Valid filters for photometry?

Home Forums Variable Stars Valid filters for photometry?

Viewing 9 posts - 1 through 9 (of 9 total)
  • Author
    Posts
  • #574428
    Kevin Gurney
    Participant

    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

    #581504
    Jeremy Shears
    Participant

    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. 

    #581507
    Kevin Gurney
    Participant

    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

    #581509
    Andy Wilson
    Keymaster

    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

    #581510
    Robin Leadbeater
    Participant

    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

    #581511
    Andy Wilson
    Keymaster

    Hi Robin,

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

    Cheers,
    Andy

    #581512
    Paul Leyland
    Participant

    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.

    #581513
    Paul Leyland
    Participant

    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?

    #581514
    Kevin Gurney
    Participant

    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

Viewing 9 posts - 1 through 9 (of 9 total)
  • You must be logged in to reply to this topic.