Publications

We present multi-instrument observations of the disc around the Herbig Ae star, HD 145718, employing geometric and Monte Carlo radiative transfer models to explore the disc orientation, the vertical and radial extent of the near-infrared (NIR) scattering surface, and the properties of the dust in the disc surface and sublimation rim. The disc appears inclined at 67-71°, with position angle, PA = -1.0 to 0.6°, consistent with previous estimates. The NIR scattering surface extends out to ∼75 au and we infer an aspect ratio, h_scat(r)/r ~ 0.24 in J band; ~0.22 in H band. Our Gemini Planet Imager images and VLTI + CHARA NIR interferometry suggest that the disc surface layers are populated by grains ≳λ/2π in size, indicating these grains are aerodynamically supported against settling and/or the density of smaller grains is relatively low. We demonstrate that our geometric analysis provides a reasonable assessment of the height of the NIR scattering surface at the outer edge of the disc and, if the inclination can be independently constrained, has the potential to probe the flaring exponent of the scattering surface in similarly inclined (i ≳ 70°) discs. In re-evaluating HD 145718's stellar properties, we found that the object's dimming events - previously characterized as UX Or and dipper variability - are consistent with dust occultation by grains larger, on average, than found in the ISM. This occulting dust likely originates close to the inferred dust sublimation radius at 0.17 au.

Links: ADS and MNRAS

We present 5 objects from the GPI-LIGHTS survey: FU Ori; MWC 789; HD 45677; Hen 3-365; and HD 139614. The observed structures are consistent with each object being a pre-main-sequence star with protoplanetary dust. The five objects' circumstellar environments could result from extreme youth and complex initial conditions, from asymmetric scattering patterns due to shadows cast by misaligned disks, or in some cases from interactions with companions. We see complex U_phi structures in most objects that could indicate multiple scattering or result from the illumination of companions. Specific key findings include the first high-contrast observation of MWC 789 revealing a newly-discovered companion candidate and arc, and two faint companion candidates around Hen 3-365. These two objects should be observed further to confirm whether the companion candidates are co-moving. Further observations and modeling are required to determine the causes of the structures.

Links: ADS and Arxiv

We presented the first images of the transition disk around the close binary system HD 34700A in polarized scattered light using the Gemini Planet Imager (GPI). The J- and H-band images reveal multiple spiral-arm structures outside a large cavity, along with a bluish spiral structure inside the cavity. The cavity wall shows a strong discontinuity, and we clearly see significant non-azimuthal polarization U ϕ , consistent with multiple scattering within a disk at an inferred inclination ∼42°. Radiative transfer modeling along with a new Gaia distance suggest HD 37400A is a young (∼5 Myr) system consisting of two intermediate-mass (∼2 M ☉) stars surrounded by a transitional disk. Conventional assumptions of the dust-to-gas ratio would rule out a gravitational instability origin to the spirals while hydrodynamical models using the known external companion or a hypothetical massive protoplanet in the cavity both have trouble reproducing the relatively large spiral-arm pitch angles (∼30°) without fine-tuning of gas temperature. We explored the possibility that material surrounding a massive protoplanet could explain the rim discontinuity after also considering effects of shadowing by an inner disk. Analysis of archival Hubble Space Telescope data suggests the disk is rotating counterclockwise as expected from the spiral-arm structure.

Links: ADS and ApJ

We presented scattered light imaging of 4 Herbig Ae/Be stars taken with Gemini/GPI. In the HD 144432 image, we detected a "double ring" structure were the outer ring is redder than the inner ring. For HD 163296 (MWC 275), we find that the ring is off-center due to the scattering surfacing being 18 au above the midplane. And finally for HD 150193 (MWC 863) we reported a weak detection of scattered light flux and HD 144432 a non-detection of scattered light. The outer rings found around HD 163296 and HD 169142 are evidence of giant planet formation or large-scale dust growth processes.

Links: ADS and ApJ