Ultra-Low Amplitude Cepheids in the Large Magellanic Cloud

Abstract

The MACHO variables of LMC Field 77 that lie in the vicinity of the Cepheid instability strip are reexamined. Among the 144 variables that we identify as Cepheids we find 14 that have Fourier amplitudes <0.05 mag in the MACHO red band, of which 7 have an amplitude <0.006 mag : we dub the latter group of stars ultra-low amplitude (ULA) Cepheids. The variability of these objects is verified by a comparison of the MACHO red with the MACHO blue lightcurves and with those of the corresponding OGLE LMC stars. The occurrence of ULA Cepheids is in agreement with theory. We have also discovered 2 low amplitude variables whose periods are about a factor of 5--6 smaller than those of F Cepheids of equal apparent magnitude. We suggest that these objects are Cepheids undergoing pulsations in a surface mode and that they belong to a novel class of Strange Cepheids (or Surface Mode Cepheids) whose existence was predicted by Buchler et al. (1997).

4 pages, 5 figures, slightly revised, to appear in ApJ Letters

References in corpus (9)

• Calibration of the MACHO Photometry Database
• The MACHO Project LMC Variable Star Inventory: I. Beat Cepheids - Conclusive Evidence for the Excitation of the Second Overtone in Classical Cepheids
• The MACHO Project 9 Million Star Color-Magnitude Diagram of the Large Magellanic Cloud
• The extra-galactic Cepheid distance scale from LMC and Galactic period-luminosity relations
• Automated Nonlinear Stellar Pulsation Calculations: Applications to RR Lyrae stars. The Slope of the Fundamental Blue Edge and the First RRd Model Survey
• Large Magellanic Cloud Bump Cepheids: Probing the Stellar Mass-Luminosity Relation
• A "pulsational" distance determination for the Large Magellanic Cloud
• Mode Switching Time Scales in the Classical Variable Stars
• Strange Cepheids and RR Lyrae

Cited by in corpus (9)

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• Survey of non-linear hydrodynamic models of type-II Cepheids
• The Cepheid Phase Lag Revisited
• Comparative clustering analysis of variable stars in the Hipparcos, OGLE Large Magellanic Cloud and CoRoT exoplanet databases
• Ultralow-amplitude RR Lyrae Stars in M4
• Ultra-low Amplitude Variables in the LMC -- Classical Cepheids, Pop. II Cepheids, RV Tau Stars and Binary Variables
• Application of the Trend Filtering Algorithm on the MACHO Database
• Testing ultralow amplitude Cepheid candidates in the Galactic disk by TESS and Gaia