Recent Selene Update
The occultation of 9.7-mag. SAO 79750 by the asteroid 580 Selene
on 1999 March 3 UT (Tuesday night) is expected to be visible from a path
about 60 km wide extending from north of Corpus Christi, Texas to Santa
Cruz, California, according to 34 ACT-relative observations of Selene
obtained at USNO-Flagstaff, Arizona and Table Mtn. Obs., Calif. from
1998 Nov. 14 to 1999 Feb. 22 reported by Ron Stone and Bill Owen,
respectively. This path is 0.11" or 3.3 path-widths south of Edwin
Goffin's nominal prediction, and the time is 2 minutes earlier than the
nominal prediction. Observations are strongly encouraged to augment a
planned attempt to record the occultation from a NASA airplane.
*** AN EVEN LATER UPDATE will be computed soon - some
observations made late last week at Table Mtn. Obs. have just been
reported (up to Feb. 26), but are not included in the analysis here.
They will appear on the Web in a few hours probably at
http://www.sky.net/~robinson/iotandx.htm but also check at the
Web site below; it will have a March 2 U.T. date (probably 0h to 1h
UT) while this one is 22h UT on March 1. But now I don't expect a
large change.
The path crosses Tobago at 6:14 UT, Cuba at 6:18, north of Corpus
Christi, Texas, at 6:25, south of San Antonio at 6:26, McDonald
Observatory (near s. limit) at 6:28, El Paso (s. of center) and Las
Cruces, N.M. (near n. limit) just before 6:29, UT, near Globe, Arizona
at 6:30; Phoenix (just s. of the s. limit) just before 6:31, Needles,
California at 6:32, then over Baker, China Lake, and Inyokern (just
before 6:33); over Tulare just after 6:33 with Fresno just n. of the
northern limit just before 6:34; and Salinas (near s. limit), Santa Cruz
(near the center), and s. of San Jose at 6:34.5 UT. The formal path
error is +/- half a path width considering Selene, but the ACT position
of the star might have a slightly larger error, so observers within two
pathwidths or 120 km of the expected center are encouraged to monitor
the star (such as in San Antonio, Victoria, and Corpus Christi, Texas;
across the Phoenix area; Las Vegas (just outside the zone but worth
looking), Bakersfield to Modesto in California's Central Valley; and the
San Francisco Bay area to south of Monterey. The time is now uncertain
by less than a minute. This path, using the latest available
observations, is 0.6 path-width or 35 km north of the one I distributed
about 12 hours ago, and the time is now 2 minutes later than that
prediction, which relied on an incorrect extrapolation of the right
ascension differences since the mid- and late February observations were
not available then.
If an occultation occurs, there will be a 5-magnitude drop
(Selene's mag. is 14.7) that will last up to 14 seconds. The star is at
J2000 RA 7h 51m 32.4s, Dec +23 deg. 24' 04", 0.7 deg. northeast of 6th-
mag. 82 Geminorum and 2 deg. southeast of kappa Geminorum. The detailed
IOTA finder chart for the event is in the recently distributed 1999
Planetary Occultation Supplement to Occultation Newsletter for North
American Observers and is available on the Web at http://near.jhuapl.edu
(or more directly at http://fermi.jhuapl.edu/temp/dunham/occ.html).
A map showing the path across the southwestern U.S.A. is also on that
Web site, with U.T. lines at 1-minute intervals (labelled at 2-min.
intervals) and showing what I consider to be the uncertainty zone marked
by curves 2 path-widths north and south of the central line, as well as
the northern and southern limits and the center.
Details of the path are given below. Mobile observers should not
go right to the central line, which should be covered from the air;
instead, stay 10 km or more north or south of it. Try to coordinate
observers in your area, targeting mobile observers to fill in gaps in
coverage that will be provided by fixed-site observers. Due to the high
altitude of the star, the path shifts only 1 km to the south for each 3
km increase in altitude above sealevel.
OCCULTATION OF 9.72-MAG. SAO 79750 (Goffin ID ACT 19251224,
SPECTRAL TYPE G0) BY 580 Selene ON 1999 Mar 3
DIAMETER= 55. KM = 0.033 SECONDS OF ARC, CENTRAL OCCN. = 14.215 SECONDS
CENTER PATH IS ABOUT 58. KM WIDE AT THE COORDINATES LISTED BELOW
UNIV. TIME Selene SUN MOON
LONGITUDE LATITUDE H M S ALT. AZI. ALT. AZI. ALT.
56.81 W 9.47 6 14 32.9 13.3 292.0 -56.5 88.3 67.7
58.60 W 10.32 6 14 47.1 15.2 291.6 -58.1 86.6 69.2
60.39 W 11.18 6 15 3.1 17.1 291.3 -59.8 84.7 70.6
62.19 W 12.04 6 15 20.9 19.0 290.9 -61.3 82.4 72.0
71.34 W 16.48 6 17 16.3 28.4 288.1 -68.3 66.4 76.1
73.21 W 17.38 6 17 44.5 30.2 287.4 -69.4 61.9 76.2
75.09 W 18.29 6 18 14.3 32.1 286.7 -70.4 56.9 76.0
76.98 W 19.19 6 18 45.6 33.9 285.8 -71.2 51.4 75.6
78.89 W 20.10 6 19 18.6 35.8 284.9 -71.9 45.4 75.0
80.82 W 21.01 6 19 53.0 37.6 284.0 -72.3 39.1 74.1
82.76 W 21.92 6 20 28.9 39.5 282.9 -72.6 32.5 73.0
84.73 W 22.82 6 21 6.2 41.3 281.8 -72.6 25.7 71.8
94.85 W 27.30 6 24 32.3 50.2 274.5 -69.6 355.1 64.3
96.94 W 28.17 6 25 17.1 52.0 272.7 -68.5 350.1 62.7
99.06 W 29.04 6 26 3.0 53.7 270.7 -67.3 345.5 61.0
101.21 W 29.90 6 26 49.8 55.4 268.5 -66.0 341.4 59.2
103.38 W 30.75 6 27 37.7 57.0 266.1 -64.6 337.6 57.5
105.58 W 31.59 6 28 26.4 58.7 263.5 -63.2 334.1 55.7
107.81 W 32.41 6 29 16.0 60.3 260.6 -61.6 330.8 53.9
110.06 W 33.22 6 30 6.3 61.8 257.5 -60.1 327.8 52.1
112.35 W 34.02 6 30 57.4 63.3 254.0 -58.4 325.0 50.3
114.67 W 34.80 6 31 49.1 64.7 250.2 -56.8 322.3 48.4
117.03 W 35.56 6 32 41.4 66.0 246.1 -55.1 319.8 46.6
119.41 W 36.30 6 33 34.2 67.3 241.5 -53.4 317.4 44.7
121.83 W 37.02 6 34 27.5 68.4 236.4 -51.6 315.0 42.9
124.28 W 37.72 6 35 21.2 69.4 230.9 -49.9 312.8 41.0
CENTER FOR 580 Selene SAO 79750 DATE 1999 Mar 3
W. LONG. LAT. W. LONG. LAT. W. LONG. LAT. W. LONG.
LAT.
81.000 21 5.6 92.000 26 4.4 104.000 30 59.4 116.000 35
13.7
82.000 21 33.7 93.000 26 30.4 105.000 31 22.2 117.000 35
32.9
83.000 22 1.5 94.000 26 56.1 106.000 31 44.8 118.000 35
51.8
84.000 22 29.3 95.000 27 21.6 107.000 32 7.0 119.000 36
10.4
85.000 22 56.8 96.000 27 46.8 108.000 32 29.0 120.000 36
28.6
86.000 23 24.2 97.000 28 11.8 109.000 32 50.6 121.000 36
46.5
87.000 23 51.4 98.000 28 36.6 110.000 33 12.0 122.000 37
4.2
88.000 24 18.4 99.000 29 1.0 111.000 33 33.0 123.000 37
21.4
89.000 24 45.3 100.000 29 25.3 112.000 33 53.8 124.000 37
38.4
89.555 25 0.1 101.000 29 49.2 113.000 34 14.2 125.000 37
55.1
90.000 25 11.9 102.000 30 12.9 114.000 34 34.4
91.000 25 38.3 103.000 30 36.3 115.000 34 54.2
AT U.T. 6 25 0, W. LONG.= 96.148, LAT.= 27.843
AT U.T. 6 26 0, W. LONG.= 98.926, LAT.= 28.988
AT U.T. 6 27 0, W. LONG.= 101.669, LAT.= 30.085
AT U.T. 6 28 0, W. LONG.= 104.387, LAT.= 31.138
AT U.T. 6 29 0, W. LONG.= 107.089, LAT.= 32.150
AT U.T. 6 30 0, W. LONG.= 109.781, LAT.= 33.122
AT U.T. 6 31 0, W. LONG.= 112.471, LAT.= 34.058
AT U.T. 6 32 0, W. LONG.= 115.163, LAT.= 34.957
AT U.T. 6 33 0, W. LONG.= 117.864, LAT.= 35.821
AT U.T. 6 34 0, W. LONG.= 120.578, LAT.= 36.650
AT U.T. 6 35 0, W. LONG.= 123.309, LAT.= 37.445
Prediction comparison
Min. Geocentric Shift from Goffin nominal
U. T. Sep. Path Time
h m " " m
6 41.7 1.28N 0.00 0.0 E. Goffin's nominal prediction
6 37.5 1.15N 0.13S -4.2 USNO & TMO obs. to 1999Feb02, RA
extrapolated
6 39.9 1.17N 0.11S -1.8 USNO & TMO obs. to 1999Feb22, Feb. weighted
The observations of February have been heavily weighted relative to
the earlier observations, but there is little change relative to the
older observations in the path. However, the time is significantly
later
because my extrapolation of the RA residuals for the earlier prediction
was proven to be incorrect based on the new observations.
David Dunham, IOTA, 1999 March 1, 22h UT
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