FIRST-LIGHT LBT NULLING INTERFEROMETRIC OBSERVATIONS: WARM EXOZODIACAL DUST RESOLVED WITHIN A FEW AU OF η Crv

Abstract

We report on the first nulling interferometric observations with the Large Binocular Telescope Interferometer (LBTI), resolving the N' band (9.81 -12.41 µm) emission around the nearby main-sequence star η Crv (F2V, 1-2 Gyr). The measured source null depth amounts to 4.40% ± 0.35% over a field-of-view of 140 mas in radius (∼2.6 AU at the distance of η Crv) and shows no significant variation over 35 • of sky rotation. This relatively low null is unexpected given the total disk to star flux ratio measured by Spitzer/IRS (∼23% across the N' band), suggesting that a significant fraction of the dust lies within the central nulled response of the LBTI (79 mas or 1.4 AU). Modeling of the warm disk shows that it cannot resemble a scaled version of the Solar zodiacal cloud, unless it is almost perpendicular to the outer disk imaged by Herschel. It is more likely that the inner and outer disks are coplanar and the warm dust is located at a distance of 0.5-1.0 AU, significantly closer than previously predicted by models of the IRS spectrum (∼3 AU). The predicted disk sizes can be reconciled if the warm disk is not centrosymmetric, or if the dust particles are dominated by very small grains. Both possibilities hint that a recent collision has produced much of the dust. Finally, we discuss the implications for the presence of dust at the distance where the insolation is the same as Earth's (2.3 AU).Subject headings: circumstellar matter -infrared: stars-instrumentation: interferometers -stars: individual (η Crv) * F.R.S.-FNRS Research Associate. † NASA Sagan Fellow. ‡ The different number of modes used on each telescope has a negligible impact on the null depth (i.e., a few 10 −7 ). Furthermore, this effect is constant during the night and calibrates out completely.

Effects of disc asymmetries on astrometric measurements

“…The origin of the warm component is unknown, but is thought to be the outcome of a system-wide recent or ongoing dynamical instability (Lisse et al 2011). Recent observations with the LBTI constrained this dust to lie within a projected distance of 1au (Defrère et al 2015), less than the 3 au predicted by modelling of the infrared spectrum (Lisse et al 2011), with one possible resolution being that the warm dust component is clumpy. The disc-to-star flux ratio at 12 µm is 1.2, roughly two times higher than the detectable limit.…”

“…For example, the ∼1 Gyr old star η Corvi hosts both warm and cool dust components (Wyatt et al 2005), with the warm component residing at about 1au (Smith et al 2009;Defrère et al 2015). The origin of the warm component is unknown, but is thought to be the outcome of a system-wide recent or ongoing dynamical instability (Lisse et al 2011).…”

Hi-5: a potential high-contrast thermal near-infrared imager for the VLTI

“…Thus, exozodis have so far mostly been observed at the CHARA array and the VLTI in the near-infrared [23][24][25][26][27] and at KIN and the LBTI in the mid-infrared. [28][29][30][31] These observations reached contrasts of a few 10 −4 to a few 10 −3 , leading to vital statistical insights into the occurrence rates of exozodis as a function of other properties of the systems such as the presence of cold, Kuiper belt-like dust disks or stellar age and spectral type. The main challenge at the moment is linking the near-infrared and the mid-infrared detections, which critically constrain the systems' architectures and the properties and origin of the dust.…”

Exozodiacal clouds: hot and warm dust around main sequence stars

“…To go beyond this state-of-the-art exozodi sensitivity, Downloaded by [University of Liege] at 05: 23 25 October 2017 NASA has funded the Large Binocular Telescope Interferometer (LBTI) to carry out a survey in the N' band (9.81-12.41 µm) on 40-50 carefully chosen nearby main-sequence stars [96]. The first-light observations were obtained on a previously known bright disc around the nearby main-sequence star η Crv and show an excess emission of 4.40% ± 0.35% over a field-of-view of 140 mas in radius [77]. This relatively low null was unexpected given the total disc-to-star flux ratio measured by Spitzer/IRS (∼23% across the N' band), suggesting that a significant fraction of the dust lies within the central nulled response of the LBTI (79 mas or 1.4 au).…”

“…The sky transmission maps of the KIN and LBTI mid-IR nulling experiments are, on the other hand, much more complex in shape, and depend sensibly on observing parameters such as the observing date/time, and the parallactic and hour angles [e.g. 77,113]. The above 1D approach (Equation (4)) is therefore not appropriate, and it is necessary to multiply the synthetic 2D disc image in the sky plane with the 2D transmission map to obtain a synthetic null value.…”