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Yet another 103P lightcurve analysis

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  • chergen
    I have posted my recent analysis of the brightness behavior of 103P/Hartley 2 at the current apparition as well as at its 1991 and 1997 returns. This analysis
    Message 1 of 2 , Sep 22, 2010
      I have posted my recent analysis of the brightness behavior of 103P/Hartley 2 at the current apparition as well as at its 1991 and 1997 returns. This analysis is based on a subset of the visual and CCD observations from 1991 and 1997, a subset of CCD data from the current return, and a all of the visual data from the current return.

      Most visual and pretty much all recent CCD magnitude estimates show the comet fainter (up to 2 magnitudes) than it was in 1997. As alluded to by Ignacio Ferrin in an earlier post, many observers may be missing a large fraction of the coma when making their measurements. This comet is very large and very diffuse. My recent images taken with the LightBuckets 8" astrograph show a coma up to ~25' across. Even that may be an underestimate. Of course, the dense Milky Way isn't helping matter either.

      Still after an August when visual estimates were falling ~2 magnitudes behind what was expected based on the '97 return, this month more observers (and my CCD data) has the comet just a tad fainter than the average from the '97 visual data.

      Based on the '97 visual data, 103P should reach magnitude +4.5 at its peak. Based on what we have seen so far, that might still be possible though a peak of +5.0 might be more realistic.

      I agree with those posters who have called for very wide-field images of the comet for photometry. I would add that filter photometry would be better than clear photometry.

      Anyway, you can read more of my analysis and see some actual lightcurve plots and images on my blog.
      http://transientsky.wordpress.com/2010/09/22/introducing-comet-hartley-2/

      BTW, let me know what you think. Getting accurate photometry for large comets, whether bright ones like Hale-Bopp or faint ones like 103P, is a complicated problem but one we should be able to solve. I do fear that more and more visual observers will not be able to get close to the true total magnitude of large diffuse comets due to ever increasing light pollution.

      As an additional note, please check out the new 103P page at the Cometary Science Center/International Comet Quarterly. We are slowly expanding this concept though finding the time and money has been slow. The goal is to archive not only all photometric observations but also all image data. Let us know what you think.

      http://www.csc.eps.harvard.edu/index.html

      - Carl
    • kaos@kommet.cz
      Hello Carl, thanks for nice analysis. This return of comet Hartley is definitively great event of this year for all comet observers and researchers. About
      Message 2 of 2 , Sep 23, 2010
        Hello Carl,

        thanks for nice analysis. This return of comet Hartley is definitively
        great event of this year for all comet observers and researchers.

        About actually magnitude evolution, my opinion is that its more caused by
        return geometry then by any photometric behaviour of this comet. The main
        reason why was comet 2 mag fainter at August and that it gained brightness
        back very fast could be that surface brightness of outter coma were lower
        background brightness. When outter coma "appears", magnitude grow very
        fast.

        For visual observing I can see many examples where observers choose a bad
        telescope for it observing. At mid September comet was at range of 10x50
        binocular, that means it should be estimated by binoculars at range 40 -
        80 mm objective diameter, while all larger instrumets usually giving too
        small FOV to catch most of coma, and outter coma is lost. I can see many
        estimates giving coma diameter ~4', that means many of visual estimations
        are just estimations of inner coma, not total comet magnitude.

        I suppose all observers using as large field of view as its possibile to
        catch most of this comet. About light pollution could help swan band
        filter, which "show how is the comet big".

        For observers who could use this filter, is a good try to use "modified"
        Morris method: comparing defocused unfiltered stars with remembered image
        of litle defocused filtered comet (comet lose about 5% luminiscence at gas
        and most of dust) ... while comet Hartley seems to be mailny gas comet.

        Best regards,
        Jakub Cerny
        Czech Republic

        > I have posted my recent analysis of the brightness behavior of
        > 103P/Hartley 2 at the current apparition as well as at its 1991 and 1997
        > returns. This analysis is based on a subset of the visual and CCD
        > observations from 1991 and 1997, a subset of CCD data from the current
        > return, and a all of the visual data from the current return.
        >
        > Most visual and pretty much all recent CCD magnitude estimates show the
        > comet fainter (up to 2 magnitudes) than it was in 1997. As alluded to by
        > Ignacio Ferrin in an earlier post, many observers may be missing a large
        > fraction of the coma when making their measurements. This comet is very
        > large and very diffuse. My recent images taken with the LightBuckets 8"
        > astrograph show a coma up to ~25' across. Even that may be an
        > underestimate. Of course, the dense Milky Way isn't helping matter either.
        >
        > Still after an August when visual estimates were falling ~2 magnitudes
        > behind what was expected based on the '97 return, this month more
        > observers (and my CCD data) has the comet just a tad fainter than the
        > average from the '97 visual data.
        >
        > Based on the '97 visual data, 103P should reach magnitude +4.5 at its
        > peak. Based on what we have seen so far, that might still be possible
        > though a peak of +5.0 might be more realistic.
        >
        > I agree with those posters who have called for very wide-field images of
        > the comet for photometry. I would add that filter photometry would be
        > better than clear photometry.
        >
        > Anyway, you can read more of my analysis and see some actual lightcurve
        > plots and images on my blog.
        > http://transientsky.wordpress.com/2010/09/22/introducing-comet-hartley-2/
        >
        > BTW, let me know what you think. Getting accurate photometry for large
        > comets, whether bright ones like Hale-Bopp or faint ones like 103P, is a
        > complicated problem but one we should be able to solve. I do fear that
        > more and more visual observers will not be able to get close to the true
        > total magnitude of large diffuse comets due to ever increasing light
        > pollution.
        >
        > As an additional note, please check out the new 103P page at the Cometary
        > Science Center/International Comet Quarterly. We are slowly expanding
        > this concept though finding the time and money has been slow. The goal is
        > to archive not only all photometric observations but also all image data.
        > Let us know what you think.
        >
        > http://www.csc.eps.harvard.edu/index.html
        >
        > - Carl
        >
        >
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