Bruce L. Gary, Hereford Arizona Observatory (G95)
Last updated 2005.01.02

0.15 mag SE, Using Several Tycho or UCAC2 Reference Stars (5 Minutes)

This method is a slight elaboration of the previous one and achieves it improved performance by using several UCAC2 or Tycho stars as "reference stars." As stated before, be sure you have UCAC2 files on your hard disk and configure your planetarium program to support this catalog.

1) Look for at least 4 stars in your image that aren't seriously saturated (i.e., maximum counts <35,000).
2) Use your planetarium program to identify these stars.
3) Use the planetarium program to determine the UCAC2 magnitudes for these stars. If Vmag >10.5, add 0.25 mag.
4) Set the photometry aperture so that most of the "light" from the reference stars fall within the signal circle, and check that no interfering stars are in the sky background reference annuli.
5) Select the Photometry Tool (in MaxIm DL click Analyze/Photometry).
6) Set the mode to Object and left-click the asteroid.
7) Set the mode to Reference, and for each UCAC2 reference star left-click it and enter the UCAC2 V-magnitude for that star.
8) Click View, and save the results to a CSV-file.
9) View the CSV-file (using your favorite utility, such as Total Commander), and read the asteroid's magnitude.

Note 1: Since the UCAC2 catalog exhibits magnitude errors that appear to be random at a given star region it's possible to reduce the UCAC2 calibration uncertainty, SEc, by using N reference stars the calibration achieves a systematic uncertainty approximately given by 0.20 / SQRT(N). If you use 4 UCAC2 stars, then you may achieve 0.10 mag SEc. This overlooks the fact that color terms are still missing from the analysis.

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This site opened:  January 1, 2005 Last Update:  January 2, 2005