English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

Context. A new four-telescope interferometric instrument called PIONIER hasrecently been installed at VLTI. It provides improved imaging capabilitiestogether with high precision. Aims. We search for low-mass companions around afew bright stars using different strategies, and determine the dynamic rangecurrently reachable with PIONIER. Methods. Our method is based on the closurephase, which is the most robust interferometric quantity when searching forfaint companions. We computed the chi^2 goodness of fit for a series of binarystar models at different positions and with various flux ratios. The resultingchi^2 cube was used to identify the best-fit binary model and evaluate itssignificance, or to determine upper limits on the companion flux in case of nondetections. Results. No companion is found around Fomalhaut, tau Cet andRegulus. The median upper limits at 3 sigma on the companion flux ratio arerespectively of 2.3e-3 (in 4 h), 3.5e-3 (in 3 h) and 5.4e-3 (in 1.5 h) on thesearch region extending from 5 to 100 mas. Our observations confirm that thepreviously detected near-infrared excess emissions around Fomalhaut and tau Cetare not related to a low-mass companion, and instead come from an extendedsource such as an exozodiacal disk. In the case of del Aqr, in 30 min ofobservation, we obtain the first direct detection of a previously knowncompanion, at an angular distance of about 40 mas and with a flux ratio of2.05e-2 \pm 0.16e-2. Due to the limited u,v plane coverage, its position can,however, not be unambiguously determined. Conclusions. After only a few monthsof operation, PIONIER has already achieved one of the best dynamic rangesworld-wide for multi-aperture interferometers. A dynamic range up to about1:500 is demonstrated, but significant improvements are still required to reachthe ultimate goal of directly detecting hot giant extrasolar planets.

Searching for faint companions with VLTI/PIONIER. I. Method and first results