Abstract
Aims. Observational data on companion statistics around young stellar systems is needed to flesh out the formation pathways for extrasolar planets and brown dwarfs. Aperture masking is a new technique that is able to address an important part of this discovery space. Methods. We observed the two debris disk systems HD 92945 and HD 141569 with sparse aperture masking (SAM), a new mode offered on the NaCo instrument at the VLT. A search for faint companions was performed using a detection strategy based on the analysis of closure phases recovered from interferograms recorded on the Conica camera. Results. Our results demonstrate that SAM is a very competitive mode in the field of companion detection. We obtained 5σ highcontrast detection limits at λ/D of 2.5 × 10−3 (ΔL′ = 6.5) for HD 92945 and 4.6 × 10−3 (ΔL′ = 5.8) for HD 141569. According to brown dwarf evolutionary models, our data impose an upper mass boundary for any companion for the two stars to, respectively, 18 and 22 Jupiter masses at minimum separations of 1.5 and 7 AU. The detection limits is mostly independent of angular separation, until reaching the diffraction limit of the telescope. Conclusions. We have placed upper limits on the existence of companions to our target systems that fall close to the planetary mass regime. This demonstrates the potential for SAM mode to contribute to studies of faint companions. We furthermore show that the final dynamic range obtained is directly proportional to the error on the closure phase measurement. At the present performance levels of 0.28 degree closure phase error, SAM is among the most competitive techniques for recovering companions at scales of one to several times the diffraction limit of the telescope. Further improvements to the detection threshold can be expected with more accurate phase calibration.
Highlights
Since the first imaging of a debris disk around β Pictoris (Smith & Terrile 1984), and the remarkable successes of the radial velocity technique for exoplanet discovery heralded nearly a decade later by a companion to solar-like 51 Pegasi (Mayor & Queloz 1995), the understanding of planetary systems formation and evolution has become one of astronomy’s greatest challenges
We have shown that aperture masking gives detection limits of the order of Δ L mag = 6, with an inner working angle close to λ/2D
These results confirm previous detection limits obtained by the same aperture masking technique on the Keck telescope (Kraus et al 2011; Hinkley et al 2011) In terms of scientific impact, this observational domain is important because it corresponds to a few astronomical units at a hundred parsec, the distance where the closest formation regions are
Summary
Since the first imaging of a debris disk around β Pictoris (Smith & Terrile 1984), and the remarkable successes of the radial velocity technique for exoplanet discovery heralded nearly a decade later by a companion to solar-like 51 Pegasi (Mayor & Queloz 1995), the understanding of planetary systems formation and evolution has become one of astronomy’s greatest challenges. Key breakthroughs have recently been made with high-contrast imaging: a
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