14,238 research outputs found
Instruments on large optical telescopes -- A case study
In the distant past, telescopes were known, first and foremost, for the sizes
of their apertures. Advances in technology are now enabling astronomers to
build extremely powerful instruments to the extent that instruments have now
achieved importance comparable or even exceeding the usual importance accorded
to the apertures of the telescopes. However, the cost of successive generations
of instruments has risen at a rate noticeably above that of the rate of
inflation. Here, given the vast sums of money now being expended on optical
telescopes and their instrumentation, I argue that astronomers must undertake
"cost-benefit" analysis for future planning. I use the scientific output of the
first two decades of the W. M. Keck Observatory as a laboratory for this
purpose. I find, in the absence of upgrades, that the time to reach peak paper
production for an instrument is about six years. The prime lifetime of
instruments (sans upgrades), as measured by citations returns, is about a
decade. Well thought out and timely upgrades increase and sometimes even double
the useful lifetime. I investigate how well instrument builders are rewarded. I
find acknowledgements ranging from almost 100% to as low as 60%. Next, given
the increasing cost of operating optical telescopes, the management of existing
observatories continue to seek new partnerships. This naturally raises the
question "What is the cost of a single night of telescope time". I provide a
rational basis to compute this quantity. I then end the paper with some
thoughts on the future of large ground-based optical telescopes, bearing in
mind the explosion of synoptic precision photometric, astrometric and imaging
surveys across the electromagnetic spectrum, the increasing cost of
instrumentation and the rise of mega instruments.Comment: Revised from previous submission (typos fixed, table 6 was garbled).
Submitted to PAS
Noise in optical synthesis images. I. Ideal Michelson interferometer
We study the distribution of noise in optical images produced by the aperture synthesis technique, in which the principal source of noise is the intrinsic shot noise of photoelectric detection. The results of our analysis are directly applicable to any space-based optical interferometer. We show that the signal-to-noise ratio of images synthesized by such an ideal interferometric array is essentially independent of the details of the beam-combination geometry, the degree of array redundancy, and whether zero-spatial-frequency components are included in image synthesis. However, the distribution of noise does depend on the beam-combination geometry. A highly desirable distribution, one of uniform noise across the entire image, is obtained only when the beams from the n primary apertures are subdivided and combined pairwise on n(n - 1)/2 detectors
High resolution imaging at Palomar
For the last two years we have embarked on a program of understanding the ultimate limits of ground-based optical imaging. We have designed and fabricated a camera specifically for high resolution imaging. This camera has now been pressed into service at the prime focus of the Hale 5 m telescope. We have concentrated on two techniques: the Non-Redundant Masking (NRM) and Weigelt's Fully Filled Aperture (FFA) method. The former is the optical analog of radio interferometry and the latter is a higher order extension of the Labeyrie autocorrelation method. As in radio Very Long Baseline Interferometry (VLBI), both these techniques essentially measure the closure phase and, hence, true image construction is possible. We have successfully imaged binary stars and asteroids with angular resolution approaching the diffraction limit of the telescope and image quality approaching that of a typical radio VLBI map. In addition, we have carried out analytical and simulation studies to determine the ultimate limits of ground-based optical imaging, the limits of space-based interferometric imaging, and investigated the details of imaging tradeoffs of beam combination in optical interferometers
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