Sirius, Betelgeuse & more from CI
Posted: Mon Oct 04, 2004 2:16 am
I analyzed Sirius, Betelgeuse, and four other bright star data from CI taken on Sep 29 taking the ratio of photometric measurements taken on the 28th at the same sidereal time. The results are interesting.
Here are the six light curves:
Here is the Excel file that generated them: http://nightskylive.net/temp/Sirius040929.xls
First of all, taken together and to a first approximation, all of the stars had light curves that were consitent with the star being constant over the measurements. This is interesting not only for the stars but as a demonstration that CI is indeed capable of providing reliable photometry. The photometry is on the level of about 5 percent accuracy for a single measurement.
Next, all of the stars are consistent with the same constant drift toward slightly decreasing apparent luminosity over the night. Since these stars don't know each other, the result is either telling us that the atmospheric opacity increased uniformly over the entire sky by about 4 percent over the night, or the CCD sensitivity decreased by that amount.
Either case should show up on the opacity maps, but of course only the first case is scientfically interesting.
This indicates that long term photometric changes for stars that seek better photometry than 5 percent might need information from a comparison star after all, since that might be the only way to detect clouds, changes in aerosol content in the air and/or dust storms blowing out of Africa.
- RJN
Here are the six light curves:
Here is the Excel file that generated them: http://nightskylive.net/temp/Sirius040929.xls
First of all, taken together and to a first approximation, all of the stars had light curves that were consitent with the star being constant over the measurements. This is interesting not only for the stars but as a demonstration that CI is indeed capable of providing reliable photometry. The photometry is on the level of about 5 percent accuracy for a single measurement.
Next, all of the stars are consistent with the same constant drift toward slightly decreasing apparent luminosity over the night. Since these stars don't know each other, the result is either telling us that the atmospheric opacity increased uniformly over the entire sky by about 4 percent over the night, or the CCD sensitivity decreased by that amount.
Either case should show up on the opacity maps, but of course only the first case is scientfically interesting.
This indicates that long term photometric changes for stars that seek better photometry than 5 percent might need information from a comparison star after all, since that might be the only way to detect clouds, changes in aerosol content in the air and/or dust storms blowing out of Africa.
- RJN