Tuesday, May 10, 2011

New Comet: C/2011 H1 (Lemmon)

IAUC nr.9206, issued on 2011, May 05, announced the discovery of an apparently asteroidal object (discovery magnitude 19.7) by Alex R. Gibbs on CCD images taken on April 26.3 with the Mt. Lemmon 1.5-m reflector. Gibbs suspected that this object might show slight cometary appearance.

We performed some follow-up measurements of this object while it was still listed in the NEO-CP. Stacking of 8 unfiltered exposures, 300-sec each, obtained remotely on 2011, April 27.5 from the Tzec Maun Observatory (near Moorook, Australia) through a 0.15-m, f/7.3 refractor + CCD, shows that this object is slightly diffused: its FWHM is nearly twice compared to that of nearby field stars of similar brightness.

Initially the object was given the minor-planet designation 2011 GK_71 on MPEC 2011-H41 based on a series of one-night astrometry (Apr. 14) from Spacewatch (that shows little or no cometary appearance). Other observations obtained with the Steward Observatory Bok 2.3-m f/3 reflector (+ 90Prime CCD camera) during Apr. 29.256- 29.301 in 1".3 seeing, shows the object appears nearly stellar, but with a coma diameter of 5" and a tail 9" long in p.a. 111 deg.

The new comet has been designated C/2011 H1 (Lemmon).

Our confirming image (click for a bigger version):

MPEC 2011-J24 assignes the following preliminary parabolic orbital elements to comet C/2011 H1: T = 2006 Jan. 31.13; Peri. = 100.93; q = 6.91 AU; Incl. = 73.98; Node = 35.58

According to COCD webpage, this is the 36th comet for the Mt. Lemmon Survey.

UPDATE - May 22, 2011

According to IAUC 9209, the name associated with C/2011 H1 on IAUC 9206 is being abandoned, due to the belated identification of this comet:

COMET C/2002 VQ_94 = C/2011 H1 (LINEAR)

by Giovanni Sostero & Ernesto Guido

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