Developing improved servos for the multiple mirror telescope

Sparse aperture telescopes represent a promising technology for increasing the effective diameter of an optical system while reducing the weight and the size. Multiple-mirror telescope (MMT) and multiple-telescope telescope (MTT) are two types of sparse aperture systems. The primary mirror of MMT consists of a number of segments that are all parts of a single primary-mirror conic. The configuration of the sparse aperture is related to the performance of the MMT. Golay configuration is nonredundant sparse aperture. Entrance pupil characteristics of Golay 6 MMT are studied to research the relationships between the sub-mirrors on the primary mirror and the shapes of sub-apertures on the entrance pupil of Golay 6. Overlay factor and efficiency factor are proposed to achieve the optimal fill factor on the entrance pupil. Given the relative aperture of Golay 6 MMT, there is some concern that the fill factor on the entrance pupil is larger than the overlay fill factor on the spherical sparse aperture primary mirror. The maximum fill factor and the maximal overlay factor are discussed, and the tangency condition when sub-mirrors of Golay 6 MMT are tangency is derived. Two Cassegrain telescopes having a spherical primary mirror with Golay6 configuration and with an aspherical secondary mirror are designed. The fill factor on the entrance pupil can be larger than the overlay factor on the primary mirror at the certain occasion. Based on the relationships between the fill factor and the overlay factor, the rational parameters of sub-mirrors on the primary mirror can be selected.

The Multiple Mirror Telescope (MMT), upgraded in 2000 to a monolithic 6.5m primary mirror from its original array of six 1.8m primary mirrors, was commissioned with axis controllers designed early in the upgrade process without regard to structural resonances or the possibility of the need for digital filtering of the control axis signal path. Post-commissioning performance issues led us to investigate replacement of the original control system with a more modern digital controller with full control over the system filters and gain paths. This work, from system identification through controller design iteration by simulation, and pre-deployment hardware-in-the-loop testing, was performed using latest-generation tools with Matlab® and Simulink®. Using Simulink's Real Time Workshop toolbox to automatically generate C source code for the controller from the Simulink diagram and a custom target build script, we were able to deploy the new controller into our existing software infrastructure running Wind River's VxWorks™real-time operating system. This paper describes the process of the controller design, including system identification data collection, with discussion of implementation of non-linear control modes and disturbance decoupling, which became necessary to obtain acceptable wind buffeting rejection.

A preliminary optical design is proposed to convert the existing Multiple Mirror Telescope (MT) on Mount Hopkins to the maximum diameter, filled-aperture optical/infrared telescope that can be accommodated by the existing telescope mounting and building without substantial modification. The design utilizes a 256-inch diameter f/1.00 primary mirror which is chosen to be parabolic in order to provide adequate field of view at the required f/45.0 infrared Cassegrain focus. A 40-arcmin-diameter flat field of view is provided at an f/4.5 optical Cassegrain focus such that the resulting image scale gives a sampling factor of 3.5 (27 μ) pixels per (2/3 arcsec) spatial information element. The three-element refracting field corrector contains material for an atmospheric dispersion compensator (ADC) and it is fully color-corrected such that the entire passband from 0.33 μ to 1.60 μ can be imaged simultaneously. An f/9.0 Cassegrain focal expander-corrector with (ADC) is provided which uses the f/4.5 secondary mirror and enables the new telescope optics to be coupled to existing ancillary MMT instrumentation without substantial modification to the latter. A two-element all-spherical null-lens design is presented which provides a diffraction limited optical null-test arrangement for the unprecedentedly large f/1.00 parabolic primary mirror.

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.

An objective of our adaptive optics research at the 7-m Multiple Mirror Telescope (MMT) is to investigate ways of reconstructing wavefront errors accurately over large spatial scales. Correction of tilt error across and piston errors between each of the six 1.8-m diameter segments of the MMT is sufficient to recover the full diffraction-limited resolution at 2.2 μm of 0.06 arcseconds full width at half maximum1.

The Space Telescope, approved for a space shuttle launch in 1985, will resolve visible and ultraviolet light orders of magnitude better than earth‐based telescopes. Even though its aperture of 2.4 m will be less than half of the aperture of the reflector at Mt. Palomar, it is considered relatively large and immensely superior to existing orbiting telescopes. It is expected that the Space Telescope, with its freedom from thermal jitter and the hindrance of atmospheric absorption, will increase the user load on larger aperture earth‐based telescopes, and construction of a new series of large telescopes is now in the planning stages. The National Academy of Sciences is expected to release shortly a report by its Astronomy Survey Committee, headed by George Field of the Harvard‐Smithsonian Observatory, that will recommend building a 15‐m optical‐infrared ‘National Telescope’ [Phys. Today, August 1981, p. 17]. In addition, a 7.6‐m single reflector is planned at the University of Texas, a 10‐m segmented reflector is planned at the University of California, and the University of Arizona is experimenting with designs of a Multiple‐Mirror Telescope (MMT) larger than their new 4.5 m (equivalent) MMT. All of these are larger than the Russian 6‐m telescope, whose Pyrex reflector has not performed well, apparently because of gravitational sag and thermal inertial stresses.

High resolution spectra are required to complement the angular dimensions of pulsating stars and binary systems determined with the Sydney University Stellar Interferometer. To meet this need a multiple mirror telescope feeding a spectrograph via optical fibers is being developed. The design has been inspired by the Multi- Telescope Telescope project at Georgia State University but much of the design of the Sydney University Multiple Mirror Telescope is new. In particular, an adjustable mirror cell has been designed to allow the accurate alignment of the starlight on the input end of the fiber in its focal plane. Alignment tests carried out on a prototype cell are reported.

The 6.86 m Multiple Mirror Telescope (MMT) has been operated as a coherently cophased interferometric imaging array since 1983. PSF observations at wavelengths from 410 to 850 nm reveal characteristics which must be controlled to achieve reliable imaging at resolutions less than 75 nanoradians (0.015 arc seconds). The MMT has been used to acquire differential speckle images of Alpha Orionis in the H-alpha line and a nearby continuum bandpass at 656.9 nm. Broadband images of a 12th magnitude geosynchronous communications satellite, from which shape and size measures have been obtained with 100 nm resolution, give evidence of the capability of the MMT in speckle imaging applications. We have recently extended the cophasing capability to infrared wavelengths by providing reflective pathlength compensation capability.

Cygnus X-3 has been detected in the I-band in four CCD images taken on the Multiple Mirror Telescope. The magnitude is within 0.2 of 17.0 and there is evidence for variability over the two months of observation. The column density of intervening hydrogen is in agreement with that deduced from the X-ray spectrum.

view Abstract Citations (158) References (53) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Spectrophotometric and model-atmosphere analyses of the hot DO and DAO white dwarfs from the Palomar-Green survey. Wesemael, F. ; Green, R. F. ; Liebert, J. Abstract Recent optical and spectrophotometric observations of all currently known DAO and DO hot white dwarf candidates from the Palomar-Green Survey are presented. The optical observations were carried out using the Kitt Peak National Observatory Intensified Image Dissector Scanner (IIDS) system, the Multiple Mirror Telescope (MMT), and two photon-counting Reticon systems. Ultraviolet spectrophotometry was obtained using the International Ultraviolet Explorer (IUE) short-wavelength and long-wavelength cameras. The following spectroscopic subgroups were identified in the observations: the cool DO stars with spectra showing H I features together with He II + H blends; the hot DO stars, with spectra exhibiting weak He II (+H) lines; and hydrogen-rich DAO stars with broad H lines and sharp H II lines at 4686 A. A fourth subgroup of stars resembling PG 1159 with He at He II lines at 4686, and a C, N ion blend in the optical spectrum were also found. The spectroscopic data were analyzed in terms of a grid of hot, high-gravity LTE model atmospheres composed of a mixture of hydrogen and helium, and atmospheric parameters are deduced for each class of objects. On the basis of the model atmosphere analysis, the local space density of the DO stars is estimated to be 1.9-3.0 x 10 to the -7th per cubic pc, depending on the scale height. Publication: The Astrophysical Journal Supplement Series Pub Date: July 1985 DOI: 10.1086/191046 Bibcode: 1985ApJS...58..379W Keywords: Stellar Atmospheres; Stellar Spectra; Stellar Spectrophotometry; Ultraviolet Spectra; White Dwarf Stars; Iue; Spectral Energy Distribution; Star Distribution; Stellar Composition; Stellar Models; Stellar Temperature; Astrophysics full text sources ADS | data products SIMBAD (21) MAST (1)

We present spectra of nine low-luminosity early-type galaxies (MB > -17.5) in the Coma Cluster. The spectra, which were obtained with the Multiple Mirror Telescope and cover the spectral region 3300–5350 A, exhibit a large variation in Balmer line strengths. In fact, the line-strength variation among the Coma low-luminosity galaxies is as large as that found among a sample of low-luminosity elliptical galaxies in the Virgo Cluster and lower density environments. When compared with detailed population synthesis models, the variation in Balmer line strengths among the Coma galaxies indicates a range in luminosity-weighted mean age from ~1 to ~12 Gyr. The two youngest galaxies are shown to be in a poststarburst state, i.e., they are not simply former spirals whose star formation was recently terminated. Moreover, the ~1 Gyr ages of these two youngest low-luminosity galaxies are similar to those of the brighter poststarburst galaxies in the Coma Cluster.

Get PDF Email Share Share with Facebook Tweet This Post on reddit Share with LinkedIn Add to CiteULike Add to Mendeley Add to BibSonomy Get Citation Copy Citation Text R. R. SHANNON, "The Multiple Mirror Telescope," Optics News 4(3), 20-23 (1978) Export Citation BibTex Endnote (RIS) HTML Plain Text Citation alert Save article

The authors report the discovery of 15 white dwarfs from among blue candidates in the Low Dispersion Northern Sky Case Survey and the Kiso Schmidt camera survey. The observations were made at the 2.3-m Steward telescope, the KPNO 2.1-m telescope, and the Multiple Mirror Telescope. Spectroscopy of Praesepe white-dwarf candidates revealed a DA star, and a possible DC star, which if confirmed would be only the second known non-DA white dwarf in an open cluster. One Praesepe white-dwarf candidate is a QSO with z = 2.1.

Binospec is a wide-field, multi-object optical spectrograph to be used at the f/5 focus of the converted 6.5 m Multiple Mirror Telescope. Its dual beams will address adjacent 8' X 15' fields of view, yielding a total slit length of 30'. Binospec will offer approximately 1 - 6 Angstrom resolution at wavelengths between 0.39 and 1.0 micrometer with a 200 mm collimated beam diameter. Although it is difficult to design an f/5 wide-field collimator, f/5 optics are compact, allowing a small and stiff instrument structure. Binospec uses refractive optics throughout; the collimator contains three lens groups and the camera contains four lens groups. Three aspheric surfaces are used: two in the collimator and one in the camera. A pair of 2048 by 4608 pixel CCD detectors are used for each beam, yielding a sampling of 0.22' per pixel. Binospec's innovative optical design allows excellent image quality. Including the contribution of the MMT optics with the f/5 wide-field corrector, the RMS image diameter at Binospec's focal plane is 18 micrometer (1.3 pixels) averaged over field angles and colors.© (1998) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

We identify SDSSJ010657.39−100003.3 (hereafter J0106−1000) as the shortest period detached binary white dwarf (WD) system currently known. We targeted J0106−1000 as part of our radial velocity programme to search for companions around known extremely low-mass (ELM; ∼0.2M⊙) WDs using the 6.5-m Multiple Mirror Telescope. We detect peak-to-peak radial velocity variations of 740kms−1 with an orbital period of 39.1min. The mass function and optical photometry rule out a main-sequence star companion. Follow-up high-speed photometric observations obtained at the McDonald 2.1-m telescope reveal ellipsoidal variations from the distorted primary but no eclipses. This is the first example of a tidally distorted WD. Modelling the light curve, we constrain the inclination angle of the system to be 67°± 13°. J0106−1000 contains a pair of WDs (0.17M⊙ primary + 0.43M⊙ invisible secondary) at a separation of 0.32R⊙. The two WDs will merge in 37Myr and most likely form a core He-burning single subdwarf star. J0106−1000 is the shortest time-scale merger system currently known. The gravitational wave strain from J0106−1000 is at the detection limit of the Laser Interferometer Space Antenna (LISA). However, accurate ephemeris and orbital period measurements may enable LISA to detect J0106−1000 above the Galactic background noise.