Analysis of Observations

Below are the results of the observations made on May 16th 2021 by Dave Gault and Peter Nosworthy. These were the first known detections of the suspected binary nature of (172379) 2002 YE25.

Below is the Occult Watcher Cloud Event Page.

Light Curves

Below are the light curves recorded from Kuriwa Observatory (Dave) and Hazelbrook Observatory (Peter) with the time scales aligned. This shows that the shadow reached Hazelbrook about 1.5 seconds before Kuriwa.

If the asteroid were a single, roughly spherical object, the shadow should have reached Kuriwa Observatory first as it is located to the east of Hazelbrook and the shadow was moving from east to west.

---

Sky Plane Chord Plots

The chords we plotted assuming a diamter of 5.7km for the asteroid. This resulted in the impossible plot (below) where the object is cleary too small to account for the occultations at both sites.

The chords were then plotted assuming two smaller objects of the same total cross sectional area as the single object. This can explain how occultations could be observed from both sites.

---

Excluding the 'Double Star' Hypothesis (Limiting Magnitude Analysis)

If the observations were the result of one body occulting two components of a double star, with the two observers each seeing the occultation of a different component star, it would require that one component of the double be brighter than Mv 11.75. This possibility can be excluded by confirming that the target star dropped below Mv 11.75 for both observers.

The asteroid was mag. 19.9, well below the limiting magnitude of both recordings. This means that the astroid makes no contribution to the recorded light. We used a dim comparison star in the field of view as a comparison to confirm that the limiting magnitudes of both recordings were below Mv 11.75. The target star dropped below the level of the comparison star in both recordings.

From this we conclude that a single body occulting a double star could not account for the observations.