A near-infrared interferometric survey of debris-disk stars

Abstract

Context. Detecting and characterizing circumstellar dust is a way to study the architecture and evolution of planetary systems. Cold dust in debris disks only traces the outer regions. Warm and hot exozodiacal dust needs to be studied in order to trace regions close to the habitable zone. Aims. We aim to determine the prevalence and to constrain the properties of hot exozodiacal dust around nearby main-sequence stars. Methods. We searched a magnitude-limited (H ≤ 5) sample of 92 stars for bright exozodiacal dust using our VLTI visitor instrument PIONIER in the H band. We derived statistics of the detection rate with respect to parameters, such as the stellar spectral type and age or the presence of a debris disk in the outer regions of the systems. We derived more robust statistics by combining our sample with the results from our CHARA/FLUOR survey in the K band. In addition, our spectrally dispersed data allowed us to put constraints on the emission mechanism and the dust properties in the detected systems. Results. We find an overall detection rate of bright exozodiacal dust in the H band of 11% (9 out of 85 targets) and three tentative detections. The detection rate decreases from early type to late type stars and increases with the age of the host star. We do not confirm the tentative correlation between the presence of cold and hot dust found in our earlier analysis of the FLUOR sample alone. Our spectrally dispersed data suggest that either the dust is extremely hot or the emission is dominated by the scattered light in most cases. The implications of our results for the target selection of future terrestrial planet-finding missions using direct imaging are discussed.

What Sets the Radial Locations of Warm Debris Disks?

“…As we will describe later, both of these possibilities predict that the locations of warm components will be set by the snow line (i.e., where water ice condensation/ sublimation occurs). However, these hypotheses differ as to whether it is the primordial snow line or the current snow line 1 identified five dust components that a debris disk can possess, which in addition to the warm and cold components described here, also include a blowout halo of small grains outside of the cold belt (Augereau et al 2001;Su et al 2005); exozodiacal dust that is hotter and nearer to the star than the warm dust and emits at ∼10 μm (Kennedy & Wyatt 2013;Ballering et al 2014); and very hot dust emitting in the near-IR (Absil et al 2013;Ertel et al 2014), likely composed of nanograins trapped in the stellar magnetic field .…”

A near-infrared interferometric survey of debris-disc stars

“…These very accurate instruments are pushed to their limits by such observations in terms of both statistical accuracy and ability to calibrate the data obtained. Until now, only two detections could be confirmed from repeated observations: Vega (Absil et al 2006;Defrère et al 2011) and β Pic (Defrère et al 2012;Ertel et al 2014). …”

“…For our observations, we followed closely the strategy motivated and outlined in Ertel et al (2014), which we only briefly summarize here. All observations were carried out in H band using the PIONIER beam combiner on the VLTI in combination with the 1.8 m Auxiliary Telescopes in the compact 0.11 ± 0.14 ± 0.05 0.11…”

“…As for our observing strategy, for the calibration and excess measurements we closely followed the procedure motivated and outlined by Ertel et al (2014). First, a global calibration of each night was performed to correct for the effect of field rotation on the instrumental visibilities (due to polarization effects in the VLTI optical train; Le Ertel et al 2014).…”

“…It is generally attributed to the presence of hot circumstellar dust. The detections have been made using near-IR interferometry mostly employing the instruments Fiber Linked Unit for Optical Recombination (FLUOR) Resolution Astronomy (CHARA) array (e.g., Absil et al 2006Absil et al , 2013 and Precision Integrated Optics Near Infrared ExpeRiment (PIONIER) at the Very Large Telescope Interferometer (VLTI; Defrère et al 2012;Ertel et al 2014). These very accurate instruments are pushed to their limits by such observations in terms of both statistical accuracy and ability to calibrate the data obtained.…”