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This occultation was seen by Albert Brakel and Patrick Purcell from two sites in ACT, Australia, with the remote possibility of an extremely brief blink (observed by video) at Dave Gault's site in NSW.
View the updated prediction.
View an animated GIF of Dave Gault's video observation: http://www4.tpgi.com.au/users/daveg/astrovideos/galatea.gif.
Observers: 1 A.Brakel, Downer, ACT, Australia 2 P.Purcell, Chapman, ACT, Australia 3 D.Gault, Hawkesbury Hts, Australia (Video)
The plots below represent two potential solutions:
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Discussion:
Dave Gault observed the star disappear for only one video frame at Hawkesbury Heights, so he is not willing to claim that an occultation may have occurred there. (For video events, the generally accepted threshold is a disappearance for three video frames to partially rule out seeing fluctuations). In plot 1 the locations of the three observers have been plotted, but a zero weight has been given to the Hawkesbury Heights observation. The circle represents the 119km expected diameter of the asteroid. It is not possible to make a fit to the two ACT chords alone as there are insufficient data points for a unique solution. It is noted that the chords are offset, as Albert Brakel said he expected them to be in his comments below.
In plot 2 all the data have been included and a partial fit has been attempted with the major axis of the asteroid being allowed to vary. When variation of the other two parameters (namely, the minor axis and the position angle) was allowed, the fitting routine was unable to converge to a solution.
Both plots look potentially feasible, although there is insufficient data to derive meaningful information about the shape or size of the asteroid. The two definite ACT observations though will allow this event to be used as a high-precision astrometric data point in further refining the orbit of Galatea.
Observational Data:
Observer's Name : Albert Brakel
Aperture (cm) : 20 cm
Focal length (cm) : 200 cm
Type (e.g. SCT; Newtonian) : SCT
Magnification : 118x
Observing site name : Downer (home)
Longitude (East +ve) : +149 08' 14"
Latitude (South -ve) : -35 14' 32"
Height above Sealevel (metres) : 575 m
Geodetic Datum (e.g.WDD84,NZ1949): AGD66
Height Datum (if known) : Australian Height Datum (AHD)
Sky Transparency (Delete two) : Good
Star Image Stability (Delete two): Good
Other Conditions:
(Wind, Clouds, Lights, etc.): Clear sky, moderate suburban light pollution
Time Source (e.g. WWV, VNG) : Watch
Recording method (e.g. tape) : Tape
Could you see the Asteroid? : No
Approx. Limiting Magnitude : ca 11.8
| Estimated |
Universal Time | Reaction | Accuracy, Remarks
h m s | Time (sec) |
Started Observing : 16:09:22
Disappearance At : 16:14:02.5 0.8 Rapid (not sudden) fade
Reappearance At : 16:14:11.6 0.5 Rapid brightening
Stopped Observing : 16:18:29
Was your reaction time (also known as Personal Equation) subtracted from
any of the above timings? : No
List all Interruptions to Observing:
(FORMAT --> __:__:__._ - __:__:__ _____________________)
FROM TO REASON
Break 1: 16:14:22 - 16:14:39 Eyepiece fell out
ADDITIONAL COMMENTS: The faint star had to be observed with averted vision, but the image was stable,
and the occultation and its duration were definite. One of the effects of the current drought is that
high-pressure systems are coming over more often than usual, giving lots of clear skies and stable air.
If the seeing had not been above average, the star would not have been visible.
However, there was no radio time signal whatsoever. This posed quite a challenge for getting accurate
absolute times. My watch had been calibrated to WWVH sometime earlier and was less than half a second from
true time, so I called times from it onto the tape both before and after the observation. The actual time
interval in between was compared to the tape playback time (a difference of 11.1 sec), and the observation
times adjusted proportionally. This assumes that the tape speed was the same each time it was restarted
on playback. Given all the uncertainties, I would not be surprised if my chord turns out to be offset
from those of other observers.
The disappearance and reappearance were not instantaneous, but seemed to be rapid fading and rapid
brightening respectively, although with the star as faint as it was, I cannot be completely certain of this.
Observer's Name : Patrick Purcell
Aperture (cm) : 40cm
Focal length (cm) : 200cm
Type (e.g. SCT; Newtonian) : Newtonian (altazimuth mount)
Magnification : 91x
Observing site name : CHAPMAN (home)
Longitude (East +ve) : 149 degrees 02 minutes 35.1 s
Latitude (South -ve) : -35 degrees 21 minutes 30.1 s
Height above Sealevel (metres) : 645
Geodetic Datum (e.g.WDD84,NZ1949): WGS84
Height Datum (if known) :
Sky Transparency (Delete two) : Fair
Star Image Stability (Delete two): Good
Other Conditions:
(Wind, Clouds, Lights, etc.): No wind
Time Source (e.g. WWV, VNG) : WWV on 5 Mhz (dipole aerial used)
Recording method (e.g. tape) : Tape
Could you see the Asteroid? : Yes (until 15:55 UT approx.)
Approx. Limiting Magnitude : ? 13.1 (the asteroid was barely visible)
| Estimated |
Universal Time | Reaction | Accuracy, Remarks
h m s | Time (sec) |
Started Observing : 15:50:00
Star and Object Merged : 15:55 approx.
Disappearance At : 16:14:05.3 0.5
Reappearance At : 16:14:12.8 0.3
Star and Object Separated : ?
Stopped Observing : 16:20:00
Was your reaction time (also known as Personal Equation) subtracted from
any of the above timings? : No
List all Interruptions to Observing:
(FORMAT --> __:__:__._ - __:__:__ _____________________)
FROM TO REASON
Break 1: 15:56 16:05 Check timing equipment etc.
ADDITIONAL COMMENTS: The star appeared to be fainter than visual mag 11.4
suggesting some high level cirrus cloud. The disappearance commenced with a rapid fade
but the reappearance was sudden (instantaneous).
Observer's Name : Dave Gault
Aperture (cm) : 25
Focal length (cm) : 122
Type (e.g. SCT; Newtonian) : EQ Newtonian
Magnification : video camera at Newtonian focus
Observing site name : Dave's Skyshed
Longitude (East +ve) : 150 38.4637
Latitude (South -ve) : -33 39.8663
Height above Sealevel (metres) : 286
Datums : WGS84 and MSL
Sky Transparency (Delete two) : Good
Star Image Stability (Delete two): Good
Other Conditions: : perfect conditions
TIMINGS: (PLEASE REPORT IN UNIVERSAL TIME)
Time Source (e.g. WWV, VNG) : GPS
Recording method (e.g. tape) : KIWI
Could you see the Asteroid? : Yes
Approx. Limiting Magnitude : 13.7 (video)
: UT Time | PE | Accuracy | Remarks
Started Observing : 16:11
Star and Object Merged : not sighted
Disappearance At : no event recorded (See comments)
Reappearance At : no event recorded (See comments)
Star and Object Separated : 16:20
Stopped Observing : 16:25
ADDITIONAL COMMENTS:
My station was about 3/4 path widths north. On reviewing the tape I noticed the target star wink
at 16:13:53.754 UT but only for one video field (1/60th sec) so I put this down to scintillation
due to atmospheric effects. I have lifted images from the video and these are available for
inspection. If the duration of the wink was 3 or more fields then I'd be more comfortable reporting
a positive event.
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