HIGH-CONTRAST STELLAR OBSERVATIONS WITHIN THE DIFFRACTION LIMIT AT THE PALOMAR HALE TELESCOPE

We report on high-accuracy high-resolution (<20 mas) stellar observations obtained with the Palomar Fiber Nuller (PFN), a near-infrared (similar or equal to 2.2 mu m) interferometric coronagraph installed at the Palomar Hale telescope. The PFN uses destructive interference between two elliptical (3m x 1.5m) sub-apertures of the primary to reach high dynamic range inside the diffraction limit of the full telescope. In order to validate the PFN's instrumental approach and its data reduction strategy, based on the newly developed Null Self-Calibration (NSC) method, we observed a sample of eight well-characterized bright giants and supergiants. The quantity measured is the source astrophysical null depth, or equivalently the object's visibility at the PFN 3.2m interferometric baseline. For the bare stars alpha Boo, alpha Her, beta And, and alpha Aur, PFN measurements are in excellent agreement with previous stellar photosphere measurements from long baseline interferometry. For the mass-losing stars beta Peg, alpha Ori, rho Per, and chi Cyg, circumstellar emission and/or asymmetries are detected. Overall, these early observations demonstrate the PFN's ability to measure astrophysical null depths below 10(-2) (limited by stellar diameters), with 1 sigma uncertainties as low as a few 10(-4). Such visibility accuracy is unmatched at this spatial resolution in the near-infrared and translates into a contrast better than 10(-3) within the diffraction limit. With further improvements anticipated in 2011/2012, a state-of-the-art infrared science camera and a new extreme adaptive optics system, the PFN should provide a unique tool for the detection of hot debris disks and young self-luminous sub-stellar companions in the immediate vicinity of nearby stars.