+--------------------------------+ +--------------------------------+ ASTERIODAL OCCULTATION - REPORT FORM +--------------------------------+ +--------------------------------+ EAON & IOTA-ES EUROPEAN ASTEROIDAL OCCULTATION NETWORK INTERNATIONAL OCCULTATION TIMING ASSOCIATION EUROPEAN SECTION +--------------------------------+ +--------------------------------+ 1 DATE : Jan 27 2010 STAR : 2UCAC 46562578 ASTEROID : (626) Notburga 2.OBSERVER: Name: Stefano SPOSETTI Address: CH-6525 Gnosca, Switzerland E-mail: stefanosposetti@ticino.com 3.OBSERVING STATION: Nearest city: CH-6500 Bellinzona Station: Gnosca Observatory Latitude: 46deg 13min 54sec (N) Longitude: 9deg 1min 30sec (E) Altitude: 260 m Single/Multiple: single 5.TELESCOPE: Type: Newtonian Aperture: 40cm f/4 Magnification: - Mount: equatorial Motor drive: yes 6.TIMING & RECORDING: Occultation recorded: POSITIVE Personal Equation Substracted: No because of electronic timing Event Time in UT Code: HH:MM:SS.ss S.ss Code: HH:MM:SS.ss S.ss S1 01:53:17 D1 01:54:14.0 ± 0.3s R1 01:54:14.7 ± 0.3s E1 01:56:29 S2 01:56:48 D2 01:59:26.4 ± 0.3s R2 01:59:31.9 ± 0.3s E2 02:02:47 Duration of the first occultation: 0.7s ± 0.1s Duration of the second occultation: 5.5s ± 0.1s Timekeeping: via Computer ("Dimension4" software) Mode of recording: CCD drift-scan ("Winscan 207" software) Device of recording: CCD (SBIG ST8XME) 7.OBSERVING CONDITIONS: Atmospheric transparency: fair, moonlight (see NOTES) Wind: none at the observatory Star image stability: good Driftscan speed at 0.01s/line Sampling: 1.2arcsec/pixel FWHM of stars: 9arcsec (because of optics misalignement) 8. NOTES: TECHNICAL NOTES The first luminosity drop lasted 0.7s ± 0.1s. The lightcurve shows a "deep" minimum: the intensity dropped from about 12000 to roughly 3000. The division gives 0.25, ie. a drop of 1.5mag (prediction: 0.9mag). The second luminosity drop lasted 5.5s ± 0.1s. The drop of luminosity was from about 10000 to 4500. This corresponds a luminosity drop of 0.87mag (prediction: 0.9mag). OBSERVATIONAL NOTES I woke up 20minutes before the predicted occultation time (01:59:18UT) and I started the telescope, the CCD, the target centering and the focusing procedure in a hurry. The sky was bright because of the low setting Moon at the West (distance: 47deg, illumination 86%). The sky was also not transparent enough. Some uniform homogeneous haze was visible. No massive clouds were visible. The somewhat low transparency of the sky in the target sky position was quite uniform. At 01:52:07UT (i.e. about 7min before the predicted occultation time) I started a first still 1s-aquisition image. I repeated a second still 1s-aquisition image at 01:52:30UT. The star image was not round enough and I knew I could improve it a bit, by better focusing. At 01:53:16UT I started a first scan image of 6mins at 0.01s/line, in order to look at the signal of the star+asteroid. The signal was not very strong and I thought it was probably better to integrate at 0.02s/line. During this scan I was trying to achieve a better image startrail by focusing the image. I thought also it was better to have a second star in the scan for checking purposes. Then, suddendly, the signal disappeared for less than 1s, like a true occultation. I remember I thought: "what happens? the predicted occultation was scheduled to be in 5 minutes." I checked the computer time, I checked the wristwatch time and I checked the predicted occultation time on my printed chart. It was really about 5min earlier. I stopped this first scan abruptly. Winscan would have stopped it after 6min anyway, i.e. just near the predicted occultation time. As soon as I could I started a second scan of 6mins at 01:56:47UT. I was looking at the screen to see if the predicted 6.8s occultation happened. The predicted time arrived and passed. No occultation showed evidently on screen. I thought it was not probable to have a shift of the occultation time of about 5mins. At 02:03:06UT I shot a still aquisition image of 1s. I started again other still images of the starfield and a last dark scan of 6mins. Indoor, when I analyzed the second scan, I could see the second predicted luminosity drop of the occultation. CONCLUSIONS The possible causes of the first unpredicted luminosity drop are, in order of decreasing probability: 1. sudden RA motor disfunction and sudden reaquisition of the RA position. I got some RA malfunctions in the past but, when the RA position was lost I got no "self" recovery. A second brilliant star in the starfield could validate/negate this suggestion. It was an error not placing a check star in the scan. 2. bird or airplane flying over. 3. cloud covering the target. In past occultations I experienced clouds coverage. Normally they cause trace interruptions bright and visible. If a thin and rapid cloud passed over the field of view its brightness should have been higher than the background sky because of the bright moonlight. Again, if a check-star was in the scan it probably showed a similar behaviour. 4. orbiting body (satellite) around Notburga. In this latter case the magnitude drop would have been 0.9mag and not 1.5mag as observed. Image of the first event is here: http://web.ticino.com/sposetti/First_occultation_Notburga_2010Jan27.gif Image of the second event is here: http://web.ticino.com/sposetti/Second_occultation_Notburga_2010Jan27.gif Mainpage: http://web.ticino.com/sposetti/html/news.html