A debris ring around the star HD 207129 (G0V; d = 16.0 pc) has been imaged in scattered visible light with the ACS coronagraph on the Hubble Space Telescope (HST) and in thermal emission using MIPS on the Spitzer Space Telescope at λ = 70 μm (resolved) and 160 μm (unresolved). Spitzer IRS (λ = 7-35 μm) and MIPS (λ = 55-90 μm) spectrographs measured disk emission at λ > 28 μm. In the HST image the disk appears as a ∼30 AU wide ring with a mean radius of ∼163 AU and is inclined by 60• from pole-on. At 70 μm, it appears partially resolved and is elongated in the same direction and with nearly the same size as seen with HST in scattered light. At 0.6 μm, the ring shows no significant brightness asymmetry, implying little or no forward scattering by its constituent dust. With a mean surface brightness of V = 23.7 mag arcsec −2 , it is the faintest disk imaged to date in scattered light. We model the ring's infrared spectral energy distribution (SED) using a dust population fixed at the location where HST detects the scattered light. The observed SED is well fit by this model, with no requirement for additional unseen debris zones. The firm constraint on the dust radial distance breaks the usual grain size-distance degeneracy that exists in modeling of spatially unresolved disks, and allows us to infer a minimum grain size of ∼2.8 μm and a dust size distribution power-law spectral index of −3.9. An albedo of ∼5% is inferred from the integrated brightness of the ring in scattered light. The low-albedo and isotropic scattering properties are inconsistent with Mie theory for astronomical silicates with the inferred grain size and show the need for further modeling using more complex grain shapes or compositions. Brightness limits are also presented for six other main-sequence stars with strong Spitzer excess around which HST detects no circumstellar nebulosity

We present ALMA mosaic observations at 1.3mm (223 GHz) of the Fomalhaut system with a sensitivity of 14μJy/beam. These observations provide the first millimeter map of the continuum dust emission from the complete outer debris disk with uniform sensitivity, enabling the first conclusive detection of apocenter glow. We adopt an MCMC modeling approach that accounts for the eccentric orbital parameters of a collection of particles within the disk. The outer belt is radially confined with an inner edge of 136.3±0.9au and width of 13.5±1.8au. We determine a best-fit eccentricity of 0.12±0.01. Assuming a size distribution power-law index of q=3.46±0.09, we constrain the dust absorptivity power-law index β to be 0.9<β<1.5. The geometry of the disk is robustly constrained with inclination 65°.6±0°. 3, position angle 337°.9±0°. 3, and argument of periastron 22°.5±4°.3. Our observations do not confirm any of the azimuthal features found in previous imaging studies of the disk with Hubble Space Telescope, SCUBA, and ALMA. However, we cannot rule out structures 10 au in size or that only affect smaller grains. The central star is clearly detected with a flux density of 0.75±0.02mJy, significantly lower than predicted by current photospheric models. We discuss the implications of these observations for the directly imaged Fomalhaut b and the inner dust belt detected at infrared wavelengths.

The Large Binocular Telescope Interferometer (LBTI) enables nulling interferometric observations across the N band (8 to 13 µm) to suppress a star's bright light and probe for faint circumstellar emission. We present and statistically analyze the results from the LBTI/HOSTS (Hunt for Observable Signatures of Terrestrial Systems) survey for exozodiacal dust. By comparing our measurements to model predictions based on the Solar zodiacal dust in the N band, we estimate a 1 σ median sensitivity of 23 zodis for early type stars and 48 zodis for Sun-like stars, where 1 zodi is the surface density of habitable zone (HZ) dust in the Solar system. Of the 38 stars observed, 10 show significant excess. A clear correlation of our detections with the presence of cold dust in the systems was found, but none with the stellar spectral type or age. The majority of Sun-like stars have relatively low HZ dust levels (best-fit median: 3 zodis, 1 σ upper limit: 9 zodis, 95% confidence: 27 zodis based on our N band measurements), while ∼20% are significantly more dusty. The Solar system's HZ dust content is consistent with being typical. Our median HZ dust level would not be a major limitation to the direct imaging search for Earth-like exoplanets, but more precise constraints are still required, in particular

Recent ALMA observations present mounting evidence for the presence of exocometary gas released within Kuiper belt analogues around nearby main sequence stars. This represents a unique opportunity to study their ice reservoir at the younger ages when volatile delivery to planets is most likely to occur. We here present the detection of CO J=2-1 emission co-located with dust emission from the cometary belt in the 440 Myr-old Fomalhaut system. Through spectro-spatial filtering, we achieve a 5.4σ detection and determine that the ring's sky-projected rotation axis matches that of the star. The CO mass derived (0.65 − 42 × 10 −7 M ⊕ ) is the lowest of any circumstellar disk detected to date, and must be of exocometary origin. Using a steady state model, we estimate the CO+CO 2 mass fraction of exocomets around Fomalhaut to be between 4.6-76%, consistent with Solar System comets and the two other belts known to host exocometary gas. This is the first indication of a similarity in cometary compositions across planetary systems that may be linked to their formation scenario and is consistent with direct ISM inheritance. In addition, we find tentative evidence that (49 ± 27)% of the detected flux originates from a region near the eccentric belt's pericentre. If confirmed, the latter may be explained through a recent impact event or CO pericentre glow due to exocometary release within a steady state collisional cascade. In the latter scenario, we show how the azimuthal dependence of the CO release rate leads to asymmetries in gas observations of eccentric exocometary belts.

We compile a sample of 341 binary and multiple star systems with the aim of searching for and characterising Kuiper belt-like debris discs. The sample is assembled by combining several smaller samples studied in previously published work with targets from two unpublished Herschel surveys. We find that 38 systems show excess emission at 70 or 100 µm suggestive of a debris disc. While nine of the discs appear to be unstable to perturbations from their host binary based on a simple analysis of their inferred radii, we argue that the evidence for genuine instability is not strong, primarily because of uncertainty in the true disc radii, uncertainty in the boundaries of the unstable regions, and orbital projection effects. The binary separation distributions of the disc-bearing and disc-free systems are different at a confidence level of 99.4%, indicating that binary separation strongly influences the presence of detectable levels of debris. No discs are detected for separations between ∼25 and 135 au; this is likely a result of binaries whose separations are comparable with typical disc radii clearing out their primordial circumstellar or circumbinary material via dynamical perturbations. The disc detection rate is 19 +5 −3 % for binaries wider than 135 au, similar to published results for single stars. Only 8 +2 −1 % of systems with separations below 25 au host a detectable disc, which may suggest that planetesimal formation is inhibited in binaries closer than a few tens of au, similar to the conclusions of studies of known planet-hosting binaries.