The FASTTRAC II adaptive optics instrument has been used at the Multiple Mirror Telescope (MMT) for the past 2 years to provide improved image resolution in the near infrared. Results have been obtained using both natural guide stars and an artificial sodium laser beacon. With the imminent closure of the MMT prior to its conversion to a single-mirror 6.5 m telescope, FASTTRAC II has come to the end of its life. The instrument has been to the telescope for a total of 8 runs, and during that time it has been of enormous value both as a learning aid, demonstrating the requirements of its successor on the 6.5 m, and as a scientific tool. At this meeting, we present a selection of astrophysical data derived from FASTTRAC II, including the first closed-loop demonstration of an adaptive optics system using a sodium laser beacon. The sodium laser has been used to obtain near diffraction-limited near-infrared images of the core of M13, allowing the construction of a color-magnitude diagram to below the main sequence turnoff. Results have also been obtained from several gravitationally lensed quasars, and the cores of nearby galaxies in the local group. We also summarize work characterizing atmospheric conditions at the site. These studies have proceeded in two areas - understanding the behavior of the phase perturbation with field angle and time, and characterizing the return from the sodium resonance beacon.
The first images of astronomical objects have been obtained with a telescope exploiting wavefront compensation with adaptive optics where the reference beacon was generated by laser excitation of mesospheric sodium. This was done using the FASTTRAC II low-order adaptive optics system at the multiple mirror telescope (MMT). FASTTRAC II is a prototype for a full-scale adaptive optics system under construction for the 6.5 m telescope that will replace the MMT in late 1997. The 6.5 m system is designed to provide correction to the diffraction limit of resolution in the near infrared (1 - 5 micrometer) with high Strehl ratio and excellent sky coverage. This paper describes the new system and its expected performance in view of the achieved performance of FASTTRAC II.
A new interim adaptive system—FASTTRAC IT—has been developed for near-infrared imaging for the Multiple Mirror Telescope (MMT), prior to upgrade to a single 6.5 m mirror. The system employs a real-time adaptive beam combiner consisting of six mirror facets which control the tip and tilt for each of the 1 .8 m primary mirrors. Since the overall piston of the mirrors is not controlled, the light from the six MMT mirrors adds incoherently at the focal plane, producing an image with the diffraction limit of a single mirror but with flux corresponding to a filled 4.5 m aperture. In operational mode the tilts over each of the 1.8 m mirrors will be sampled using a sodium laser guide star. Overall tilt is compensated using a field star imaged in the visible. We present a brief discussion of the various error sources entering into the system performance. Simulations of performance are presented showing the dependence on field star magnitude and angle. the time delay between sense and application of the required correction, and the angle between laser guide star and field position. These simulations demonstrate that FASTTRAC II should readily achieve diffraction limited imaging for a 1.8 m aperture with 6 times the light collection at near-infrared wavelengths.
A new adaptive optics system has been constructed for moderately high resolution in the near infrared at the Multiple Mirror Telescope (MMT). The system, called FASTTRAC II, has been designed to combine the highest throughput with the lowest possible background emission by making the adaptive optical element be an existing and necessary part of the telescope, and by eliminating all warm surfaces between the telescope and the science camera's dewar. At present, only natural guide stars are supported, but by the end of 1995, we will add the capability to use a single sodium resonance beacon derived from a laser beam projected nearly coaxially with the telescope. In this paper, we present a description of FASTTRAC II, and show results from its first test run at the telescope in April 1995.