Empirical instability strip for classical Cepheids II. The Small Magellanic Cloud galaxy

Abstract

Aims. This study aims to determine empirical intrinsic edges of the classical Cepheids instability strip (IS) in the Small Magellanic Cloud (SMC) galaxy, considering various effects that alter its shape, and compare them with theoretical models and other galaxies. Methods. We used the data of classical fundamental-mode (F) and first-overtone mode (1O) SMC Cepheids from the OGLE-IV variable star catalog, with the final cleaned sample including 2388 F and 1560 1O Cepheids. The IS borders are determined by tracing the edges of the color distribution along the strip. Based on that, and using evolutionary tracks, the IS crossing times are computed. Results. We obtained the blue and red edges of the IS in V- and I-photometric bands and in the HR diagram, and detected breaks at periods between 1.4 and 3 days. A comparison with existing theoretical models showed good agreement for the blue edge and significant differences for the red edge. We also found that the IS of the SMC is wider than that of the Large Magellanic Cloud (LMC), with its red edge being redder despite its lower metallicity. The analysis of crossing times showed that the expected number of Cepheids as a function of period agrees with the observed distribution for P > 1 days but differs for P < 1 days. Conclusions. Slope changes along the SMC IS borders are most likely explained by the distribution of metallicity. The behavior of the blue loops at the SMC metallicity is not consistent with observations, and at the LMC metallicity, the blue loops are too short for lower-mass stars. A comparison of theoretical edges with our empirical ISs imposes constraints on the models and enables the identification of valid ones. Based on the positions of the breaks, our study also suggests that fundamental-mode Cepheids with periods longer than 3 days should be used for distance determination.

12 pages, 11 figures, appendix 1 page. Accepted for publication in Astronomy & Astrophysics

References in corpus (33)

• Modules for Experiments in Stellar Astrophysics (MESA)
• Modules for Experiments in Stellar Astrophysics (MESA): Giant Planets, Oscillations, Rotation, and Massive Stars
• Modules for Experiments in Stellar Astrophysics (MESA): Binaries, Pulsations, and Explosions
• Modules for Experiments in Stellar Astrophysics (MESA): Convective Boundaries, Element Diffusion, and Massive Star Explosions
• Modules for Experiments in Stellar Astrophysics (MESA): Pulsating Variable Stars, Rotation, Convective Boundaries, and Energy Conservation
• A distance to the Large Magellanic Cloud that is precise to one per cent
• Modules for Experiments in Stellar Astrophysics (MESA): Time-Dependent Convection, Energy Conservation, Automatic Differentiation, and Infrastructure
• The Updated BaSTI Stellar Evolution Models and Isochrones: I. Solar Scaled Calculations
• New Period-Luminosity and Period-Color Relations of Classical Cepheids: I. Cepheids in the Galaxy
• An Empirical UBVRIJHK Color-Temperature Calibration for Stars
• A distance determination to the Small Magellanic Cloud with an accuracy of better than 2 percent based on late-type eclipsing binary stars
• On the Effect of Rotation on Populations of Classical Cepheids II. Pulsation Analysis for Metallicities 0.014, 0.006, and 0.002
• New Period-Luminosity and Period-Color Relations of Classical Cepheids: II. Cepheids in LMC
• OGLE-ing the Magellanic System: Optical Reddening Maps of the Large and Small Magellanic Cloud from Red Clump Stars
• The VMC Survey. XXV. The 3D structure of the Small Magellanic Cloud from Classical Cepheids
• Small Magellanic Cloud Cepheids Observed with the Hubble Space Telescope Provide a New Anchor for the SH0ES Distance Ladder
• Cepheid pulsation models at varying metallicity and DY/DZ
• New period-luminosity and period-color relations of classical Cepheids: III. Cepheids in SMC
• An Improved Calibration of the Wavelength Dependence of Metallicity on the Cepheid Leavitt law
• Photometric metallicity map of the Small Magellanic Cloud
• On the Blue Loops of Intermediate-Mass Stars
• An updated metal-dependent theoretical scenario for Classical Cepheids
• Evolutionary tracks, ejecta, and ionizing photons from intermediate-mass to very massive stars with PARSEC
• Cepheids with giant companions. I. Revealing a numerous population of double-lined binary Cepheids
• B,V Photometry of Variable Stars in the Northeast Arm of the Small Magellanic Cloud
• The State of Cepheid Pulsation Theory
• Empirical instability strip for classical Cepheids: I. The LMC galaxy
• Discovery of a binary-origin classical Cepheid in a binary system with a 59-day orbital period
• Period Change Rates of Large Magellanic Cloud Cepheids using MESA
• Cepheids with giant companions. II. Spectroscopic confirmation of nine new double-lined binary systems composed of two Cepheids
• Implications of a turbulent convection model for classical Cepheids
• The stellar evolution perspective on the metallicity dependence of classical Cepheid Leavitt laws
• Convective shells in the interior of Cepheid variable stars: overshooting models based on hydrodynamic simulations