Exploring intermediate (5-40AU) scales around AB Aurigae with the Palomar Fiber Nuller

TL;DR

This study uses the Palomar Fiber Nuller to explore intermediate circumstellar scales around AB Aurigae, revealing extended dust emission and constraining models of its circumstellar environment.

Contribution

First application of the Palomar Fiber Nuller to probe 5-40AU scales around AB Aurigae, providing new insights into its circumstellar dust distribution.

Findings

Detected a consistent circumstellar excess with a null of 1.52%.

Identified a dust ring at approximately 4.3AU fitting combined data.

Suggested possible azimuthal asymmetry or a point source at 17AU.

Abstract

We report on recent Ks-band interferometric observations of the young pre-main-sequence star AB Aurigae obtained with the Palomar Fiber Nuller (PFN). Reaching a contrast of a few 10-4 inside a field of view extending from 35 to 275 mas (5-40AU at AB Aur's distance), the PFN is able to explore angular scales that are intermediate between those accessed by coronagraphic imaging and long baseline interferometry. This intermediate region is of special interest given that many young stellar objects are believed to harbor extended halos at such angular scales. Using destructive interference (nulling) between two sub-apertures of the Palomar 200 inch telescope and rotating the telescope pupil, we measured a resolved circumstellar excess at all probed azimuth angles. The astrophysical null measured over the full rotation is fairly constant, with a mean value of 1.52%, and a slight additional azimuthal modulation of +/-0.2%. The isotropic astrophysical null is indicative of circumstellar emission dominated by an azimuthally extended source, possibly a halo, or one or more rings of dust, accounting for several percent of the total Ks-band flux. The modest azimuthal variation may be explained by some skewness or anisotropy of the spatially extended source, e.g., an elliptical or spiral geometry, or clumping, but it could also be due to the presence of a point source located at a separation of ~120 mas (17AU) with ~6*10-3 of the stellar flux. We combine our results with previous Infrared Optical Telescope Array observations of AB Aur at H band, and demonstrate that a dust ring located at ~30 mas (4.3AU) represents the best-fitting model to explain both sets of visibilities.We are also able to test a few previously hypothesized models of the incoherent component evident at longer interferometric baselines.