Dear observers of minor planet occultations,
The asteroid (45) Eugenia (diameter about 210 km, V=13.2 mag) will occult the V=11.9 mag star GSC 1283 0410 (on the border Orion/Taurus; approximate position J2000 RA 5h 14m 40.2s DE +16 04'40") at about 12 h UT on the early morning of 1998 Sep 9 for observers in the western US.
(45) Eugenia is a well observed asteroid; I calculated a reliable orbit for it using accurate positions obtained with the meridian instruments at La Palma (CAMC), Bordeaux, and Flagstaff (USNO) between 1985 and 1997. The rms residuals are 0.21" and 0.18" in right ascension and declination, respectively.
Normally updates for occultations are issued to improve a prediction. In this particular case this is not true, because no agreement on the exact position of the target star could be reached. Unfortunately the target star is not in the ACT and was not accessible for meridian instruments during the last weeks. Fiona Vincent (St. Andrews/Scottland) and Gordon Garradd (Loomberah/Australia) took over the challanging job to obtain an accurate as possible position despite the facts that there are only 2 nearby ACT stars and that the star is at low altitude from Australia. Fiona's attempt to use the two ACT stars to derive an offset correction between the ACT and the GSC1.2 reference frame didn't give a convincing result. Comparison with positions of ACT stars obtained from DSS frames gave contradicting results at an unacceptable level for the declination of the target star. The positions of the two observers with respect to the GSC1.2 reference don't agree either:
Position of GSC 1280 0410: 5 14 40.199 +16 04 39.12 (mean Gerradd) 5 14 40.188 +16 04 39.72 (Vincent)
There is a 0.6" difference in declination. In this situation I decided to use a mean position which also gives weight to the somehow uncertain GSC->ACT reference frame correction; however, an uncertainty of 0.4" in declination remains. With the new Eugenia orbit and this star position I obtain the following central line:
Central line for an occultation by (45) Eugenia
(45) Eugenia occults GSC 1283 0410 (RA 5 14 40.194 DE +16 4 39.63)
orbit from CAMC/Bordeaux/USNO positions, star Garradd/Vincent
Minimum geocentric distance:
date: 1998 9 9 time: 11 51 34.UT; d=1.13", PW=4.96 deg, pi=3.13", mu=29.52"/h
substellar point on earth (lat., long.), PA of least distance:
16.07 -87.57 4.96
Lat. Long. hh:mm:ss UT StarAlt° StarAzi° SunAlt° SunAzi°
26.95 -177.97 11:45:41. ! 5.7 74.8 -57.8 358.3
29.78 -167.36 11:45:53. ! 15.4 80.0 -53.7 16.6
31.31 -161.03 11:46: 6. ! 21.1 83.5 -50.3 25.7
32.44 -155.93 11:46:19. ! 25.5 86.5 -47.2 32.1
33.35 -151.50 11:46:31. ! 29.3 89.4 -44.3 37.2
34.11 -147.49 11:46:44. ! 32.7 92.1 -41.6 41.5
34.76 -143.78 11:46:57. ! 35.7 94.8 -39.0 45.1
35.31 -140.29 11:47:10. ! 38.6 97.5 -36.5 48.4
35.79 -136.97 11:47:22. ! 41.2 100.2 -34.1 51.3
36.21 -133.80 11:47:35. ! 43.7 102.9 -31.7 54.1
36.57 -130.75 11:47:48. ! 46.0 105.7 -29.5 56.6
36.88 -127.79 11:48: 1. ! 48.2 108.6 -27.3 58.9
37.14 -124.92 11:48:13. ! 50.3 111.6 -25.1 61.1
37.36 -122.11 11:48:26. ! 52.3 114.7 -23.0 63.3
37.55 -119.38 11:48:39. ! 54.2 117.9 -20.9 65.3
37.70 -116.69 11:48:51. ! 56.0 121.3 -18.9 67.2
37.81 -114.06 11:49: 4. ! 57.7 124.9 -16.9 69.1
37.89 -111.47 11:49:17. ! 59.4 128.7 -14.9 70.9
37.94 -108.92 11:49:30. ! 60.9 132.7 -12.9 72.6
37.97 -106.40 11:49:42. ! 62.3 136.9 -11.0 74.3
37.96 -103.92 11:49:55. ! 63.6 141.5 -9.0 76.0
37.93 -101.46 11:50: 8. ! 64.8 146.3 -7.1 77.6
37.87 -99.03 11:50:21. ! 65.9 151.4 -5.2 79.2
37.79 -96.62 11:50:33. ! 66.8 156.8 -3.3 80.7
37.68 -94.24 11:50:46. ! 67.6 162.5 -1.4 82.2
Given the large uncertainty of the star position the actual path can the US anywhere from west to east (see the attached map). Due to the morning twilight the occultation is only observable from the western US.
Despite great effort especially of Fiona Vincent and Gordon Garradd whom I want to thank here explicitly it was in this particular case not possible to obtain high-quality data which permit an accurate update. I am sorry for that. In addition, the target star is 1 mag fainter then publisched in the Sky & Telescope occultation list, which makes this event less attractive.
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 -------------------------------------------------------------------------