한국천문학자들을 위한 GALEX 공동연구
GALEX 우주망원경 정보 : GALEX 공식 홈페이지
GALEX Survey Plan
i) All sky imaging Survey
Below are several plots related to several different proposed strategies for conducting the All Sky Imaging Survey (AIS). In contrast to the other surveys, the AIS data wil be taken as scans. In all of the plots shown below, I have assumed that there are 2000 seconds per orbit of useful observing time. I have also assumed that in each orbit, GALEX would be able to scan a total of 90 degrees on the sky, which corresponds to a scanning rate of about 162 arcsec/sec. As a compromise between minimizing the number of slew commands sent during an orbit and insuring that we do not run into problems with viewing constraints within each orbit, we have assumed the scan pattern shown below. It consists of three 30 degree-long great circle segments with a 1 degree spacing between the end-points of each segment. We have begun exploring different strategies for covering the entire sky using the above scan pattern. Below are three such strategies. For each AIS plan, there is an all-sky exposure map (in an Aitoff projection) and a histogram showng the distribution of exposure times across the sky. Please keep in mind that at this point, these maps are not assumed to be in any particular coordinate system. In principle each of them could be carried out equally well in equatorial or Galactic coordinates.
AIS Option 1: In this strategy, the area between -45 and +45 degrees latitutude is covered by three of the 30-degree long zigzag patterns, each oriented roughly along lines of constant longitude. The starting points of neighboring scans are separted by one-degree of longitude at the equator. The polar regions are convered by taking a 90 degree wide portion of the equatorial pattern and rotating it up or down to each pole. This results in four triangular overlap regions in each hemishere where the exposure time is roughly twice that of the rest of the sky.
AIS Option 2: In this strategy, 30 zigzag patterns are polaced together to form a series of 30x30 degree patches which are then used to cover the sky.
AIS Option 3: This strategy simply aligns all of the zigzag patterns along lines of constant longitude. This results in the exposure time increase with the distance from the equator. If this pattern were in Galactic coordinates, this would be a very simple way of spending more time observing the Galactic caps and less time in the Galactic plane. Note that the distribution of the exposure times shown in the seond plot does not show the enitre distribution.