TransformGenerator with Sloan GRI filters-can I?

Science Photometry
1

Hi All,
New to AAVSO and still a beginner with photometry. My friends and I have a telescope in Spain, primarily used for pretty pictures, but equipped with a QHY600 and Sloan g’r’i’ filter set. During winter we provide photometric data and assist Undergrad students at the Uni of Glasgow. We have never gone downthe road of transforming magnitudes, but with T CrB teeterring on the edge, I thought its time to use the T coefficients.

I took some data of M67, probably several hours per filter with 120s subs, and combined in to a single master image for each filter.

I have downloaded and got working the Transform Generator, and so I proceeded to upload my M67 data.

With a quick play in VPhot, I tried to import Standard Stars (having told the uploader that my filter is ‘SG’ etc). However, it says that no standard stars exist for that filter.

I hope I am wrong, but M67 has to have been imaged in SDSS filters surely.

Am I doing something wrong, how do I use TG with Sloan filters?

Many Thanks
Paul

2

No one have any suggestions?

3

I’ve made a quick search through the literature for papers describing photometry of M67 in the SDSS passbands. It seems as if

https://ui.adsabs.harvard.edu/abs/2010ApJ...711..559D/abstract

would have just what you want, but the authors don’t seem to have made their photometry of stars in M67 available in a table. Rats.

You can find photometry of a small number (53) of stars, in the range 14 < g < 16.5, described by

 https://ui.adsabs.harvard.edu/abs/2008AJ....136.2050L/abstract

in Vizier. Go to

 https://vizier.cds.unistra.fr/viz-bin/VizieR?-source=J/AJ/136/2050

and specify the constraint that the name of the entry’s cluster is “M 67”.

One could, of course, query the SDSS Archive for its measurements of the stars, either one by one (tiresome) or based on some table of positions (requires some arcane knowledge). But that’s not easy. I hope that the small set of 53 stars mentioned above might help you a bit.

Good luck.