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Bringing the Visible Universe into Focus with Robo-AO

Baranec, Christoph and Riddle, Reed and Law, Nicholas M. and Ramaprakash, A. N. and Tendulkar, Shriharsh P. and Bui, Khanh and Burse, Mahesh P. and Chordia, Pravin and Das, Hillol K. and Davis, Jack T. C. and Dekany, Richard G. and Kasliwal, Mansi M. and Kulkarni, Shrinivas R. and Morton, Timothy D. and Ofek, Eran O. and Punnadi, Sujit (2013) Bringing the Visible Universe into Focus with Robo-AO. Journal of Visualized Experiments, 72 . Art. No. e50021. ISSN 1940-087X. doi:10.3791/50021.

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The angular resolution of ground-based optical telescopes is limited by the degrading effects of the turbulent atmosphere. In the absence of an atmosphere, the angular resolution of a typical telescope is limited only by diffraction, i.e., the wavelength of interest, λ, divided by the size of its primary mirror's aperture, D. For example, the Hubble Space Telescope (HST), with a 2.4-m primary mirror, has an angular resolution at visible wavelengths of ~0.04 arc seconds. The atmosphere is composed of air at slightly different temperatures, and therefore different indices of refraction, constantly mixing. Light waves are bent as they pass through the inhomogeneous atmosphere. When a telescope on the ground focuses these light waves, instantaneous images appear fragmented, changing as a function of time. As a result, long-exposure images acquired using ground-based telescopes - even telescopes with four times the diameter of HST - appear blurry and have an angular resolution of roughly 0.5 to 1.5 arc seconds at best. Astronomical adaptive-optics systems compensate for the effects of atmospheric turbulence. First, the shape of the incoming non-planar wave is determined using measurements of a nearby bright star by a wavefront sensor. Next, an element in the optical system, such as a deformable mirror, is commanded to correct the shape of the incoming light wave. Additional corrections are made at a rate sufficient to keep up with the dynamically changing atmosphere through which the telescope looks, ultimately producing diffraction-limited images. The fidelity of the wavefront sensor measurement is based upon how well the incoming light is spatially and temporally sampled. Finer sampling requires brighter reference objects. While the brightest stars can serve as reference objects for imaging targets from several to tens of arc seconds away in the best conditions, most interesting astronomical targets do not have sufficiently bright stars nearby. One solution is to focus a high-power laser beam in the direction of the astronomical target to create an artificial reference of known shape, also known as a 'laser guide star'. The Robo-AO laser adaptive optics system employs a 10-W ultraviolet laser focused at a distance of 10 km to generate a laser guide star. Wavefront sensor measurements of the laser guide star drive the adaptive optics correction resulting in diffraction-limited images that have an angular resolution of ~0.1 arc seconds on a 1.5-m telescope.

Item Type:Article
Related URLs:
URLURL TypeDescription
Baranec, Christoph0000-0002-1917-9157
Riddle, Reed0000-0002-0387-370X
Law, Nicholas M.0000-0001-9380-6457
Tendulkar, Shriharsh P.0000-0003-2548-2926
Kasliwal, Mansi M.0000-0002-5619-4938
Kulkarni, Shrinivas R.0000-0001-5390-8563
Morton, Timothy D.0000-0002-8537-5711
Ofek, Eran O.0000-0002-6786-8774
Additional Information:© 2013 Creative Commons Attribution-NonCommercial License. Date Published: 2/12/2013. The Robo-AO system is supported by collaborating partner institutions, the California Institute of Technology and the Inter-University Centre for Astronomy and Astrophysics, by the National Science Foundation under Grant Nos. AST-0906060 and AST-0960343, by a grant from the Mt. Cuba Astronomical Foundation and by a gift from Samuel Oschin.
Funding AgencyGrant Number
Inter-University Centre for Astronomy and AstrophysicsUNSPECIFIED
Mt. Cuba Astronomical FoundationUNSPECIFIED
Subject Keywords:Physics; Issue 72; Astronomy; Mechanical Engineering; Astrophysics; Optics; Adaptive optics; lasers; wavefront sensing; robotics; stars; galaxies; imaging; supernova; telescopes
Record Number:CaltechAUTHORS:20130225-163035595
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Official Citation:Baranec, C., Riddle, R., Law, N.M., Ramaprakash, A.N., Tendulkar, S.P., Bui, K., Burse, M.P., Chordia, P., Das, H.K., Davis, J.T.C., Dekany, R.G., Kasliwal, M.M., Kulkarni, S.R., Morton, T.D., Ofek, E.O., Punnadi, S. Bringing the Visible Universe into Focus with Robo-AO. J. Vis. Exp. (72), e50021, doi:10.3791/50021 (2013).
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:37125
Deposited On:26 Feb 2013 19:49
Last Modified:09 Nov 2021 23:26

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