17P/Holmes - Photometry
The Photometry of my comet images is made with MaxIm DL Version 3.22. This program offers a quite good possibility to easily perform the photometry of a series of images.
First I select some reference stars with a magnitude around the comet's mag using TheSky level VI. Only USNO magnitudes are used. The Aperture Radius of the photometry area depends on the size of the inner coma of the comet. In the case of comet 17P/Holmes I selected the aperture of 4. The Gap Width is selected to its maximum size of 10. The Annulus Thickness is set to 5, not too much. The stars should have no neighbors around.
The result of the photometry made by MaxIm DL is the following graph:
Photometry performed by Bernhard H�usler, Germany
It shows the performed photometry data of all selected reference stars and of the comet. The program is automatically snaping the "moving" comet on all images, no manual work has to be done. Finally I save the data on a .CSV file and load them into an excel sheet.
In this case the photometry curve of the comet seemed to have a regular frequency of around half an hour with peaks every 45 minutes. Maybe this is an indication of a rotation period. More investigation is necessary.
|
T (JD) |
Ref1 |
Ref2 |
Ref3 |
Ref4 |
Ref5 |
Obj1 |
|
245.483.138.365 |
13.976 |
16.225 |
17.032 |
18.594 |
15.782 |
17.771 |
|
245.483.138.729 |
13.731 |
16.040 |
16.807 |
19.503 |
15.528 |
17.853 |
|
245.483.139.094 |
14.066 |
16.405 |
16.986 |
18.289 |
15.864 |
17.990 |
|
245.483.139.461 |
13.819 |
16.126 |
16.911 |
19.139 |
15.615 |
18.193 |
|
|
|
|
|
|
|
|
|
average |
|
|
|
|
|
17.952 |
In excel I compute the average values of the object and use the computed value of 17.952 mag for the comet.