Rare Occultation of Regulus by (166) Rhodope Timed in S.
Europe on Oct. 19
Rhodope was found to be about 60 km in diameter rather than the
predicted 35 km
The path predictions were quite accurate, within 0.2 sigma
Positive observations were made from two sites in Portugal,
five sites in Spain, and one each in Italy and Greece
Updated: 2005 November 28
On Wednesday morning, October 19th, the asteroid (166) Rhodope
occulted the star Regulus, the brightest star in the constellation
Leo (the Lion) for up to two seconds in a path crossing southern
Portugal, southern Spain, southern Italy, and Greece. Several
observers were clouded or fogged out in southern Italy, and in
south-central and southeastern Spain; the weather was best in
Portugal and Greece. Observers travelled from Germany and the USA
to observe the occultation. You can read about the predictions for this
outstanding occultation, and an ambitious effort to publicize the
occultation and to try to involve many others to observe the event,
as well as information about the unusual star, here.
My report of the occultation, and preliminary information about the
analysis of all the observations, is below. The latest compilation
of all of the observations are on the Euraster Web site.
_________________________________
From: PLANOCCULT-owner@AULA.COM on behalf of David Dunham
[dunham@starpower.net]
Sent: Wednesday, October 19, 2005 12:10 PM
To: planoccult@aula.com; IOTAoccultations@egroups.com
Subject: [PLANOCCULT] Regulus/Rhodope positive s. of Monesterio, Spain
I ran a remote station with a 50mm telephoto lens and
old image intensifier at a location a few km south of
Monesterio, Badajoz province, Spain, at GPS coordinates
long. 6 deg. 14.4045' W., lat. 38 deg. 03.3429' N., h 610m
as determined by my McAfee GPS time inserter, but did not
realize until after we returned to Arturo Montesinos' place
and played the tape that it actually recorded an
approximately half-second occultation at 4:23:50 UT
(will get more accurate times later; the events were
gradual, and I don't think Regulus' image was saturated -
with the moonlight, 4th-mag. stars were the faintest that
seemed to be recorded). I was able to start that system
running 20 minutes before the occultation, just after
starting it, I drove another 11 km farther south relative
to the path, stopping about 7 minutes before the
occultation, giving me enough time to put a camcorder on
a small tripod on top of my rental car and record Regulus.
No occultation occurred at that location, as far as I can
tell; that was north of the town of Santa Olala Del Cala,
just across the border in Andalusia province, Spain,
at GPS long. 6 deg. 13' 45.4" W., lat. 37 deg. 56' 55.2" N.,
h 1600 feet. I was a little dejected after seeing the
miss at my station, but of course now elated that the
remote station recorded a positive event. According to
Arturo's calculations, the remote site was 19 km s. of
Steve Preston's central line and 31 km s. of Jan Manek's
center. So the true s. limit must have been a few km s.
of Steve Preston's s. limit (which was also at 19 km s.)
- congratulations, Steve, your time was also good
(predicted 4h 23.8m UT).
Arturo Montesino and his wife also tried to observe
the occultation, video recording it with my other digital
tape camcorder and a less sensitive digital camera of his
own, but the star did not disappear at their location
about 40 km north of Preston's central line near
Retamal de Llerena, Badajoz, Spain, at GPS location
long. 5 deg. 50' 20.16" W., lat. 38 deg. 34' 27.23" N.,
h 509m. We purposely set up at locations a little outside
of Jan Manek's limits, thinking that observers in s. Italy
and elsewhere in Spain and Portugal would cover his path,
especially near the center; we just wanted to increase
chances that someone would have an occultation with the
1-sigma uncertainty greater than a path-width. We wanted
to set up two more remote stations, one being my camcorder
that Arturo used and a 5-inch SCT. We set up the 5-inch
SCT and started to locate an appropriate star field, but
didn't succeed in pointing it before a large band of
clouds moved over the field, with motion showing that it
would stay cloudy in the critical area awhile; that was
less than 3 hours before the event. So we gave up on
that, and not being sure that Arturo's camcorder could
record the star well enough and wanting to get an observation
to the north in case there was a north shift of the path,
I also gave up the idea of using the 2nd camcorder as a
remote station and instead gave it to Arturo so he could
move to avoid the clouds, which he succeeded in doing.
So rather than trying to run 5 stations according to our
original plan near the A66 highway between Merida and
Sevilla, we ended up with 3 useful video observations
in that area of southwestern Spain. The forecast was for
clear skies there, and it was mostly clear during our
long drive from Madrid, but it was partly cloudy while
we were in the occultation path (fortunately in the clear
at the right time) and became mostly cloudy not long
after the occultation.
Farther east, observers who had planned to try to
observe from the Valencia area mostly travelled west, setting
up, along with other observers from Madrid, near the A4
highway some 200 km s. of Madrid. It remained very cloudy
along the southeast coast of Spain, and was foggy in the
path where it crossed A4, preventing most video observers
from recording the star. Eberhard Bredner telephoned saying
that Otto Farago probably was able to video record the
occultation with his system, but would have to check his tape
for that later. There are about 4 other positive reports
from Spain and one from Greece on the Planoccult list.
It looks like we will have good results from this
rare bright event after all; we look forward to details of
other observations (some already provided on Planoccult).
It makes my trans-Atlantic flight, and over 800 km
round-trip drive from the Madrid area, worthwhile.
David
_________________________________
Details of my remote successful observation:
2005 October 19, occultation of Regulus by (166) Rhodope, south of
Monesterio, Spain, WGS84 long. 06 deg. 14.4051' W.,
lat. +38 deg. 03.3429', h 605m, 50mm telephoto lens & old image
intensifier:
U.T.
3:54:00 Started recording Regulus
4:23:50.21 Start of disappearance
4:23:50.25 - 50.30 Star stayed near 50% level
4:23:50.33 - 50.40 Star 4th mag.
4:23:50.41 Star 5th mag.
4:23:50.43 Star at noise level, maybe gone, end disappearance
4:23:51.06 Start of reappearance, barely visible in noise
4:23:51.09 Star 6th mag.
4:23:51.13 Star 4th mag.
4:23:51.16 Star 3rd mag.
4:23:51.18 - 51.25 Star stayed near 50% level
4:23:51.36 End reappearance, star at full brilliance
4:49:18 Stopped recording Regulus
_________________________________
The European Asteroidal Occultation Network attempted a preliminary
reduction of the Regulus occultation by (166) Rhodope on 2005 10 19 .
Using the three observations where the observers DID RECORD the penumbra
that really existed around the shadow, one finds an ellipse as shown below.
The other reports are discrepant. Any observer should try to recover the
gradual ingress and egress, and try to find the 0.75 mag drop levels, of
which the timing gives the exact edges of the (166) limb.
We are sure that this work is in progress (at least for Anthony, David
and Rui - in alpha order !).
Of course, the David Dunham observation is very important, since he was
the "shepherd".
Then fitting the other reports (sometimes as much as 2.55 seconds), one
finds an ellipse 45.9+/-0.5km (width) by 63.4+/-0.4km (length).
All this is preliminary, since the study of recordings is everywhere in
progress.
For EAON :
Raymond DUSSER
Gilles REGHEERE
Jean SCHWAENEN
_________________________________
From: PLANOCCULT-owner@AULA.COM on behalf of rdapt@tele2.fr
Sent: Tuesday, October 25, 2005 11:20 AM
To: planoccult
Subject: Fw: [PLANOCCULT] Shadow basics for Rhodopists
Bruno Sicardy asked me to planoccult this mail, since he is not a
subscriber.
----- Original Message -----
From: "Bruno SICARDY"
To:
Cc: "planoccult"
Sent: Tuesday, October 25, 2005 12:34 PM
Subject: Re: [PLANOCCULT] Shadow basics for Rhodopists
Hello Raymond,
yes, you are absolutely right, Regulus has really a strange shape! I put
McAlister's paper on Regulus interferometric measurements, together with
other papers on stellar angular sizes, on my web site.
Concerning Regulus, I don't know about the various Rhodope occn
recordings, but it would be great if some information on Regulus' size
could be derived from this exceptional event...
Cheers,
Bruno
_________________________________
David Dunham, President,
International Occultation Timing Association (IOTA)
e-mail: home, dunham@starpower.net office david.dunham@jhuapl.edu
telephone: home, +1-301-474-4722, office +1-240-228-5609
cell phone +1-562-430-2391 (sorry, not international)