The strange evolution of the Large Magellanic Cloud Cepheid OGLE-LMC-CEP1812

Neilson, Hilding R.; Izzard, Robert G.; Langer, N.; Ignace, Richard

doi:10.1051/0004-6361/201526716

Cited by 13 publications

(11 citation statements)

References 59 publications

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“…For all systems but one, OGLE-LMC-CEP-1812, the mass ratio is very close to, or consistent with unity. The exception in the case of OGLE-LMC-CEP-1812 is probably explained by the result reported by Neilson et al (2015a) that the Cepheid in that system is actually the product of a stellar merger of two main sequence stars. From an observational point of view, there is a bias which favors the finding of systems composed of a Cepheid in orbit with a giant star of similar mass and radius which leads not only to a higher probability to observe both eclipses, but also to observe the lines of both components in the composite spectra.…”

Section: Discussionmentioning

confidence: 88%

The Araucaria Project: A Study of the Classical Cepheid in the Eclipsing Binary System Ogle LMC562.05.9009 in the Large Magellanic Cloud

Gieren

Pilecki

Pietrzyński

et al. 2015

ApJ

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We present a detailed study of the classical Cepheid in the double-lined, highly eccentric eclipsing binary system OGLE-LMC562.05.9009. The Cepheid is a fundamental mode pulsator with a period of 2.988 days. The orbital period of the system is 1550 days. Using spectroscopic data from three 4-8-m telescopes and photometry spanning 22 years, we were able to derive the dynamical masses and radii of both stars with exquisite accuracy. Both stars in the system are very similar in mass, radius and color, but the companion is a stable, non-pulsating star. The Cepheid is slightly more massive and bigger (M 1 = 3.70 ± 0.03M ⊙ , R 1 = 28.6±0.2R ⊙ ) than its companion (M 2 = 3.60±0.03M ⊙ , R 2 = 26.6±0.2R ⊙ ). Within the observational uncertainties both stars have the same effective temperature of 6030±150K. Evolutionary tracks place both stars inside the classical Cepheid instability strip, but it is likely that future improved temperature estimates will move the stable giant companion just beyond the red edge of the instability strip. Within current observational and theoretical uncertainties, both stars fit on a 205 Myr isochrone arguing for their common age.-5 -From our model, we determine a value of the projection factor of p = 1.37 ± 0.07 for the Cepheid in the OGLE-LMC562.05.9009 system. This is the second Cepheid for which we could measure its p-factor with high precision directly from the analysis of an eclipsing binary system, which represents an important contribution towards a better calibration of Baade-Wesselink methods of distance determination for Cepheids.

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Section: Discussionmentioning

confidence: 88%

The Araucaria Project: A Study of the Classical Cepheid in the Eclipsing Binary System Ogle LMC562.05.9009 in the Large Magellanic Cloud

Gieren

Pilecki

Pietrzyński

et al. 2015

ApJ

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“…Observational data for fundamental mode Cepheids is plotted as black squares with errorbars, overtone pulsators as green squares with errorbars. OGLE-LMC-CEP-1812 (yellow hexagon, LMC) is an expected outlier as there is evidence it may have undergone a merger and does not appear to be a classical Cepheid (Neilson et al 2015). Note that blue loops of low-mass LMC models do not cross the blue IS edge, hence only red boundary predictions can be shown.…”

Section: Dependence Of the Pl-relation On Is Position Crossing Metamentioning

confidence: 98%

On the effect of rotation on populations of classical Cepheids

Anderson

Saio

Ekström

et al. 2016

A&A

170

257

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Classical Cepheid variable stars (from hereon: Cepheids) are high-sensitivity probes of stellar evolution and fundamental tracers of cosmic distances. While rotational mixing significantly affects the evolution of Cepheid progenitors (intermediate-mass stars), the impact of the resulting changes in stellar structure and composition on Cepheids and their pulsational properties is hitherto unknown. Here we present the first detailed pulsational instability analysis of stellar evolution models that include the effects of rotation, for both fundamental mode and first overtone pulsation. We employ Geneva evolution models spanning a three-dimensional grid in mass (1.7-15 M ), metallicity (Z = 0.014, 0.006, 0.002), and rotation (non-rotating, average & fast rotation). We determine (1) hot and cool instability strip (IS) boundaries taking into account the coupling between convection and pulsation; (2) pulsation periods; and (3) rates of period change. We investigate relations between period and (a) luminosity; (b) age; (c) radius; (d) temperature; (e) rate of period change; (f) mass; (g) the flux-weighted gravity-luminosity relation (FWGLR). We confront all predictions aside from those for age with observations, finding generally excellent agreement. We tabulate period-luminosity relations (PLRs) for several photometric passbands and investigate how the finite IS width, different IS crossings, metallicity, and rotation affect PLRs. We show that a Wesenheit index based on H, V, and I photometry is expected to have the smallest intrinsic PLR dispersion. We confirm that rotation resolves the Cepheid mass discrepancy. Period-age relations depend significantly on rotation, with rotation leading to older Cepheids, offering a straightforward explanation for evolved stars in binary systems that cannot be matched by conventional isochrones assuming a single age. We further show that Cepheids obey a tight FWGLR. Rotation is a fundamental property of stars that has important implications for the study of intermediate-mass stars, intermediate-age clusters, and classical Cepheid variable stars.

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“…The state of the evolution of the system is unclear, in part because there is a large mass difference between the stars, yet they are in a relatively short stage of common giant phase evolution which they should have normally entered after 190 and 369 Myr, respectively. Neilson et al (2015) suggested that the system was originally a triple and the current Cepheid is a merger of two lower mass components of an inner binary. They have also proposed that the Cepheid is crossing the instability strip for the first time, which is quite a rare phenomenon as typically only a few percent of the Cepheids should be found at this stage (Neilson et al 2012).…”

Section: Ogle Lmc-cep-1718mentioning

confidence: 99%

The Araucaria Project: High-precision Cepheid Astrophysics from the Analysis of Variables in Double-lined Eclipsing Binaries*

Pilecki

Gieren

Pietrzyński

et al. 2018

ApJ

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Based on new observations and improved modeling techniques, we have reanalyzed seven Cepheids in the Large Magellanic Cloud. Improved physical parameters have been determined for the exotic system OGLE LMC-CEP-1718 composed of two first-overtone Cepheids and a completely new model was obtained for the OGLE LMC-CEP-1812 classical Cepheid. This is now the shortest period Cepheid for which the projection factor is measured. The typical accuracy of our dynamical masses and radii determinations is 1%. The radii of the six classical Cepheids follow periodradius relations in the literature. Our very accurate physical parameter measurements allow us to calculate a purely empirical, tight period-mass-radius relation that agrees well with theoretical relations derived from non-canonical models. This empirical relation is a powerful tool to calculate accurate masses for single Cepheids for which precise radii can be obtained from Baade-Wesselink-type analyses. The mass of the type-II Cepheid κ Pav, 0.56 ± 0.08M ⊙ , determined using this relation is in a very good agreement with theoretical predictions. We find large differences between the p-factor values derived for the Cepheids in our sample. Evidence is presented that a simple period-pfactor relation shows an intrinsic dispersion, hinting at the relevance of other parameters, such as the masses, radii, and radial velocity variation amplitudes. We also find evidence that the systematic blueshift exhibited by Cepheids, is primarily correlated with their gravity. The companion star of the Cepheid in the OGLE LMC-CEP-4506 system has a very similar temperature and luminosity, and is clearly located inside the Cepheid instability strip, yet it is not pulsating.

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The strange evolution of the Large Magellanic Cloud Cepheid OGLE-LMC-CEP1812

Cited by 13 publications

References 59 publications

The Araucaria Project: A Study of the Classical Cepheid in the Eclipsing Binary System Ogle LMC562.05.9009 in the Large Magellanic Cloud

The Araucaria Project: A Study of the Classical Cepheid in the Eclipsing Binary System Ogle LMC562.05.9009 in the Large Magellanic Cloud

On the effect of rotation on populations of classical Cepheids

The Araucaria Project: High-precision Cepheid Astrophysics from the Analysis of Variables in Double-lined Eclipsing Binaries*

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