A near-infrared interferometric survey of debris-disk stars

Abstract

Context. Hot exozodiacal dust has been shown to be present in the innermost regions of an increasing number of main sequence stars over the past 15 yr. However, the origin of hot exozodiacal dust and its connection with outer dust reservoirs remains unclear. Aims. We aim to explore the possible connection between hot exozodiacal dust and warm dust reservoirs (≥100 K) in asteroid belts. Methods. We use precision near-infrared interferometry with VLTI/PIONIER to search for resolved emission at H-band around a selected sample of 62 nearby stars that show possible signs of warm dust populations. Results. Our observations reveal the presence of resolved near-infrared emission around 17 out of 52 stars with sufficient data quality. For four of these, the emission is shown to be due to a previously unknown stellar companion. The 13 other H-band excesses are thought to originate from the thermal emission of hot dust grains, close to their sublimation temperature. Taking into account earlier PIONIER observations, where some stars with warm dust were also observed, and after re-evaluating the warm dust content of all our PIONIER targets through spectral energy distribution modeling, we find a detection rate of 17.1−4.6+8.1% for H-band excess around main sequence stars hosting warm dust belts, which is statistically compatible with the occurrence rate of 14.6−2.8+4.3% found around stars showing no signs of warm dust. After correcting for the sensitivity loss due to partly unresolved hot disks, under the assumption that they are arranged in a thin ring around their sublimation radius, we find tentative evidence at the 3σ level that H-band excesses around stars with outer dust reservoirs (warm or cold) could be statistically larger than H-band excesses around stars with no detectable outer dust. Conclusions. Our observations do not suggest a direct connection between warm and hot dust populations at the sensitivity level of the considered instruments, although they bring to light a possible correlation between the level of H-band excess and the presence of outer dust reservoirs in general.

Planetesimal/Debris discs

“…First, 10-30% of nearby stars present emission in the near-or mid-IR that indicates the presence of high levels of hot or warm dust (Kral et al, 2017;Ertel et al, 2020;Absil et al, 2021). The warm dust is typically located at distances of ∼ 1 au, i.e.…”

Dust Accretion onto Exoplanets

“…One might have hoped that emission from the outer debris disk could be observed, and hence M d  near the star estimated. However, Absil et al (2021) find no strong correlation between the presence of a near-infrared excess for the hot dust and a mid or far-infrared excess for an outer debris disk. Hot dust excesses are not necessarily accompanied by warm or cold dust excesses.…”

“…If true, then this maximum accretion rate may limit the abundances due to accreted dust to be subsolar by a factor of 10 or more. Such small accretion rates would also likely not deliver dust to near the sublimation zone at a high enough rate to explain the observed near-infrared excesses (Absil et al 2021).…”

“…This paper presents a study of the accretion of dust and its possible observable consequences for exoplanets orbiting very near their star. Infrared excess due to dust thermal emission has been observed from other stars, with the far, mid, and nearinfrared arising from cold, warm, and hot dust at different distances from the star (Trilling et al 2008;Absil et al 2013;Eiroa et al 2013;Ertel et al 2014Ertel et al , 2020Absil et al 2021). It is the hot dust component that would directly interact with closein planets.…”

“…Detection is more favorable for warm dust at ∼ au separations, e.g., Large Binocular Telescope Interferometer (LBTI) can detect warm dust down to tens of zodi for some systems (Ertel et al 2020). While ∼15%-20% of stars have detectable hot dust excess (Absil et al 2013;Ertel et al 2014;Absil et al 2021), undetected systems with far larger M d  could be more common and perhaps ubiquitous.…”