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Re: 26P/Grigg-Skjellerup + C/2007 W1 brightening trend.

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  • Juan Jose Gonzalez Suarez
    Dears Reinder, Michael, Alexandre and others, Taking into account the previous returns and the actual CCD photometry [ e.g.: 15.0 (T), Ken-ichi Kadota, Mar. 22
    Message 1 of 2 , Apr 6, 2008
      Dears Reinder, Michael, Alexandre and others,

      Taking into account the previous returns and the actual CCD photometry [ e.g.: 15.0 (T), Ken-ichi Kadota, Mar. 22 ], I was also skeptical about the recent m1=11.7-11.9 estimates for 26P ( Marco Goiato, Mar. 22 and Apr. 5 ). The splendid Michael's image ( Apr. 5 ) further reinforced the skepticism.

      So, when planning this night's observing session I was thinking in a diffuse comet in the 12.5-13.5 magnitude range, located in a crowded field of faint stars in Aquila. After midnight, I traveled to a good dark site in the Cantabrian Mountains ( background brightness in this session: 21.4 mag/arcsec**2 at the zenith, 21.0 at the comet area near the horizon
      ), and set up the telescope.

      Unexpectedly, the diffuse comet was relatively easy to find and clearly brighter than previously thought:

      26P/Grigg-Skjellerup:
      2008 Apr. 6.18 UT: m1=11.3, Dia.=2.8', DC=2, 20 cm SCT (100x) [ Nearby field stars checked in DSS. Motion checked during a 50-min period. Faint, diffuse outer coma, slightly enhanced through Swan Band filter. Limiting star magnitude near comet : 14.5 (Henden). Mountain location, very clear sky. Altitude: 28 deg ]
      ( Sierra del Aramo, alt. 920 m, Asturias, N. Spain ).


      Best regards and clear skies,


      J. J. Gonzalez

      P.S.: Regarding C/2007 W1 estimates, Maik wrote: " ... I hope JJ does not mind post his observation from the CometObs list here: 2008 Apr. 3.98 UT: m1=8.9, Dia.=10', DC=3, 10x50B ... ".
      The brightening trend continues. Data from this night's session: 2008 Apr. 6.11 UT: m1=8.6, Dia.=12', DC=3, 10x50B ).


      ------------------------------------------------


      Reinder Bouma wrote:

      > I checked this report, and found that at the reported time of this visual observation 26P was right on top of a magn. 11 star, which was surrounded by several fainter stars. This may have given the impression of a rather condensed comet, particularly in a moonlit sky, but a check with the DSS or any decent planetarium programm should have revealed the error.

      > Also a DC of 5 is rather suspect and should have activated the alarm bells; during previous returns this comet was always very diffuse to visual observers, and Michael's fine image confirms that this time around it has a very similar appearance.

      ------------------------------

      Michael Jäger wrote:

      > > on april 5 UT 2.50 26P was not brighter than 12m5
      > > on images i found a faint outer coma only 1-1,5'
      > >
      > > M.Jäger

      ----------------------------

      Alexandre Amorim wrote:

      > >> That's last reports from Brazil:
      > >>
      > >> 26P/Grigg-Skjelerup
      > >>
      > >> 2008 Mar.
      > >> 9.22 I[12.8 18L 360 Alexandre Amorim, Florianopolis, Brasil
      > >> 22.29 S 11.7: 3' 5 22L 160 Marco A.C. Goiato, Araçatuba, Brasil
    • Alan Hale
      Hi everyone, After several unsuccessful attempts over the past month, I finally got this comet visually this morning -- but it was a very faint, vague, and
      Message 2 of 2 , Apr 6, 2008
        Hi everyone,

        After several unsuccessful attempts over the past month, I finally got this
        comet visually this morning -- but it was a very faint, vague, and diffuse
        object, not much brighter than 14th magnitude. (The very rich star fields
        that the comet has been moving through haven't helped.) I followed it for
        close to an hour. I don't think I would have seen it had I not known exactly
        where to look, and to my eyes it is clearly fainter intrinsically then it
        was when I last observed it in 1987. (Perhaps the larger perihelion distance
        has kept the usual dramatic brightness increase that this comet normally
        undergoes around perihelion from being triggered?)

        I'll have more details when I post the "Countdown" announcement, hopefully
        later today.


        Sincerely,

        Alan
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