Occultation by (71) Niobe and possible satellite, Feb. 15/16
A year ago, Niobe occulted an 8th-mag. star; observations with large telescopes in the Midwestern USA indicated that it probably has a satellite at least 16 km in diameter about 600 km away Good occultations across North America Dec. 30, Jan. 4 & 5
This is a trans-Atlantic event, visible from central Mexico, southern Florida, and southern Europe, but an occultation by the satellite is possible over a wider area
New: 2006 Febuary 13 UT
Occultation of 10.5-mag. TYC 0240-00025-1 by the 83-km asteroid 71 Niobe Wednesday evening, Feb. 15 in North America; Feb. 16 about 4h UT, Thursday morning, Feb. 16, in southern Europe. The predicted path crosses central Mexico over 200 km north of Mexico city at 4:05 UT; over southern Florida (Miami near the southern limit, Ft. Myers near the northern limit) at 4:03 UT = 11:03 pm EST; over southern Portugal (Lisbon near the northern limit) at 3:56 UT; over southern Spain (Valencia near the s. limit) and Majorca at 3:55 UT; and over southern Italy (Naples near the 1-sigma n. limit) and northern Greece at 3:54 UT. But as noted above, Niobe may have a relatively large satellite, so you should try to observe for 1.5 minutes before and after the predicted time for your location, and observers within 800 km of the predicted path should watch for an occultation by the satellite. Information about the observations of last year's occultation by Niobe and its satellite are in the March issue of Sky and Telescope, with details here. Accuweather is forecasting only scattered cirrus in southern Florida; I plan to try to observe the occultation there from three separate stations. Let me know your plans so that I don't duplicate your chord with my mobile telescopes. The star is at J2000 R.A. 9h 57m 35.2s, Dec. +02 deg. 44' 45", in Sextans about 9 deg. south and a little west of Regulus, 4 deg. northwest of alpha Sextantis, 0.8 deg. southwest of 12 Sextantis, and 0.4 deg. east and a little south of an 8th-mag. star halfway between 7 and 12 Sextantis. Two other 10th-mag. stars are within 3' of the target star to its west, and a 9th-mag. star is about 8' west of the target star. Niobe is as bright as the target star, so if an occultation occurs, the combined brightness will decrease by 0.8 mag. for up to 6 seconds, but the brightness drop could be less if Niobe is near a maximum of its light curve; current photometry would be useful to know if that's the case or not. An occultation by the 16-km (min. size) satellite could last just over a second. The 92% sunlit Moon will be 30 deg. away. Steve Preston's link for this event gives path maps and detailed finder charts of different scales. Charlie Ridgway's interactive maps site is here. Derek Breit's station list is here. From this station list, arranged by distance from the predicted central line, you can see the predicted time of the occultation for your location, as well as the altitudes of the star and Sun, and the probability for an occultation by Niobe (but it doesn't take into account the probability of an occultation by Niobe's satellite). I'll distribute a list of planned sites where observations might be attempted late this evening (Feb. 13) or certainly by Tues. evening, for better planning for this event. Oliver Kloes has prepared a map of the path of this occultation, including the zone from which the satellite might occult the star, for Europe that you can see here with a Word version here. It shows many observatories from which the event might be monitored, but none of those shown are in the main path. __________________________________________________ David Dunham, IOTA home dunham@starpower.net 301-474-4722 cell 301-526-5590 office david.dunham@jhuapl.edu 240-228-5609