2020 May 11 occultation of 14 Cancri by (363) Padua
On 2020 May 11 UT (May 10 local time), the 86-km diameter asteroid (363) Padua will occult the 5.7 mag. star 14 Cancri for observers along a path across the southwestern USA and northeastern Mexico.
In the case of an occultation, the combined light of the asteroid and the star will drop by 9 magnitudes, to 14.7 mag (the magnitude of the asteroid) for at most 3.3 seconds. There’s a small chance the star is a close double, in which case, the occultation events could occur in two steps. A previous claim for close duplicity of the star is probably wrong; see the possible duplicity section below.
Several path maps below including possible satellite search area
Duplicity of 14 Cancri = psi2 Cancri = ZC 1233 = SAO 79995 = HIP 40023??
An occultation of this bright (V-mag. 5.7) star by the asteroid (363) Padua will occur on May 11 UT (evening of May 10 local time); Steve Preston’s prediction for it is at http://www.asteroidoccultation.com/2020_05/0511_363_64924.htm - with the orbit updated recently by the JPL Horizons team to include Gaia DR2 data for Padua, as well as the results of 3 past-observed occultations (only one chord each, but they’re much better than any “traditional” direct ground-based astrometry). However, uncertainly in the path prediction remains, as 14 Cancri was not in the Gaia DR2 (maybe because it was too bright??) and Steve Preston, echoing the Washington Double Star (WDS) catalog, says that the star is a close double with equal components; since only one of those components might be occulted while the other remains unocculted, he gives the magnitude as 6.6, the component magnitudes in WDS for “components Aa,Ab”.
But is this star really a close double? I doubt it. The Wikipedia entry for 14 Cancri notes no duplicity for the star, spectroscopic or otherwise (it has a mistake, saying the constellation is Canis Major in its table of data about the star). WDS gives the duplicity source as “OCC 73”. And I confess, it’s mainly my fault that the entry is there. In the 1970’s, during the early heydays of grazing occultations, we were constantly improving the first software systems to predict and analyze both total and grazing lunar occultations. We realized then that stars sometimes disappeared in steps, revealing close duplicity not detectable by direct observation, and we continue to discover new close doubles that way. We scoured the literature, looking for past observations that might have been missed, especially for events where the observer indicated anything unusual. We compiled a list of many possible double stars found by occultation observations. One of these observations was made by W. M. Worssell at Union Observatory, S. Africa, on 1928 Nov. 30, when he saw an occultation of 14 Cancri and noted in his log, “gradual” reappearance. This was published in a Union Observatory publication, where we read it, and added the star, ZC 1233, to our list of possible doubles discovered during occultation. In those days, we were naïve, thinking that these events, almost all observed visually, often involved close stellar duplicity, but during this century, we have observed occultations of dozens of these stars with video recordings, and in virtually all cases, the light curves measured from the video recordings only showed a single drop in brightness at the occultation, showing no hint of duplicity. For bright stars observed during lunar occultations, “gradual” events do often occur, noticeable even visually, especially under near-grazing conditions when the rate of apparent motion towards the lunar limb is reduced, but these are mainly caused by Fresnel diffraction, sometimes amplified by stellar angular diameters. Even in the 1970’s, we realized this could be the case, so the 1928 observation (as well as a large number of others) was give code “K”, meaning “possibly spurious”. Unfortunately, this distinction was lost when we gave our list to those maintaining the WDS at the time, so the many “K”-coded observations were lumped with good photoelectric observations that quantified close stellar duplicity well. So that is the basis of the shaky close duplicity of 14 Cancri. I wonder if the Gaia team decided to exclude this star from DR2 because of the WDS entry, or was its exclusion only (or mainly) due to the star’s brightness? The data for 14 Cancri for the occultation are from HIP2, which I believe has rather small positional errors, even at the current epoch (10.2 mas and 6.1 mas in RA & Dec, respectively, compared with Padua’s expected 39mas diameter). I assume from that, that HIP found no sign of close duplicity of the star. Tony George notes that in UCAC4, there is an 11.4-mag. companion 15ʺ away, but I think that is too faint and too far away to significantly affect the astrometry for the star. There was a similar faint companion (with separate Gaia DR2 entry) of 18 Aurigae, the star that was occulted by (55) Pandora last December, and our occultation observations of it showed no problems with the prediction due to that companion.
[current map by Steve Preston showing the path]
The occultation of 5.7-mag. 14 Cancri by the asteroid (363) Padua at 10:16 pm PST/MST Sunday May 10, visible from the Sacramento, Phoenix, and Tucson regions (and s.w. of Las Vegas), can be observed with steadily-held binoculars, likely the best asteroidal occultation in the s.w. USA during 2020. We need help to observe this event; we hope that as many as possible will try to observe it. Those who do astro-imaging are especially asked to help out; they can use the drift-scan technique to time the occultation described at http://www.asteroidoccultation.com/observations/DriftScan/Index.htm and some information about using DSLR cameras is at http://occultations.org/observing/educational-materials/equipment/dslr/ . I have more equipment than I can use for this event, so I want to loan some of it to other observers in the Phoenix area, so they can accurately record the event, if they currently don't have any timing equipment or a good camera. We especially need help to cover the southern and western suburbs of Phoenix, but useful observations can be made throughout the area (or ANYWHERE in/near the path), wherever you can observe. The maps below, generated from IOTA’s free Occult Watcher (OW) software, http://www.occultwatcher.net/, show the path over the southern Sacramento Valley in California, and over central and southern Arizona. The green line is the predicted central line, the blue lines are the predicted northern and southern limits, the thick read lines are the limits in case of a very possible “1-sigma” shift of the path (to the northeast or to the southwest), and the thin red lines are the limits in case of a much less-likely “3-sigma” shift. The thin black lines show the current coverage by observers who have signed up to observe the event with OW.
The path should be fairly accurate since the orbit of Padua has been updated recently with Gaia observations of Padua, and past occultation data, by the JPL Horizons team. But some uncertainty remains since the star was too bright to be included in the last release of Gaia data, so its positional data are taken from older (but still fairly accurate; see the possible duplicity section below) Hipparcos satellite observations.
Observations from and near Phoenix: Besides deploying remote stations, many on paver mounts set up on paver stones aligned on previous nights, we also want to use our 16-in. scope to obtain a high-speed recording of the target star, to augment the VERITAS data from a different chord. We will need more local help than usual to accomplish this.
Runcam Mighty Mini Systems for the May 10th occultation of 14 Cancri by (363) Padua
If there is a satellite orbiting this asteroid, an occultation by it would likely be somewhere between the gray lines
Information on different methods to time occultations
Arizona message, May 5
Timing CCD video with a smartphone flash timing app
Updated 5/10 PM
If you can find Castor and Pollux, you can help create a detailed map of asteroid (363) Padua Sunday evening
Below is a message I sent earlier tonight to observers in Arizona. But the occultation is also predicted to occur over Sacramento, Calif. (May 11 U.T. 5:15:55, alt. 35 deg.); s.w. of Las Vegas, Nev. (UT 5:16:10, alt. 30 deg.); and Monterrey, N.L., Mexico (May 11 U.T. 5:16:43, alt. 14 deg.). In Phoenix, as shown on the finder charts, the U.T. is 5:16:20, alt. 26 ½ deg., while in Tucson, the time is only 3 seconds later and half a deg. lower. But for observers away from the path, from Texas to Colorado to western British Columbia, and everywhere west of there to the Pacific coast, as well as all of Mexico west of Yucatan, essentially everywhere within 600 miles of the predicted path, they are within 10 diameters of Padua and could have a brief occultation by any satellite of Padua. The 5.7-magnitude star will give a strong signal, easy to record, if anything passes in front of it.
May 5, 2020 late pm
Reporting your observation
Instructions, star lists and charts to prepoint your scope
Station list from OccultWatcher