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RE: [sohohunter] Comet Lulin (invisible) in LASCO

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  • Matson, Robert D.
    Hi Karl, I m having no trouble seeing stars as dim as magnitude +9 in C2 in the 11/26 images: HD 143785 +7.31 HD 144273 +7.54 HD 143956 +7.80 HD 143616
    Message 1 of 5 , Dec 4, 2008
      Hi Karl,

      I'm having no trouble seeing stars as dim as magnitude +9
      in C2 in the 11/26 images:

      HD 143785 +7.31
      HD 144273 +7.54
      HD 143956 +7.80
      HD 143616 +8.28
      HD 143899 +8.29
      HD 144689 +8.93
      HD 143599 +9.36

      The last one surprised me a bit since it actually looks brighter
      than some of the considerably brighter stars above it in the list.
      I started to question whether it was actually a star, or if in
      fact Lulin was masquerading as a star close to where HD 143599
      should be. But no, the motion was consistent with all the other
      stars, so it was indeed HD 143599. I concluded it must be a very
      cool star (CCDs are red-sensitive), and indeed looking it up I
      found that its color index is +1.486 -- very red. No sign of
      Lulin to this limiting magnitude.

      --Rob
    • karlbattams
      Hi Rob, Thanks for taking a detailed look at this. It doesn t surprise me that red stars are showing up unusually bright in C2, given the bandpass of its
      Message 2 of 5 , Dec 5, 2008
        Hi Rob,

        Thanks for taking a detailed look at this. It doesn't surprise me
        that red stars are showing up unusually bright in C2, given the
        bandpass of its orange filter. Your point about the motion of Lulin
        being so similar to that of the stars is a very good one -- that makes
        it much trickier. I should probably have added the disclaimer to my
        earlier emails that my ephemeris was not pixel-accurate, but it should
        certainly have been in the ballpark.

        I used a few of our 'favorite' LASCO processing technique on the
        images to enhance them and try and find something, but like you I
        couldn't see anything at all that looked like it might be Lulin.

        So either it isn't m7 (or anything close to that), or it's not a very
        'red' comet (because as we know, LASCO C2 strongly favors the sodium
        emission lines).

        It would have been nice to see Lulin, but sometimes negative reports
        can be just as useful...

        Regards,
        ~~Karl

        --- In sohohunter@yahoogroups.com, "Matson, Robert D." <matsonr@...>
        wrote:
        >
        > Hi Karl,
        >
        > I'm having no trouble seeing stars as dim as magnitude +9
        > in C2 in the 11/26 images:
        >
        > HD 143785 +7.31
        > HD 144273 +7.54
        > HD 143956 +7.80
        > HD 143616 +8.28
        > HD 143899 +8.29
        > HD 144689 +8.93
        > HD 143599 +9.36
        >
        > The last one surprised me a bit since it actually looks brighter
        > than some of the considerably brighter stars above it in the list.
        > I started to question whether it was actually a star, or if in
        > fact Lulin was masquerading as a star close to where HD 143599
        > should be. But no, the motion was consistent with all the other
        > stars, so it was indeed HD 143599. I concluded it must be a very
        > cool star (CCDs are red-sensitive), and indeed looking it up I
        > found that its color index is +1.486 -- very red. No sign of
        > Lulin to this limiting magnitude.
        >
        > --Rob
        >
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