Occultation of TYC 0728-01958-1 by (663) Gerlinde on Oct. 29
observed in Saskatchewan - New 2007 Oct. 31, 21h UT
Vance Petriew's drift scan recording of the 4.8s occ'n near Regina
and my miss observations in Calif. showed that the path shifted half
a path-width (1 sigma) southeast
I give an account of my observations after the description of Vance
Petriew's observations given in the following messages; his
observatory is at longitude 104.5682 W., latitude 50.43872 north,
h 580 m, which is 11 km southeast of the predicted central line.
_________
Subject: RE: 663 Gerlinde Event - probable positive observation
shows 0.5 path width south shift
Date: Tue, 30 Oct 2007 09:24:08 -0600
From: "Petriew, Vance"
To: "David Dunham" ,
Thanks for the detailed replies, David. I was expecting closer to a
12 second event based on the prediction but if the shadow ended up
passing more south, then a 4.8 second event is plausible. Here
is a screen shot showing the event which ended up being a 48 pixel
gap (at 10 lines per second).
This is my second successful timing and I was glad the clouds and
brightening twilight didn't shut me down. I'm looking forward to
the next one so keep me posted :o)
All the best,
Vance
-----Original Message-----
From: David Dunham [mailto:dunham@starpower.net]
Sent: October 29, 2007 8:41 PM
To: IOTAoccultations@egroups.com
Subject: Re: 663 Gerlinde Event - probable positive observation shows
0.5 path width south shift
Vance,
I answered your first message first, but this one sounds much
more plausible, a 4.8-sec. occultation at close to the right time at
your location at 11 km south. I should probably recheck my tape
made at 5 km north to see if there might be a very short event there
corresponding to your event, but I'm confident that there's nothing
there of 0.2s or more duration. So it's likely that the actual path
really was 0.5 pathwidths southeast of the prediction, which is
about a 1.0-sigma path shift. Many thanks again for your
observation.
David
______________________
Hi David,
I double checked my computer clock tonight and it does look like it
was out by 1 minute 50 seconds. Therefore the event I registered at
4.8 seconds was indeed the correct time. Now I'll have to find out
why my NTP time synch didn't work this morning. Hmmm.
I'll send you a picture later.
Thanks,
Vance
______________________
At 11:03 AM 10/29/2007, you wrote: (Vance's first message)
Hi David,
There was cirrus clouds in Regina but I think I may have captured it
with drift-scanning in the morning twilight. My SNR is pretty low
since I was scanning at 10 lines per second close to the moon through
the clouds.
How accurate was the prediction of the event? I may have an event at
12:59:50 UT in my image but I'm not convinced as it looks more like a
wind gust. I do see a 4.8 second event at about 13:01:40 UT. Can you
confirm this? My timing could be out by a couple seconds but not a
couple minutes [but it was out by close to 2 min.; see his later
message above]. I'll send pictures later.
Clear Skies,
Vance Petriew
Regina, SK
______________________
And now my story:
I tried to observe the occultation myself from sites near I-5
in the western San Joaquin Valley of California, but had no
occultation at two locations, and most likely at a third one as
well. They were:
Remote station with 5-inch SCT north of Lost Hills, Calif., at long.
119d 45.086' W., lat. 35d 43.921' N., h 64m
start recording star 13:02:11 UT,
stop recording at 13:04:07 UT (star drifted out of field of view)
location about 5 km northwest of the central line
Remote station with 4-inch SCT southwest of Kettleman Junction,
Calif., at long. 119d 58.0879' W, lat. 35d 58.3506' N., h 125m,
about 35 km northwest of the predicted central line.
Start recording star about 13:02:10 UT,
stop recording at 13:04:35 UT (star drifted out of field of view)
Two 8th-mag. stars show clearly at the right time, and the triangle
of stars of about mag. 9.0 about 8' north of the target star also
are faintly visible most of the time as they drifted through, but
the background seems to be moving, as if there are thin clouds,
which I wouldn't be surprised about considering the thin clouds I
had much of the time at my attended station only about 15 km farther
northwest (that station, using a similar telescope, had the
advantage of an image intensifier). The target star is only
intermittently visible. But since my other two stations at +5 and
+51 km from center clearly had no occultation, I assume that this
remote station was also a miss. Digitization and use of Registax
would probably bring out the target star with reduced time
resolution, but it may not be worth the effort, except to check for
Gerlinde satellite occultations (but even if there would be one of
those, it would be very suspect under the circumstances). The IR
weather satellite image for 13:02 confirms that it was overcast at
the time of the occultation at the -71 km location where I first set
up this telescope, but then moved it to this location when overcast
skies prevented accurately pre-pointing the telescope at the -71 km
location about 3h before the occultation.
Attended station with 4-inch SCT & image intensifier in the Kettleman
Hills, Calif.,
at long. 120d 06.3394' W., lat. 36d 03.9278' N., h 230m
start recording star 13:02:11 UT,
stop recording at 13:04:00 UT
The time interval was limited by passing clouds; fortunately during
the critical minute, the star remained visible. Location was about
1 km southeast of the predicted northern limit (or 51 km n.w. of
center). It's curious that this time interval is nearly the same
as that for my remote station.
It's curious that my northern two stations were within 10 miles of
the "California" standard station at long. 120d W., lat. 36d N. used
for occultation predictions in the late 1950's; it was the
prediction at that location for the occultation of beta 2 Cap by the
moon 50 years before that caused me to observe the appulse of the
bright star over the lunar mountains near the south pole that made
me realize that grazing occultations existed and should be
predicted, effectively the start of my quest to observe those
events, and start IOTA.
Observers near Springville, Calif., on the other side of the San
Joaquin Valley, attempted the occultation but were clouded out.
David
____________________
Extensive pre-event predictions and plans are here.
________________________________________________
David Dunham, 2007 Nov. 5, 17h UT
Phones home 301-474-4722; office 240-228-5609; cell 301-526-5590
office e-mail david.dunham@jhuapl.edu with Blackberry for mobile use
home e-mail: dunham@starpower.net .