Jonas Kuhn (JPL)

We report on recent K-band interferometric observations of the young pre-main sequence star AB Aurigae obtained with the Palomar Fiber Nuller (PFN). With a null precision of a few 10-4 inside a field-of-view extending from 35 to 275 mas (5 to 40 AU at AB Aur distance), the PFN is able to explore angular scales intermediate between those accessed by coronagraphic imaging and by long baseline interferometry. A mean astrophysical null of 1.52% was detected around AB Aur at all probed azimuthal angles, with a slight ą0.2% modulation in addition to the average null level. The isotropic astrophysical null is indicative of circumstellar emission dominated by an azimuthally extended source, possibly a halo or one or more ring of dust. The modest azimuthal variation may be explained by some skewness or anisotropy of the spatially-extended source, e.g. with 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) and carrying ~6*10-3 of the stellar flux. We combine our results with previous IOTA observations of AB Aur at H-band, and demonstrate that a dust ring located at ~30 mas (4.3 AU) represents the best-fitting model to explain both sets of reported visibilities. We are also able to reject a few previously hypothesized models of the incoherent component evidenced at longer interferometric baselines, such as a blob at 30 mas (4.3 AU) or a point source at 9 mas (1.3 AU).