Saturday, July 12, 2008

Comet 6P/d'Arrest update

We imaged again periodic comet 6P/d'Arrest on 2008, July 11.96, from the Remanzacco Observatory (click on the image for a bigger version):

Image processing show the possible presence of a tiny coma, nearly 20 arcsec in diameter. The crowded stellar field hampers a sure identification of this feature, however this faint "halo" moves with the proper motion of the comet; moreover, the FWHM of the comet appears to be significantly larger compared to that of neary field stars of similar brightness, and this seems to confirm the presence of a detectable coma. The brightness of the comet has been measured at about magnitude 15 (Ru). This is still somehow fainter compared to the ephemerides (that indicates instead a visual total magnitude m1 equal to about magnitude 14), however we do know that i) CCDs magnitudes are frequently fainter than visual magnitudes and ii) the lightcurve of 6P/d'Arrest is known to show a striking asymmetric lightcurve, with lower pre-perihelion brightness. The Afrho parameter is still rather low (about 16-cm for a radius of nearly 3,000 Km at the comet distance).

Updated ephemerides are available (as always) at the Minor Planet Center website.

Giovanni Sostero and Ernesto Guido

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