Latest Information as of 2:00UT from D. Dunham
OCCULTATION OF PPM 717678 BY THE ASTERIOD 62 ERATO IS NOW EXPECTED TO CROSS THE N.E. COAST OF NEWFOUNDLAND IN BRIGHT TWILIGHT
Ten CCD images made with a 25cm telescope by Gordon Garradd, Loomberah, N.S.W., Australia on March 11 around 16h UT essentially confirm the results obtained on March 5th by Jan Manek at Ondrejov Observatory, Czech Republic. But my reductions, recently completed and with some software improvements to perform the calculations with much less editing of input files than was needed previously, gives a result 0.14" (3 path widths) and two minutes earlier than the reduction of the same data by E. Goffin and distributed by me at 22h U.T. March 11 (4 hours ago). The central line of my path is in the Atlantic Ocean just off the northeastern coast of Newfoundland, but the path is wide enough that St. John's is within the path, with the event occurring there at 9:45 UT with the Sun only 2 deg. below the horizon. Path uncertainties remain such that the path could pass farther west across Newfoundland, and less likely as far west as Nova Scotia and Prince Edward Island. A summary of the astrometric results for this event are below, where the corrections are relative to the data shown in Sky and Telescope, p. 68 (in turn based on Edwin Goffin's nominal prediction) as follows:
Observational data 1996 MIN. GEOCENTRIC Correction to Feb. S&T Path
Astrometry by #Obs March U. T. SEP. Time, min. Widths " error
h m "
(none, nominal) 9 36.5 2.14N 0 0
B. Bolster 1 4.4 9 33.5 2.21N -3.0 +/-8 1.5 +0.07 +/-0.5
J. Manek 8 5.6 9 32.5 2.73N -4.0 +/-2 13 +0.59 +/-0.15
G. Garradd (Goffin) 10 11.7 9 34.8 2.73N -1.7 +/-1.5 13 +0.59 +/-0.10
G. Garradd (Dunham) 10 11.7 9 32.5 2.59N -4.0 +/-1.5 10 +0.35 +/-0.10
The path corrections given in the last 3 columns are measured perpendicular
to the nominal path shown on the S&T map, all towards the northeast, and
are expressed in path widths and in arc seconds on the sky; note that Erato
subtends only 0.045", so small errors can shift the path a lot. Some points
in the central line are given below.
CENTER PATH IS ABOUT 229. KM WIDE AT THE COORDINATES LISTED BELOW
UNIV. TIME Erato SUN MOON
LONGITUDE LATITUDE H M S ALT. AZI. ALT. AZI. ALT.
51.37 W 46.55 9 44 39.1 19.9 218.3 -0.6 93.9 43.0
51.73 W 47.40 9 45 11.5 19.3 217.9 -0.8 93.7 42.2
52.05 W 48.25 9 45 43.0 18.7 217.5 -1.0 93.6 41.4
52.33 W 49.11 9 46 13.4 18.1 217.2 -1.2 93.5 40.5
52.56 W 49.96 9 46 42.9 17.5 217.0 -1.3 93.3 39.7
52.76 W 50.82 9 47 11.3 16.8 216.7 -1.4 93.3 38.9
52.91 W 51.68 9 47 38.6 16.2 216.5 -1.5 93.2 38.0
53.01 W 52.54 9 48 4.9 15.5 216.4 -1.5 93.2 37.2
53.07 W 53.40 9 48 29.9 14.7 216.3 -1.5 93.2 36.3
53.07 W 54.26 9 48 53.8 14.0 216.3 -1.5 93.3 35.4
53.01 W 55.11 9 49 16.5 13.3 216.3 -1.5 93.4 34.6
52.89 W 55.97 9 49 38.0 12.5 216.4 -1.4 93.5 33.7
51.27 W 60.13 9 51 5.9 8.6 217.8 -0.7 95.1 29.4
David Dunham, International Occ'n Timing Association 1996 March 12 UT, 2h UT
Telephones home 301-474-4722, office 301-953-5609, fax 301-953-6556.
E-mail dunham@erols.com (home) and David_Dunham@jhuapl.edu (office).
Based on one CCD image made with a 35cm telescope by Bob Bolster, Alexandria, VA, on March 4 and 8 images by Jan Manek with the 65cm telescope at Ondrejov Observatory, Czech Republic, on March 5, an occultation of 9.7- mag. PPM 717678 by the 99-km asteroid 62 Erato might be seen from somewhere in the northeastern part of North America sometime between 9:45 and 10:00 UT March 12th. If you have access to a telescope of 6-inches or larger aperture that has setting circles and/or a good finder scope for locating stars this faint, you can help us measure the size and shape of this asteroid with simple visual timing techniques described below. Anyone familiar with finding variable stars and obscure comets or deep-sky objects can help with this program, and is encouraged to observe; the detail that we obtain of the asteroid's shape will be directly proportional to the number of observers who time the occultation. Please share this with other observers in your area, since this is being sent usually to only one person in each astronomical society in the target area.
The two observations agree that the event is likely to occur a few minutes earlier, with the path north of, that shown for this event on p. 68 of the February issue of Sky and Telescope. But the error remains large in both time and position; more astrometric observations, preferably at altitudes of 30 deg. or higher above the horizon, are needed to get a better prediction. The occultation could still occur as far south as the Mid- Atlantic States region, or the path could narrowly miss the Earth's surface. The corrections relative to the data shown in Sky and Telescope (in turn based on Edwin Goffin's nominal prediction) are as follows:
alt., Time corr. Path correction
Observer deg. min. error widths " error,"
Bolster 36 -3 +/-8 1.5 ne. 0.07 ne. +/-0.5
Manek 25 -4 +/-2 13 ne. 0.59 ne. +/-0.15
The 2nd column gives the altitude of Erato when the observations were made.
The path corrections are measured perpendicular to the nominal path shown on
the S&T map, both towards the northeast, and are expressed in path widths
and in arc seconds on the sky; note that Erato subtends only 0.045", so
small errors can shift the path a lot. Bolster's error is from his single
image solution (the differential positions may be better than his GSC
solution indicates), while Manek's errors are computed from the scatter of
his 8 observations. So although the formal error of Manek's result is
smaller due to the averaging of 8 observations, the lower altitude could
result in systematic error larger than the formal error.
The path computed from Bolster's observations, 155 km wide, passes over Rhode Island at 9:51 UT, the Conn. River valley of Massachusetts and southern Vermont at 9:52, northeastern New York at 9:53, and between Montreal and Ottawa at 9:54 UT. But the path is very uncertain, as the errors indicate. The path computed from Manek's solution almost misses the Earth's surface, being in the Atlantic Ocean east of Newfoundland and east of the sunrise terminator.
A central occultation is expected to last over 43 seconds, but it could be even longer if the asteroid is elongated in the direction of its motion. Telephone the IOTA occultation line at 301-474-4945 to find out the latest information.
A chart is also included in the 1996 Planetary Occultation Supplement to Occultation Newsletter for North American Observers distributed to IOTA members and Occ'n Newslet. subscribers last Dec. If you don't have it, and can't download the chart from this Web site and want a copy, I can send one to you by fax, if you send me your fax phone number. If you don't have that chart, or want to refer others by phone to a chart, there is also one published on page 73 of the March issue of Sky and Telescope.
Even if a future updated prediction shifts the path away from your fixed site, observation is valuable in case of larger-than-expected astrometric error, or for the possibility of seeing a secondary occultation by a possible satellite of Erato, like the one of Ida found by the Galileo spacecraft.
62 Erato's magnitude will be 14.8, so there should be over a 5-mag. drop, very noticeable, if an occultation occurs. If the star is a close double, there could be a smaller drop, or step events. The B1950 position of the star is R.A. 15h 09m 30.0s, Dec. -14 deg. 54' 37" and its J2000 position is R.A. 15h 12m 17.1s, Dec. -15 deg. 05' 51". If possible, practice finding the star beforehand; otherwise, allow at least an hour for this job if you don't have accurate setting circles. A form for reporting observations is available here.
This is being sent to ON subscribers, IOTA members, & those for whom I have e-mail addresses over a wide area, and to many others within the uncertainty zone of this event. If you are in the latter group, info. about IOTA and timing occultations is given in my articles starting on p. 76 of the Jan. issue and p. 68 of the Feb. issue of S&T. Those without short-wave receivers for obtaining the time signals of WWV (5 or 10 megaHertz) or CHU can calibrate watches with seconds displays by calling the U.S. Naval Observatory master clock at 1-900-410-8463, or an IOTA coordinator in your area can record WWV and a selected AM radio station that can then be used as a time standard by others. If you don't have a tape recorder, the audio of a camcorder can be used as a tape recorder.
David Dunham, International Occ'n Timing Association 1996 March 7. Telephones home 301-474-4722, office 301-953-5609, fax 301-953-6556. E-mail dunham@erols.com (home) and David_Dunham@jhuapl.edu (office).
DATE Day UT Star Mag Asteroid dmag dur. Location (uncertain) Mar21 Wed 10:17 SAO 161881 8.9 137 Meliboea 4.4 6s southern Florida Mar18 Mon 5:33 SAO 111486 8.8 6 Hebe 1.7 5s s. Brit. Col. Mar28 Wed 9:52 Z.C. 2305 5.9 517 Edith 9.5 33s DC,MD,n.VA,DE,s.OH Apr02 Tue 9:30 GSC62070146 10.7 1994 JR1 12.4 9s s. South America?
The Mar. 28th event, like the Erato occultation, has unusually slow asteroidal motion, giving more time than usual for obtaining effective path updates by CCD astrometry; also, it is a much brighter star. 1994 JR1 is of interest because it is a Kuiper-belt object; the uncertainty in the path prediction is likely to remain larger than the Earth.
