Occultation by the Asteroid Petropolitana, from Cabrillo Observatory

Friday morning Sept 18, 2015

This event passed centrally across Aptos and though narrow, had a high rank. Chris Angelos got up at 2:30am and joined me at the observatory, where I had slept, after arriving just after midnight from home. The event was at 4:01 am and we planned to videorecord using the PC165DNR on the Orion ShortTube refractor mounted on the 12" dome LX200 on G11 mount..

The target star is v=12.3, the asteroid is v=14.9. The predicted time is 11:05:01 for Cabrillo Observatory.

 

       

Some preliminary reduction playing around in LiMovie. It's a new updated version and I need to find how to set the optimum parameters again. But here's a quick-o light curve that's very preliminary. The sharp drop is at 11:04:59.02 UT. The "R" is hard to tell, but less than or equal to 1.5 seconds. It was at 16x fields integration, so that's 1/4 second integrations, meaning that several points in a row will be the same except for random noise it seems.

Target rings=3,5
Tracking star rings=3,5
Comparison star ring=3,5

Target rings=default
tracking star rings=5,8
comparison star rings=5,8

Target rings=default
Tracking rings=5,8
No comparison star used

 

Tried again on Oct 7... Got nice stable circles if I made big circles around target, let the comparison and tracking be default values, and left all 3 on 'drift'.

The faint star at right is target. Comparison and tracking star are the same; the star to the left of the target. Target inner rings 5,14. Tracking rings 3,5. Comparison rings 4,6. All set on 'drift'

Points are in groups, since there is 16x integration of fields, or 8x integration of frames. The light curve is clearly grouped into sets of 8 points which only differ by small noise. Times advance for each field, but the field otherwise remains unchanged until the next integration starts. Photometry measurement noise must be why they are not completely identical for the frames within a single integration. The actual occultation is centered in this chart.

Same, but zoomed in on the event, which is only 3 integrations long. I took the D and R as the sharp drop and sharp recovery frame times, raw read from the image.

   

 

From visual inspection, it looks like there are only 3 groups of points which are truly in occultation, and the higher points after the R are likely somewhat or completely out of occultation, given the many comparable low values. D at frame 1337 and 1338, and R at 1362.

Begin 11:04:00

D: 11:04:59.006 ----------- midway between frame 1337 and 1338
R: 11: 04:59.824---------- frame 1362

End 11:06:00

These take no account of whatever corrections there must be for the PC165dnr at 16x integration.

The raw video .avi file is here

Tony George took my raw video and did a R-OTE analysis on the video and got the following results:

D  (seconds) =  43.777012 - 0.266900 (camera delay) - 0.016700 (VTI offset) = 43.493412   @ 2015-09-18 11:04:57.922145
R  (seconds) =  46.179409 - 0.266900 (camera delay) - 0.016700 (VTI offset) = 45.895809   @ 2015-09-18 11:05:00.324542

(compare to Derek's D=58.3 and R=01.3 and that the predicted time for me was 1 sec earlier, that says my timings should have been near 04:57.3 and 05:00.3, which matches quite well with R-OTE above.)

dur (block integrated readings) =   9.00

dur  (seconds) =   2.402397
B =   187.93 (+/-) 5.990
A =    -8.75 (+/-) 29.593

logLikelihood = -2093.76
nominal magDrop =  0.00
maximum magDrop =  0.00
minimum magDrop =  2.35
Bnoise   =   109.48
Anoise   =    88.78
SNR      = 1.80
symmetry = 0.81

Table of candidates

D

R

relativeLikelihood

logLikelihood

B

A

magDrop

duration

1

165.00

174.00

1.00

-2094.62

188.19

5.00

3.94

9

2

161.00

174.00

0.46

-2095.39

189.11

38.11

1.74

13

3

162.00

174.00

0.36

-2095.65

188.84

32.88

1.90

12

4

163.00

174.00

0.35

-2095.67

188.61

25.68

2.16

11

5

165.00

173.00

0.26

-2095.97

187.69

2.95

4.51

8

6

161.00

173.00

0.12

-2096.75

188.60

39.50

1.70

12

7

160.00

174.00

0.10

-2096.90

189.04

50.38

1.44

14

8

162.00

173.00

0.09

-2097.02

188.34

33.92

1.86

11

9

163.00

173.00

0.09

-2097.04

188.11

26.11

2.14

10

10

164.00

174.00

0.07

-2097.22

188.07

27.46

2.09

10

Square Wave Error Bar Report
confidence  edge +/-  (in readings)
   0.6827   D(rdgs) +1.64 -0.91
   0.6827   R(rdgs) +0.91 -1.64
   0.9500   D(rdgs) +9.00 -7.70
   0.9500   R(rdgs) +7.70 -9.00
   0.9973   D(rdgs) +15.91 -15.80
   0.9973   R(rdgs) +15.80 -15.91
 
@ time delta per reading: 0.266933 (seconds) ...
confidence  edge +/-  (in seconds)
   0.6827   D(secs) +0.437 -0.242
   0.6827   R(secs) +0.242 -0.437
   0.9500   D(secs) +2.401 -2.056
   0.9500   R(secs) +2.056 -2.401
   0.9973   D(secs) +4.246 -4.219
   0.9973   R(secs) +4.219 -4.24

 

The times of the most likely event corrected for camera delay and VTIoffset (highlighted in yellow above) are early when compared to the predicted times for Aptos, CA.  The duration of the ‘event’ is longer than the predicted maximum duration for the event.  The False Positive Analysis indicates the event is likely to be spurious.  You should discuss with Brad whether or not the ‘event’ should be reported.  If they are reported, the timing error bars are highlighted in yellow.

 

 

         

The sky-plane plot is here