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.
The details of the event as shown in Occult Watcher
Below is the
Occult Watcher Cloud Event Page
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
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
Peter's light curve showing that the target star (blue) drops below the comparison star (yellow) during the occultation.
Dave's light curve showing that the target star (blue) drops below the comparison star (black) during the occultation.