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                ASTERIODAL OCCULTATION - REPORT FORM

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                      EAON & IOTA-ES

              EUROPEAN ASTEROIDAL OCCULTATION NETWORK

   INTERNATIONAL OCCULTATION TIMING ASSOCIATION EUROPEAN SECTION

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1. DATE: 29 dec 2011
   STAR: UCAC2 40143290
   ASTEROID: (198) Ampella

2. OBSERVER
   Name: Stefano SPOSETTI, Mauro DELUIGI
   Address: 6525 GNOSCA - Switzerland
   Email: stefanosposetti@ticino.com

3. OBSERVING STATION
   Nearest city: CH-6954 Bigorio
   Longitude: 8d 56m 34.94s E
   Latitude: 46d 05m 3.78s N
   Altitude: 870m

4. TIMING OF EVENTS
   Occultation recorded: POSITIVE
   Type of event:
   "S"tart observation;
   "I"nterrupt-start;
   "D"isappearance;
   "B"link;
   "F"lash;
   "E"nd observation;
   "I"nterrupt-end;
   "R"eappearance;
   "O"ther (specify)

   Personal Equation Substracted: No
   Event Time (UTC)       Accuracy + Comments
   code: HH:MM:SS.ss      S.ss
    -S : 01:56:05
    -D : 01:56:49.71    +/- 0.1s
    -R : 01:56:55.71    +/- 0.1s
    -E : 01:57:29

    Duration: 6.0s ± 0.2s

5.TELESCOPE:
   Type: Schmidt-Cassegrain, Celestron 8-inch
   Aperture: 200mm
   Focal length: 500mm (with 2 focal reducers)
   Magnification: FOV about 50x40arcmin
   Mount: Equatorial
   Motor drive: No

6. TIMING & RECORDING
   Timekeeping: KIWI-OSD with GPS Garmin 18 LVC
   Sensor/Camera: Videocamera WAT-120N+, CCIR, 1/2" Sony CCD-Sensor ICX419ALL
   Videocamera settings: Shutter mode=1, Gain=HI , Gamma=HI
   Device of recording: Personal computer, Imaging Source DFG/SV1 PCI, Composite-video,
   Virtualdub software, saved on Harddisk
   Mode of recording: Integration time=0.040s (25 Img/s), CCIR, Huffyuv
   Time insertion: KIWI-OSD

7. OBSERVING CONDITIONS
   Atmospheric transparency: good
   Wind: no
   Star image stability: good
   Minor Planet Visible: yes

8. ADDITIONAL COMMENTS

The telescope was pre-pointed to the target position. No RA motor was present.

Because the WAT-120N+ was setted in shutter mode "SLOW=1" (ie. integration time=40ms), a correction factor of -50ms was made to the video inserted times accordingly to the table:
http://www.dangl.at/ausruest/vid_tim/vid_tim1.htm#wat_120n

A visual inspection of the avi file shows evident vertical dark bars probably given by the 12VAC converter. This regular sequence of dark bars was invisible during the acquiring process (made with a laptop and the screen in low-light emitting mode).
Only in the analysis phase, made with Tangra(C), one can see the stars moving across several of these bars. The final lightcurve does not reveal any evident regular lightdrop infuenced by this background.

No darks and flat fields were used.

Because of the low SNR of the individual frames, Tangra was used in "stepped averaging" in "integration mode" with 3 and 5 frames. The lightcurve presents the 6s long evident lightdrop of 0.5mag at the prediction time. The final lightcurve showed two other drops of light.

A 5 frames integration was used to evaluate these two secondary lightdrops. Their results are:
    -D1: 01:56:56.3    +/- 0.1s
    -R1: 01:56:56.7    +/- 0.1s
    -duration: 0.4s ± 0.2s

    -D2: 01:56:57.4    +/- 0.1s
    -R2: 01:56:58.1    +/- 0.1s
    -duration: 0.7s ± 0.2s

All these times were corrected because of the use of a WAT120N+ operating in "SLOW=1" mode.
These two similar lightdrops were seen in other 5 frames integration sequences, starting from 5 different frames.

I mention these two lightdrops in this point 8.ADDITIONAL COMMENTS and not in the point 4.TIMING OF EVENTS because I'm skeptik about their true nature, and specifically:
-the mentioned dark bars in the avi
-the low SNR of the target star+asteroid
-the not complete mastery of the several reduction methods of Tangra

An image made with Tangra using "stepped averaging" in "5 frames integration" mode is here:
http://www.sposetti.ch/images/stories/Minor_planets/2011_12_29_(198)Ampella_Bigorio_5.png

An additional lightcurve image made with Tangra in "stepped averaging" and "3 frames integration" mode is also posted:
http://www.sposetti.ch/images/stories/Minor_planets/2011_12_29_(198)Ampella_Bigorio_3.png