Yes, VariableStarObserver (VSO) allows checking of measured magnitudes with photometric standards of known colors. After successful completion of such checking, VSO could very well become a boon for people who are already accustomed to using Pixinsight (Credit is due Joƫl who developed the new VSO add-in process to Pixinsight. In its initial release, VSO is cost-free.)
In every photometric measurement, VSO employs a comp star and check star. As an indicator of measurement accuracy, VSO calculates the difference between the measured value of the check starās magnitude and its accepted (i.e., standard) magnitude. In the case of one-shot color cameras, VSO calculates three such differences, one for each of the three RGB colors. In the case of monochrome cameras, I believe that VSO assumes the image was taken in the V passband, which in the future may be extended to other photometric passbands.
Because I have recently started using the Seestar S50, which is like a DSLR with 250mm focal length, my main interest is how well Seestarās observed magnitude (TG filter) compares to the standard (V) magnitude.
As we know, the spectral bandpasses of TG and V are not exactly the same. Nevertheless, I did a spot check of the measured (TG) magnitudes versus AAVSOās standard (V) magnitudes of nine comparison stars in the R Leo Minoris field. All nine AAVSO comparison stars were of moderate color with 0.5 < B-V < 1.0. The Seestar S50 integration was 30x10s for a total of 300 seconds. The new VariableStarObserver process was used to reduce Seestarās multi-color FIT image.
The calculated differences between VSOās measured magnitudes and the accepted standard magnitudes are presented in the table below, for these nine comparison stars in the field of R Leo Minoris. The differential expresses the measurement error relative to the comparison starās standard V magnitude.
| Comp Star |
Label |
Differential |
| 000-BBQ-809 |
97 |
-0.003 |
| 000-BBQ-753 |
102 |
-0.005 |
| 000-BBQ-781 |
107 |
0.009 |
| 000-BBQ-737 |
111 |
-0.074 |
| 000-BBQ-726 |
116 |
-0.115 |
| 000-BNY-485 |
119 |
0.066 |
| 000-BBQ-749 |
120 |
-0.039 |
| 000-BBQ-743 |
127 |
0.074 |
| 000-BBQ-736 |
129 |
0.034 |
In the case of these nine comparison stars, the computed mean differential is -0.006 magnitude. This result suggests that VariableStarObserver and Seestar, working in concert with each other, can achieve very good accuracy.
This small snapshot could (and should) be extended to other AAVSO fields, to include comparison stars that are bluer than B-V = 0.5 and redder than B-V = 1.0.
I hope this post sheds some light into the VSO āblack box,ā in connection with photometric analysis of multi-color RGB images taken by Seestar and similar imaging setups. The VSO add-in certainly shows promise for variable star observing, especially by observers who already have a Pixinsight license.
