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Update about C/2006 W3 and C/2006 P1

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  • gvnn64
    Hi all, on 2006, Nov. 30.11 we measured C/2006 W3 (Christensen): we found it at R~ 18.1 +/- 0.2 (0.45m rflector + CCD); this is a bit brighter compared to the
    Message 1 of 9 , Dec 1, 2006
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      Hi all,
      on 2006, Nov. 30.11 we measured C/2006 W3 (Christensen): we found it at
      R~ 18.1 +/- 0.2 (0.45m rflector + CCD); this is a bit brighter compared
      to the ephemerids (however we don't know how much of this is due to the
      different reference photometric bands, V and R). Anyway, the Afrho
      parameter is close to ~600 cm, a pretty high amount, if we consider
      that the comet is placed at almost 8 AU from the Sun! The coma appears
      condensed:
      http://tinyurl.com/ylj6y8

      About C/2006 P1 (McNaught): thanks to Robert McNaught and Michael
      Jaeger, we performed some preliminary calculation from their original
      images: the rough afrho plot, show a striking slope change around r~
      2.2 AU. This is interesting , since the professionals place around this
      distance the limit where water sublimations in cometary nuclei is
      supposed to became effective. Also considering all the uncertainties
      due to the different scopes, CCDs, and the approximation in the
      unfiltered magnitudes, the slope change in the graph seems to be pretty
      convincing:
      http://tinyurl.com/squ4x

      Cheers,
      Giovanni Sostero and Ernesto Guido (Remanzacco Obs., CARA)

      http://www.afamweb.com
      http://cara.uai.it
    • Robert McNaught
      ... This is an interesting result, but I want to make clear that with the systematic measurement of m1 from short exposures with the Uppsala Schmidt (not m2 or
      Message 2 of 9 , Dec 1, 2006
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        On Fri, 1 Dec 2006, gvnn64 wrote:

        > About C/2006 P1 (McNaught): thanks to Robert McNaught and Michael
        > Jaeger, we performed some preliminary calculation from their original
        > images: the rough afrho plot, show a striking slope change around r~
        > 2.2 AU. This is interesting , since the professionals place around this
        > distance the limit where water sublimations in cometary nuclei is
        > supposed to became effective. Also considering all the uncertainties
        > due to the different scopes, CCDs, and the approximation in the
        > unfiltered magnitudes, the slope change in the graph seems to be pretty
        > convincing:
        > http://tinyurl.com/squ4x

        This is an interesting result, but I want to make clear that with
        the systematic measurement of m1 from short exposures with the Uppsala
        Schmidt (not m2 or condensation as I've been at pains to point out) there
        was no evidence of any change in the slope of brightening between
        1.9<r<3.1AU. You will see from the photometric fit at

        http://msowww.anu.edu.au/~rmn/2006P1.htm

        that the residuals are small and the recent reported magnitudes are
        reasonably in line with an extrapolation of this fit as given in the
        ephemeris on the same page.

        However we are not talking of the same quantities here, but as the Uppsala
        measures are numerous and systematic, I would consider it a strong
        conclusion that the slope of *brightening* has not changed down to 1.9 AU
        and possibly beyond. I suspect that there could be a systematic effect in
        the derived Afrho values due to earlier points being from the Uppsala and
        the latter three from Michael, unless Michael had some images from the same
        dates as the Uppsala.

        I meant to comment on the brightening a couple of weeks ago but was
        overseas and not able to post.

        Cheers, Rob
      • gvnn64@libero.it
        Hi Robert, the data reduction method used is the same for both data sets. The difference, as you pointed out, is mainly in the equipment, and in the parameters
        Message 3 of 9 , Dec 1, 2006
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          Hi Robert,
          the data reduction method used is the same for both data sets. The difference, as you pointed out, is mainly in the equipment, and in the parameters considered (magnitudes Vs, afrho). If you, or any other observer, can provide some additional .FITS obtained during the last month, it should be easy to cross-check the results of the latter part of the curve, where the afrho rise is so obvious. Please, send me the material privately.
          Cheers,
          Giovanni


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        • gvnn64@libero.it
          P.S. I forgot to mention that Michael s data has been obtained on a number of nights, with a combination of two different CCD s and scopes. Giovanni ... Passa
          Message 4 of 9 , Dec 1, 2006
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            P.S. I forgot to mention that Michael's data has been obtained on a number of nights, with a combination of two different CCD's and scopes.
            Giovanni


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          • Robert Warren
            Hello everyone, Has anyone heard of any bright meteor over the SouthEastern Tennessee area over the past three days? I have not seen anything on any of the
            Message 5 of 9 , Dec 1, 2006
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              Hello everyone,

              Has anyone heard of any bright meteor over the SouthEastern Tennessee area
              over the past three days?

              I have not seen anything on any of the lists I belong to, nor have I heard
              anything on any of the national news boradcasts, just one local broadcast.

              Thankyou,

              Bob Warren

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            • Terry Lovejoy
              Thank you for posting, I notice that the last afrho values for P1 are close to double 2002 V1 at the same distance from the sun. I hope that trend continues
              Message 6 of 9 , Dec 2, 2006
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                Thank you for posting, I notice that the last afrho values for P1 are
                close to double 2002 V1 at the same distance from the sun. I hope that
                trend continues :). The big question being is whether the comet will
                display 'dynamically' new behaviour as it gets closer.

                Terry
              • gvnn64@libero.it
                Hi Robert and all, I obtained an additional observation from Antonio Milani. This further data point has been inserted on the graph I posted yesterday:
                Message 7 of 9 , Dec 2, 2006
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                  Hi Robert and all,
                  I obtained an additional observation from Antonio Milani. This further data point has been inserted on the graph I posted yesterday:
                  http://tinyurl.com/yz4lcx
                  The scope and CCD is different. The observer has reduced the data by himself. If we consider the respective error bars, and the fact that through an I filter the afrho must be higher than in R due to the solar continuum effect, then I think that the result speaks for itself...

                  So, why you don't have slope changes in your m1 trend? One possible reason is that your data stops before the point where on my graph the slope change becames obvious. Secondly, m1 and afrho's are really two different approaches: in the afrho we consider a fix apertures at the comet distance, so any measured variation is likely related with actual physical changes in the coma; on the other hand, m1 are by definition "total apertures" brightness measurements; this means that you are likely selecting different apertures with changing distances; in this way you put an additional variable in the framework, that complicates the physical interpretation of the observed behaviour. I think that one additional problem in your data tabulation, is due to the fact that you don't provide the aperture those m1 refers; as we know from previous exeperiences, different apertures can make a significant difference when you provide m1 values; without apertures details, m1 data is almost useless.

                  To make it short, I'm pretty confident that the afrho graph I posted is not affected by instrumental effects or similar biases, and that the reported changes in the lightcurve reflects an actual variation of the coma regime. Comparison with afrho data whit other quantities (m1 or whatever) is not straightforward, since these amounts are obtained with different assumptions. Anyway, further data is always wellcome...
                  Cheers,
                  Giovanni


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                • gvnn64@libero.it
                  Addendum: I insert in the plot also the Log (Afrho) values Vs. heliocentric distances (black data points): http://tinyurl.com/yhnko3 I think that this display
                  Message 8 of 9 , Dec 2, 2006
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                    Addendum: I insert in the plot also the Log (Afrho) values Vs. heliocentric distances (black data points):
                    http://tinyurl.com/yhnko3

                    I think that this display tell us something...
                    Cheers,
                    Giovanni


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                  • gvnn64@libero.it
                    Hi all, thanks to Mike Holloway, I inserted a further data point in the C/2006 P1 lightcurve. Expecially the last couple of observations (A. Milani and M.
                    Message 9 of 9 , Dec 4, 2006
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                      Hi all,
                      thanks to Mike Holloway, I inserted a further data point in the C/2006 P1 lightcurve. Expecially the last couple of observations (A. Milani and M. Hollowey) has been obtained under critical circumstances and through different passabands, so we must take these results just as an "order of magnitude". Anyway, these are the updated panels:
                      http://tinyurl.com/y8mvdd
                      http://tinyurl.com/ydgk24

                      Cheers,
                      Giovanni


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