ABSTRACT. We present the first infrared interferometric observations of a young stellar object with a spatial projected resolution better than 2 AU. The observations were obtained with the Palomar Testbed Interferometer (PTI). FU Orionis exhibits a visibility of V²=0.72 ± 0.07 for a 103 ± 5 m-projected baseline at λ=2.2 μm. On the spatial scale probed by the PTI, the data are consistent with both a binary system scenario (a maximum magnitude difference of 2.7 ± 0.5 mag and the smallest separation of 0.35 ± 0.05 AU) and a standard luminous accretion disk model ( ~6 × 10⁻⁵ M yr^-1), where the thermal emission dominates the stellar scattering, and are inconsistent with a single stellar photosphere.

Subject headings: accretion, accretion disks; circumstellar matter; infrared: stars; instrumentation: interferometers; stars: individual (FU Orionis); stars: pre-main sequence

Print publication: Issue 2 (1998 November 10)
Received 1998 April 22, accepted for publication 1998 August 26
Published 1998 September 24