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2004 DN25 (fourth discovery made at Great Shefford)

Discovery field of 2004 DN25 on 22 Feb 2004.
All images binned 2x2, field 25'x25'
Inset 4'x3' magnified x2 to show movement of 2004 CK
3 and 2004 DN25.
Main image and frame 1 of inset: 22:05-22:28 UT 22 Feb, 15 mins total exposure
Frame 2: 22:29-22:51 UT 22 Feb, 15 mins total exposure
Frame 3: 23:46-00:01 UT 22/23 Feb, 10 mins total exposure
Frame 4: 01:45-02:01 UT 23 Feb, 10 mins total exposure, clouding over
Note there are a number of internal reflections from the bright stars in the image (largest is above right side of inset box)

On the morning of Saturday 21st Feb 2004 we received an e-mail request from Michel Ory (Vicques, Switzerland, code 185) to help follow up two of his recent discoveries (2004 CJ3 and 2004 CK3) because bad weather was hampering any further observations by him and the full moon was approaching.

The two main belt minor planets were about 2 apart in Cancer and fairly faint, 2004 CJ3 listed as mag +20.7 and 2004 CK3 at +20.0.

The next night was clear at Great Shefford and the minor planets were well placed, 2004 CJ3  nearly in the centre of M44 Praesepe and 2004 CK3 very close to the naked eye star delta Cnc flanking M44 to the south. During the evening separate runs of 30 minutes total exposure were made on each object and both minor planets were recorded. The astrometry was sent off to the Minor Planet Center (MPC) and to Michel.

Both fields recorded a number of other minor planets, with seven moving objects being detected on the 2004 CK3 images. A quick comparison with the MPC's Minor Planet Checker identified all but one of the objects.

The missing one was about mag +20.0 and just 45" south of the target 2004 CK3 when first imaged and approached to within 30" just after midnight on the 23rd Feb!

This unidentified object was given the temporary designation GS42MB and a further two runs were completed during the course of the next few hours so that as good a prediction as possible could be made to find it the next clear night. The astrometry was sent off to the MPC just after midnight.

Fortunately the next night (23rd Feb 2004) was clear and both 2004 CK3 and GS42MB were recorded again (still in the same field of view) and astrometry for both was sent off to the MPC. Almost immediately an e-mail came back from the MPC indicating that GS42MB had been given the preliminary designation 2004 DN25 and that its discovery had been credited to Great Shefford!

As Tim Spahr later commented "serendipity at its best".

Update May 2005

During routine minor planet searching Michel Ory picked up 2004 DN25 on 27 and 28 May 2005 at its next apparition and was assigned a new ID of 2005 KW8. By the next day these two positions were the key for the Minor Planet Center to be able to link a one night stand from LINEAR on 14 May 2005 and the Spacewatch survey on 30 April 2005 to the same object. This allowed identification with the 2004 DN25 positions from 2004 and then to link it to one night stands in Aug 2001 from both Cerro Tololo and NEAT. With 3 oppositions and an uncertainty parameter of 4, it should be picked up easily at subsequent oppositions.

When Michel recovered it the ephemeris uncertainty was about 2, making direct recovery of 2004 DN25 a difficult task with small field telescopes, well done Michel!

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