Friday, July 4, 2008

Comet C/2007 N3 (Lulin)

On 2008, July 3.03 we performed some follow-up of C/2007 N3 (Lulin), through the 0.3-m, f/6.9 reflector + SBIG St8 XME CCD of one of us (Gustavo Muler, Observatorio Nazaret, Lanzarote, Spain), while the comet was moving in Capricornus. Geometrical circumstances at the moment of the observation: airmass: 1.52, T-152 days, delta~ 2.0 AU, r~ 2.9 AU and phase angle~ 10 deg.

Comet Lulin show a nearly circular coma, about 30 arcsec in diameter, slightly elongated toward North-West. Photometrically the coma show a very uniform profile, a kind of "disk", of nearly uniform brightness; just the outermost ~ 5 or 10 arcsec being very faint compared to the central part. This outlooking reminds somehow the aspect of 17P/Holmes shortly after its 2007 outburst (however this doesn't mean necessarily that these two comets share the same behaviour: it's just a morphological evidence!).

This is a link to the false colors image:

The same image, treated with an azimuthal median subtraction algorithm:

and a 1/r theoretical coma profile:

show clearly the unusual photometric morphology of the coma.

The total magnitude turned out to be Ru~ 12,7. Since we operated unfiltered, in our case the afrho parameter (proxy of the dust abundance within the coma) determination has just to be considered an upper limit; anyway it turned out to be a fairly high value, close to ~ 1,500 cm.

The photometric profile appears rather flat:

We acknowledge the use of the C.A.R.A. algorithms for the image processing (developed by Martino Nicolini) and the afrho calculations (develped by Roberto Trabatti).

Gustavo Muler, Giovanni Sostero and Ernesto Guido

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