Discovery of a peculiar Cepheid-like star towards the northern edge of the Small Magellanic Cloud

Abstract

For seven years, the EROS-2 project obtained a mass of photometric data on variable stars. We present a peculiar Cepheid-like star, in the direction of the Small Magellanic Cloud, which demonstrates unusual photometric behaviour over a short time interval. We report on data of the photometry acquired by the MARLY telescope and spectroscopy from the EFOSC instrument for this star, called EROS2 J005135-714459(sm0060n13842), which resembles the unusual Cepheid HR 7308. The light curve of our target is analysed using the Analysis of Variance method to determine a pulsational period of 5.5675 days. A fit of time-dependent Fourier coefficients is performed and a search for proper motion is conducted. The light curve exhibits a previously unobserved and spectacular change in both mean magnitude and amplitude, which has no clear theoretical explanation. Our analysis of the spectrum implies a radial velocity of 104 km s${}^{-1}$ and a metallicity of -0.4$\pm$0.2 dex. In the direction of right ascension, we measure a proper motion of 17.4$\pm$6.0 mas yr${}^{-1}$ using EROS astrometry, which is compatible with data from the NOMAD catalogue. The nature of EROS2 J005135-714459(sm0060n13842) remains unclear. For this star, we may have detected a non-zero proper motion for this star, which would imply that it is a foreground object. Its radial velocity, pulsational characteristics, and photometric data, however, suggest that it is instead a Cepheid-like object located in the SMC. In such a case, it would present a challenge to conventional Cepheid models.

arXiv commentCorrection of typos in the abstract

References in corpus (10)

• Limits on the Macho Content of the Galactic Halo from the EROS-2 Survey of the Magellanic Clouds
• The Magellanic Clouds Photometric Survey: The Small Magellanic Cloud Stellar Catalog and Extinction Map
• Spectroscopic Survey of Red Giants in the SMC. I: Kinematics
• The DENIS Point Source Catalogue towards the Magellanic Clouds
• Galactic Bulge Microlensing Optical Depth from EROS-2
• Classifying Luyten Stars Using An Optical-Infrared Reduced Proper Motion Diagram
• Observation of Microlensing towards the Galactic Spiral Arms. EROS II 3 year survey
• Observation of periodic variable stars towards the galactic spiral arms by EROS II
• A Cepheid is No More: Hubble's Variable 19 in M33
• The effects of blending on the light curve shape of Cepheids

Cited by in corpus (1)

• Long Period Variables in the Large Magellanic Cloud from the EROS-2 survey