Cepheids with giant companions. II. Spectroscopic confirmation of nine new double-lined binary systems composed of two Cepheids

Abstract

Binary Cepheids with giant companions are crucial for studying the physical properties of Cepheid variables, providing the best means to measure their masses. Systems composed of two Cepheids are even more important but to date, only one such system in the Large Magellanic Cloud (LMC) was known. Our current aim is to increase the number of these systems tenfold and provide their basic characteristics. The final goal is to obtain the physical properties of the component Cepheids, including their masses and radii, and to learn about their evolution in the multiple systems, also revealing their origin. We started a spectroscopic monitoring of nine unresolved pairs of Cepheids from the OGLE catalog, to check if they are gravitationally bound. Two of these so-called double Cepheids are located in the LMC, five in the Small Magellanic Cloud (SMC), and two in the Milky Way (MW). We report the spectroscopic detection of binarity of all 9 of these double Cepheids with orbital periods from 2 to 18 years. This increases the number of known binary double (BIND) Cepheids from 1 to 10 and triples the number of all confirmed double-lined binary (SB2) Cepheids. For five BIND Cepheids disentangled pulsational light curves of the components show anti-correlated phase shifts due to orbital motion. We show the first empirical evidence that typical period-luminosity relations (PLRs) are rather binary Cepheid PLRs that include the companion's light. The statistics of pulsation period ratios of BIND Cepheids do not agree with those expected for pairs of the same-age Cepheids. These ratios together with the mass ratios far from unity suggest merger-origin of at least one component for about half of the systems. The SMC and MW objects are the first found in SB2 systems composed of giants in their host galaxies. The Milky Way BIND Cepheids are also the closest such systems, being located at about 11 and 26 kpc.

arXiv comment13 pages, 7 figures, 4 tables, accepted for publication in Astronomy & Astrophysics

References in corpus (25)

• The Gaia mission
• Gaia Data Release 3: Summary of the content and survey properties
• Gaia Early Data Release 3: The astrometric solution
• On the Effect of Rotation on Populations of Classical Cepheids II. Pulsation Analysis for Metallicities 0.014, 0.006, and 0.002
• The Araucaria Project. Near-Infrared Photometry of Cepheid Variables in the Sculptor Galaxy NGC 300
• Accurate dynamical mass determination of a classical Cepheid in an eclipsing binary system
• The MACHO Project LMC Variable Star Inventory: I. Beat Cepheids - Conclusive Evidence for the Excitation of the Second Overtone in Classical Cepheids
• Multiplicity of Galactic Cepheids and RR Lyrae stars from Gaia DR2 - I. Binarity from proper motion anomaly
• Improving the mass determination of Galactic Cepheids
• An Improved Calibration of the Wavelength Dependence of Metallicity on the Cepheid Leavitt law
• Mass and p-factor of the type II Cepheid OGLE-LMC-T2CEP-098 in a binary system
• A Classical Cepheid in a LMC eclipsing binary: evidence of shortcomings in current stellar evolutionary models?
• The Araucaria Project: High-precision Cepheid astrophysics from the analysis of variables in double-lined eclipsing binaries
• A geometrical 1% distance to the short-period binary Cepheid V1334 Cygni
• The Araucaria Project: The First-Overtone Classical Cepheid in the Eclipsing System OGLE-LMC-CEP-2532
• The MACHO Project LMC Variable Star Inventory: XII. Three Cepheid Variables in Eclipsing Binaries
• The Araucaria Project: A study of the classical Cepheid in the eclipsing binary system OGLE LMC562.05.9009 in the Large Magellanic Cloud
• Cepheids with giant companions. I. Revealing a numerous population of double-lined binary Cepheids
• The Araucaria Project. OGLE-LMC-CEP-1718: An exotic eclipsing binary system composed of two classical overtone Cepheids in a 413-day orbit
• The Mass of the Cepheid V350 Sgr
• Empirical instability strip for classical Cepheids: I. The LMC galaxy
• The Cepheids of NGC1866: A Precise Benchmark for the Extragalactic Distance Scale and Stellar Evolution from Modern UBVI Photometry
• Binarity among Cepheids in the Magellanic Clouds
• Discovery of a binary-origin classical Cepheid in a binary system with a 59-day orbital period
• Orbit determination for the binary Cepheid V1344 Aql

Cited by in corpus (4)

• Multiplicity of Galactic Cepheids from long-baseline interferometry V. High-accuracy orbital parallax and mass of SU Cygni
• Cepheid Metallicity in the Leavitt Law (C-MetaLL) survey: IX. Metallicity dependence of Period-Wesenheit relations based on a homogeneous spectroscopic sample
• Empirical instability strip for classical Cepheids II. The Small Magellanic Cloud galaxy
• Near-IR CO and CN in classical Cepheids