Exploring Intermediate (5-40 au) Scales around AB Aurigae with the Palomar Fiber Nuller
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 (5–40 AU 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 (17 AU) 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 (4.3 AU) 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.
© 2015. The American Astronomical Society. Received 30 May 2014; accepted for publication 8 December 2014; Published 9 February 2015. This work was performed at the Jet Propulsion Laboratory, California Institute of Technology, under contract with NASA. The data presented are based on observations obtained at the Hale Telescope, Palomar Observatory, as part of a continuing collaboration between Caltech, NASA/JPL, and Cornell University. We particularly thank the staff of the Palomar Observatory for their assistance in mounting the PFN and in conducting the observations at the Hale telescope. J.K. is supported by a Swiss National Science Foundation Advanced Postdoc Mobility fellowship (PA00 P2 136416). We also thank Rens Waters for the helpful discussions.
Published - 0004-637X_800_1_55.pdf