Differences in Photometric Filter sets.

[Mr Ian David Sharp]

Hi all,

I’ve just completed the installation of a new C11-based imaging and photometry rig at the PixelSkies facility in Southern Spain. Up to recently, I had a 104mm APO in the same place, but now I’ve upgraded to a lovely C11 with 0.7x reducer. The CCD is an SX TRIUS 694 Pro which is excellent for both imaging and photometry.

My kit here in the UK is almost identical with a C9.25 (both are Edge HD) with the 0.7x reducer and the same CCD.

However, I have Baader Bessel Photometric R, V and B filters in Spain, and here I have Astrodon Rc and Johnson B and a Bessel V from Custom Scientific.

I am attaching my recent photometric results for SN 2023ixf in M101 where I have many nights of data in R, V and B from here in the UK (round points) and I’ve just started to add results from the C11 in Spain (square points).

I would add that I have taken *great* care with the data capture and the photometry. I have excellent S/N and all in the linear region of the CCD. I use the same set of AAVSO comparison stars and the calibration is excellent. Also the object has been very high in the sky with very low airmass throughout. I’m getting typical uncertainties of around 0.003 mags and I have been taking 5 images for each filter and averaging. The variation across the 5 is tiny.

Can I ask if the differences I’m seeing here in the magnitudes due to the different manufacturer of the photometric filters are typical? I guess that’s what the AAVSO Transformation process is designed to deal with? Is there anything else I should be doing?

Thanks
Ian.

Attachments:

1. 

   SN-Filters.jpg
   

[Dr Paul Leyland]

Ian: it’s hard to tell.

Perhaps a longer series of measurements at a very wide range of magnitudes (from 7 to 17 perhaps) of a standard field (likely a Landolt field) may be mre informative.

A plot of differences between the two filter sets against magnitude may be informative too, as it will give a much larger y scale and accentuate the readings.

Paul

[Mr Ian David Sharp]

Dr Paul Leyland wrote:

Perhaps a longer series of measurements at a very wide range of magnitudes (from 7 to 17 perhaps) of a standard field (likely a Landolt field) may be mre informative.

Thanks Paul,

I’ve been reading about the Landolt fields in the AAVSO Transformation process. I think I’ll try and give it a shot…

Cheers
Ian.

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