Scattering and sublimation: a multi-scale view of $μ$m-sized dust in the inclined disc of HD 145718

Abstract

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 − 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 GPI 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 characterised 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.

Gemini-LIGHTS: Herbig Ae/Be and massive T-Tauri protoplanetary disks imaged with Gemini Planet Imager

“…We define continuous disks as disks that are resolved and do not appear to have a gap or hole in their PDI or show strong non-azimuthal structure as shown in Figure 8. Some of these disks may have gap or ringed structure but is not shown in the polarized light imagery due to the inclination (HD 145718: Davies et al 2022) or Inner Working Angle (IWA) (MWC 614: Kluska et al 2018). We note that this does not imply that these disks do not have gaps at all, but those gaps are not visible in our polarized light imaging.…”

“…If the masked method left a quadrupole structure, we utilized annulus regions of 10 pixels wide that minimized the quadrupole structure in the Q φ and U φ images and recalculated Q * and U * described in Equations 1 and 2. These methods are compared in the appendix of Davies et al (2022). Systems hosting bright point sources in the FOV occasionally exhibited some quadrupole structure in the Q φ and U φ that could not be removed with the above methods (e.g.…”