On Monday morning, February 18th, the 4.2-mag. star chi Virginis, 11 deg. west-northwest of Spica, will be occulted for about 11 seconds by the 37-km asteroid (396) Aeolia in a path expected to cross southern Texas at 12:39 UT (6:39 am CST), from 12:40 to 12:45 UT over n. Mexico, while at 12:44 UT (4:44 am.PST) over southern Baja California Norte. It’s the 2nd brightest asteroidal occultation in North America this year, but may be overshadowed by the occultation of Sirius by the small asteroid Jurgenstock 17 hours later. Bright occultations like this provide an opportunity to obtain high signal-to-noise (more believable) observations of occultations by possible satellites of the asteroid, so observers out to 10 times the width of the occultation path should try to observe (although the Hill sphere is much larger, nearly all of the known Main Belt asteroidal satellites orbit within 10 diameters of the primary) That is the wide range shown between the two dark gray lines on the map near the bottom of the special page that Steve Messner has set up for this event at http://www.occultationpages.com/rasc/20190218_396Aeolia.html.That page includes other useful maps of the path, showing more detail of it across southern Texas, augmenting Steve Preston’s prediction page with finder charts of different scales for locating the target star available at http://www.asteroidoccultation.com/2019_02/0218_396_62622.htm . Because the asteroid is relatively small, the event rank is 85, meaning that an observer at the predicted central line has a 71% chance of an occultation. More observers are needed to try this event, to try to cover the path and the 1-sigma prediction uncertainty zone (between the two red lines on the maps; the 1-sigma error in this case is half a path-width), to give a good chance for getting a few chords across the asteroid. So far, nobody has signed up with Occult Watcher to observe this event.

The star is HIP 61740 at J2000 RA 12h 39m 14.7s, Dec -7 59m 44s. For a central occultation, the star will disappear for 11 seconds with a spectacular 10-mag. drop to the 14.5 mag. of Aeolia, that you don’t need to see. If the spectral type K2III star is an unknown close binary, the drop could be less, or in quick steps. The angular diameter of the star should be 0.002 arc second ("), while Aeolia will subtend 0.029". The disappearance and reappearance of the star should take about 0.8 second to cover and uncover the star’s disk for a central event, but longer for near-grazing conditions. There will be partial occultation zones 8 km wide at the northern and southern limits of the actual occultation path, which should be about 60 km wide. The 98% sunlit waxing Moon will be below the horizon for Texas, but may be above the horizon in Baja; it is 59 deg. from chi Virginis. Finder charts of different scales and other event details are on S. Preston’s prediction page with link given above.

The occultation of Sirius occurs only 17h after the Aeolia event along a path that may cross southernmost Baja California, then centrally over New Mexico, eastern Colorado, and on to the Winnipeg area. Much information about it has already been posted at http://www.occultationpages.com/rasc/20190219_4388Jurgenstock.html . The paths for the chi Virginis occultation and the Sirius one cross in Sonora, Mexico; a lucky observer there might see two occultations of naked-eye stars (both the Sun and Moon should be down there, for the Aeolia occultation) on the same local date, February 18.

Some cloudcover forecast maps will be added later this week.
If you click on the “Files” tab at the top of this page, you get Derek Breit’s RASC events page; scroll down to the line for this event, on 2019 Feb 18, and several items to the right bring up other pages that are useful, especially the interactive “Google Map”; useful to some might be the pre-point list obtainable with the “Stars” link, and event times and circumstances for several observatories and cities with the “Sites” link. But times and circumstances (except accurate Sun altitude) can be estimated well enough from the North American map at the top of this page for this event.

The occultation will occur in bright twilight across southern Texas. Although observers there can observe the star under those conditions with a small telescope, and possibly with binoculars, it will be necessary to locate the star perhaps half an hour before, while the sky is dark enough to easily find it, then keep following the star until 12:42 UT (6:42am CST), which is 3 minutes after the expected time in Texas. The approximate Sun altitudes at 1-deg. intervals of longitude across southern Texas are given below:

W. Long.  Sun alt.   Place
  97   -6.0      Port Aransas/Corpus Christi
  98   -6.8   Alice, US 281
  99   -7.2   east of Encinal and I-35
100   -8.4   Rio Grande

David Dunham, IOTA, dunham@starpower.net, cell 301-526-5590
Binoculars occultation of 4.2-mag. chi Vir by asteroid (396) Aeolia
Mon. am, Feb. 18, sTX & nMex
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More static maps of path