Multiplicity of Galactic Cepheids from long-baseline interferometry. I. CHARA/MIRC detection of the companion of V1334 Cygni

This is the final version of the article. Available from the publisher via the DOI in this record.Context. More than 60% of Cepheids are in binary or multiple systems. Studying such systems could lead to a better understanding
of the age and evolution of Cepheids. These are also useful tools to estimate the mass of Cepheids, and constrain theoretical models
of their pulsation and evolution.
Aims. We aim at determining the masses of Cepheids in binary systems, as well as their geometric distances and the flux contribution
of the companions. The combination of interferometry with spectroscopy will offer a unique and independent estimate of the Cepheid
masses.
Methods. Using long-baseline interferometry at visible and infrared wavelengths, it is possible to spatially resolve binary systems
containing a Cepheid down to milliarcsecond separations. Based on the resulting visual orbit and radial velocities, we can then derive
the fundamental parameters of these systems, particularly the masses of the components and the geometric distance. We therefore
performed interferometric observations of the first-overtone mode Cepheid V1334 Cyg with the CHARA/MIRC combiner.
Results. We report the first detection of a Cepheid companion using long-baseline interferometry. We detect the signature of a
companion orbiting V1334 Cyg at two epochs. We measure a flux ratio between the companion and the Cepheid f = 3.10 ± 0.08%,
giving an apparent magnitude mH = 8.47 ± 0.15 mag. The combination of interferometric and spectroscopic data have enabled
the unique determination of the orbital elements. P = 1938.6 ± 1.2 days, Tp = 2 443 616.1 ± 7.3, a = 8.54 ± 0.51 mas, i =
124.7 ± 1.8
◦
, e = 0.190 ± 0.013, ω = 228.7 ± 1.6
◦
, and Ω = 206.3 ± 9.4
◦
. We derive a minimal distance d ∼ 691 pc, a minimum
mass for both stars of 3.6 M , with a spectral type earlier than B5.5V for the companion star. Our measured flux ratio suggests that
radial velocity detection of the companion using spectroscopy is within reach, and would provide an orbital parallax and model-free
massesThe authors would like to thank the CHARA Array and
Mount Wilson Observatory staff for their support. Research conducted at the
CHARA Array is funded by the National Science Foundation through NSF
grant AST-0908253, by Georgia State University, the W. M. Keck Foundation,
the Packard Foundation, and the NASA Exoplanet Science Institute. J.D.M.
acknowledges funding from the NSF grants AST-0707927 and AST-0807577.
W.G. and G.P. gratefully acknowledge financial support for this work from
the BASAL Centro de Astrofísica y Tecnologías Afines (CATA) PFB-06/2007.
Support from the Polish National Science Centre grant MAESTRO and the
Polish Ministry of Science grant Ideas Plus (awarded to G. P.) is also acknowledge.
This research received the support of PHASE, the high angular
resolution partnership between ONERA, Observatoire de Paris, CNRS,
and University Denis Diderot Paris 7. A.G. acknowledges support from
FONDECYT grant 3130361. LSz has been supported by the ESTEC Contract
No.4000106398/12/NL/KML. This work made use of the SIMBAD and VIZIER
astrophysical database from CDS, Strasbourg, France and the bibliographic informations
from the NASA Astrophysics Data System. This research has made
use of the Jean-Marie Mariotti Center LITpro service, co-developed by CRAL,
LAOG and FIZEAU, and SearchCal service, co-developed by FIZEAU and
LAOG/IPAG, and of CDS Astronomical Databases SIMBAD and VIZIER