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PLANETARY OCCULTATIONS: 1998 RESULTS


This page provides a brief summary of observational attempts for the following important 1998 events. Full details were published in the Section's Circulars.

(147) Protogeneia - 1998 December 9
(51) Nemausa - 1998 December 4
(62) Erato - 1998 October 20
(410) Chloris - 1998 October 7
(47) Aglaja - 1998 September 29

[Return to master results page]

Occultation of PPM 143088 by (147) Protogeneia - 1998 December 9:

Peter Nelson, Ellinbank, Vic, Australia:
Started Observing: 11 15 00
Stopped Observing: 11 33 00
No Event. Could not see the MP because of the glare of the star.

Alfred Kruijshoop, Mount Waverley, Vic, Australia:
Started Observing : 11:20:40
No occultation seen throughout this period; star remained visible
Stopped Observing : 11:40:30
Target star easy to locate.
Could not see asteroid

Grant Murphy, Sydney, Australia:
Sydney was clouded out again. Perhaps I should move.

Colin Bembrick, Bathurst, NSW, Australia:
As I was on site and the original predictions gave a track through Sydney and Adelaide I monitored this event in spite of the updates! As expected a nil result. Monitored from 1120 to 1135 UT, conditions fair - clear but poor stability - a NE gale blowing actually.

Charlie Smith, Woodridge, Qld, Australia:
Started Observing : 11:19:00.0
Stopped Observing : 11:43:00.0
Cloud persistent, seeing poor. Conditions were woeful, no hope of seeing an occultation of the secondary. No events were observed.

Albert Brakel, Downer, A.C.T., Australia:
Started Observing :11:21
Stopped Observing :11:43
The seeing was not good enough to resolve the binary star even with 235x power.

In anticipation of other observations close to my home chord, I moved to another site to the NW of Canberra. However, I found that passing cars were quite a hindrance. On what I had assumed to be a quiet rural back road at about 10:30 pm on a Wednesday, I was nevertheless blasted by passing headlights 8 times in half an hour. I will not use this site again if I can find another in the area.

When I played the tape back, I found that the recording was of poor quality, and much of it was unintelligible because of static. This static was not apparent at the time of recording; it did not come from the radio or other external source, and must have originated in the tape recorder itself.

I saw two series of "events", but I do not believe that these were real. They consisted of irregular sequences of dimmings and brightenings, fluctuating in magnitude by more than 2 mags., and at one point the star disappeared completely for 1-3 seconds. The brightenings between the dimmings often brought the star back to its original brightness. The two sequences were separated by about a minute, and each lasted for about the predicted maximum duration of the occultation, or longer. They occurred while passing cars were blasting me with their headlights. Because of the poor quality of the tape, there's not much I can say definitely about timings. What I can say is that at 11:28:24 I shouted "Dim!" followed at 11:28:28 by "Gone!". Then the tape has a period of static until 11:28:46, by which time the sequence of fluctuating events was already over. I can't be certain when the other sequence took place, but it was probably between 11:29:20 and 11:29:47 where the tape contains undecipherable comments. Otherwise the star was continuously visible. I believe the events were not real for the following reasons:
(1) The character of the fluctuations was unlike what would be expected for an occultation event;
(2) There were two sequences of these events;
(3) At one point the star disappeared completely, and had the primary component been occulted, the 9.1 mag. secondary would have been easily visible;
(4) The events coincided with passing cars;
(5) The events occurred well before the time of 11:32 predicted by the last astrometric update; and
(6) I was later able to reproduce the effects (see below).

At the time I thought the headlights were affecting my night vision, but that would not explain the brightenings. Later I experimented with the eyepiece I was using, and was able to reproduce similar dimmings and brightenings at will. I have never used this eyepiece for occultation work before, and only used it to try to split the double star. It has short eye relief. I could get the effects by moving my head so that the light cone did not fully enter my eye. With my normal lower-power, longer eye-relief eyepiece this is much more difficult to achieve accidentally. I suspect that when the headlights moved past, I moved my head a bit to shield my eyes from the glare, and inadvertently moved my eye partly out of the light cone of the eyepiece a number of times.

Eric Pozza, Mt Stromlo Observatory, A.C.T., Australia:
Started Observing :11:28
Stopped Observing :11:37
Components of the binary star could not be resolved. The star was clearly visible throughout the period, and no change in magnitude was noticed.


Occultation of PPM 145718 by (51) Nemausa - 1998 December 4:

Grant Christie, Auckland, NZ:
I used the 0.5m Zeiss Cassegrain at the Auckland Observatory and located the field at 0925UT. I could easily see Nemausa as it approached the star. I started observing (and taping comments) from 0945UT and continued until 1010UT without observing any change in the brightness of star. There were brief periods of cloud, during which the star became completely obscured but these were short. By 1010UT I could again resolve the star and Nemausa which is why I stopped recording. During the observing run I did not look away from the eyepiece. Unless we were unlucky and the occultation occurred during a brief interval when cloud blocked the view, we had a miss here. Marc Bos and I spoke at 1015UT and he reported being clouded out during the critical phase. He was recording with his ST6 CCD camera in planetary mode.

Barbara Ives, Whangamata, NZ:
No rain, no Nemausa, plenty of cloud cover and a brilliant Moon.

Diana Watson, Whakatane, NZ:
ref. Nemausa, no luck, complete cloud cover at Whakatane.

Grant Murphy, Sydney, Australia:
I'd intended to have a look on Friday night despite the expectation that Sydney would be well outside the shadow path. The weather had other ideas, however.

Charlie Smith, Woodridge, Qld, Australia:
Started Observing : 09:47:00.0
Star and Object Merged : 09:52:35.0
Estimated Closest Approach : 09:59:49.0 +/- 30secs.
Star and Object Separated : 10:07:03.0
Stopped Observing : 10:15:00.0
My "guesstimate" is that it passed < 1.5" to the South.
Seeing was rather variable, and some wind gusts made things a little difficult at times, but star was clearly seen at all times, and no events were observed.


Occultation of TAC +0200345 by (62) Erato - 1998 October 20:

Dave Girling, Mornington, VIC:
From my location cloud, cloud, cloud, rain, rain, rain!

Charlie Smith, Woodridge, QLD:
I found the star and asteroid easily enough, and the field was clear until 15h.14m., when some cloud rolled in. I stuck it out, but things just got worse, and I did not get another sighting of the objects before finally giving up at 16h.20m., when there was nearly complete cloud cover. Judging by the separation seen at 15h.14m., it looked like the closest approach would have been later than Goffin's prediction and probably nearer the updated time given by Bill Owen. It also appeared to me that the magnitude difference between star and asteroid was less than predicted.

Stephen Kerr, Rockhampton, QLD:
Just a short note to let you know that the Erato (and Amphitrite) events last night were clouded out. After a hot day with a lot of broken cloud, the evening was clear albeit with a fair bit of smoke. However, the cloud came back with a vengence around 10:20 UTC cutting short a variable star run.... and here we are on Wednesday evening and there hasn't been a gap in it since.


Occultation of TAC +1601099 by (410) Chloris - 1998 October 7:

Peter Nelson, Ellinbank, VIC:
I had patchy skies up until 15:30, then solid cloud. No observation.

Peter Skilton, Frankston Heights, VIC:
The Chloris event yesterday was completely under cloud and, for me, also drizzle.

Rod Austin, New Plymouth, NZ:
No go. Total overcast, and now it's raining. I'm sure we never had so much cloud and rain before MP occultations were discovered.

Joe Grida, Adelaide, SA:
I got up very early this morning to try the Chloris occultation, however cloudy, drizzly weather prevented me from seeing anything. I had passed details of the occultation to some 35 other ASSA members, but I have heard nothing from any of them. The cloud cover was fairly widespread, so I suspect they would have experienced the same problem as me.

Brett McMillan, Sutherland AS, NW:
I wish to advise that I observed what I believed to be the correct star (my digital setting circles were used to find field from the map and details provided on the web page) between 15h 30m and 16h 00m UTC (01:30 - 02:00 Eastern Australian Standard Time) from my home in Western Sydney. I did not observe any significant fading of this star during this period. Weather conditions were excellant but sky was bright due to a near full moon in the vicinity. No withstanding the moon, the field stars shown on the map were visible once dark adapted, however the minor planet was not visible. I was using a 13 inch f4.5 (aprox 35cm) newtonian, dobson mounted with digital setting circles, telescope with 21mm plossl eyepiece giving approx mag. of 67x.

Albert Brakel, Canberra, ACT:
This was not an easy one to observe. In fact only got brief intermittent glimpses of the target star in the bright moonlight, at the limit of vision, and it was invisible at least 95 per cent of the time. The Law of Perversity being what it is, it would come as no surprise if the rare event of an asteroid's shadow passing across my site came in circumstances when I could not observe it.

Col Bembrick, Bathurst, NSW:
Quick report on the above occn. - CLOUD, CLOUD, CLOUD!!!


Occultation of PPM 733363 by (47) Aglaja - 1998 September 29:

[Original prediction and charts by Edwin Goffin]
[Aglaja Update from astrometry by Gordon Garradd]

Peter Skilton, Frankston Heights, VIC:
With about 15 clouded attempts in the last 18 months and only 1 negative observation (Iris) to show for it, there had to be an end to the drought. I observed a definite, rapid disapp/reapp for 47 Aglaja right on the predicted time at my home location. Preliminary results from a quick listen last night were:
Disapp: 11:27:28.83UTC
Reapp: 11:27:30.97UTC
Duration: 2.1 secs

Michael Mattiazzo, Wallaroo, SA:
As expected, the occultation of 47 Aglaja on Sep 29th was not observed here in Wallaroo, South Australia.

Vello Tabur, Wanniassa, ACT:
No occultation.

Alfred Kruijshoop, Mount Waverley, VIC:
Most of the early evening was ~80% overcast, ie overcast, but with a few "travelling holes" in the clouds. Even when there was no cloud, there was a general slight haze, which - with the nearby Moon - did not help things. I continually tried to locate the field - and spent quite some time "in the general area", but - in the short breaks between clouds - was never able to determine the target star with confidence. At the time of the event (around 11:28?) there were still streaks of cloud drifting over the target area.

Grant Murphy, Baulkam Hills, NSW:
Conditions here in Sydney were clear, though my seeing was only average - due to a hot day I think. I observed from 11:17 to 11:37 UT. There are a couple of seconds each minute when I reposition my Dob and the view gets a bit shaky and/or my eye falls out of the exit pupil, so there's always a possibility that a brief event went unseen. There was a brief dimming of about one second at about 11:27:15, which seemed a bit more than just the seeing, but I'm not confident that it was an actual event.

Dave Girling, Mornington, VIC:
No occultation was observed from my location!

Albert Brakel / Eric Pozza, Canberra, ACT:
Attached are reports on the 47 Aglaja appulse by myself and Eric Pozza. Both are "no events" I'm afraid.

Stephen Kerr, Rockhampton, QLD:
No occultation.

Col Bembrick, Bathurst, NSW:
No positive observation. The correct star was identified by 2000 EST, and we monitored the star visually under good conditions, apart from the strong Moonlight, from 2115 to 2130 EST.

Summary of other observers from Peter Skilton:
- Jim Blanksby had a rapid possible glitch a few minutes before predicted event time and therefore thinks it was only cloud. He uses an identical instrument to mine, but different eyepieces.
- Ken Self at Rosanna was clouded out.
- Patricia Larkin at Burwood (unknown so far).
- Renato Alessio at Noble Park gives a negative report for ca 11:17 to 11:42, but cloud was thought to interfere 3 times for a few seconds each time between 11:26 and 11:29. He is either incredibly unlucky, or he saw a disappearance during one of the interferences.
- Ed Barber at Chelsea (unknown so far).
- Roger Giller at Berwick was clouded out.
- Me at Frankston, definitely positive.
- Ken Bryant - I heard 2nd hand report he was observing from home but saw no change. Unsure what his sky conditions were like.
- Bruce Tregaskis at MtEliza (unknown so far).
- Ian Porter did not observe as he was away on holidays without his instrument and tells me he spent a frustrated evening expecting that something would occur because he wasn't looking.


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