, and how do they compare to known objects?
• RQ3 Are the new β Cephei stars preferentially located in specific regions of the Milky Way, such as spiral arms or young open clusters?
• RQ4 To what extent do selection effects in the ASAS-3 survey influence the detection of large-amplitude versus low-amplitude pulsators?
• RQ5 Can photometric methods and periodogram analysis alone distinguish β Cephei stars from δ Scuti stars when spectral types are unavailable?

Key findings

• Fourteen new β Cephei stars were identified in the ASAS-3 catalogue, all exhibiting large-amplitude pulsations with main-mode semi-amplitudes between 35 and 80 mmag.
• The new stars are multiperiodic, with up to four pulsation modes detected in individual objects, confirming complex nonradial mode excitation.
• Two (possibly three) of the new β Cephei stars are confirmed members of southern young open clusters: ASAS 164409−4719.1 in NGC 6200, ASAS 164630−4701.2 in Hogg 22, and ASAS 164939−4431.7 possibly in NGC 6216.
• The new stars are located in the Sagittarius-Carina spiral arm, with galactic longitudes between 300° and 20°, consistent with their young stellar population origin.
• The detection threshold for most stars was 5–10 mmag, but cluster stars had higher thresholds (up to 14 mmag), indicating that cluster fields enhanced detectability of large-amplitude signals.
• The study confirms that periodogram analysis is more effective than magnitude-dispersion diagrams for detecting bright, large-amplitude pulsators like β Cephei stars.