Combined Method of Photometric Correction
Posted: Sun Jun 19, 2005 7:58 pm
It was recently discussed that we have two different methods used to correct star counts for various photometric difficulties (Atmospheric extinction, Air Glow, Clouds).
In whatever form the methods amount to either A) Comparing a star to its history B) Compare a star to other stars at the same time.
A combination of these methods would seem a logical approach to try
1) Choose star to study and find an optically clear night to study.
2) Choose a number of check stars based only upon proximity to study star. Perhaps three would be enough, I would recommend eight, and the more used the better precision I would expect.
3) Collect as much history on the check stars as possible. 1 month would perhaps be enough, I would recommend six, and the longer history used the better precision I would expect. (History should include only data free of major changes to Concam being used)
4) Using Data from Step 3 an average value should be calculated for each integer of altitude.
5) Collect a list of the average C5-B for each check star at each degree of altitude possible.
6) Collect data for study star and all check stars for night to be studied.
7) Each check star C5-B would be divided by its average value for that altitude.
8) An average of all check star ratios obtained in seven it taken
9) The value of C5-B for the study star is divided by average from 8) and considered a corrected C5-B.
20-second history can compose a separate average to correct 20-second exposures. I have tried correcting 20-sec exposure time as a photometric defect with limited success, however have never attempted it on major scale (many check stars, large history).
I have attached an Excel File with a layout, which may be clearer than what I have laid out above.
http://www.geocities.com/aceofspace03/Photometry.xls
This method CANNOT be practically tested until more stars have photometry collected on easily available web pages.
In whatever form the methods amount to either A) Comparing a star to its history B) Compare a star to other stars at the same time.
A combination of these methods would seem a logical approach to try
1) Choose star to study and find an optically clear night to study.
2) Choose a number of check stars based only upon proximity to study star. Perhaps three would be enough, I would recommend eight, and the more used the better precision I would expect.
3) Collect as much history on the check stars as possible. 1 month would perhaps be enough, I would recommend six, and the longer history used the better precision I would expect. (History should include only data free of major changes to Concam being used)
4) Using Data from Step 3 an average value should be calculated for each integer of altitude.
5) Collect a list of the average C5-B for each check star at each degree of altitude possible.
6) Collect data for study star and all check stars for night to be studied.
7) Each check star C5-B would be divided by its average value for that altitude.
8) An average of all check star ratios obtained in seven it taken
9) The value of C5-B for the study star is divided by average from 8) and considered a corrected C5-B.
20-second history can compose a separate average to correct 20-second exposures. I have tried correcting 20-sec exposure time as a photometric defect with limited success, however have never attempted it on major scale (many check stars, large history).
I have attached an Excel File with a layout, which may be clearer than what I have laid out above.
http://www.geocities.com/aceofspace03/Photometry.xls
This method CANNOT be practically tested until more stars have photometry collected on easily available web pages.