British Astronomical Association
Supporting amateur astronomers since 1890

Secondary menu

Main menu

Home Forums Variable Stars
Terms of use

Valid filters for photometry?

9 posts / 0 new
Last post
k.gurney's picture
Offline
Last seen: 5 days 9 hours ago
Joined: 08/01/2016 - 18:58
Valid filters for photometry?

I have just carried out my first foray into photomery with a CCD session on the eclispsing binary CW Cas. Being easily pleased, I was really happy with the resulting light curve (see my personal page). However, using what I had to hand, I used a luminance filter designed for imaging (which does IR and UV cut  as I understand it).

My question is whether these data are candidates for the BBA database? I intend to invest in a proper V-filter but was curious whether there is an option to include Lum-filtered data for now...

Kevin

Jeremy's picture
Offline
Last seen: 14 hours 47 min ago
Joined: 04/03/2014 - 22:00
Valid filters for photometry

I enjoyed seeing your light curve, Kevin.

You can submit the data as "Clear" filter (abbreviated to C).

For some purposes (like time series photometry of cataclysmic variables), C is perfectly acceptable (when you use a filter, you lose some of the light, so your signal to noise deteriorates). However, for many applications a filter is much preferred as it's easier to compare data from different observers. 

k.gurney's picture
Offline
Last seen: 5 days 9 hours ago
Joined: 08/01/2016 - 18:58
Many thanks Jeremy,

Many thanks Jeremy,

I see Richard Lee has a tutorial on  AstroImageJ which also details how to submit to BAA via output from  this package

Andy Wilson's picture
Offline
Last seen: 20 hours 13 min ago
Joined: 29/03/2014 - 16:05
Clear Filter V-band comparison stars

Kevin,

I will just a bit of clarification.

Yes, you can submit clear photometry, though you should probably use CV. This means clear filter (or unfiltered) using V-band comparison stars. The important point here is that while your own observation might be made with a clear filter, the comparison star magnitudes will have been made through a V filter, or at least you should try to obtain V filter magnitudes from the BAA or AAVSO charts.

The full list of filters can be seen near the bottom of the review observations page of the BAA Photometry Database. Note as far as possible we try to stay in-line with the AAVSO on filters and filter codes. This makes life easier when combining data from different databases.

https://britastro.org/photdb/data.php

If you have a spare slot in the filter wheel, it might also be worth trying truly unfiltered observations, as for some targets a slightly higher signal may be preferable to a luminance filter.

Best wishes,

Andy

BAA Photometry Database Manager

Robin Leadbeater's picture
Offline
Last seen: 8 hours 35 min ago
Joined: 05/03/2014 - 00:50
CR ?

Hi Andy,

With completely unfiltered CCD measurements (ie without cutting the IR) I vaguely remember something about CR (ie using R comparison star magnitudes) correlating better because of the extended response. Do you know if this is the case ?

Cheers

Robin

Andy Wilson's picture
Offline
Last seen: 20 hours 13 min ago
Joined: 29/03/2014 - 16:05
CR ?

Hi Robin,

It is possible and I must admit I have not checked. It would be a useful and interesting experiment.

Cheers,
Andy

Xilman's picture
Offline
Last seen: 11 hours 29 min ago
Joined: 24/03/2018 - 15:17
Photometry experiment.

I can see a few images of Landolt fields being taken when I'm next back in La Palma.  Let's see, I've RGB&Luminance filters, pretty pictures for the taking of (and which I've used precisely once, on M57, just to see whether they work); Johnson-V which is by far the most used for VS work; Sloan g, r and i (only ever used the second for production work, though i was once used as an experiment to see whether it improved contrast of Jovian surface features).  A "H-alpha + continuum" is in there too, but it's never been used because I'm not interested in either visual work or in taking pretty pictures of H-II regions.  Two slots are empty --- one will remain that way and I'm tempted to get a Star Analyser SA200 to play with.

Any suggestions as to what other photometric filters may be worth purchasing, possibly part-funded by selling off the ones I don't use?

Xilman's picture
Offline
Last seen: 11 hours 29 min ago
Joined: 24/03/2018 - 15:17
unfiltered and comparisons

That is also my belief.  Unfiltered magnitudes also correlate very well indeed with Gaia-G magnitudes.  This should come as no great surprise ...

That's why I generally quote Gaia-G magnitudes for objects on unfiltered images I've taken.  Please note, these are NOT images taken for photometric analysis, for which I almost always use V or Sloan r filters.

k.gurney's picture
Offline
Last seen: 5 days 9 hours ago
Joined: 08/01/2016 - 18:58
CV designation

Hi Andy

OK, I'll go with CV for this one... (V-filter to follow :)

Tomorrow night should be clear here and I am keen to try a comparison on the same target with a mono (cooled) CMOS camera. I'll stick with Lum filter on this experiment  for a better comparison.

Kevin