A Bright Naked-Eye Asteroid Occultation

Please watch 4.2-magnitude Iota Cancri blink, and time its occultation by asteroid 411 Xanthe, in s.w. Georgia and n.e. Florida at 8:56 p.m. EDT Tuesday evening, April 17th, to help the International Occultation Timing Association (IOTA) measure the size and shape of the asteroid, estimated to be 76 kilometers in diameter. Please let us know your plans so that mobile observers don't duplicate your observation. We need as many observers as possible to try to observe this occultation of the brightest star by a medium-sized asteroid to occur in North America this year. At least four observers will be mobile for this and they want to fill in gaps of coverage by fixed-site observers to best determine the shape of Xanthe.

Such a bright star should be easy to observe with binoculars, or even with the naked eye; if you're observing visually, you don't need to bother to set up a telescope. Accuweather currently is forecasting clear skies in n.e. Florida for the event, so please spread the word to others to try it. For methods of timing occultations, see http://iota.jhuapl.edu/timng920.htm and the links below.

The 76-km-wide path extends from northwest to southeast, passing over the s.w. corner of Georgia, and then sweeping across n.e. Florida. Jacksonville is north of the predicted path, but within the "1-sigma" uncertainty zone, so an occultation could occur there. Similarly, Gainesville is at the predicted southern limit, so observers there also have a good chance for an event.

The target star, also known as SAO 80416 or HIP 43103, is at J2000 RA 8h 46m 41.8s, Dec. +28° 45' 35". It has a 6.6-magnitude companion, SAO 80415, 30" to the northwest that will not be occulted. Since the Sun altitude will be –14° at the Atlantic coast, you will need to find the star in diminishing twilight. It's altitude above the horizon at the time of the event will be 85°, so finder (and maybe main) scopes with a diagonal eyepiece will help. Richard Nugent wrote on April 11th:

"This evening, at my house just 2 miles from downtown Houston, Texas, I found the target star in my 4-inch Meade 30 minutes after sunset, and had my video on the star 5 minutes later. The target star is a double and was easily seen on video with the Watec 902H Ultimate.

"Rather than strain my neck with an 85° altitude star and a straight-thru finder, I used manual setting circles to find the target star. Its declination is very close to that of the 4th-mag star (Sigma Geminorum) just 1° north of Pollux. With my scope on Pollux I turned the telescope east 1h 3m in right ascension using the RA setting circle. With a 20' x 25' field of view in the video, this was a simple find."

Maps and More Information

A North American path map and finder charts of different scales are on Steve Preston's website at http://www.asteroidoccultation.com. If an occultation occurs, there will be a 10-magnitude drop, easily noticeabe by visual observers, lasting 8 seconds for a central event.

Detailed maps for this event are on Derek Breit's interactive Web page at http://www.poyntsource.com/New/Global.htm, which links to the very detailed maps and satellite imagery of maps.google.com with overlays of the occultation paths. Also on Breit's website are station lists giving local circumstances for many observer stations. It gives the predicted time of the event, distance from the updated central line, probability that an occultation will occur there, and altitudes of the star and the Sun. If your station is not in that list, please let me and Derek (breit_ideas@hotmail.com) know so that you can be added to future lists. Also included there now are lists of stars with offset times and declination differences for pre-pointing telescopes. For those observing near I-95 in Virginia and N. Carolina, I have calculated the UT and EDT times for the pre-point stars in the table that you can get at http://iota.jhuapl.edu/st019413.txt.

A list of some stations is below, a shortened version of the longer list on Derek Breit's website given above. I've indicated the locations of prospective observers from the messages that I've received so far; please let me know your plans so I can add you to an updated version of this list that I'll be sending later. I plan to arrive at Jacksonville airport at 2:40 p.m. and can bring an extra video recording system if a local observer could use it with their telescope to try to record the occultation. Between the distance and probability columns, I've added codes for those who have said that they will try this occultation, with * for a fixed-site visual observer, V for fixed video observer, m for mobile visual observer, and M for mobile video observer. Let me know your plans so I can add a code for your station in a later update. For example, I plan to try to observe from -35 and -40 km, but I will change that if anyone in Gainesville plans to try to observe the event from there. Observers even out to the 2-sigma limits are useful to ensure coverage of the occultation. For example, for the Fortuna occultation last week, we have a nearly 2-sigma south shift of the path. Fortunately, a fixed-site observatory at about 1.2 sigma south observed and had an 11-second occultation, giving a valuable observation near the actual southern limit for that event, completing the "picture" of that asteroid that was also well-observed across its predicted path.

Occultation of HIP 43103 (Iota Cnc) by 411 Xanthe, 2007 Apr 18

Proba- Location Star Sun km* bility UT alt alt 91 15% ** Northern limit plus 1-Sigma ** h m s o o 76 22% Montgmry AL Whigham & McGraw 0 55 29 86 -9 74 23% GEORGETO GA TONY P. MURRAY 0 55 44 85 -10 60 31% JACKSONVILLE FL CRUM~DAVID A. 0 56 25 84 -13 43 40% Valdosta GA Martha Leake 0 56 7 85 -12 38 43% *** Northern limit *** 15 M 51% Paul Maley mobile 0 53% **** Centre Line **** 0 M 53% Roger Venable remote -2 m 53% Roger Venable mobile -3 53% FlaglerB FL E Noel 0 56 35 83 -14 -12 52% Lloyd FL Stephen Wingreen 0 56 2 85 -12 -17 51% ORMOND B FL WALTER L. DOBBINS 0 56 37 83 -14 -20 M 50% Richard Nugent mobile -23 49% DaytonaBeach FL 0 56 38 83 -14 -35 M 44% David Dunham remote -37 43% Gainesvl FL C.Siopis &S.Fisher 0 56 22 84 -13 -38 43% Tallahassee FL 0 55 59 86 -11 -38 43% *** Southern limit *** -40 M 44% David Dunham mobile -57 32% H74 Bar J Observatory, New Smyr 0 56 38 83 -14 -70 25% RIDGELAN MS SPEER-LYELL Ob.c/oD 0 54 51 85 -6 -72 24% 831 Rosemary Hill Observatory, 0 56 21 85 -13 -77 22% ALTAMONT FL CentralFLAst.Noeml. 0 56 34 84 -14 -91 15% ** Southern limit plus 1-Sigma ** -93 14% 758 BCC Observatory, Cocoa 0 56 45 83 -15 -100 11% H47 Vicksburg 0 54 45 85 -5 -105 10% ORLANDO FL Laurent Pellerin 0 56 39 84 -14 -109 9% INDIAN H FL HAROLD R. POVENMIRE 0 56 48 83 -15 -143 2% ** Southern limit plus 2-Sigma **

*Distance from center of occultation path in km

Reporting Your Observations

For occultations of stars by asteroids, we have special report forms (.xls versions preferred, but plain-text forms are available as well) at these URLs:

Once you complete one of these forms, please send it to IOTA's e-mail address for reporting asteroid-occultation observations: reports@asteroidoccultation.com.

Additional resources for reporting your observations are available at the website of the North American Asteroid Occultation Program:

Please check the online version of this AstroAlert on Sky & Telescope's website for possible minor updates:

Any major updates will be announced via subsequent AstroAlert messages. Good luck, and clear skies!

David Dunham
Contributing Editor
Sky & Telescope
david.dunham@jhuapl.edu
dunham@starpower.net

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