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Four observers recorded positive chords for this event.
View the updated prediction.
Observers: 1(M) B Loader,Darfield, NZ (off the plot below) 2 M Streamer, Wiruna, NSW, AU 3 P Purcell, Wiruna, NSW,AU 4 T Dobosz,Ilford - Wiruna, NSW,AU s 5 T Dobosz,Ilford - Wiruna, NSW,AU P 6 H Pavlov,Ilford, NSW, AU P 7 H Pavlov,Ilford, NSW, AU s 8(P) Predicted, 7 March 9(M) D Gault,Lake Windamere,,NSW,AU 10 I Mackay - Saw event from same location as Ted Dobosz but did not record times.
Discussion:
This event happily occured during the NSW Star Party on April 5. The ellipse above is plotted at the fitted dimensions of 95 km by 35 km for Mabella. The locations used by Ted, Patrick, and Margaret were effectively on the same chord line so they effectively overlap in this plot but help to confirm the timing.
The figures below show the light curve data for the occultation and we believe that they are showing a possible dim secondary star.
Hristo Pavlov - Light Curve
Ted Dobosz - Light Curve
Hristo's curve (top of the above two) shows several interesting points:
1. We do not believe there is any case for an occultation between A and B. The light level in that region is consistent with the preceding several seconds.
2. We think there is a possibility of a step event at the first two points at B. Reason- these two data points are above the subsequent light level, and consistent with the step at C.
The three points at the start, and end, of Ted's curve are interesting. They do not have the scatter that is otherwise present in the light curve, and they are generally above the level of the main D part of the curve. So there is a case for interpreting a D of a fainter star, starting 0.12s after, and ending 0.12s before, the main star.
Editor's Note:
I have checked the historical observations for Mabella and there are 3 single observations with chords of 23 km, 59 km and 68 km. With predicted circular diam of 57km (presumably based on magnitude and standard albedo) an ellipse could be from 68 x 49.8 to anything longer and thinner.
I have also done a quick search in the latest AsteroidObservations.dat file to see if there were any other reports involving TYC 4947-00852-1 butfound none. Of course probability of same star involved in many Occs is low so not surprising.
Tried to see if this could have been in the ZX or SAO sets as it is near ecliptic and might already be known in those as a double.
Eventually found that ZX equivalent is 35062 and checked to see if there was any hint of double in the ZX cat but nothing showed up.
In desperation a Google search for TYC 4947-00852 found 9 occurrences, all for predictions of this event :-)
I note that Steve Preston's page prediction also shows it going over Java, India, Oman, UAE, and Saudi. Don’t know if we have any observers in those parts but it may be worth checking with the Europe IOTA guys.
Finally I looked at the image in Google Sky to see if anything could be seen but this star is way too bright to resolve a secondary at the separation we are looking at. In the attached picture the square cursor is about 1 arc sec square.
Summary:
We have Four timed chords.
Three were almost on the same path.
The two positives with video observations show steps in the light curve.
Best explanation is a possible secondary star.
Fitting with Occult suggests that the separation is only a few milli arcseconds.
Clearly the MP is not eliptical, but we dont have enough chords to know the actual shape.
An alternative explanation is that both observers had near graze, but that seems unlikely.
Observational Data:
Observation details for MP (510) Mabella By Star TYC 4947-00852-1 On 2008-04-05 at 15:59:00.0 _______________________________ Observer Margaret Streamer Location Wiruna, NSW, AU Longitude +149:46:0. (inexact location) Latitude -33:01:0. (inexact location) Altitude 1016 m (assumed from other obs) Datum WGS84 Telelscope SCT including Cass and Mak Apperture 20 cm Seeing Strong flickering Clear Timing Tape Recorder + time signal Visual, PE applied Disappearance 15:59:15.90 Reappearance 15:59:21.13 Comments: _______________________________ Observer Ted Dobosz Location Ilford - Wiruna, NSW,AU Longitude +149:46:48.0 Latitude -33:00:48.3 Altitude 1015 m Datum WGS84 Telelscope SCT including Cass and Mak Apperture 28 cm Seeing Slight flickering Clear Timing GPS - time inserted Video with frame analysis Disappearance 15:59:16.46 Reappearance 15:59:21.74 Comments : This is Primary star Observer Ted Dobosz Location Ilford - Wiruna, NSW,AU Longitude +149:46:48.0 Latitude -33:00:48.3 Altitude 1015 m Datum WGS84 Telelscope SCT including Cass and Mak Apperture 28 cm Seeing Slight flickering Clear Timing GPS - time inserted Video with frame analysis Disappearance 15:59:16.58 Reappearance 15:59:21.62 Comments: : This is the occultation events for the secondary star. _______________________________ Observer Patrick Purcell Location Wiruna NSW, AU Longitude +149:46:49.1 Latitude -33:00:48.8 Altitude 1016 m Datum WGS84 (Google Earth) Telelscope Newtonian Apperture 40 cm Seeing Steady Clear Timing Tape Recorder + time signal Disappearance 15:59:16.80 (after PE adjustment) Reappearance 15:59:22.20 (after PE adjustment) Comments: (1)Ian Mackay also observed the event from the same site (within a couple of metres) with a 60mm Televue refractor with 7mm eyepiece but did not record times. As far as we know, this is the first time an asteroid occultation has been observed at the South Pacific Star Party at Wiruna NSW hosted by the Astronomical Society of NSW. (2) Dave Gault travelled north & recorded a miss. Hristo Pavlov travelled south & recorded a brief (? 1.8s) disappearance. We infer from this that the occultation path was south of that predicted. (3) The occultation occurred several seconds later than predicted. (4) The duration of the occultation (5.5 secs) as observed at Wiruna was greater than the predicted maximum of 4.6 secs. _______________________________ Observer Hristo Pavlov Location Ilford, NSW, AU Longitude +149:51:31.2 Latitude -32:57:48. Altitude 825 m Datum WGS84 Telelscope SCT including Cass and Mak Apperture 20 cm Seeing Steady Clear Timing GPS - time inserted Video with frame analysis Disappearance 15:59:18.50 Reappearance 15:59:20.98 Comments: Very humid! Had to wipe off the dew from the Schmidt corrector plate every 5-10 min There is a clearly visible step event at 15:59:20.06 (patial reappearance). May be close double star? _______________________________ Observer Hristo Pavlov Location Ilford, NSW, AU Longitude +149:51:31.2 Latitude -32:57:48. Altitude 825 m Datum WGS84 Telelscope SCT including Cass and Mak Apperture 20 cm Seeing Steady Clear Timing GPS - time inserted Video with frame analysis Disappearance 15:59:18.58 Reappearance 15:59:20.06 Comments: This is the occultation events for the secondary star Conditions were very humid. _______________________________ Observer Dave Gault Location Lake Windamere,Mudgee Rd,NSW,AU Longitude +149:45:25.1 Latitude -32:44:45.2 Altitude 618 m Datum WGS84 Telelscope SCT including Cass and Mak Apperture 20 cm Seeing Steady Clear Timing GPS - time inserted Video with frame analysis Missed Comments: _______________________________ Observer Brian Loader Location Darfield, NZ Longitude +172:06:24.4 Latitude -43:28:52.9 Altitude 210 m Datum WGS84 Telelscope SCT including Cass and Mak Apperture 25 cm Seeing Slight flickering Fog Timing GPS - time inserted Video, photo or photoelectric Missed Comments: _______________________________