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Suitable filters to use

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  • David Kennedy
    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
    Message 1 of 5 , Jun 9, 2013
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      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, 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 2 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 3 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 4 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 5 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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