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Re: [vsx-dis] Suitable filters to use

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  • arne
    ... Hi David, NSV 10242 is an M-star, so very red. The tricolor G filter can normally be used for obtaining photometry that is very similar to what would be
    Message 1 of 5 , Jun 10, 2013
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      On 6/9/13 9:07 AM, David Kennedy wrote:
      >
      >
      > Hello everyone,
      > I’m a new member to the group, joining after noticing a possible variable star
      > in my CCD images of the nebula NGC6559. Through the VSX website I’ve found
      > out the star is a suspected variable listed as NSV 10242. I’ve made
      > observations of the star on 3 nights over the past 3.5 weeks and using MaxIm DL
      > have measured that it’s decreasing in brightness. However, I’ve been
      > collecting data using the filters I use for imaging (LRGB and Ha Astronomik
      > filters) and I would like to know if useful photometric data can been gained
      > with these or do I need to use different filters instead? Can anyone help?
      > Thanks,
      > David Kennedy
      >
      Hi David,
      NSV 10242 is an M-star, so very red. The tricolor G filter can normally be used
      for obtaining photometry that is very similar to what would be obtained using a
      true photometric Johnson V filter. However, my one concern is that some
      tricolor filters tend to have "red leaks"; that is, they permit some red light
      in the 800-1000nm range to pass through the filter. With an extreme red star
      like this one (16th magnitude at V/550nm, but 3rd magnitude at K/2200nm), any
      kind of an out-of-bandpass transmission will screw up the results. So I'd see
      if the results come out about 16th magnitude; if they are, say, 10th magnitude
      instead, then you may have such a leak.

      This is only true with the red variables, of course. Stars like eclipsing
      binaries, cataclysmic variables, or RR Lyr pulsators, can be measured using the
      tricolor filters and can be compared favorably with the standard photometric
      filters.
      Arne
    • Patrick Wils
      Hi David, LRGB filters are difficult to transform to the standard photometric system, especially for red stars such as this one.  It would be better to use
      Message 2 of 5 , Jun 10, 2013
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        Hi David,


        LRGB filters are difficult to transform to the standard photometric system, especially for red stars such as this one.  It would be better to use e.g. Johnson-Cousins filters.

        As this forum has been inactive and most questions are dealt with on one of the AAVSO forums <http://www.aavso.org/forum>, I suggest to ask your questions there.  There are many more experienced photometrists available to give you more complete advice.


        Patrick

        ________________________________
        From: David Kennedy <dken@...>
        To: vsx-dis@yahoogroups.com
        Sent: Sunday, June 9, 2013 3:07 PM
        Subject: [vsx-dis] Suitable filters to use

        Hello everyone,

        I’m a new member to the group, joining after noticing a possible variable
        star in my CCD images of the nebula NGC6559.  Through the VSX website I’ve
        found out the star is a suspected variable listed as NSV 10242.  I’ve made
        observations of the star on 3 nights over the past 3.5 weeks and using MaxIm DL
        have measured that it’s decreasing in brightness.  However, I’ve been
        collecting data using the filters I use for imaging (LRGB  and Ha
        Astronomik filters) and I would like to know if useful photometric data can been
        gained with these or do I need to use different filters instead?  Can
        anyone help?

        Thanks,

        David Kennedy
      • David Kennedy
        Hi everyone, thank you for replying to my questions. Most of my data for NSV 10242 is with a Ha 12nm astronomik filter, with blue or green filters the star
        Message 3 of 5 , Jun 12, 2013
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          Hi everyone,
           
          thank you  for replying to my questions.  Most of my data for NSV 10242 is with a Ha 12nm astronomik filter, with blue or green filters the star is hardly visible. For an extreme red star which photometric filter would be most useful for making observations?.
           
          Thanks,
           
          David
           
           
           
           
          Sent: Tuesday, June 11, 2013 6:36 AM
          Subject: Re: [vsx-dis] Suitable filters to use
           
           

          Hi David,

          LRGB filters are difficult to transform to the standard photometric system, especially for red stars such as this one.  It would be better to use e.g. Johnson-Cousins filters.

          As this forum has been inactive and most questions are dealt with on one of the AAVSO forums <http://www.aavso.org/forum>, I suggest to ask your questions there.  There are many more experienced photometrists available to give you more complete advice.

          Patrick

          ________________________________
          From: David Kennedy <mailto:dken%40live.com.au>
          To: mailto:vsx-dis%40yahoogroups.com
          Sent: Sunday, June 9, 2013 3:07 PM
          Subject: [vsx-dis] Suitable filters to use

          Hello everyone,

          I’m a new member to the group, joining after noticing a possible variable
          star in my CCD images of the nebula NGC6559.  Through the VSX website I’ve
          found out the star is a suspected variable listed as NSV 10242.  I’ve made
          observations of the star on 3 nights over the past 3.5 weeks and using MaxIm DL
          have measured that it’s decreasing in brightness.  However, I’ve been
          collecting data using the filters I use for imaging (LRGB  and Ha
          Astronomik filters) and I would like to know if useful photometric data can been
          gained with these or do I need to use different filters instead?  Can
          anyone help?

          Thanks,

          David Kennedy

        • arne
          Hi David, Johnson V is almost always your first choice for photometric filters, as the next star you observe may be a different color and V is very generic.
          Message 4 of 5 , Jun 12, 2013
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            Hi David,
            Johnson V is almost always your first choice for photometric filters, as the
            next star you observe may be a different color and V is very generic. You may
            have to expose longer for your current red star, but you do that for deep-sky
            images anyway and scientific photometry always takes about the same amount of
            on-sky time. If you only want to image very red stars, your best filter is
            Cousins Ic, which is a very red filter (redder than Halpha).
            Arne

            On 6/12/13 11:52 AM, David Kennedy wrote:
            >
            >
            > Hi everyone,
            > thank you for replying to my questions. Most of my data for NSV 10242 is with
            > a Ha 12nm astronomik filter, with blue or green filters the star is hardly
            > visible. For an extreme red star which photometric filter would be most useful
            > for making observations?.
            > Thanks,
            > David
            > *From:* Patrick Wils <mailto:patrickwils@...>
            > *Sent:* Tuesday, June 11, 2013 6:36 AM
            > *To:* vsx-dis@yahoogroups.com <mailto:vsx-dis@yahoogroups.com>
            > *Subject:* Re: [vsx-dis] Suitable filters to use
            >
            > Hi David,
            >
            > LRGB filters are difficult to transform to the standard photometric system,
            > especially for red stars such as this one. It would be better to use e.g.
            > Johnson-Cousins filters.
            >
            > As this forum has been inactive and most questions are dealt with on one of the
            > AAVSO forums <http://www.aavso.org/forum>, I suggest to ask your questions
            > there. There are many more experienced photometrists available to give you more
            > complete advice.
            >
            > Patrick
            >
            > ________________________________
            > From: David Kennedy <mailto:dken%40live.com.au>
            > To: mailto:vsx-dis%40yahoogroups.com
            > Sent: Sunday, June 9, 2013 3:07 PM
            > Subject: [vsx-dis] Suitable filters to use
            >
            > Hello everyone,
            >
            > I’m a new member to the group, joining after noticing a possible variable
            > star in my CCD images of the nebula NGC6559. Through the VSX website I’ve
            > found out the star is a suspected variable listed as NSV 10242. I’ve made
            > observations of the star on 3 nights over the past 3.5 weeks and using MaxIm DL
            > have measured that it’s decreasing in brightness. However, I’ve been
            > collecting data using the filters I use for imaging (LRGB and Ha
            > Astronomik filters) and I would like to know if useful photometric data can been
            > gained with these or do I need to use different filters instead? Can
            > anyone help?
            >
            > Thanks,
            >
            > David Kennedy
            >
            >
            >
            >
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