click image to enlarge
In the evening of October 8-9 2011, the Draconid meteor shower performed a rare meteor outburst. In normal years, hardly any Draconid meteors can be seen. But in 1933, 1946, 1952, 1985 and 1998, short but (very, in the cases of 1933 and 1946) intense outburst were observed. The earth crossed through dust trails left by the parent comet 21P Giacobini-Zinner those years. Zenith Hourly Rates were in the several hundreds in 1985 and 1998, in the thousands in 1933 and 1946.16 Draconid meteors photographed between 19:27 and 21:18 UTC, 8 October 2011. Canon EOS 450D + EF 2.0/35mm, 800 ISO, Dunkelsdorf, Germany. Photo by author.
Last October 8th (2011), the earth was predicted to encounter a dust trail left by the comet in 1900. Predictions for the activity varied, from virtually nil to several hundreds/hour, depending on the modeller and model (see summary in sidebar here).
Several scientific efforts were set up to monitor the event. I joined one of them, a joint effort lead by Peter Jenniskens (SETI/NASA-Ames) in cooperation with the Leibniz-Institut für Atmosphärenphysik (IAP) in Kühlungsborn, Germany (Michael Gerding), and Carl Johannink and me from the Dutch Meteor Society (DMS). Our project was a groundbased part of a wider effort including two aircraft flying with scientific equipment (the Draconid 2011 Multi-Instrument Aircraft Campaign, see here).
Our goal was to do observations that could not be easily done from the aircraft: determine 3D trajectories of meteors in the atmosphere by triangulation of images taken from two locations, in combination with an attempt to detect debris/ionization trails of these same meteors using a LiDAR.
The LiDAR in question, was the LiDAR of the Leibniz-Institut für Atmosphärenphysik (IAP) in Kühlungsborn, a small bathing resort at the Baltic coast of eastern Germany. This part of the observations was done by Dr Michael Gerding of the IAP, who was also our host during the effort. Peter Jenniskens, Carl Johannink and me would employ and operate the multistation video network, using the CAMS system build by Peter and his team at SETI/NASA-Ames (the CAMS project is part of NASA's Planetary Astronomy program).
click images to enlarge
Wednesday 5 OctoberThe CAMS systems (4 low-light level video cameras per station) used. Top: the setup at Lebatz station operated by Carl Johannink and the author (DMS). Bottom: the setup at the IAP Kühlungsborn station operated by Peter Jenniskens (left; SETI/NASA-Ames) and Michael Gerding (right, IAP).
I fetched Peter Jenniskens from Schiphol airport near Amsterdam on Wednesday the 5th. We hauled his equipment (two heavy metal cases, apart from Peter and mine personal luggage) into the train to Enschede in the eastern Netherlands, where Carl fetched us and drove us the few remaining kilometers to Gronau, just over the Dutch-German border. This was our first base-station. The weather prospects were still very uncertain at that time. Peter wanted to press on with the plan to go to Kühlungsborn (because of the LiDAR). Carl and I were less certain: southern Europe had the best papers in terms of clear sky prospects at that moment.
Thursday 6 October
Weather predictions now suggested Northern Germany (where Kühlungsborn is situated) could benefit from a zone of clear air created over Denmark and Sleswig-Holstein in northern Germany in the "shadow" of the Norwegian mountains. It was settled that we would try Kühlungsborn. The early part of the day was spent running various errands. More seriously, one of the PC systems operating CAMS had a malfunction and Peter was not able to solve it. We left in the afternoon, driving several hundreds of kilometers to Kühlungsborn, where Michael Gerding of the IAP welcomed us near 22h local time after a long exhausting drive.
Friday October 7
This day, we set up shop in the LiDAR control room of the IAP, which was to become our headquarters for the campaign. An IT specialist of the IAP was brought in to solve the PC trouble - eventually, he managed to find what was wrong and got everything operating again! Meanwhile, we had gotten a sightseeing tour of the IAP facilities. It is a beautiful, modern institute and the guest lodging in town where Michael put us up for the night was very fine. Kühlungsborn itself is a small cozy town, a bathing resort on the Baltic coast in the former Eastern Germany. Peter held a lecture before the institute members, Carl and I made a small beachwalk that afternoon.
click images to enlarge
The LiDAR control room at the IAP became our headquarters. Top: Peter (right) and Carl (left) with the CAMS systems. Bottom: checking the weather predictions and plotting potential locations for our second station (left Peter, middle Carl, right our host Michael)
That evening was a test evening for the LiDAR, to see whether anything needed trouble-shooting. There actually was a problem initially with the LiDAR, but it was solved and didn't hamper the actual observations the next night.
click images to enlarge
the IAP Kühlungsborn LiDAR at work during a test run a day before the actual observing night. Second image shows the beam hitting a low cloud. Photograph by author using an 8mm semi-fisheye.Seeing the massive laser beam of the LiDAR shooting up into the sky was quite impressive. Meanwhile, the weather was still very dynamic, so we worried about the next night, when all had to happen.
Saturday, October 8th
Based on the latets weather forecasts, we picked a location 91 km to the west for our second site, right in the middle of the projected clear area in the weather forecast. Carl and I would run it, and so we drove away at noon, to the small village of Lebatz (53 deg 58' N, 10 deg 35' E) in Sleswig Holstein, about 30 km north of Lübeck. We had picked a small hotel from the internet there. The hotel owner was a bit surprised by our demand for a room "with a view to the north east". We needed the latter, as the mutual aiming point we had calculated for the Kühlungsborn and Lebatz CAMS systems meant we had to point at 46 degrees elevation to the northeast. Peter at Kühlungsborn filmed 15 degrees north of the Zenith, just north of the LiDAR beams. In that way, we would film the same meteors from both stations, appearing at 95 km altitude over the Baltic sea just north of Kühlungsborn: meteors whose ionization trails next would drift into the LiDAR beams, as a result of a high altitude wind blowing from the north-northeast at 95 km altitude.
Meanwhile, two other Dutch observers, Peter van Leuteren and Sietse Dijkstra, had joined us: they had driven to Lebatz from the eastern Netherlands that same day, arriving about an hour after us.
Just before our car turned into Lebatz (which, by the way, turned out to be one of the rare spots in NW Europe without cellphone coverage), I had noted a small roadsign saying: 'Dunkelsdorf, 1 km'. 'Dunkelsdorf' means "dark village" in German. So naturally, that name appealed to us! After setting up shop in the hotel in Lebatz (our CAMS system would run from the open hotel window, as we needed electric power and a dry place for the PC), we drove the 2 km to Dunkelsdorf, and found a nice hiltop with 360 degrees view. The farmer was working nearby, and gave us permission to use the field that night (he turned out to be an astronomy enthusiast himself).
click image to enlarge
Our observing spot (bottom) near Dunkelsdorf, photographed the morning after
After a good meal in the small tavern at the hotel, Peter v. L. and Sietse left for the observing field at dusk. The sky was clearing at that moment, witha few remnant fields of clouds. This looked very promising for the night! Carl and I stayed at the hotel waiting for the sky to become dark enough to aim and focus the cameras. That took some effort, also because we were not used to this new equipment. But with some trial and error, we managed to get the whole system running: and after the cameras are aimed, and focussed well, the PC takes over and the whole system runs automatically, and we could leave for the field. Neat!
So after setting up, aiming, focussing and initiating the camera systems, Carl and I drove to the observing field as well, arriving there at 20:30 local time. Sietze and Peter v. L. already had seen some bright Draconids, they reported as we arrived. We set up our gear (field bed, sleeping bag, handheld memorecorders, and in my case a tripod with my photo camera) and joined the observations. The last cumulus clouds were moving out of the sky and it became brilliantly clear. Observing due North away from the moon, I determined a limiting magnitude of +6.3 in Draco to my (and my fellow observer's) astonishment, with the milky way visible into Perseus. This was wonderful, I have never experienced such a good sky with moonlight before! Directly in the minutes after I started observing, the first Draconids were seen. So there was activity, at least! Would it lead to a peak near 20h UTC (22h local time)?
Observing the activity peak
It did indeed lead up to a peak just after 22h local time. More and more meteors appeared, shooting away from a radiant in the head of Draco. Around 20 UTC, I counted 3-4 Draconid meteors per minute. Most were rather faint, so we wondered what we would have seen without the moon.... Nevertheless, even in a moonlit sky, the show was impressive, and it was clear the Zenith Hourly Rates must be in the hundreds. We were excited!
We were also worried. Low in the east, below 5 degrees elevation, we could see persistent clouds. That was where our other station was, Kühlungsborn with Peter, Michael and the LiDAR..... Telephonic contact (our cell phone did have coverage from the hilltop) revealed that they had a lot of clouds, but also clear periods.
click diagram to enlarge
ZHR diagram of my observations, suggesting a peak ZHR near 250 just after 20 UTC
My observations suggest that the ZHR at the peak was in the order of 250. This is just an indication, as it are observations with moonlight, from one observer. In total, I observed 248 Draconid meteors in 2.77h effective observing time.
My photo camera with EF 2.0/35mm lens captured 16 Draconids (image above) in slightly less than two hours time: most meteors were simply too faint to be photographed. Our video camera's meanwhile, sensitive to much fainter meteors, filmed hundreds of meteors.
Some meteors left persistent trains. It are these trains of course, that were the target for the LiDAR. Below animated GIF shows a bright Draconid I photographed, with traces of a dissipating persistent trail drifting on the wind in several images obtained after it appeared:
The short movie shows the trail drifting from bottom right to upper left in about 2 minutes time: indeed consistent with a high altitude wind direction from the NE to SW.
After 22h local time (20h UT), activity was on the decline again. The peak was over. Around midnight, we stopped our observations (the CAMS system would run untill 1 am). It was still brilliantly clear: we couldn't have been in a better spot!
click image to enlarge
Four happy observers the morning after the outburst observations. From left to right: Carl Johannink, Peter van Leuteren, Sietse Dijkstra, and the author
Kühlungsborn
The next day, Peter van Leuteren and Sietse drove back to the Netherlands, and Carl and I drove back to Kühlungsborn. Ariving there near 11 am, we heard the story of Peter and Michael. They had a lot of clouds, but luckily also a largely clear period of about an hour around the peak time. This increased our hopes to have filmed at least a few meteors multistation, hopefully with a LiDAR detection as well.
With the data reduced we can now say we filmed at least 34 Draconids plus two sporadic meteors from both stations, yielding accurate atmospheric trajectories, lightcurves, and orbits in the solar system. The LiDAR did have detections as well, but work to correlate these with meteors filmed by us is still in progress. If we do have LiDAR detections that we can correlate with meteors we filmed (more precisely: with the atmospheric trajectories and lightcurves that our multistation filming produced), that will yield a lot of information about processes happening in the upper atmosphere because of these meteors.
Below is a compilation of video meteors filmed by three of the Lebatz cameras and one of the Kühlungsborn cameras. The latter images also shows the LiDAR beams (and clouds, unfortunately). Draconid meteors are moving from top to bottom, everything from another direction is an aircraft, satellite, or sporadic meteor.
It was ten years ago that I last had been involved in such a scientific meteor observing effort - I participated in several of the Leonid meteor outburst scientific campaigns in the 1990-ies. It was exciting to get involved again for the Draconids.
note: I want to warmly thank the people of the IAP and especially Dr Michael Gerding for housing us during the campaign.
No comments:
Post a Comment
Note: only a member of this blog may post a comment.