Pupil plane optimization for single-mode multiaxial optical interferometry with a large number of telescopes

Incoming optical interferometers will allow spectro-imaging at high angular resolution. Non-homothetic Fizeau concept combines good sensitivity and high spectral resolution capabilities. However, one critical issue is the design of the beam recombination scheme, at the heart of the instrument. We tackle the possibility of reducing the number of pixels that are coding the fringes by compressing the pupil plane. Shrinking the number of pixels -- which drastically increases with the number of recombined telescopes -- is indeed a key issue that enables to reach higher limiting magnitude, but also allows to lower the required spectral resolution and fasten the fringes reading process. By means of numerical simulations, we study the performances of existing estimators of the visibility with respect to the compression process. We show that, not only the model based estimator lead to better signal to noise ratio (SNR) performances than the Fourier ones, but above all it is the only one which prevent from introducing baseline mixing biases in the visibilities as the pupil plane compression rate increases. Furthermore, we show that moderate compression allows to keep the visibilities SNR unaffected. In the light of these conclusions, we propose an optimized pupil arrangements for 6 and 8 beam recombiners

A PIONIER View on Mass-Transferring Red Giants

Symbiotic stars display absorption lines of a cool red giant together with emission lines of a nebula ionized by a hotter star, indicative of an active binary star system in which mass transfer is occurring. PIONIER at the VLT has been used to combine the light of four telescopes at a time to study in unprecedented detail how mass is transferred in symbiotic stars. The results of a mini-survey of symbiotic stars with PIONIER are summarised and some tentative general results about the role of Roche lobe overflow are presented.Comment: Report for the ESO Messenger June issu

Searching for faint companions with VLTI/PIONIER. II. 92 main sequence stars from the Exozodi survey

The Exozodi survey aims to determine the occurrence rate of bright exozodiacal discs around nearby main sequence stars using infrared interferometry. Although the Exozodi survey targets have been carefully selected to avoid the presence of binary stars, the results of this survey can still be biased by the presence of unidentified stellar companions. Using the PIONIER data set collected within the Exozodi survey, we aim to search for the signature of point-like companions around the Exozodi target stars. We use both the closure phases and squared visibilities collected by PIONIER to search for companions within the ~100 mas interferometric field of view. The presence of a companion is assessed by computing the goodness of fit to the data for a series of binary models with various separations and contrasts. Five stellar companions are resolved for the first time around five A-type stars: HD 4150, HD 16555, HD 29388, HD 202730, and HD 224392 (although the companion to HD 16555 was independently resolved by speckle interferometry while we were carrying out the survey). In the most likely case of main sequence companions, their spectral types range from A5V to K4V. Three of these stars were already suspected to be binaries from Hipparcos astrometric measurements, although no information was available on the companions themselves so far. In addition to debiasing the statistics of the Exozodi survey, these results can also be used to revise the fraction of visual binaries among A-type stars, suggesting that an extra ~13% A-type stars are visual binaries in addition to the ones detected in previous direct imaging surveys. We estimate that about half the population of nearby A-type stars could be resolved as visual binaries using a combination of state-of-the-art interferometry and single-aperture imaging, and we suggest that a significant fraction of these binaries remains undetected to date.Comment: Accepted for publication in A&

Masses and age of the Chemically Peculiar double-lined binary χ\chi~Lupi

8 pages, accepted in AandAWe aim at measuring the stellar parameters of the two Chemically Peculiar components of the B9.5Vp HgMn + A2 Vm double-lined spectroscopic binary HD141556, whose period is $15.25$~days. We combined historical radial velocity measurements with new spatially resolved astrometric observations from PIONIER/VLTI to reconstruct the three-dimensional orbit of the binary, and thus obtained the individual masses. We fit the available photometric points together with the flux ratios provided by interferometry to constrain the individual sizes, which we compared to predictions from evolutionary models.The individual masses of the components are \Ma = 2.84 \pm 0.12\ \Msun and \Mb = 1.94 \pm 0.09\ \Msun. The dynamical distance is compatible with the Hipparcos parallax. We find linear stellar radii of \Ra=2.85 \pm 0.15\ \Rsun and \Rb=1.75 \pm 0.18\ \Rsun. This result validates a posteriori the flux ratio used in previous detailed abundance studies. We determine a sub-solar initial metallicity $Z=0.012\pm0.003$ and an age of $(2.8\pm0.3)\times10^8\$years. Our results imply that the primary rotates more slowly than its synchronous velocity, while the secondary is probably synchronous. We show that strong tidal coupling during the pre-main sequence evolution followed by a full decoupling at zero-age main sequence provides a plausible explanation for these very low rotation rates

Astronomical interferometry with near-IR e-APD at CHARA: characterization, optimization and on-sky operation

We characterize a near-infrared C-RED ONE camera from First Light Imaging (FLI). This camera uses a SAPHIRA electron avalanche photo-diode array (e-APD) from Leonardo (previously Selex). To do so, we developed a model of the signal distribution. This model allows a measurement of the gain and the Excess Noise Factor (ENF) independently of preexisting calibration such as the system gain. The results of this study show a gain which is 0.53 +/- 0.04 times the gain reported by the manufacturer. The measured ENF is 1.47 +/- 0.03 when we expected 1.25. For an avalanche gain of 60 and a frame rate larger than 100 Hz, the total noise can be lower than 1 e-/frame/pixel. The lowest dark current level is 90e-/s/pixel, in agreement with the expected H-band background passing through the camera window. These performance values provide a significant improvement compared to earlier-generation PICNIC camera and allowed us to improve the performance of the Michigan infrared combiner (MIRC) instrument at the Center for High Angular Resolution Astronomy (CHARA), as part of our MIRC-X instrumentation project.Comment: 18 pages, 15 figures, presented at SPIE Astronomical Telescopes + Instrumentation 2018, Austin, Texas, US

Intricate visibility effects from resolved emission of young stellar objects: the case of MWC158 observed with the VLTI

In the course of our VLTI young stellar object PIONIER imaging program, we have identified a strong visibility chromatic dependency that appeared in certain sources. This effect, rising value of visibilities with decreasing wavelengths over one base, is also present in previous published and archival AMBER data. For Herbig AeBe stars, the H band is generally located at the transition between the star and the disk predominance in flux for Herbig AeBe stars. We believe that this phenomenon is responsible for the visibility rise effect. We present a method to correct the visibilities from this effect in order to allow "gray" image reconstruction software, like Mira, to be used. In parallel we probe the interest of carrying an image reconstruction in each spectral channel and then combine them to obtain the final broadband one. As an illustration we apply these imaging methods to MWC158, a (possibly Herbig) B[e] star intensively observed with PIONIER. Finally, we compare our result with a parametric model fitted onto the data.Comment: 14 pages, 7 figure

The third version of the AMBER data reduction software

We present the third release of the AMBER data reduction software by the JMMC. This software is based on core algorithms optimized after several years of operation. An optional graphic interface in a high level language allows the user to control the process step by step or in a completely automatic manner. Ongoing improvement is the implementation of a robust calibration scheme, making use of the full calibration sets available during the night. The output products are standard OI-FITS files, which can be used directly in high level software like model fitting or image reconstruction tools. The software performances are illustrated on a full data set of calibrators observed with AMBER during 5 years taken in various instrumental setup.Comment: To be published in the proceedings of the SPIE'2010 conference on "Optical and Infrared Interferometry II