A 14.8 second occultation was timed using the CCD drift-scan technique by John Broughton in Reedy Creek, Qld. A 17.26 second occultation was also timed by Terry Butt in Te Horo, NZ using video.
View the updated prediction.
John Broughton's CCD drift-scan image is displayed below:
Terry Butt's occultation data is shown below. Data points are at 40 ms intervals. It will be seen that both the D and R events were quite sudden.
Observers: 1 J. Broughton, Reedy Creek, Qld, Aust. 2(M) S.Kerr, Glenlee, Qld, Australia 3(M) K. Barker, Auckland, NZ 4 T. Butt, Te Horo, NZ 5(C) P. Graham, Martinborough, NZ 6(C) J. O'Kane, Upper Hutt, NZ 7(C) G.Blow/M.Forbes, Wellington, NZ 8(C) D. Brock, Hamilton, NZ 9(C) D. Gault, Hawkesbury Hgts, NSW, Austr 10(C) A. Walker, Te Puke, NZ 11(C) A. Dodson, Waitara, NZ 12(C) G. Hudson, Pukerua Bay, NZ 13(C) D. Watson, Whakatane, NZ 14(C) P. Anderson, Brisbane, Qld, Australia 15(P) Updated Prediction M = Miss C = Cloud
The above plot shows the relative locations of all the potential observers of this event (most of whom were
clouded out - as indicated by the dotted lines).
The dashed line #15 shows the central line of the path according to the updated prediction.
The circle represents the expected 210km diameter of Metis (assumed circular).
The plot below shows observers close to the asteroid's path in more detail, again with Metis plotted as a circle of 210 km diameter.
What is immediately clear is the number of observers who were unlucky to have missed seeing the event owing to cloud or other factors. While the two chords obtained are insufficient to derive a shape or exact diameter for Metis, it is also clear that they don't conform very well to a circle of 210 km.
Bearing in mind that attempting to fit an ellipsoidal shape will result in a large number of possible solutions, we have nevertheless allowed the major and minor axes to change, resulting in the representative plot below:
It is unfortunate that even one additional chord was not obtained for this event.
Observer's Name : John Broughton Aperture (cm) : 50.1 (25 equivalent used) Focal length (cm) : 140 Type (e.g. SCT; Newtonian) : Newtonian Magnification : CCD drift-scan, 4.1 pixels per second Observing site name : Reedy Creek, Gold Coast Longitude (East +ve) : +153 23' 49" Latitude (South -ve) : -28 06' 36" Height above Sealevel (metres) : 66 Geodetic Datum (e.g.WDD84,NZ1949): AGD66 Sky Transparency (Delete two) : Poor Star Image Stability (Delete two): Fair Other Conditions: (Wind, Clouds, Lights, etc.): Bright moonlight and haze. Time Source (e.g. WWV, VNG) : WWVH. Recording method (e.g. tape) : Tape. Could you see the Asteroid? : Only combined light monitored though asteroid is visible during occultation. Approx. Limiting Magnitude : 11 | Estimated | Universal Time | Reaction | Accuracy, Remarks h m s | Time (sec) | Started Observing : 12:41:30.21 n/a 0.01 Disappearance At : 12:41:49.80 n/a 0.2 Reappearance At : 12:42:04.64 n/a 0.2 Stopped Observing : 12:42:30.66 n/a 0.01 Duration : 14.8 ADDITIONAL COMMENTS: CCD drift-scan. Measurements done with Scanalyser. On the previous night, I positioned the telescope aided by my Scantracker software. That was necessary to check line-of-sight for the event since the big scope cannot reach most azimuths below 30 degrees elevation. An overcast sky meant I had to do a blind slew, accurate to about 2' barring any stepper motor stall. Scantracker can also be used any time after halting the drive to predict when stars cross the field for pointing confirmation, but under the conditions I never got the chance to do so. With little expectation, CCD cooling was commenced 25 minutes before the event under a blanket of cloud. It wasn't until 10 minutes to go when I noticed the sky in the direction of the event was improving by the minute and fortunately a gap in the cloud arrived with 5 minutes to spare, lasting long enough for a usable image to be acquired. Often I can reach 15th magnitude but a reduced effective aperture of 25cm, bright moonlight and fleeting haze cut the limiting magnitude to 11. This and the small magnitude drop accounts for the measurement accuracy of 0.2 being relatively poor compared to previous results. Observer's Name : Terry Butt Aperture (cm) : 250 Focal length (cm) : 1600 Type (e.g. SCT; Newtonian) : SCT Magnification : ? Observing site name : Te Horo Longitude (DD MM SS ; East +ve) : 175 07 26.53 E Latitude (DD MM SS ; South -ve) : 40 48 47.31 S Height above Sealevel (metres) : 52 Geodetic Datum (e.g.WGS84,NZ1949): WGS84 Height Datum (if known) : MSL Sky Transparency (Delete two) : Good Star Image Stability (Delete two): Fair Time Source (e.g. WWVH, GPS) : Kiwi OSD Recording method (e.g. tape) : VCR Could you see the Asteroid? : No Approx. Limiting Magnitude : | Estimated | Universal Time | Reaction | Accuracy, Remarks h m s | Time (sec) | COLUMN FORMAT TO USE---> __:__:__._ _._ _________________) Disappearance At : 12:37:13.409 +/- 10 ms Reappearance At : 12:37:30.669 +/- 10 ms Duration : 17.26 sec ADDITIONAL COMMENTS: None
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