Station sort for along the path
More static maps of path
Pre-point star opportunities
You might see the best asteroidal occultation of February over the Phoenix region Friday evening
A 10.1-mag. star in Gemini, halfway between Castor and Mebsuta, will be occulted for 5 seconds at 10:05pm MST Friday evening, Feb. 8, across the southern suburbs of Phoenix, and southward to Florence. We need your help to obtain good coverage of this event. It’s the best asteroidal occultation this month in Arizona, so we hope that you might be able to observe the event, to help us determine the size, shape, and possible satellites of this asteroid, like we did for Euryanthe on Jan. 19/20; the results for that event will be posted tomorrow (Thurs.) at http://iota.jhuapl.edu/AZoccsPast.htm and were distributed (sky plane plot) with a message that I sent to many of you on February 1st. Although the path for Iva is expected over the southern part of Phoenix, the path could shift north to pass over even some of the northern suburbs, as actually happened with Euryanthe. Anyone with a 4-in. or larger telescope should be able to observe the event; if you don’t have video gear or an astronomical CCD (see http://www.asteroidoccultation.com/observations/DriftScan/Index.htm for CCD’s), you can still observe it visually using a cell phone (or two of them, one to record your audio event calls, and the other to provide time signals, like those from the free apps Time the Sat for Androids and Emerald Time for iPhones. A visual observation is better than no observation. If your telescope doesn’t have a good GoTo capability or if you have trouble finding stars like this, there’s a relatively easy way to “pre-point” your telescope to the direction (altitude and azimuth) at which the occultation will occur, by using stars close to 1.65-mag. El Nath (beta Tauri) around 8:30 pm; details for doing that are given below. Even if you don’t have a telescope, we could use your help with our multi-station deployment for the event, like Dale Stanbridge provided for Euryanthe. The weather forecast looks rather good for the region, with some models indicating clear skies across most of Arizona, while others show high clouds approaching from the west, possibly reaching the Phoenix area.
Some path maps and the latest weather forecast maps, and the finder charts, have been posted at http://www.occultationpages.com/rasc/20190209_497Iva.html. For a central occultation, the star will disappear for 5 seconds with a large 4.5-mag. drop to the 14th mag. of Iva, which is expected to be 38 km in diameter. But if the star is an unknown close binary, the drop could be less, or in quick steps. The thin crescent Moon will be below the horizon, but the very high altitude for the Phoenix area, 85 deg. in the southeast (azimuth 151 deg.) might make this difficult for fork alt-az mounts (camera or eyepiece holder clearance); a right-angle finder will be virtually a necessity. Finder charts of different scales and other event details are at http://www.asteroidoccultation.com/2019_01/0120_527_59090.htm but my finder charts at the above Web site, directly at http://www.occultationpages.com/temp/PHXcharts.pdf, are better. Let us or IOTA’s free Occult Watcher asteroidal occultation planning tool (http://www.occultwatcher.net/ ) know your plans; we would prefer not to duplicate your observation with one of our mobile sites, so we can optimize observational coverage of Euryanthe with the most detail possible.
FINDING THE TARGET STAR
The star is UCAC4 596-039036, sometimes known as TYC 1507-00048-1, is at J2000 RA 7h 04m 17.4s, Dec +29° 10¢ 45². This is about halfway between Castor and Mebsuta (epsilon Gem, mag. 3.1), 2 deg. southwest of 3.7-mag. tau Geminorum (tau Gem), only 14 arc minutes southeast of 5.6-mag. SAO 79009 (marked “B” on my charts), and 3 arc minutes south of 8.7-mag. PPM 96985 (marked “A” on my charts). These stars should help you find and ID the star, especially when used with my star charts (pages 2 - 5) of the target field; the Guide chart level is the number in the lower left corner of the legend of the chart, which all use Universal Time (as noted at the bottom of the charts, add the UT to 5pm to obtain MST of Feb. 8).
But especially at the high altitude, it might not be very easy to find the star directly. Another way, that always works because the Earth’s rotation is so exact, is to point your telescope at a bright star at nearly the target’s declination at a specified time before the event, then turn off all tracking with your telescope (keep it fixed), and the target field will drift through at the right time (then, you should be able to spot “A”, and the target star just south of it). For this occultation, the best opportunity for this “pre-pointing” is provided by three stars close to 1.65-mag. El Nath (or Elnath or Alnath, = beta Tauri) that I label as D, E, and F as shown on the last 3 charts of my charts .pdf file at http://www.occultationpages.com/temp/PHXcharts.pdf. The Feb 8th MST times to pre-point to these stars are:
D (SAO 77137) at 8:24.2 pm; 8.0-mag. D is 1 deg. n.w. of El Nath and about 15 arc minutes n.w. of 6th-mag. 22 Aur. Point your telescope 2 arc min. north of D and the target will be centered at the occultation time, 10:05.2 pm MST.
E (SAO 77158) at 8:26.6 pm; 8.6-mag. E is near a group of fainter stars to its n.e. Point your telescope 4.5 arc min. south of E at the time to center the target at 10:05.2 pm.
F (SAO 77205) at 8:30.9 pm; F is 6.2 mag. and 1 deg. n.e. of El Nath. Point your telescope 3 arc min. south of F at the time, to center the target at 10:05.2 pm.
More details of these (esp. star coordinates) and other pre-point opportunities are given in the attached plain text file, st497PHX.txt.
On Friday morning, there will be two other occultations expected over the Phoenix region, of a 14.2-mag. star by (907) Rhoda at 5:30am MST, and of a 12.2-mag. star by the NASA “metal worlds” mission target (16) Psyche, a large asteroid with 100% chance for an occultation in the area. But Psyche is brighter than the star, so there will be only a 0.5-mag. drop when the occultation occurs, and an unobstructed southeastern horizon will be needed, as the event will occur only 9 deg. high in azimuth 121 deg. More information about these other future occultations is at http://iota.jhuapl.edu/AZoccs.htm .
Last Friday evening, Feb. 1 MST, Tony George, Paul Maley, Wayne Thomas, Ted Blank, and Joan and I recorded the Hispania occultation; the result will be posted in the past events at the Arizona past observed events page at http://iota.jhuapl.edu/AZoccsPast.htm with details at http://www.asteroidoccultation.com/observations/Results/Reviewed/index.html .
A good write-up about multiple-station deployments is at http://iota.jhuapl.edu/elektra.pdf . A good general write-up about observing occultations, especially the latest for observing with video, is at the link, “This .pdf document” prepared by George Viscome near the bottom of http://iota.jhuapl.edu/AZoccs.htm .
David Dunham, firstname.lastname@example.org, cell 301-526-5590
I sent the message below about this event to observers in central Arizona, but the path also passes over northernmost Baja California and Yuma, and then east across central NM, the TX panhandle, OK, and on to NC. Actually, the path goes the other way, over eastern NC at 4:58 UT (11:58pm EST Friday evening, Feb. 8), western NC and s.w. corner of TN at 4:59 UT, over southern Tenn. at 5:00 (11:00 pm CST), n. Ark. At 5:01 UT, s. OK at 5:02, the s. TX panhandle and part of e. NM at 5:03 UT, and 5:04 UT (10:04pm MST) over the rest of NM and east-central AZ. Steve Messner has posted much information about the event at http://www.occultationpages.com/rasc/20190209_497Iva.html and will post some more, including updated cloud cover forecast maps, in the morning (of Feb. 7). Unfortunately, the current forecast looks quite poor in the path from central OK to NC. The forecasts say it will be clear in NM, and mostly clear over the TX panhandle and AZ, but clouds possibly moving in over the Yuma area. Read the first page of the finder charts and El Nath pre-point opportunity at http://www.occultationpages.com/temp/PHXcharts.pdf - the charts are for the Phoenix area, where the altitude will be 85 deg. in the southeast (azimuth 151 deg.) Near where the path crosses I-25 in NM, the target will be on the meridian, due south, and east of there, the target will be high in the southwest, rather than the south. The pre-point list currently at the occultationpages Web page is generic (from Derek Breitís Web site), just giving the time offset that has to be subtracted from the time of the occultation from your station. Itís easiest to obtain the event time for your location from OW, but if you donít have that, then you can download the text data from the Sites.txt button and edit it (with Notepad or Word) to search for the name of an observatory or city near your location, or you can just use the map to estimate your time to 5s or 10s, which will be good enough for most observers. Sometime later this morning, the pre-point list specifically for the Phoenix area will be on the occultationpages page for Iva, and itís worth downloading for its annotations, giving the letters of a number of pre-point stars that are shown on both the target star and El Nath pre-point opportunity star charts.