Thursday, May 8, 2008

Comet C/2008 J2 (BESHORE)

IAU Circular nr. 8941, issued on 2008, May 7, announces the discovery by E. Beshore of a new comet named C/2008 J2 (BESHORE).

It was discovered with the 1.5-m reflector of the "Mount Lemmon Sky Survey" on 2008, May 6.44, and it has been described by the discoverer as having a bright condensed coma, diameter of 20 arcsec. Preliminary orbital elements from the Minor Planet Center show that this object moves along a parabolic orbit (i= 16.6 deg, q= 1.1 AU); perihelion is expected to occour on 2008 October 7th. According the current ephemerids, the new comet "Beshore" will reach approximately magnitude 8.5 at perihelion.

Soon after its posting in the M.P.C. NEO_Confirmation Page (around noon, April 6th) with the ID code "8JBD660", we wanted to get a close look at this relatively bright object, picked up just hours earlier. Unfortunately the weather conditions in our traditional observing site (Remanzacco Observatory, MPC code 473) were poor. So we decided to gave it a try from a new observatory (now under completion) that is operated by our astro club:

This new observing site is located about 20 Km East of Remanzacco, in the slopes of a nice mountain, named Mount Matajur. Since the Mount Matajur Observatory is 1340-m high, we hoped to skip at least some part of the haze that was affecting the plains where the Remanzacco observatory is located.

It was a wise decision, since while there, the sky suddently cleared up, so we were finally able to inaugurate our NEO/comets follow-up observing program from the recently "appointed" astrometric site MPC #B68!

When we located this relatively slow moving interloper in Ophiucus through a 0.2-m f/3 reflector + CCD, we initially considered it a star-like object (or at least, this was our very first impression looking at the single raw images that appeared on the PC monitor). However, when we carefully inspected the final stacking of 20 unfiltered exposures (60 seconds each) obtained on 2008, May 6.95, we immediately realized that this was not the case, since we noticed an extremely compact coma of almost uniform brightness about 20 arcsec in diameter, slightly elongated toward south-west:

The total magnitude m1 was measured to be R~14.

Afterwards, we decided to continue the study of this comet candidate (still listed in the NEO-Confirmation Page as object "8JBD660") with the instruments of the "Rent A Scope" network. So, on 2008, May 7.3 we connected with a 0.25-m f/3.4 reflector + CCD located near Mayhill (NM), where we initially collected 10 unfiltered exposures, 60-seconds each, that we stacked. Analyzing the result, we were able to confirme the existence of a coma nearly 25 arcsec in diameter elongated toward PA 240 deg, with a very flat photometric profile:

Filtered photometry performed soon afterwards (on 2008, May 7.37) through the same scope and a Cousins Red filter provided a total m1 magnitude of R~ 13.9, while a preliminary afrho calculation (proxy of the dust abundance within the coma) gave a value of nearly 450 +/- 80 cm; considering its current distance from the Sun, this seems to point toward an active comet.

by Giovanni Sostero & Ernesto Guido

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