August 25, 2013

New Adaptive Optics enable the partially completed Giant Magellan Telescope to take the sharpest space images ever

To correct for atmospheric turbulence, the Giant Magellan Telescope team developed a very powerful adaptive optics system that floats a thin (1.6 mm –1/16 of inch thick) curved glass mirror (85 cm across) on a magnetic field 9.2m above the big primary mirror of the telescope. This, so-called Adaptive Secondary Mirror (ASM) can change its shape at 585 points on its surface 1000 times a second. In this manner the “blurring” effects of the atmosphere can be removed, and thanks to the high density of actuators on this mirror, astronomers can see the visible sky more clearly than ever before.

They can resolve objects just 0.02 arcseconds across—this is a very small angle—it is like resolving the width of a dime seen from 100 miles away, or like resolving a convoy of three school busses driving together on the surface of the Moon.

The reason for the factor of 2 improvement over past efforts is that, for the first time, a large 6.5m telescope is being used for digital photography at its theoretical resolution limit in wavelengths of visible light. “As you move from infrared to visible light, your image sharpness improves”, said Dr. Jared Males, a NASA Sagan Fellow at the University of Arizona , “Up until now, large telescopes could make the theoretically sharpest photos only in infrared (long wavelength) light, but our new camera can work in the visible and make photos twice as sharp”. These images are also at least twice as sharp as what the Hubble Space Telescope (HST) can make because the 6.5m Magellan telescope is much larger than the 2.4m HST.

The Giant Magellan Telescope (GMT) will be a ground-based extremely large telescope planned for completion in 2020. It will consist of seven 8.4 m (27.6 ft) diameter primary segments, with the resolving power of a 24.5 m (80.4 ft) primary mirror and collecting area equivalent to a 22.0 m (72.2 ft) one. The telescope is expected to have over 5-10 times the light-gathering ability of existing instruments.


The power of visible light adaptive optics. Here we show (on the left) a “normal”photo of the theta 1 Ori C binary star in red light (in the r’ filter, 630 nm). It just looks an unresolved star. Then the middle image shows how if we remove (in real time) the blurring of the atmosphere with MagAO’s adaptive optics’ the resulting photo becomes ~17 times sharper (corrected resolutions range from 0.019-0.029 arcseconds on theta 1 Ori C). Both photos are 60 seconds long, and no post-detection image enhancement has been applied.These are the highest resolution photos taken by a telescope. Photo credit Laird Close,University of Arizona.



Arxiv - The First Circumstellar Disk Imaged in Silhouette with Adaptive Optics: MagAO Imaging of Orion 218-354.

ABSTRACT - We present high resolution adaptive optics (AO) corrected images of the silhouette disk Orion 218-354 taken with Magellan AO (MagAO) and its visible light camera, VisAO, in simultaneous differential imaging (SDI) mode at H-alpha. This is the first image of a circumstellar disk seen in silhouette with adaptive optics and is among the first visible light adaptive optics results in the literature. We derive the disk extent, geometry, intensity and extinction profiles and find, in contrast with previous work, that the disk is likely optically-thin at H-alpha. Our data provide an estimate of the column density in primitive, ISM-like grains as a function of radius in the disk. We estimate that only ~10% of the total sub-mm derived disk mass lies in primitive, unprocessed grains. We use our data, Monte Carlo radiative transfer modeling and previous results from the literature to make the first self-consistent multiwavelength model of Orion 218-354. We find that we are able to reproduce the 1-1000micron SED with a ~2-540AU disk of the size, geometry, small vs. large grain proportion and radial mass profile indicated by our data. This inner radius is a factor of ~15 larger than the sublimation radius of the disk, suggesting that it is likely cleared in the very interior.



The VisAO camera and MagAO wavefront sensors at the focus of the 6.5m Magellan telescope (all optics inside dark ring) that were used to make the visible wavelength images. Dr. Jared Males (VisAO instrument scientist/NASA Sagan Fellow) and Professor Laird Close (MagAO project scientist) are shown for scale from left to right. Photo credit Dr. Katie Morzinski, NASA Sagan Fellow at the University of Arizona.



The Magellan Telescope with MagAO’s Adaptive Secondary Mirror (ASM) mounted at the top looking down (some 9 meters) onto the 6.5m (21 foot) diameter Primary Mirror (not visible, inside blue mirror cell). Moonlight image, credit: Yuri Beletsky, Las Campanas Observatory.

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