deletions | additions       diff --git a/Description of LSST.tex b/Description of LSST.tex  index f5dedcd..43e3348 100644  --- a/Description of LSST.tex  +++ b/Description of LSST.tex 
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The LSST camera contains a 3.2-gigapixel focal plane array comprised of 189 4096x4096 CCD sensors with 10 μm pixels. The focal plane is 0.64 m in diameter, and covers 9.6 {deg$^2$} field-of-view with a plate scale of 0.2 arcsec/pixel. The CCD sensors are deep depletion, back-illuminated devices with a highly segmented architecture, 16 channels each, that enable the entire array to be read out in two seconds. The detectors are grouped into 3x3 arrays, all identical and each containing its own dedicated front-end and back-end electronics board, which fits within the footprint of its sensors, thus serving as a 144-Megapixel camera on its own. The CCDs will be maintained at an operating temperature of −100$^°$C. The grid also contains two guide sensors and a wavefront sensor positioned at each of the four corners at the edge of the field.   %The entrance window to the cryostat is the third of three refractive lenses.   The camera body also contains a mechanical shutter and a filter exchange system holding five large optical filters, any of which can be inserted into the camera field of view for a given exposure. The system will in fact have six filters; the A  sixth filter can replace any of the these  five via an automated procedure accomplished during daylight hours. The LSST filter choice (u, g, r, i, z, y) is modeled on the system used for the SDSS, which covers the available wavelength range with roughly logarithmic spacing while avoiding the strongest telluric emission features and sampling the Balmer break. %\textbf{Extension of the SDSS system to longer wavelengths (y-band) is possible because the deep-depletion CCDs have}  %\textbf{high sensitivity to 1 μm.}   Four %Four  special purpose rafts, mounted at the corners of the science array, contain wavefront sensors and guide sensors. %\textbf{Wavefront measurements are accomplished using curvature sensing,}  %\textbf{in which the spatial intensity distribution of stars is measured at equal distances on either side}  %\textbf{of focus. Each curvature sensor is composed of two CCD detectors, with one positioned slightly} 
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%\textbf{locations of bright stars at a frequency of ∼ 10 Hz to provide feedback for a loop that controls}  %\textbf{and maintains the tracking of the telescope at an accurate level during an exposure.}   The observation strategy is entirely based on a “universal cadence” that scans the sky "\textit{deep, “\textit{deep,  wide, and fast}" so as to provide a data set that simultaneously satisfies the majority of the science goals. This main survey, that will use about 90\% of the observing time, will consist in series of pairs of 15-second exposures with each filter, optimized to cover the southern sky (20000 deg$^2$) in about 3 to 4 days, with a single visit reaching magnitude ~24.5 in the r band. As often as possible, each field will be observed twice, with visits separated by 15 to 60 minutes, so as to optimize sampling of short-period variability phenomena. Over the planned 10 years of observations, this will represent about 2.8 million visits. The remaining 10\% of the observing time will be used to obtain improved coverage of parameter space such as very deep (r ∼ 26) observations, observations with very short revisit times (∼ 1 minute), and observations of “special” regions such as the ecliptic, Galactic plane, and the Large and Small Magellanic Clouds. Is also considered a third type of survey, micro-surveys, that would use  about 1\% of the time, or about 25 nights over ten years.  Finally, with its planned \emph{wide, deep, and fast} survey, the LSST will generate a formidable amount of information, which puts the computing and data archive model to unprecedented challenges. For instance, one night of observation will prooduce produce  about 1.5 TB of data, about 2 billion objects will be routinely monitored for photometric and astrometric change, and online processing needs to guarantee that transient events will be posted in less than 60 seconds to the worldwide community. In ten years of survey, the LSST database is expected to serve information for about 20 billion objects, and will grow in size to ~30 PB eventually.