Dear observer of minor planet occultations,
on behalf of IOTA/ES I calculated another update for the Sep 18 event
of Abnoba/TAC-2 11988. This calculation is based on USNO data only
for both the star and the asteroid (18 positions June 23-September 17,
Sep 7 and one Sep 15 rejected). The accuracy of both the orbit and
the star position is very good and I expect the remaining uncertainty
to be 0.08" (about 120 km or 2.5 path widths) in this case. This means
that Tenerife (Izana) is out of the race (400 km distance to the central
line). Observers on northern Lanzarote might have a chance. Unfortunately,
I don't know of any observers in those regions of Africa which are touched
by the occultation path.
The updated central line follows in the table; further details of the occultation may be extracted from my previous note.
Central line for an occultation by (456) Abnoba
(456) Abnoba occults TAC -2 11988 (RA 19 36 5.069 DE -2 19 36.45)
orbit from 18 USNO positions only, star USNO
Minimum geocentric distance:
date: 1998 9 18 time: 20 16 11.UT; d=1.29", PW=45.93 deg, pi=4.40",mu=18.72"/h
substellar point on earth (lat., long.), PA of least distance:
-2.33 -7.58 45.93
Lat. Long. hh:mm:ss UT StarAlt° StarAzi° SunAlt° SunAzi°
60.39 -66.87 20: 3: 0. ! 11.1 115.3 17.9 239.8
57.19 -54.47 20: 3:28. ! 18.3 126.2 13.2 252.0
54.40 -46.90 20: 3:56. ! 23.4 132.8 9.7 259.2
51.85 -41.35 20: 4:25. ! 27.6 137.6 6.8 264.1
49.48 -36.95 20: 4:53. ! 31.3 141.5 4.1 267.9
47.24 -33.28 20: 5:21. ! 34.6 144.8 1.6 270.8
45.11 -30.14 20: 5:49. ! 37.6 147.6 -.8 273.2
43.07 -27.37 20: 6:17. ! 40.4 150.2 -3.0 275.1
41.11 -24.90 20: 6:46. ! 43.0 152.6 -5.1 276.7
39.21 -22.65 20: 7:14. ! 45.5 154.9 -7.1 278.1
37.38 -20.59 20: 7:42. ! 47.9 157.1 -9.1 279.2
35.59 -18.68 20: 8:10. ! 50.2 159.3 -11.0 280.2
33.85 -16.89 20: 8:38. ! 52.3 161.5 -12.9 280.9
32.15 -15.20 20: 9: 6. ! 54.4 163.7 -14.7 281.6
30.49 -13.60 20: 9:35. ! 56.4 166.1 -16.5 282.1
28.86 -12.07 20:10: 3. ! 58.3 168.5 -18.2 282.5
27.25 -10.60 20:10:31. ! 60.1 171.1 -19.9 282.8
25.68 -9.18 20:10:59. ! 61.9 173.8 -21.6 283.1
24.13 -7.81 20:11:27. ! 63.5 176.8 -23.3 283.2
22.60 -6.48 20:11:55. ! 65.1 180.1 -24.9 283.2
21.09 -5.18 20:12:24. ! 66.5 183.7 -26.6 283.2
19.60 -3.90 20:12:52. ! 67.9 187.6 -28.2 283.1
18.13 -2.65 20:13:20. ! 69.1 191.9 -29.8 282.9
16.67 -1.41 20:13:48. ! 70.2 196.7 -31.3 282.6
15.23 -.19 20:14:16. ! 71.2 201.9 -32.9 282.3
13.80 1.03 20:14:44. ! 71.9 207.5 -34.5 281.9
12.38 2.24 20:15:13. ! 72.5 213.5 -36.0 281.4
10.97 3.44 20:15:41. ! 72.8 219.8 -37.6 280.8
9.57 4.65 20:16: 9. ! 73.0 226.3 -39.1 280.1
8.18 5.85 20:16:37. ! 72.9 232.7 -40.6 279.4
6.80 7.07 20:17: 5. ! 72.6 238.9 -42.2 278.5
5.42 8.30 20:17:33. ! 72.0 244.9 -43.7 277.6
4.05 9.53 20:18: 2. ! 71.3 250.4 -45.2 276.5
2.68 10.79 20:18:30. ! 70.4 255.4 -46.7 275.3
1.32 12.06 20:18:58. ! 69.3 259.9 -48.2 274.0
-.04 13.36 20:19:26. ! 68.1 263.8 -49.7 272.6
-1.39 14.68 20:19:54. ! 66.8 267.3 -51.1 271.0
-2.74 16.04 20:20:23. ! 65.4 270.4 -52.6 269.2
-4.09 17.43 20:20:51. ! 63.8 273.1 -54.1 267.2
-5.44 18.86 20:21:19. ! 62.2 275.3 -55.5 265.1
-6.79 20.34 20:21:47. ! 60.4 277.3 -57.0 262.6
-8.14 21.87 20:22:15. ! 58.6 279.0 -58.4 259.9
-9.49 23.46 20:22:43. ! 56.7 280.4 -59.8 256.9
-10.85 25.12 20:23:12. ! 54.8 281.5 -61.1 253.5
-12.20 26.86 20:23:40. ! 52.7 282.4 -62.4 249.6
-13.55 28.69 20:24: 8. ! 50.6 283.1 -63.6 245.3
-14.91 30.62 20:24:36. ! 48.3 283.6 -64.8 240.4
-16.27 32.67 20:25: 4. ! 46.0 283.9 -65.8 234.9
-17.64 34.87 20:25:32. ! 43.5 284.0 -66.7 228.7
-19.00 37.23 20:26: 1. ! 40.9 283.9 -67.4 221.7
-20.37 39.80 20:26:29. ! 38.1 283.6 -67.9 213.9
-21.74 42.62 20:26:57. ! 35.1 283.1 -68.1 205.2
-23.11 45.77 20:27:25. ! 31.9 282.3 -67.8 195.8
-24.47 49.35 20:27:53. ! 28.3 281.2 -67.1 185.7
-25.83 53.56 20:28:21. ! 24.2 279.7 -65.8 174.8
-27.16 58.76 20:28:50. ! 19.3 277.5 -63.6 163.1
-28.42 66.04 20:29:18. ! 12.7 274.2 -59.8 149.4
Good luck to those observers who want to try their luck anyway!
Martin Federspiel (IOTA/ES)
------------------------------------------------------------------------- Martin Federspiel ******** E-mail: martin@astro.unibas.ch Astronomisches Institut ******** oder: federspi@astro.unibas.ch der Universitaet Basel **** oder: federspielm@ubaclu.unibas.ch Venusstr. 7 Telefon: (CH)-61/2055413 CH-4102 Binningen (Schweiz) Fax: (CH)-61/2055455 -------------------------------------------------------------------------
Dear observers of minor planet occultations,
the occultation of the star TAC-2 11988 (V=10.8 mag) near iota Aql by (456) Abnoba (V=13.8 mag) on the evening (UT) of 1998 July 18 is coming up. This event is of interest for observers on the Canary Islands and will at most last for 6 seconds. The occultation path is about 50 km wide.
For this update several persons supplied astrometry, all claimed in the ACT
reference frame:
* Angel Lopez from Mallorca: 25 measurements of the star, 43 of the asteroid
obtained during 7 nights
* Fiona Vincent (St. Andrews/Scottland): 16 measurements of the asteroid
obtained during 2 nights
* Ron Stone (USNO/Flagstaff): 14 measurements of the asteroid, 1 of the star
obtained during 14 nights (June 23 until Sep 7)
I tried several combinations of the data to calculate an optimal orbit of the asteroid. First I calculated normal places for each night for Angel's and Fiona's data; however, it turns out that the residuals of the Mallorca and St. Andrews data are at an unacceptable level (0.2-0.3") in the presence of the USNO data. The orbit from the USNO data alone has a rms residuum of 0.05" and 0.06" in right ascension and declination, respectively. Since the USNO data essentially cover the same arc as the Mallorca and St. Andrews data I decided to use the USNO data exclusively for the orbit calculation.
The available positions of the target star (TAC, USNO, Mallorca) agree
quite well with one another. I adopted a mean position from the single
USNO measurement and from the mean Mallorca position.
With the described data I get the following central line, which is shifted about 0.8" to the southwest compared to Edwin Goffin's nominal prediction. The event is of interest for observers on the Canary Islands and in Africa (where I don't know of potential observers):
Central line for an occultation by (456) Abnoba
(456) Abnoba occults TAC-2 1198 (RA 19 36 5.066 DE - 2 19 36.50)
orbit from 15 USNO positions only, star USNO/Mallorca
Minimum geocentric distance:
date: 1998 9 18 time: 20 15 54.UT; d=1.20", PW=45.89 deg,pi=4.40", mu=18.72"/h
substellar point on earth (lat., long.), PA of least distance:
-2.33 -7.51 45.89
Lat. Long. hh:mm:ss UT StarAlt° StarAzi° SunAlt° SunAzi°
43.99 -30.81 20: 5:32. ! 38.2 146.3 -.3 272.6
41.99 -28.09 20: 6: 1. ! 41.0 148.8 -2.5 274.5
40.06 -25.65 20: 6:29. ! 43.7 151.1 -4.6 276.1
38.19 -23.42 20: 6:57. ! 46.2 153.3 -6.6 277.4
36.38 -21.38 20: 7:25. ! 48.5 155.4 -8.6 278.5
34.62 -19.47 20: 7:53. ! 50.8 157.6 -10.5 279.5
32.90 -17.69 20: 8:21. ! 53.0 159.7 -12.3 280.2
31.22 -16.00 20: 8:50. ! 55.1 161.9 -14.1 280.9
29.57 -14.41 20: 9:18. ! 57.1 164.1 -15.9 281.4
27.95 -12.88 20: 9:46. ! 59.0 166.5 -17.6 281.8
26.37 -11.41 20:10:14. ! 60.9 169.0 -19.3 282.1
24.80 -9.99 20:10:42. ! 62.6 171.8 -21.0 282.3
23.26 -8.62 20:11:11. ! 64.3 174.7 -22.7 282.4
21.75 -7.29 20:11:39. ! 65.9 177.9 -24.3 282.4
20.25 -5.99 20:12: 7. ! 67.4 181.5 -25.9 282.4
18.76 -4.71 20:12:35. ! 68.8 185.5 -27.5 282.3
17.30 -3.45 20:13: 3. ! 70.1 189.9 -29.1 282.1
15.85 -2.22 20:13:31. ! 71.2 194.8 -30.7 281.8
14.41 -.99 20:13:60. ! 72.2 200.2 -32.3 281.4
12.98 .22 20:14:28. ! 73.0 206.1 -33.8 281.0
11.57 1.43 20:14:56. ! 73.6 212.4 -35.3 280.5
10.16 2.64 20:15:24. ! 74.0 219.2 -36.9 279.9
8.77 3.84 20:15:52. ! 74.2 226.1 -38.4 279.2
7.38 5.05 20:16:20. ! 74.1 233.0 -39.9 278.5
6.00 6.27 20:16:49. ! 73.7 239.6 -41.4 277.6
4.62 7.49 20:17:17. ! 73.2 245.9 -42.9 276.7
3.26 8.73 20:17:45. ! 72.4 251.7 -44.4 275.6
1.89 9.98 20:18:13. ! 71.4 256.9 -45.9 274.4
.53 11.26 20:18:41. ! 70.3 261.6 -47.4 273.1
-.83 12.55 20:19: 9. ! 69.1 265.7 -48.8 271.6
-2.18 13.87 20:19:38. ! 67.7 269.2 -50.3 270.0
-3.54 15.23 20:20: 6. ! 66.2 272.3 -51.7 268.3
-4.89 16.62 20:20:34. ! 64.6 274.9 -53.2 266.3
-6.24 18.05 20:21: 2. ! 63.0 277.1 -54.6 264.1
-7.59 19.52 20:21:30. ! 61.2 279.1 -56.0 261.7
-8.95 21.05 20:21:58. ! 59.4 280.7 -57.4 259.0
-10.30 22.64 20:22:27. ! 57.5 282.0 -58.7 256.1
-11.66 24.29 20:22:55. ! 55.5 283.1 -60.0 252.7
-13.01 26.03 20:23:23. ! 53.4 283.9 -61.3 249.0
-14.37 27.85 20:23:51. ! 51.2 284.6 -62.5 244.8
-15.74 29.77 20:24:19. ! 49.0 285.0 -63.6 240.1
-17.10 31.82 20:24:48. ! 46.6 285.3 -64.6 234.8
-18.47 34.00 20:25:16. ! 44.1 285.3 -65.5 228.9
-19.85 36.35 20:25:44. ! 41.5 285.2 -66.2 222.2
-21.23 38.90 20:26:12. ! 38.8 284.8 -66.7 214.8
-22.60 41.70 20:26:40. ! 35.8 284.2 -66.9 206.7
-23.98 44.82 20:27: 8. ! 32.6 283.4 -66.7 197.8
-25.36 48.35 20:27:37. ! 29.0 282.2 -66.1 188.1
-26.73 52.47 20:28: 5. ! 25.0 280.7 -64.9 177.7
-28.08 57.52 20:28:33. ! 20.3 278.5 -63.0 166.4
-29.38 64.36 20:29: 1. ! 14.1 275.3 -59.7 153.4
I estimate the possible error of this prediction to be 0.15" or about 200 km on the Earth.
Good luck to Ricard and to all other observers!
Martin
------------------------------------------------------------------------- Martin Federspiel ******** E-mail: martin@astro.unibas.ch Astronomisches Institut ******** oder: federspi@astro.unibas.ch der Universitaet Basel **** oder: federspielm@ubaclu.unibas.ch Venusstr. 7 Telefon: (CH)-61/2055413 CH-4102 Binningen (Schweiz) Fax: (CH)-61/2055455 -------------------------------------------------------------------------
Dear observers of minor planet occultations,
I computed a preliminary update for the occultation from data by Angel Lopez. The line shifts for more than 1" to the southwest and now crosses only Africa (see attached map). I will calculate a new update shortly before the event with additional data (from Angel Lopez and Fiona Vincent/ St. Andrews, Scottland).
There are now enough positions to compute an independent orbit. This orbit is considerably
different (at the 1" level) from the "official" orbits available so far.
The remaining residuals are quite homogenous for one night but differ
from night to night. Probably they depend on the set of selected comparison
stars.
Central line for an occultation by (456) Abnoba
(456) Abnoba occults TAC-2 11988 (RA 19 36 5.068 DE - 2 19 36.51)
orbit from Mallorca/ACT positions only, star Mallorca/ACT
Minimum geocentric distance:
date: 1998 9 18 time: 20 18 4.UT; d=.56", PW=45.84 deg, pi=4.40", mu=18.72"/h
substellar point on earth (lat., long.), PA of least distance:
-2.33 -8.06 45.84
Lat. Long. hh:mm:ss UT StarAlt° StarAzi° SunAlt° SunAzi°
51.06 -72.19 20: 4:26. ! 12.1 109.2 25.1 238.2
48.50 -62.09 20: 4:54. ! 19.1 117.1 20.3 248.2
46.19 -55.43 20: 5:22. ! 24.3 122.2 16.7 254.4
44.02 -50.34 20: 5:50. ! 28.5 126.0 13.6 258.9
41.96 -46.17 20: 6:18. ! 32.2 129.1 10.9 262.4
39.99 -42.62 20: 6:46. ! 35.6 131.7 8.3 265.2
38.09 -39.52 20: 7:15. ! 38.7 134.0 6.0 267.5
36.25 -36.77 20: 7:43. ! 41.7 136.0 3.7 269.4
34.46 -34.28 20: 8:11. ! 44.4 137.8 1.6 271.0
32.72 -32.00 20: 8:39. ! 47.0 139.5 -.5 272.3
31.02 -29.90 20: 9: 7. ! 49.6 141.1 -2.4 273.5
29.36 -27.94 20: 9:35. ! 52.0 142.6 -4.3 274.4
27.73 -26.10 20:10: 4. ! 54.3 144.1 -6.2 275.2
26.13 -24.36 20:10:32. ! 56.6 145.5 -8.0 275.9
24.55 -22.71 20:10:60. ! 58.8 147.0 -9.7 276.4
23.00 -21.14 20:11:28. ! 60.9 148.5 -11.5 276.8
21.47 -19.63 20:11:56. ! 63.0 150.1 -13.1 277.2
19.96 -18.17 20:12:24. ! 65.0 151.8 -14.8 277.4
18.47 -16.76 20:12:53. ! 67.0 153.6 -16.4 277.5
17.00 -15.39 20:13:21. ! 68.9 155.7 -18.0 277.6
15.53 -14.06 20:13:49. ! 70.8 158.0 -19.6 277.6
14.09 -12.75 20:14:17. ! 72.7 160.8 -21.1 277.5
12.65 -11.47 20:14:45. ! 74.4 164.0 -22.7 277.3
11.23 -10.22 20:15:13. ! 76.2 167.9 -24.2 277.0
9.81 -8.97 20:15:42. ! 77.8 172.9 -25.7 276.7
8.41 -7.75 20:16:10. ! 79.3 179.1 -27.2 276.3
7.01 -6.53 20:16:38. ! 80.6 187.2 -28.6 275.8
5.62 -5.32 20:17: 6. ! 81.7 197.5 -30.1 275.2
4.24 -4.11 20:17:34. ! 82.4 210.3 -31.5 274.6
2.86 -2.90 20:18: 3. ! 82.7 224.9 -32.9 273.9
1.48 -1.69 20:18:31. ! 82.5 239.6 -34.3 273.1
.11 -.48 20:18:59. ! 81.8 252.6 -35.7 272.2
-1.26 .75 20:19:27. ! 80.8 263.2 -37.1 271.2
-2.63 1.99 20:19:55. ! 79.5 271.4 -38.5 270.1
-3.99 3.24 20:20:23. ! 78.0 277.6 -39.8 268.9
-5.36 4.51 20:20:52. ! 76.4 282.4 -41.2 267.6
-6.72 5.80 20:21:20. ! 74.7 286.1 -42.5 266.1
-8.09 7.12 20:21:48. ! 73.0 288.9 -43.8 264.6
-9.46 8.46 20:22:16. ! 71.1 291.1 -45.1 262.8
-10.83 9.85 20:22:44. ! 69.3 292.8 -46.4 261.0
-12.21 11.27 20:23:12. ! 67.3 294.2 -47.6 258.9
-13.58 12.74 20:23:41. ! 65.3 295.2 -48.8 256.7
-14.97 14.25 20:24: 9. ! 63.3 296.0 -50.0 254.3
-16.35 15.83 20:24:37. ! 61.2 296.5 -51.2 251.6
-17.75 17.47 20:25: 5. ! 59.1 296.9 -52.3 248.7
-19.15 19.19 20:25:33. ! 56.9 297.0 -53.3 245.6
-20.56 21.00 20:26: 1. ! 54.7 297.0 -54.3 242.1
-21.97 22.90 20:26:30. ! 52.4 296.8 -55.3 238.3
-23.40 24.93 20:26:58. ! 50.0 296.5 -56.1 234.1
-24.83 27.09 20:27:26. ! 47.5 296.0 -56.9 229.5
-26.27 29.40 20:27:54. ! 44.9 295.3 -57.5 224.5
-27.73 31.92 20:28:22. ! 42.1 294.4 -58.0 219.0
-29.19 34.66 20:28:50. ! 39.2 293.3 -58.3 213.0
-30.66 37.69 20:29:19. ! 36.1 292.0 -58.3 206.4
-32.14 41.10 20:29:47. ! 32.8 290.3 -58.1 199.2
-33.63 45.00 20:30:15. ! 29.1 288.3 -57.6 191.2
-35.11 49.61 20:30:43. ! 25.0 285.8 -56.6 182.2
-36.58 55.35 20:31:11. ! 20.0 282.5 -54.9 172.0
-37.98 63.36 20:31:40. ! 13.4 277.6 -51.9 159.1
Best regards,
Martin Federspiel
------------------------------------------------------------------------- Martin Federspiel ******** E-mail: martin@astro.unibas.ch Astronomisches Institut ******** oder: federspi@astro.unibas.ch der Universitaet Basel **** oder: federspielm@ubaclu.unibas.ch Venusstr. 7 Telefon: (CH)-61/2055413 CH-4102 Binningen (Schweiz) Fax: (CH)-61/2055455 -------------------------------------------------------------------------