[Paper Review] The Optical Gravitational Lensing Experiment. Cepheids in the Magellanic Clouds. VI. Double-Mode Cepheids in the Large Magellanic Cloud

I. Soszyński, A. Udalski+5 more|arXiv (Cornell University)|Jan 19, 2001

Astro and Planetary Science3 citations

TL;DR

This paper presents a sample of 76 double-mode Cepheids in the Large Magellanic Cloud (LMC), detected via long-term photometric monitoring using the OGLE-II survey. It analyzes period ratios and Fourier parameters of light curves, revealing distinct pulsation characteristics: 19 FU/FO (fundamental/first overtone) and 57 FO/SO (first/second overtone) pulsators, with the latter showing more sinusoidal light curves and bluer colors than single-mode Cepheids.

ABSTRACT

We present a sample of 76 double-mode Cepheids detected in the 4.5 square degree area in the central part of the LMC. 19 stars from the sample pulsate in the fundamental mode and the first overtone while 57 objects are the first and second overtone pulsators. We analyze the period ratio of double-mode Cepheids and Fourier parameters of decomposition of the light curves of these objects. We also present location of different type Cepheids from the LMC in the color-magnitude diagram and show the distribution of their ${V-I}$ color indices.

Motivation & Objective

• To identify and characterize double-mode Cepheids in the Large Magellanic Cloud using long-term photometric data.
• To analyze period ratios and Fourier decomposition parameters of light curves for insights into pulsation modes and stellar structure.
• To compare color-magnitude distributions of double-mode Cepheids with single-mode Cepheids to assess differences in temperature and evolutionary state.
• To provide a complete photometric dataset for the detected double-mode Cepheids to support future distance and metallicity studies.

Proposed method

• Long-term BVI photometric monitoring of 4.5 square degrees in the central LMC using the 1.3m Warsaw telescope at Las Campanas Observatory.
• Application of a two-stage algorithm to detect double-mode pulsators: initial period folding followed by residual analysis for secondary periodic signals.
• Fourier decomposition of light curves to extract amplitude ratios (R21) and phase differences (φ21) for both pulsation modes.
• Color-magnitude diagram construction with E(B-V) = 0.120 extinction correction to compare location and (V-I)0 color distributions.
• Statistical fitting of color distribution histograms with Gaussians to quantify mean colors and dispersions.
• Data availability via the OGLE archive for public access and further analysis.

Experimental results

Research questions

• RQ1 What is the distribution of period ratios in double-mode Cepheids in the LMC, and how do they compare to known Galactic and SMC samples?
• RQ2 How do the Fourier parameters (R21 and φ21) of double-mode Cepheids differ between fundamental/first overtone and first/second overtone pulsators?
• RQ3 How do the (V-I)0 color distributions of double-mode Cepheids compare to those of single-mode Cepheids in the LMC?
• RQ4 What is the significance of the bluer color distribution observed in FO/SO double-mode Cepheids compared to single-mode first overtone Cepheids?

Key findings

• Seventy-six double-mode Cepheids were detected in the LMC: 19 in the FU/FO mode and 57 in the FO/SO mode.
• The period ratio distribution shows two distinct peaks at ~0.72 (FU/FO) and ~0.805 (FO/SO), consistent with previous MACHO survey results.
• FO/SO double-mode Cepheids exhibit small-amplitude, nearly sinusoidal light curves (low R21) and higher φ21 values compared to first overtone pulsations.
• The mean (V-I)0 color for FO/SO Cepheids is 0.513 ± 0.03, which is bluer than the single-mode first overtone Cepheids (0.496 ± 0.08) and shifted blueward relative to the single-mode distribution.
• FU/FO double-mode Cepheids have (V-I)0 colors intermediate between single-mode fundamental and first overtone Cepheids, with a mean of 0.594 ± 0.08.
• The light curves of fundamental-mode pulsations in double-mode Cepheids are more sinusoidal (lower R21) than in single-mode fundamental Cepheids, though their φ21 values align with the single-mode sequence.