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:
http://tinyurl.com/5n8f96
The same image, treated with an azimuthal median subtraction algorithm:
http://tinyurl.com/6h39n8
and a 1/r theoretical coma profile:
http://tinyurl.com/5otnkt
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:
http://tinyurl.com/6af3r5
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
http://www.cara-project.org/index.php
No comments:
Post a Comment