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Two observations were recorded by Chris Wyatt using visual and Steve Quirk using video.
View the updated prediction.
Observers:
1 S Quirk,Mudgee, NSW, AU
2 C Wyatt,Walcha, NSW, AU
3(M) J Broughton,Tyagarah, QLD , AU
4(M) J Broughton,Reedy Crreek, QLD , AU
5(P) Prediction 17 Sept
Discussion:
The circle above is plotted at the expected 123 km diameter of Johanna. These two chords are displaced by almost a minute. We seem to have either an observation error or a very unusual object.
Geneva Observatory has a note for 127 Johanna that says "Binaire à petite éclipse ?" Binary small eclipse? So do we in fact have a binary asteroid with each observer having seen one of the two components ?
Probably not. The speed of the shadow on earth surface is predicted to be about 16 km/sec (see Prediction above). A 60 sec offset for binary objects would imply a separation of about 964 km and the similarity of the chord times would imply two fairly equal sized bodies. If this were a binary object at these separations then the orbit time would be much longer than the published figures by at least 1 magnitude. Again this has not been observed before or implied in any of the literature found by web search.
Johanna has been observed for over 130 years now and its parameters are such that a prediction error of 60 seconds is very unlikely. The predicted error was +/-8 seconds.
There are 4 previous occultation events for Johanna with positive results in our archives and none of them report any unuusal object effects. One of the others was just back in June when Steve observed the same MP from the same site.
The best one (2008 February 08, Jones and Lyzenga) with two chords gave an ellipse measuring 133 by 96 km.
If an ellipse of this size is selected and the time for Chris's observation is adjusted by 59 seconds then a good fit to the previous data is obtained in the plot below.
Observational Data:
Observation details for MP (127) Johanna By Star TYC 7411-06092-1 On 2008-09-29 at 11:20:45.0 _______________________________ Observer Christopher G Wyatt Location Walcha, NSW Longitude +151:33:13.7 Latitude -31:00:23.3 Altitude 1168 m Datum WGS84 Telescope SCT including Cass and Mak Aperture 20 cm Seeing Slight flickering Clear Timing Tape Recorder + time signal Visual, no PE applied Disappearance 11:19:43.07 Reappearance 11:19:49.76 Comments: There was a gusty breeze blowing at times, from the SE. The skies were quite clear though, the observation was good! I'm so happy to have bagged my first! All times are in UT, and times were taken from analysing through "Audacity". _______________________________ Observer Steve Quirk Location Mudgee Longitude +149:39:45.6 Latitude -32:27:21.3 Altitude 508 m Datum Telescope Newtonian Aperture 32 cm Seeing Slight flickering Clear Timing GPS - time inserted Video with frame analysis Disappearance 11:20:29.57 Reappearance 11:20:36.52 Comments: _______________________________ Observer J Broughton Location Tyagarah,Reedy Creek, QLD 4227, Australia Longitude +153:32:8.5 Latitude -28:35:39.5 Altitude 10 m Datum WGS84 Telescope SCT Aperture 25 cm Seeing Steady Broken cloud Timing Tape Recorder + time signal Visual, PE applied Missed Comments: The star was obscured by cloud several times during this period and The star was obscured by cloud several times during this period and those were gradual events. Unfortunately I didn't think to record the times of each one but I do vaguely remember the star being visible for several seconds prior to 11:21:08; about the time an occultation was due. The only abrupt drop I saw occurred between 11:21:08.1 and 11:21:10.2 but that seems too late to have been an occultation, given the time of Chris Wyatt's positive observation. _______________________________ Observer J Broughton Location Reedy Creek,Reedy Creek, QLD 4227, Australia Longitude +153:23:52.8 Latitude -28:06:30.3 Altitude 66 m Datum WGS84 Telescope Newtonian Aperture 51 cm Seeing Slight flickering Clear Timing Tape Recorder + time signal + shutter Drift scan Missed Comments: The exposure of this unattended drift scan was limited to 28s The exposure of this unattended drift scan was limited to 28s to prevent the trail being overlapped by a brighter one.