295 research outputs found
Roche-lobe filling factor of mass-transferring red giants - the PIONIER view
Using the PIONIER visitor instrument that combines the light of the four
Auxiliary Telescopes of ESO's Very Large Telescope Interferometer, we measure
precisely the diameters of several symbiotic and related stars: HD 352, HD
190658, V1261 Ori, ER Del, FG Ser, and AG Peg. These diameters - in the range
of 0.6 to 2.3 milli-arcseconds - are used to assess the filling factor of the
Roche lobe of the mass-losing giants and provide indications on the nature of
the ongoing mass transfer. We also provide the first spectroscopic orbit of ER
Del, based on CORAVEL and HERMES/Mercator observations. The system is found to
have an eccentric orbit with a period of 5.7 years. In the case of the
symbiotic star FG Ser, we find that the diameter is changing by 13% over the
course of 41 days, while the observations of HD 352 are indicative of an
elongation. Both these stars are found to have a Roche filling factor close to
1, as is most likely the case for HD 190658 as well, while the three other
stars have factors below 0.5-0.6. Our observations reveal the power of
interferometry for the study of interacting binary stars - the main limitation
in our conclusions being the poorly known distances of the objects.Comment: A&A, in pres
Multiplicity of massive O stars and evolutionary implications
Nearby companions alter the evolution of massive stars in binary systems.
Using a sample of Galactic massive stars in nearby young clusters, we
simultaneously measure all intrinsic binary characteristics relevant to
quantify the frequency and nature of binary interactions. We find a large
intrinsic binary fraction, a strong preference for short orbital periods and a
flat distribution for the mass-ratios. Our results do not support the presence
of a significant peak of equal-mass `twin' binaries. As a result of the
measured distributions, we find that over seventy per cent of all massive stars
exchange mass with a companion. Such a rate greatly exceeds previous estimates
and implies that the majority of massive stars have their evolution strongly
affected by interaction with a nearby companion.Comment: 4 pages, 2 figures. Conference proceedings to appear in "370 years of
astronomy in Utrecht
Binary interaction dominates the evolution of massive stars
The presence of a nearby companion alters the evolution of massive stars in
binary systems, leading to phenomena such as stellar mergers, X-ray binaries
and gamma-ray bursts. Unambiguous constraints on the fraction of massive stars
affected by binary interaction were lacking. We simultaneously measured all
relevant binary characteristics in a sample of Galactic massive O stars and
quantified the frequency and nature of binary interactions. Over seventy per
cent of all massive stars will exchange mass with a companion, leading to a
binary merger in one third of the cases. These numbers greatly exceed previous
estimates and imply that binary interaction dominates the evolution of massive
stars, with implications for populations of massive stars and their supernovae.Comment: 9 page, 2 figures. This is the authors' version. Final version and
supplementary materials available at http://www.sciencemag.or
Modeling the e-APD SAPHIRA/C-RED ONE camera at low flux level: An attempt to count photons in the near-infrared with the MIRC-X interferometric combiner
This is the final version. Available on open access from EDP Sciences via the DOI in this recordContext. We implement an electron avalanche photodiode (e-APD) in the MIRC-X instrument, upgrade of the 6-telescope nearinfrared imager MIRC, at the CHARA array. This technology should improve the sensitivity of near-infrared interferometry.
Aims. We characterize a near-infrared C-RED ONE camera from First Light Imaging (FLI) using an e-APD from Leonardo (previously SELEX).
Methods. We first used the classical Mean-Variance analysis to measure the system gain and the amplification gain. We then developed
a physical model of the statistical distribution of the camera output signal. This model is based on multiple convolutions of the Poisson
statistic, the intrinsic avalanche gain distribution, and the observed distribution of the background signal. At low flux level, this model
constraints independently the incident illumination level, the total gain, and the excess noise factor of the amplification.
Results. We measure a total transmission of 48 ± 3% including the cold filter and the Quantum Efficiency. We measure a system
gain of 0.49 ADU/e, a readout noise of 10 ADU, and amplification gains as high as 200. These results are consistent between the two
methods and therefore validate our modeling approach. The measured excess noise factor based on the modeling is 1.47 ± 0.03, with
no obvious dependency with flux level or amplification gain.
Conclusions. The presented model allows measuring the characteristics of the e-APD array at low flux level independently of preexisting calibration. With < 0.3 electron equivalent readout noise at kilohertz frame rates, we confirm the revolutionary performances of
the camera with respect to the PICNIC or HAWAII technologies. However, the measured excess noise factor is significantly higher
than the one claimed in the literature (<1.25), and explains why counting multiple photons remains challenging with this camera.European Union Horizon 2020Labex OSUG@2020CNRS/INS
MYSTIC: Michigan Young STar Imager at CHARA
This is the final version of the article. Available from SPIE via the DOI in this record.We present the design for MYSTIC, the Michigan Young STar Imager at CHARA. MYSTIC will be a K-band, cryogenic, 6-beam combiner for the Georgia State University CHARA telescope array. The design follows the image-plane combination scheme of the MIRC instrument where single-mode fibers bring starlight into a non-redundant fringe pattern to feed a spectrograph. Beams will be injected in polarization-maintaining fibers outside the cryogenic dewar and then be transported through a vacuum feedthrough into the ~220K cold volume where combination is achieved and the light is dispersed. We will use a C-RED One camera (First Light Imaging) based on the eAPD SAPHIRA detector to allow for near-photon-counting performance. We also intend to support a 4-telescope mode using a leftover integrated optics component designed for the VLTI-GRAVITY experiment, allowing better sensitivity for the faintest targets. Our primary science driver motivation is to image disks around young stars in order to better understand planet formation and how forming planets might influence disk structures.MYSTIC is funded by the USA National Science Foundation (PI: Monnier, NSF-ATI 1506540) while the MIRC-X project is funded by the European Research Council (PI: Kraus, ERC, Grant # 639889)
The MIRC-X 6-telescope imager: Key science drivers, instrument design and operation
This is the final version of the article. Available from SPIE via the DOI in this recordMIRC-X is a new beam combination instrument at the CHARA array that enables 6-telescope interferometric imaging on object classes that until now have been out of reach for milliarcsecond-resolution imaging. As part of an instrumentation effort lead by the University of Exeter and University of Michigan, we equipped the MIRC instrument with an ultra-low read-noise detector system and extended the wavelength range to the J and H-band. The first phase of the MIRC-X commissioning was successfully completed in June 2017. In 2018 we will commission polarisation control to improve the visibility calibration and implement a 'cross-talk resiliant' mode that will minimise visibility cross-talk and enable exoplanet searches using precision closure phases. Here we outline our key science drivers and give an overview about our commissioning timeline. We comment on operational aspects, such as remote observing, and the prospects of co-phased parallel operations with the upcoming MYSTIC combiner.MIRC-X is funded by a Starting Grant from the European Research Council (ERC; grant agreement No. 639889,
PI: Kraus) and funds from the University of Exeter. The project builds on earlier investments from the University
of Michigan and the National Science Foundation (NSF, PI: Monnier)
Validité discriminante d'épreuves de dépistage de la dyslexie chez des enfants de CE2-CM1
La dyslexie est un trouble spécifique du langage écrit. Les recherches menées sur l'origine de la dyslexie ont conduit à de multiples hypothèses (i.e. hypothèse phonologique, hypothèse du traitement auditif temporel, hypothèse cérébelleux, etc.). Cette diversité des hypothèses a engendré des traitements multiples et variés et, aujourd'hui, les praticiens expriment le besoin d'un outil d'aide au diagnostic de la dyslexie prenant en compte l'ensemble des déficits de l'enfant afin de proposer une rééducation adaptée. Ce papier présente la conception d'un test préliminaire contenant les épreuves d'évaluation de la dyslexie les plus représentatives de la littérature et les premiers résultats concernant la validité discriminante de ce test préliminaire chez des enfants en âge scolaire (8-10 ans)
MIRC-X/CHARA: sensitivity improvements with an ultra-low noise SAPHIRA detector
This is the final version of the article. Available from Society of Photo Optical Instrumentation Engineers (SPIE) via the DOI in this record.MIRC-X is an upgrade of the six-telescope infrared beam combiner at the CHARA telescope array, the world's largest baseline interferometer in the optical/infrared, located at the Mount Wilson Observatory in Los Angeles. The upgraded instrument features an ultra-low noise and fast frame rate infrared camera (SAPHIRA detector) based on e-APD technology. We report the MIRC-X sensitivity upgrade work and first light results in detail focusing on the detector characteristics and software architecture.MIRC-X is funded, in parts, by a Starting Grant from the European Research Council (ERC; grant agreement No. 639889, PI: Kraus) and builds on earlier investments from the University of Michigan and the National Science Foundation (NSF, PI: Monnier). This research has made use of the Jean-Marie Mariotti Center OIFits Explorer service (http://www.jmmc.fr/oifitsexplorer)
A new interferometric study of four exoplanet host stars : {\theta} Cygni, 14 Andromedae, {\upsilon} Andromedae and 42 Draconis
Studying exoplanet host stars is of the utmost importance to establish the
link between the presence of exoplanets around various types of stars and to
understand the respective evolution of stars and exoplanets.
Using the limb-darkened diameter (LDD) obtained from interferometric data, we
determine the fundamental parameters of four exoplanet host stars. We are
particularly interested in the F4 main-sequence star, {\theta} Cyg, for which
Kepler has recently revealed solar-like oscillations that are unexpected for
this type of star. Furthermore, recent photometric and spectroscopic
measurements with SOPHIE and ELODIE (OHP) show evidence of a quasi-periodic
radial velocity of \sim150 days. Models of this periodic change in radial
velocity predict either a complex planetary system orbiting the star, or a new
and unidentified stellar pulsation mode.
We performed interferometric observations of {\theta} Cyg, 14 Andromedae,
{\upsilon} Andromedae and 42 Draconis for two years with VEGA/CHARA (Mount
Wilson, California) in several three-telescope configurations. We measured
accurate limb darkened diameters and derived their radius, mass and temperature
using empirical laws.
We obtain new accurate fundamental parameters for stars 14 And, {\upsilon}
And and 42 Dra. We also obtained limb darkened diameters with a minimum
precision of \sim 1.3%, leading to minimum planet masses of Msini=5.33\pm 0.57,
0.62 \pm 0.09 and 3.79\pm0.29 MJup for 14 And b, {\upsilon} And b and 42 Dra b,
respectively. The interferometric measurements of {\theta} Cyg show a
significant diameter variability that remains unexplained up to now. We propose
that the presence of these discrepancies in the interferometric data is caused
by either an intrinsic variation of the star or an unknown close companion
orbiting around it.Comment: 10 pages + 2 pages appendix, 16 figures, accepted for publication in
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