arXiv subjects

Bruce A. Macintosh

Publications and source records attributed to Bruce A. Macintosh.

23 records · Page 2Linked to original sources

arXiv2012

MEMS practice, from the lab to the telescope

Micro-electro-mechanical systems (MEMS) technology can provide for deformable mirrors (DMs) with excellent performance within a favorable economy of scale. Large MEMS-based astronomical adaptive optics (AO) systems such as the Gemini Planet Imager are coming on-line soon. As MEMS DM end-users, we discuss our decade of practice with the micromirrors, from inspecting and characterizing devices to evaluating their performance in the lab. We also show MEMS wavefront correction on-sky with the "Villages" AO system on a 1-m telescope, including open-loop control and visible-light imaging. Our work demonstrates the maturity of MEMS technology for astronomical adaptive optics.

astro-ph.IM↗

arXiv2010

Performance of MEMS-based visible-light adaptive optics at Lick Observatory: Closed- and open-loop control

At the University of California's Lick Observatory, we have implemented an on-sky testbed for next-generation adaptive optics (AO) technologies. The Visible-Light Laser Guidestar Experiments instrument (ViLLaGEs) includes visible-light AO, a micro-electro-mechanical-systems (MEMS) deformable mirror, and open-loop control of said MEMS on the 1-meter Nickel telescope at Mt. Hamilton. In this paper we evaluate the performance of ViLLaGEs in open- and closed-loop control, finding that both control methods give equivalent Strehl ratios of up to ~ 7% in I-band and similar rejection of temporal power. Therefore, we find that open-loop control of MEMS on-sky is as effective as closed-loop control. Furthermore, after operating the system for three years, we find MEMS technology to function well in the observatory environment. We construct an error budget for the system, accounting for 130 nm of wavefront error out of 190 nm error in the science-camera PSFs. We find that the dominant known term is internal static error, and that the known contributions to the error budget from open-loop control (MEMS model, position repeatability, hysteresis, and WFS linearity) are negligible.

astro-ph.IM↗

arXiv2003

Deep Keck adaptive optics searches for extrasolar planets in the dust of Epsilon Eridani and Vega

A significant population of nearby stars have strong far-infrared excesses, now known to be due to circumstellar dust in regions analogous to the Kuiper Belt of our solar system, though orders of magnitude more dense. Recent sub-mm and mm imaging of these systems resolves the circumstellar dust and reveals complex structures, often in the form of rings with azimuthal non-axisymmetric variations. This structure might well be due to the presence of embedded brown dwarfs or planets. We have carried out deep adaptive optics imaging of two nearby stars with such asymmetric dust: Epsilon Eridani and Vega. Ten and seven candidate companions were seen in and near the dust rings of Epsilon Eridani and Vega respectively, but second-epoch proper motion measurements indicate that all are background objects. Around these two stars we can thus exclude planetary companions at spatial scales comparable to the radius of the dust structures to a level of MK=24, corresponding to 5 Jupiter masses, for Epsilon Eridani, and MK=19-21, corresponding to 6-8 Jupiter masses, for Vega.

astro-ph↗

arXiv2003

Speckle Decorrelation and Dynamic Range in Speckle Noise Limited Imaging

The useful dynamic range of an image in the diffraction limited regime is usually limited by speckles caused by residual phase errors in the optical system forming the image. The technique of speckle decorrelation involves introducing many independent realizations of additional phase error into a wavefront during one speckle lifetime, changing the instantaneous speckle pattern. A commonly held assumption is that this results in the speckles being `moved around' at the rate at which the additional phase screens are applied. The intention of this exercise is to smooth the speckles out into a more uniform background distribution during their persistence time, thereby enabling companion detection around bright stars to be photon noise limited rather than speckle-limited. We demonstrate analytically why this does not occur, and confirm this result with numerical simulations. We show that the original speckles must persist, and that the technique of speckle decorrelation merely adds more noise to the original speckle noise, thereby degrading the dynamic range of the image.

astro-ph↗

arXiv2002

NOTE: Titan's Atmosphere in Late Southern Spring Observed with Adaptive Optics on the W.M. Keck II 10-meter Telescope

Using adaptive optics on the W.M. Keck II telescope we imaged Titan several times during 1999 to 2001 in narrowband near-infrared filters selected to probe Titan's stratosphere and upper troposphere. We observed a bright feature around the south pole, possibly a collar of haze or clouds. Further, we find that solar phase angle explains most of the observed east-west brightness asymmetry of Titan's atmosphere, although the data do not preclude the presence of a `morning fog' effect at small solar phase angle.

astro-ph↗