Of Possible General Interest

  • Use of a Guide Star to Improve Phase Measurements - When doing interferometry one correlates measurements from multiple telescopes. The correlation measurement between two telescopes is called the visibility. In general visibility is measured as a complex number, but only the magnitude provides a useable measure. Using a guide star it is possible to also determine the phase of a visibility measurement.

  • Solving for Visibility Phase - The present linear baseline configuration of the ISI gives us the ability to measure closure phase for a continuous range of spatial frequencies. In this case it is possible to solve for the individual visibility phases given the closure phase.

  • Combining Multiple Averaged Data Points - When multiple identical measurements are made the average is taken as the final measured value and the standard deviation is used to compute an error. When data has been averaged by another person or group it is sometimes desirable at a later time to combine datapoints by further averaging. The new average is simply the average of the old points weighted by how many measurements are contained in each. It is less obvious how to use the errors on the averaged points to find the error for the new point. A method for doing so is presented.

  • Guider Camera Optimization - When guiding on a star using a camera is it best to magnify the star so its position can be accurately measured, or to demagnify the image to make the spot as intense as possible? The optimum magnification for our guider camera system is explored and a possible configuration to achieve it is discussed.

  • Theodolite Measurements - A theodolite (surveying tool) is used to measure the locations of objects such as our telescopes. In this document some calculations based on theodolite measuremnets are discussed as well as methods for determining an absolute orientation for the theodolite using stars as reference points. As part of this process, the conversion between equitorial coordinates (right ascension and declination) to horizon coordinates (altitude and azimuth) are disucssed.

  • Discussion of the Fourier Transform of a Uniform Disk - A few brief notes about the Fourier transform and visibility functions of a uniform disk.

  • Oblateness of a Rotating Body - Several ways of calculating the oblateness of a spinning body are explored, all of which yield the same answer.


    Of Little Use to Anyone but ISI Group Members

  • Useful ISI Related Formulae - Just a listing of a few useful relations that help convert between quantities used by the ISI.

  • ISI Calibrations - For all dates with closure phase data.

  • Error in Telescope Throughput Measurement - We use a somewhat lengthy formula to compute the throughput of our system. An even more complicated expression gives us the expected error of our throughput measurement. Last time we cleaned our mirrors we found some improvement, but for two of our primary mirrors the improvement was within the probable error.

  • Intprofile Manual - Using the method described in "Solving for Visibility Phase" a program has been created that generates intensity profiles of stars and surrounding material based on our interferometric measurements. The program is written in IDL and the manual gives a brief description and a discussion of how it is used.