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Re: Comet ISON brightness trend

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  • cometas71
    The calculations of rate production of dust of this web page observadores-cometas of astrophysicist Mark Kidger are erroneous , the last observations of SWIFT
    Message 1 of 11 , May 8, 2013
      The calculations of rate production of dust of this web page observadores-cometas of astrophysicist Mark Kidger are erroneous , the last observations of SWIFT :

      http://www.nasa.gov/mission_pages/swift/bursts/ison.html

      The Jan. 30 UVOT observations reveal that ISON was shedding about 112,000 pounds (51,000 kg) of dust every minute , or 850 kg/sec. ,in R=4.9 au. , the next link indicate Q dust ~ 20 kg/sec. in R=5.0 :

      http://www.observadores-cometas.com/cometas/2012s1/qdust.html


      ¡ the calculation error is greatly exaggerated +830 kg/sec ¡ ...


      J.P.Navarro Pina



      --- In comets-ml@yahoogroups.com, "Richard Miles" <rmiles.btee@...> wrote:
      >
      > Thanks David.
      > It strikes me as unusual that a comet's brightness has a marked phase angle
      > dependency, which C/2012 S1 appears to. Indeed, the standard formulae for
      > comet brightness at low phase angles (<20deg) do not include phase angle as
      > a dependent parameter - just Delta and Heliocentric Radius (rh) are
      > included.
      >
      > So is this comet especially unusual and therefore interesting?
      >
      > In addition to the lightcurve at:
      > http://www.astrosurf.com/cometas-obs/C2012S1/10x10.gif
      >
      > There's a good set of plots at the Observadores-cometas webpage:
      > http://www.observadores-cometas.com/cometas/2012s1/2012s1.html
      >
      > If we try and understand the underlying physical basis for the observed
      > behaviour, the usual fine (micron-size) dust in the coma would not be able
      > to exhibit the observed brightness surge towards low phase angle witnessed
      > in January at 5 AU: most of the mass in the coma would need to be in the
      > form of comparatively large particles (>10 micron say) to show phase angle
      > effects. Without jet activity, larger particles are difficult to lift off of
      > the surface of the nucleus through relatively uniform outgassing of
      > volatiles and so while the comet is beyond 3 AU, the coma may be starved of
      > fresh particles. Furthermore, large particles are also subject to much much
      > less acceleration by light pressure and so the tail of the comet fails to
      > develop in any marked fashion (as we have seen). Closer-in to the Sun (say
      > <2.0 AU - from September onwards), sublimation of H2O ice will take over and
      > drive the activity and then all bets are off as to what the outcome will be!
      >
      > Richard Miles
      > BAA
      >
      > ----- Original Message -----
      > From: "David Seargent" <seargent@...>
      > To: <comets-ml@yahoogroups.com>
      > Sent: Wednesday, May 08, 2013 12:40 AM
      > Subject: RE: [comets-ml] Re: Comet ISON brightness trend
      >
      >
      > > Hi Richard and all,
      > > Maybe activity is bubbling away at a leval just sufficient to replace dust
      > > being lost to the tail with newly released particles. If the coma remains
      > > in a steady state in this way, the value of n should be close to 2.
      > > Presumably, dust will be lost to the coma more rapidly as the comet draws
      > > closer to the Sun, so if activity does not pick up, the value of n will
      > > become less than 2. More likely, water-ice sublimation will soon start to
      > > dominate and n should increase to between 3 and 4 ... at least, that is my
      > > guess at the moment!
      > > Cheers,
      > > David
      > >
      > >
      > >
      > >
      > > David et al.,
      > >
      > > Faustino Garcia has posted a nice 'Observadores-cometas' lightcurve for a
      > > 10" photometric aperture on Facebook covering this entire apparition. See:
      > >
      > > https://www.facebook.com/home.php?clk_loc=5#!/photo.php?fbid=601192049892872&set=pcb.601192306559513&type=1&theater
      > >
      > > Studying this lightcurve, it appears almost to behave as a simple
      > > reflection body changing in brightness as 5log(delta)+5log(rh) on which is
      > > superimposed an opposition effect / phase angle brightening component
      > > amounting to ~0.6 mag.
      > >
      > > This is probably just a chance coincidence but the brightness surge is
      > > almost exactly centred on the time of minimum phase angle (1.8 deg on 2013
      > > Jan 11). However, it does rather fit with an object that has lost much of
      > > its most volatile species (CO and N2). There may be relatively large
      > > aggregates of material close to the nucleus causing this brightness trend
      > > and which need more heating before evolving further. As it is now
      > > approaching low solar elongations, we'll have to await the next apparition
      > > before we see what happens next!
      > >
      > > Richard Miles
      > > BAA
      > >
      > > --- In comets-ml@yahoogroups.com, David Seargent <seargent@> wrote:
      > >>
      > >>
      > >> Hi all,
      > >>
      > >> I recall seeing an article about the past orbit of this comet, estimating
      > >> that there is a small chance that it passed perihelion not far inside
      > >> Jupiter's orbit millions of years ago (although the greater probability
      > >> is that its earlier perihelion lay beyond the planetary system). IF the
      > >> smaller q is correct, it is likely that the comet showed some activity
      > >> then and that much of the volatile coating responsible for the activity
      > >> of new comets while far from the Sun was evaporated. During its present
      > >> return, the remaining volatile "frosting" may already have evaporated
      > >> (giving rise to its early activity) and this might be why the brightness
      > >> development has apparently stalled. On this view, the comet may start
      > >> brightening more rapidly again as water ice begins to sublimate within
      > >> 2.5 - 3.0 AU of the Sun. Will be interesting to see what happens as the
      > >> comet comes closer.
      > >>
      > >> David
      > >>
      > >>
      > >>
      > >>
      > >> [Non-text portions of this message have been removed]
      > >>
      > >
      > >
      > >
      > >
      > >
      > > [Non-text portions of this message have been removed]
      > >
      > >
      > >
      > > ------------------------------------
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      >
    • terryjlovejoy
      I ve noticed some brighter visual estimates of this comet around mag 13, which suggests an intrinsic brightness somewhere around 5-6. I hope this holds as
      Message 2 of 11 , May 17, 2013
        I've noticed some brighter visual estimates of this comet around mag 13, which suggests an intrinsic brightness somewhere around 5-6. I hope this holds as this suggests an object like Comet Seki-Lines but with better orbital geometry relative to the earth.

        Terry
      • cnj999
        Terry - Where are you finding these bright obs? I cannot find any estimates that are anywhere near magnitude 13. Could you enlighten me? If true, this is a
        Message 3 of 11 , May 17, 2013
          Terry - Where are you finding these bright obs? I cannot find any
          estimates that are anywhere near magnitude 13. Could you enlighten me? If true,
          this is a dramatic change from the photometric data trend of the past two
          months and a bit difficult to explain..

          J.Bortle


          In a message dated 5/17/2013 11:39:39 P.M. Eastern Daylight Time,
          terryjlovejoy@... writes:




          I've noticed some brighter visual estimates of this comet around mag 13,
          which suggests an intrinsic brightness somewhere around 5-6. I hope this
          holds as this suggests an object like Comet Seki-Lines but with better orbital
          geometry relative to the earth.

          Terry






          [Non-text portions of this message have been removed]
        • terryjlovejoy
          Oh my mistake I was looking at observations of C/2010 S1 not C/2012 S1...Doh! There are just too many comets....
          Message 4 of 11 , May 18, 2013
            Oh my mistake I was looking at observations of C/2010 S1 not C/2012 S1...Doh! There are just too many comets....

            --- In comets-ml@yahoogroups.com, jbortle@... wrote:
            >
            > Terry - Where are you finding these bright obs? I cannot find any
            > estimates that are anywhere near magnitude 13. Could you enlighten me? If true,
            > this is a dramatic change from the photometric data trend of the past two
            > months and a bit difficult to explain..
            >
            > J.Bortle
            >
            >
            > In a message dated 5/17/2013 11:39:39 P.M. Eastern Daylight Time,
            > terryjlovejoy@... writes:
            >
            >
            >
            >
            > I've noticed some brighter visual estimates of this comet around mag 13,
            > which suggests an intrinsic brightness somewhere around 5-6. I hope this
            > holds as this suggests an object like Comet Seki-Lines but with better orbital
            > geometry relative to the earth.
            >
            > Terry
            >
            >
            >
            >
            >
            >
            > [Non-text portions of this message have been removed]
            >
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