Using a Web Cam CCD to Do V-Band Photometry (Abstract)

Volume 37 number 2 (2009)

Rev. Paul Temple

Abstract

(Abstract only) With the plethora of cheap web cam-based CCD cameras in the market today, it seemed expedient to find out if they can be used to do photometry. An experiment was planned to determine if it was possible to perform this kind of exacting measurement. Arne Henden (AAVSO) believed it would be possible to do V-band photometry to 0.05 magnitude accuracy with a web cam CCD. Using a 6-inch refractor, the heart of M42 was repeatedly imaged. θ2 Ori and SAO 132322 were the comparison stars and V361 Ori was the target variable. Since the 1/4 HAD CCD chip only allows for a field of 10 × 7 arc minutes using the 6-inch refractor, the number of targets was limited. The RGB on the chip itself provides the filters needed for photometry. The G bandpass on the chip ranges from 425 to 650 nm with a peak band pass at 540, and V bandpass is 475–645 with a peak at 525. The results indicate that a web cam CCD can be used for V-band photometry. With a 10-second calibrated exposure without the Peltier cooling being engaged, the results for the two target stars were ± 0.18 magnitude. q2 Ori was 0.18 brighter in V than the actual measurement from the Tycho catalog. SAO 132322 was 0.012 magnitude dimmer than the listed Tycho measurement. Then, using SAO 132322 and q2 Ori as comparison stars, V361 Ori was estimated at magnitude 7.786. This is in line with visual estimates received before and after this date. With more estimates of known magnitude comparison stars, a correction factor should be estimated and applied to the variable work that will make it more accurate. This correction factor should bring it close to Arne Henden’s estimate of 0.05 mag accuracy.