منابع مشابه
Building Large Telescopes: Ii- Reflectors
On the turn of the twentieth century the refractor was rapidly approaching its limits in terms of aperture. The main reason for this was the difficulty in manufacturing discs of crown and flint glass with diameters greater than 100 cm. Manufactures of plate-glass could however cast large disks of ordinary crown glass, of lower optical quality, that were suitable for mirrors. It was also known t...
متن کاملMicrolens Parallaxes with SIRTF
The Space Infrared Telescope Facility (SIRTF) will drift away from the Earth at ∼ 0.1 AU yr. Microlensing events will therefore have different characteristics as seen from the satellite and the Earth. From the difference, it is possible in principle to measure ṽ, the transverse velocity of the lens projected onto the observer plane. Since ṽ has very different values for different populations (d...
متن کاملFabrication of large-area patterned porous silicon distributed Bragg reflectors.
A process to fabricate porous silicon Bragg reflectors patterned on a micrometer lateral scale over wafer areas of several square centimeters is described. This process is based on a new type of projection system involving a megavolt accelerator and a quadrupole lens system to project a uniform distribution of MeV ions over a wafer surface, which is coated with a multilevel mask. In conjunction...
متن کامل20. Verification of Parallaxes
Hipparcos parallaxes will play a major role in the astrophysical applications of the Hipparcos results and in this respect their accuracy is more important than their precision, at least for all the investigations of statistical character. In this Chapter, the systematic errors of the Hipparcos astrometric parameters, including the parallaxes, are evaluated by examining the possible sources of ...
متن کاملFinding “absolute” parallaxes directly
We develop the formalism for estimating parallaxes, proper motions and positions from long-focus astrometric observations as well as additional extraneous reference material whenever this is available and relax the constraints on the star parameters (basically their sums and correlations with the coordinates on the frames), thus generating (albeit correlated) quasiobservations whose inclusion w...
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ژورنال
عنوان ژورنال: Symposium - International Astronomical Union
سال: 1986
ISSN: 0074-1809
DOI: 10.1017/s0074180900076683