2,836 research outputs found

    Diffraction, chopping, and background subtraction for LDR

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    The Large Deployable Reflector (LDR) will be an extremely sensitive infrared telescope if the noise due to the photons in the large thermal background is the only limiting factor. For observations with a 3 arcsec aperture in a broadband at 100 micrometers, a 20-meter LDR will emit 10(exp 12) per second, while the photon noise limited sensitivity in a deep survey observation will be 3,000 photons per second. Thus the background subtraction has to work at the 1 part per billion level. Very small amounts of scattered or diffracted energy can be significant if they are modulated by the chopper. The results are presented for 1-D and 2-D diffraction calculations for the lightweight, low-cost LDR concept that uses an active chopping quaternary to correct the wavefront errors introduced by the primary. Fourier transforms were used to evaluate the diffraction of 1 mm waves through this system. Unbalanced signals due to dust and thermal gradients were also studied

    Angular Power Spectra of the COBE DIRBE Maps

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    The angular power spectra of the infrared maps obtained by the DIRBE (Diffuse InfraRed Background Experiment) instrument on the COBE satellite have been obtained by two methods: the Hauser-Peebles method previously applied to the DMR maps, and by Fourier transforming portions of the all-sky maps projected onto a plane. The two methods give consistent results, and the power spectrum of the high-latitude dust emission is C_\ell \propto \ell^{-3} in the range 2 < \ell < 300.Comment: ApJ in press. 15 pages with 5 included figure
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