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OCCULTATION OF TYC 4947-00852-1 BY 510 Mabella
2008 April 05


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.

Mabella occultation - 2008 April 05

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

Mabella - Hristo Pavlov

Ted Dobosz - Light Curve

Mabella - Ted Dobosz

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.

TYC 4947-00852-1 on Google Sky

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:  

_______________________________

Return to 2008 occultation results



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