Journal for

Occultation
Astronomy
Volume 12 · No. 42022-04

NEAs - An Occultation Observation Challenge

Dear reader,

COVER

this issue of the JOA reports on the IOTA meeting in the USA
and discusses observations of the, fortunately very small, NEOs.
Of course, the Beyond Jupiter series is continued and there is aCall for Observations for upcoming stellar occultations by the
Jupiter Trojan (624) Hektor and its satellite Skamandrios.
However, we do not report on an issue that is currently keeping
us in Europe very busy: The end of Euraster.net at the end of2022. With Euraster.net, Eric Frappa operated an excellent portal
for the collection of observation data.
Now, IOTA/ES will create a successor solution. At the moment
we are still very busy with this, but I would like to thank all those
who are involved now and in the future. Even though there are stillsome problems, it is nice to see how everyone involved is helping
to find a solution. Our friends from overseas have also helped
energetically from day one in this work. Perhaps this will lead toa globally uniform database and the phrase: "Every problem isan opportunity in disguise" will prove true once again.

Konrad Guhl
President IOTA/ES

The observation of near-Earth asteroids (NEAs) is challenging.
The small dimensions of these objects and their fast movements
across the sky plane push observers to the limits of their observing
capabilities. There are pitfalls in the evaluation process of theseoccultations as Roger Vernable reports in this issue. Nevertheless,they are an important part of the Pro-Am collaboration today.
Artistic impression: O. Klös, with images from Celestia 1.6.6.2.

Copyright Transfer

JOA Volume 12 · No. 4 · 2022- 4 $ 5.00 · $ 6.25 OTHER (ISSN 0737-6766)

In this Issue:■ Call for Observations: Stellar Occultations by (624)
Hektor and Skamandrios, October 2022 - March 2023
Oliver Klös . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3■ Thoughts on the Observations of Occultations by NearEarth Asteroids
Roger Venable, David W. Dunham . . . . . . . . . . . . . . . . . . . 11
■ Beyond Jupiter: (341520) Mors-Somnus
Konrad Guhl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
■ The International Occultation Timing Association's 40th
Annual Meeting, 2022 August 13 - 14 via Zoom Online
Richard Nugent . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
■ Imprint . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

22022- 4 I JOURNAL FOR OCCULTATION ASTRONOMY

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Journal for

Occultation Astronomy

C A L L F O R O B S E RVAT I O N S :Stellar Occultations by (624) Hektor andSkamandrios, October 2022 - March 2023
Oliver Klös · IOTA/ES · Eppstein-Bremthal · Germany· oliverkloes@nexgo.de

ABSTRACT: Between October 2022 and March 2023, Jupiter's Trojan (624) Hektor and its moon
Skamandrios will go through their retrograde phase. Especially, stellar occultations close to thestationary points offer the possibility to obtain high-resolution data on (624) Hektor and to detect
the satellite. 19 events with stars brighter than 15th magnitude are observable during this period.
Introduction
ct [7].

Past Observations

the occultation by the satellite. (O. Canales)

JOURNAL FOR OCCULTATION ASTRONOMY I 2022- 43

presented in Table 1. Blue diamonds show the fainter occultations (14 - 15 mag). (Project Pluto’s GUIDE 9.1)

Upcoming Occultations
At the end of 2022 and the beginning of 2023, (624) Hektor ismoving through the constellation Auriga with an apparent
magnitude of 14 - 15. Its retrograde movement across the sky
plane begins in October 2022 and ends it in March 2023.
Date (UT)2022 Oct 06, ~05:04
2022 Oct 11, ~01:52
2022 Nov 08, ~05:23
2022 Nov 10, ~20:27
2022 Nov 16, ~10:17
2022 Nov 21, ~02:42
2022 Nov 26, ~05:52
2022 Dec 11, ~18:49
2022 Dec 18, ~22:27
2022 Dec 22, ~21:27
2022 Dec 27, ~21:58
2023 Jan 14, ~00:51
2023 Feb 04, ~15:32
2023 Feb 10, ~16:52
2023 Feb 14, ~09:29
2023 Feb 21, ~06:36
2023 Mar 13, ~01:14
2023 Mar 25, ~23:49
2023 Mar 31, ~19:53

Star
UCAC4 664-041893
UCAC4 666-042131
TYC 2923-00251-1
UCAC4 673-042055
UCAC4 674-040310
UCAC4 675-040602
UCAC4 676-038960
UCAC4 676-037147
UCAC4 676-036283
UCAC4 675-036563
UCAC4 675-035793
UCAC4 670-034015
UCAC4 664-031199
UCAC4 662-029770
UCAC4 661-029848
UCAC4 658-029167
UCAC4 653-028642
TYC 2900-016541
UCAC4 648-028293

Vmag
13.8
14.7
10.9
13.9
14.6
14.3
14.4
13.9
11.8
14.3
13.8
14.4
14.8
14.6
13.0
14.1
14.5
10.5
13.9

Since the Jupiter Trojan will occult stars close to its stationary
phases and thus moves quite slowly across the sky plane, theduration of an occultation by Skamandrios is relatively long forsuch a small satellite. Table 1 shows the observable occultationsof stars brighter than mag 15 from October 2022 until the end of
March 2023.
Max. Duration (s)(624) Hektor
18.9
21.2
16.2
15.4
13.8
12.8
12.0
10.7
10.7
10.8
11.0
13.3
19.1
19.5
8.6
7.8

Observable in
Skamandrios
1.24
1.38
1.07
1.00
0.90
0.84
0.78
0.70
0.73
0.70
0.72
0.87
1.25
1.29
1.28
1.15
0.73
0.57
0.51

Europe, W. Africa
Europe, Africa
Europe, N. Canada, Alaska
Asia, N. Europe
N. Canada, Asia
S. America
Mexico, Florida, C. America
Asia, Europe, N. Africa
Asia, E. Canada, E. USA
S. Asia, Middle East, Africa
Asia, Europe
Africa, S. America
Asia
E. Europe, E. Africa
E. Russia
FloridaEuropeSouth America
Europe, E. Africa

Table 1. Stellar occultations by (624) Hektor and its satellite Skamandrios between October 2022 and March
2023. For 3 events only an occultation by Skamandrios is observable. Predictions were calculated with datafrom JPL Horizons and Miriade orbit solution #1 using D. Herald’s Occult 4.2022.9.1. on 2022 September 29.

42022- 4 I JOURNAL FOR OCCULTATION ASTRONOMYJournal for

Occultation Astronomy

Figure 4. The orbit of (624) Hektor. The plot presents the position on 2023 Jan 1, 00:00 UT. (Source: NASA JPL Small-Body Database
Lookup, https://ssd.jpl.nasa.gov/tools/sbdb_lookup.html#/?sstr=624%20Hektor)

At the time of publication of this issue of the Journal for
Occultation Astronomy, Oscar Canales' observation was still being
evaluated. Miriade's orbit solution #1 was used for the predictions
calculated for this call for observations. This is recommended
because this solution is fitted to the complete set of data [9].

Updates to the orbit solutions are highly possible. Potential
observers should therefore check the latest data from Miriade
via Occult before an occultation and the predictions on Occult
Watcher Cloud [10] and the Lucky Star project webpage [11].

Figures 5 - 8. Path maps of occultations by (624) Hektor and Skamandrios from 2022 Oct 6 and 11 based on data from Miriade and JPL
Horizons available on 2022 Sep 29. Plotted with Occult 4.2022.9.27.

JOURNAL FOR OCCULTATION ASTRONOMY I 2022- 4

5

Figures 9 - 16. Path maps of occultations by (624) Hektor and Skamandrios from 2022 Nov 8 to 21 based on data from Miriade and JPL
Horizons available on 2022 Sep 29. Plotted with Occult 4.2022.9.27.

62022- 4 I JOURNAL FOR OCCULTATION ASTRONOMYJournal for

Occultation Astronomy

Figures 17 - 24. Path maps of occultations by (624) Hektor and Skamandrios from 2022 Nov 26 to Dec 22 based on data from Miriade
and JPL Horizons available on 2022 Sep 29. Plotted with Occult 4.2022.9.27.

JOURNAL FOR OCCULTATION ASTRONOMY I 2022- 4

7

Occultation by (624) Hektor not observable.

Figures 25 - 31. Path maps of occultations by (624) Hektor and Skamandrios from 2022 Dec 27 to 2023 Feb 10 based on data from
Miriade and JPL Horizons available on 2022 Sep 29. Plotted with Occult 4.2022.9.27.

82022- 4 I JOURNAL FOR OCCULTATION ASTRONOMYJournal for

Occultation Astronomy

Occultation by (624) Hektor not observable.

Occultation by (624) Hektor not observable.

Figures 32 - 37. Path maps of occultations by (624) Hektor and Skamandrios from 2023 Feb 14 to Mar 25 based on data from Miriade
and JPL Horizons available on 2022 Sep 29. Plotted with Occult 4.2022.9.27.

JOURNAL FOR OCCULTATION ASTRONOMY I 2022- 4

9Figures 38, 39. Path maps of occultations by (624) Hektor and Skamandrios on 2023 Mar 31 based on data from Miriade and JPL Horizons
available on 2022 Sep 29. Plotted with Occult 4.2022.9.27.

Conclusion
There are some good opportunities to determine the profile
of (624) Hektor in the upcoming months. Observing a stellar
occultation by the moon Skamandrios will be a challenge, but theobservation on 2022 Aug 30 by Oscar Canales showed that thisis possible. Occultations near stationary points on the asteroid's
path across the sky plane facilitate observations and yield highresolution data.
Don't forget to check any available prediction updates.

Acknowledgements
This research has made use of IMCCE's Miriade VO tool, Dave
Herald’s software Occult, and JPL Horizons. Special thanks toOscar Canales, Dave Herald and Frédéric Vachier.

102022- 4 I JOURNAL FOR OCCULTATION ASTRONOMY

References[1] NASA/JPL Small-Body Database Lookup
https://ssd.jpl.nasa.gov/tools/sbdb_lookup.html#/?sstr=2000624[2] IAUC 8732: S72006 (624) 1,
http://www.cbat.eps.harvard.edu/iauc/08700/08732.html[3] Marchis, F.; Durech, J.; Castillo-Rogez, J.; Vachier, F.; Cuk, M.; Berthier,J.; et al. (March 2014). "The Puzzling Mutual Orbit of the Binary Trojan
Asteroid (624) Hektor". The Astrophysical Journal Letters. 783 (2): 6.
https://iopscience.iop.org/article/10.1088/2041-8205/783/2/L37[4] M.P.C. 103031, p. 937, https://minorplanetcenter.net/iau/ECS/MPCArchive/2017/MPC_20170312.pdf[5] Miriade - The Virtual Observatory Solar System Object Ephemeris
Generator
https://ssp.imcce.fr/webservices/miriade/[6] Herald, D., Occult software,
http://www.lunar-occultations.com/iota/occult4.htm[7] Personal communication with O. Canales, September 2022
[8] Occultation Portal https://occultation.tug.tubitak.gov.tr/[9] Personal communication with F. Vachier, August 2022
[10] Pavlov, H., Occult Watcher Cloud, https://cloud.occultwatcher.net/[11] Lucky Star project, Predictions of stellar occultations by TNOs,
Centaurs and Trojans, https://lesia.obspm.fr/lucky-star/predictions.php

Journal for

Occultation Astronomy

Thoughts on the Observation ofOccultations by Near-Earth Asteroids
Roger Venable · IOTA · Chester, GA · USA · rjvmd@progressivetel.com
David W. Dunham · IOTA · Greenbelt, MD · USA · dunham@starpower.net

ABSTRACT: Predictions of occultations by near-Earth asteroids (NEAs) have been improved by astep-wise approach in which radar observations are followed by a major campaign of occultation
observers, after which some confirmatory observations are made. These occultation observations
are difficult due to the narrowness of the paths, the brevity of the events, and the peculiar
appearances of the expected light curves. Scintillation noise and instrument noise limit anobserver's ability to successfully document these events even when other problems are solved. It
is expected that cameras of the near future will have lower noise and will assist in this effort.
Introduction
Few occultations by near-Earth asteroids (NEAs) have been
observed, mainly because of poor prediction accuracy. The lackof accuracy has involved star positions and asteroid orbit models.
The much improved accuracy in star positions provided by theGaia astrometry satellite has done much to lessen the problem
with star positions. However, the small sizes of most NEAs require
highly precise orbital models, without which the narrow shadow
paths will simply miss the observer. Occultations by NEAs arequite challenging to observe.
UT Date

Star

Star
Vis.
Mag.

Star
Diam*
(mas)

ApophisDist.
(AU)

2021 March 7

HIP 45887

8.58

0.176

2021 March 22

TYC 0218-00224-1

10.1

2021 April 4

TYC 0789-01041-1

2021 April 10
2021 April 11

Radar observations of 6 km diameter (3200) Phaethon were madein 2007 and in 2017, resulting in a highly precise orbital model[1]. Incorporating Gaia's star position accuracy, a prediction wasmade that (3200) Phaethon would occult a star on 2019 July 29
visible from the southwestern USA. The campaign to observe
this occultation involved 35 observers who set up more than 60
telescopes, of which 52 obtained data and six recorded an
occultation. This major effort provided a precise astrometric pointthat allowed a further refinement of the orbit, which in turn has
led to positive observations of about six more (3200) Phaethon
events since then. These events are reviewed by Dunham [2].

F.L.**
(m)

ρ˟

Max.
Duration##(sec)

Altitude(degr)

0.11273

ApophisSky
Motion(mas/sec)
56

Orbit
Calculation48

1-sigma
Cross-path
Uncertainty‡(pathwidths)
1.91

71

2.4

0.075

0.07090.12386

38

75

2.3

0.10

38

0.31

JPL#20711.4

0.06710.14089

23

80

2.1

0.14

44

0.76

JPL#211

UCAC4 528-046251
TYC 1376-00848-1

12.6
10.1

0.01670.05570.14889
0.14983

19
19

82
82

2.1
2.1

0.17
0.16

69
~ 52

0.76
0.75

JPL#211
JPL#2112021 May 6

TYC 1929-01244-1

11.6

0.02310.16851

15

87

2.0

0.18

~ 55

1.27

JPL#2162021 Sept 272022 April 9

TYC 1392-01042-1
TYC 5782-01139-1

8.7
8.5

0.02250.379

0.87972
0.53721

35
58

199
155

0.85
1.1

0.015
0.015

8
8.3

1.27
1.27

JPL#216
JPL#216

JPL#204

Observers
Positive(Parentheses indicate #of observing sites if >1)
D. & J. Dunham (2),
R. Nugent
R. Venable (1)N. Carlson, K. Getrost,
R. Venable (1)? H. Yamamura
N. Carlson, K. Getrost,
V. Sempronio
S. Aguirre, T. Blank (1),
N. Carlson, A. George-----* Star's subtended sky diameter estimated from Gaia DR2 parallax, colour, and g magnitude.
** Fresnel length = sqrt(lambda*distance/2), all in metres. Computed with lambda of 600 nm as this is near the peak sensitivity of most video cameras.
˟ ρ (Greek letter rho) is the asteroid's radius in metres divided by the Fresnel length in metres.
## Maximum duration assumes a diameter of 340 metres, which is the mean diameter now used by the Horizons ephemeris system. Some predictions of these events have used a larger diameter,
such as 500 metres, to compute duration.
‡ Uncertainty as assessed at event time, based on a diameter of 340 metres. This differs from uncertainties expressed at different times or using different diameters.
The observers who recorded negative observations on March 7 are C. Bicknell, N. Carlson, P. & D. Ceravolo, P. Cervantes, D. & J. Dunham (3), K. Getrost, B. Gowe, J. Horst, R. MacArthur, F. Marchis,R. McClure, J. Moore (2), S. Sivley, M. Skrutskie, R. & S. Tirashi, R. Venable (4), and M. Ziegler.
The two observers of the 2021 Sept 27 event actually had "no observation" results rather than misses.

Table 1. Previous observations of occultations and appulses by (99942) Apophis

JOURNAL FOR OCCULTATION ASTRONOMY I 2022- 4

11

The pattern of progressive refinement of the orbital model,
beginning with radar observation, followed by a major occultation
campaign, followed by further confirming observations was
repeated with 340 metres diameter NEA (99942) Apophis in
2021. Table 1 gives details of most of the occultations andappulses by (99942) Apophis that have been observed. We can
expect a continuation of this pattern of serial observations
yielding progressive improvement in orbital models. For example,
NEA (65803)_Didymos has already been the subject of radar
astrometry, and we are hoping to observe some occultations by
it in a campaign in late 2022, perhaps even catching its known
moon Dimorphos in the process [3].

were the elevation corrections not applied. For several of the(99942) Apophis events in Table 1, elevation corrections werekindly incorporated into the prediction by John Irwin, upon specificrequest.

Although it may appear that occultation observers are now
beginning a golden age of observation of NEAs, in fact any
such a golden age may be brief. The star positions will graduallydegrade, beginning in just a few years, as their proper motions
have been less precisely ascertained than their mean positions[4]. We encourage every occultation observer to seize the present
opportunity to capture the uniquely precise astrometric data on
NEAs that occultations now provide.

The maximum durations of the (99942) Apophis events in Table
1 range from 0.18 seconds down to 0.015 seconds. Since the frame
duration of a video camera is either 0.033 or 0.040 seconds, theshortest of these events will cause the light drop of the occultation
to be blurred with the full light of the star in a single video frame.
Keep in mind that this applies not only to the briefest diametric
events, but also to events with longer diametric durations when theobserver is near the edge of the asteroid's shadow. A higher frame
rate will be advantageous in identifying an occultation in these
events. Digital cameras can provide higher frame rates thananalogue video cameras, with comparable quantum efficiency. Kai
Getrost used a frame rate of 100 frames per second for the
2021_April 11 (99942) Apophis event [5], and Venable used 380
frames per second for the events of 2021 September 27 and
2022_April 9. Higher frame rates result in dimmer images, so larger
telescope apertures are appropriate.

The focus of this paper is to highlight the difficulties andunusual characteristics of some of these events, using a recent(99942) Apophis appulse as an example. It is hoped that thesedetails will foster interest and wisdom about performing andinterpreting such observations.

Pitfall #1: The Paths Are Narrow
Small asteroids produce narrow occultation paths. It is unlikelythat the small shadow of a NEA will pass over an observer's
home observatory, so an observer should be prepared to travelto the shadow path. Observers who often utilize remote stations
have made a variety of adaptations to their equipment to makeit transportable, such as with collapsible "suitcase" telescopes.
Having said that, it is our impression that most mobile observers
simply lug their home observatory equipment into the field. The
camera and recording computer will require batteries, but
miniature computers and monitors can allow the use of relatively
small batteries. Skill in prepointing can eliminate the need for aclock drive for the telescope mounting, so the mounting can be
simple.
Elevation corrections to the shadow path and to the locationsof each observing chord can be very important when the pathis very narrow. Initial path predictions are generally made forobservers at sea level. In the first successful (3200) Phaethon event,elevation corrections were not made, with the result that two of
the six successful chords coincided with one another, effectively
yielding five chords across the asteroid rather than six. These two
mobile observers were at different elevations at widely separated
points along the shadow path. With some of the (99942) Apophis
events, the elevations of the observing sites in the western USA
would have caused observers to miss the event completely,

122022- 4 I JOURNAL FOR OCCULTATION ASTRONOMY

If the event is the subject of a campaign, the chords ofobservers will be close together. The observer will do well to let
the campaign organiser assign him or her a chord, so as to avoid
the chords of other observers.

Pitfall #2: Event Duration

Pitfall #3: Non-Zero Occultation Bottom
With the briefest occultations, the light is unlikely to drop tozero at the event bottom. This effect is multifactorial, related todiffraction, the frame rate, and the stellar diameter.
The computation of diffraction effects involves double integrals
in the complex plane, Lommel functions, and Bessel functions [6,7], and thus is beyond the capability of most amateur astronomers.
In this article, Venable uses Fresnel length and rho values in
expressing diffraction ideas because they are simple to calculate
and they are helpful in elucidating the expected diffraction pattern.
The Fresnel lengths and rho values of the (99942) Apophis eventsare given in Table 1 and defined in the footnotes of that table.
Fresnel length or Fresnel scale has been defined several ways
in the astronomical literature, but for the purpose of this article
it is:
Fresnel length =√(λ * distance)2where λ is the wavelength of the incident light, and distance is the
distance to the occulting object such as an asteroid. In making
this calculation of Fresnel length, if one converts λ and distanceto metres, the Fresnel length will also be in metres. Note that theJournal for

Occultation Astronomy

duration of an occultation and the velocity of the asteroid's
shadow do not enter into this calculation. Thus, Fresnel length
expresses some of the characteristics of diffraction effects interms of distances alone. Diffraction effects are prominent when
an asteroid's radius is approximately equal to the Fresnel length.
Accordingly, a simple way to express the importance of diffraction
is to divide the asteroid's radius by the Fresnel length, resulting
in a value that is often designated by the Greek letter rho: ρ.
When ρ is much greater than 1, diffraction effects are slight,
although a Poisson's spot may be detected from the exact centreof the shadow if the object is round. (This central Poisson's spot
is not to be confused with the central flash observed from thecentreline of an occultation by an object with an atmosphere,
such as Pluto or Triton.) When ρ is near 1, diffraction effects areprominent. When it is much less than 1, there will be much lightdiffracted into the shadow, possibly so much that the shadow
cannot be detected and the event will be "diffracted out", toborrow an expression from Marshall Eubanks. An event with
ρ_=_1 cannot have a brightness of zero at its nadir.

Figure 1. Simulated diffraction patterns as expected from selectedoccultation circumstances. The two patterns are with ρ of 0.88. [Rhois the Fresnel length divided by half the length of the chord acrossthe occulting body. Fresnel length = sqrt(wavelength*distance/2).]
With a midline event, the pattern on the top can occur when thelong axis of the asteroid is in the sky plane, while the pattern on
the bottom occurs when the long axis is perpendicular to the sky
plane. For further explanation, see the text. Adapted from Roques,
Moncuquet, and Sicardy [6].

Although in this article we refer to occultations by NEAs as being"brief", an understanding the significance of Fresnel length conveys
the fact that it is not actually the duration of the event that
renders diffraction events to be prominent, but the distances -the length of the light wave and the distance to the asteroid.
The orientation of a nonspherical body such as (99942) Apophis
will have significant effects on the diffraction pattern. Roques,
Moncuquet, and Sicardy worked out diffraction computations
for various occultation presentations [6]. Figure 1 is adaptedfrom their article. It diagrams two presentations of a hypotheticalocculting body detected at a single wavelength when the star isa point source and the ρ value is 0.88. As indicated in Table 1,
these values of ρ are similar to those of the (99942) Apophis
events of 2021_September_27 and 2022 April 9, and thus suggest
the appearance of some of the diffraction effects that might havebeen expected in those occultations if they had been successfully
observed.
The diffraction patterns in Figure 1 can be thought of as due tooccultations along an axis perpendicular to the long axis of anelongated body such as (99942) Apophis. The top pattern applies
to some cases in which the long axis is in the sky plane, while thebottom pattern applies to cases in which the long axis isperpendicular to the sky plane. The dashed lines are thegeometrical edge of the shadow. Notice that the series ofdiffraction peaks and valleys before and after the occultation aremuch more prominent than those seen in most asteroidal
occultations. These peaks and valleys will be blurred when an
occultation is recorded by a camera with a broad spectral
sensitivity, though the peaks nearest the occultation will be no lessprominent. In Figure 1, the central brightening, which is essentially aPoisson's spot, will be present regardless of wavelength when theoccultation is diametric across a circular object (lower panel), but it
is markedly suppressed, even with a midline chord, when theoccultation crosses the waist of an elongated body (upper panel).
Generally speaking, it will not be seen when the occultation is off
the asteroid's centre. It is also important to notice in Figure 1 that,
due to diffraction, the brightness does not drop to zero during theoccultation.
Interestingly, there was a prominent central brightening at
the bottom of Miyoshi Ida's light curve in the 2021 October 15
occultation by (3200) Phaethon [2], which is of uncertain naturebut may be a Poisson's spot widened by the broad spectral
response of the camera. There were prominent diffraction spikes
immediately before and after Getrost's recording of the 2021 April
11 occultation by (99942) Apophis, and that recording showed anon-zero bottom [5].
Siraj and Loeb computed diffraction effects that would be seen
when interstellar objects occult stars [7]. With regard to diffraction,such light curves could appear similar to occultations by NEAs,
because the ρ values can be similar. One of their simulated light
curves with ρ of 0.66 is presented here as Figure 2, adapted fromJOURNAL FOR OCCULTATION ASTRONOMY I 2022- 4

13their article. The numbers on the abscissa are camera frames,
not time per se, but serve here to reveal the manner in which
the Poisson's spot is obscured by the camera's frame rate when
the occultation is very brief. Notice that the camera's response
does not record zero brightness during such an event, and with
ρ_=_0.66 and a video frame duration of 1/2 of the geometricalevent duration, its lowest measurement is at 60% of theunocculted brightness.

Figure 2. Simulated diffraction pattern and consequential camera
response at a frame rate of half the geometrical occultation
duration, with ρ = 0.66. The calculation assumed that the star
was a point source and that the observation was made through afilter passing a single wavelength. Adapted from Siraj and Loeb
[7].
In most occultations by asteroids, the star's apparent subtended
diameter does not play a significant role because it is very small
compared to that of the asteroid. In contrast, at the 2022 April 9
appulse (99942) Apophis's 340 metres diameter subtended 0.873
milliarcseconds (mas), while the star's diameter subtended about
0.379 mas (see Table 1). The accurate computation of the effect of
the star's subtended diameter on the light curve would require
knowledge of the limb darkening function of the star, the shapeand orientation of the asteroid, and the exact offset of theoccultation chord from the asteroid's midline. Although precise
calculations cannot be made, Figure 3 presents some geometricscenarios that suggest that the large stellar diameter may affectthe light curve by introducing frames of intermediate brightness atthe start and end of the event.

142022- 4 I JOURNAL FOR OCCULTATION ASTRONOMY

Notice in Figure 3 that the large stellar diameter may cause
the periphery of the star to be near the middle of the event at
the same time that the opposite periphery of the star is near the
beginning or the end of the event. In comparison with Figure 1,
which shows the diffraction effects from a point source, the large
stellar diameter will blur the diffraction effect, as light from partof the star diffracts to the central bright spot at the same timethat light from another part of the star diffracts to the adjacentdark part of the diffraction pattern. In short, the occultation willlack a Poisson's spot, and the large stellar diameter will level out
the occultation bottom, at a brightness that is near the mean of
all the brightness measures that will be obtained within thegeometric shadow.

Figure 3. Star diameters superimposed on (99942) Apophis's
approximate size for the purpose of illustration, with three verticalpaths of occultation across the asteroid. The actual configuration of
the asteroid is not well known and its presentation aspect in the
2022_April 9 occultation is not known. The proportions in the
diagram are such that the top to bottom distance across the asteroid
is 0.873 milliarc seconds, and each of the representations of the staris of 0.379 milliarc seconds diameter, as in the occultation of
2022_April_9. The spacing of the star figures in each of the 3 verticalrows is the distance of a single camera frame, at the frame rate that
Venable used in that observation. The central row shows a scenario
in which there would be 4 frames in which the star is completely
occulted, with at least one additional frame of intermediatebrightness at the beginning and end of the occultation. The left row
shows a scenario of 3 frames of complete occultation, also with atleast one frame of intermediate brightness at the beginning and end.
Note that this left scenario increases the duration of intermediatebrightness only slightly as compared to the central scenario. The
right row shows an incomplete occultation that has at least threeframes of intermediate brightness both before and after the central
event.

Journal for

Occultation Astronomy

made from a site

Pitfall #4: Scintillation
The problem of scintillation is well illustrated by the light curvein Figure 4, which shows the severe scintillation in the light curve of
the 2022 April 9 event. The observation was made from a site nearsea level with the event occurring at an angular elevation of 8.3
degrees, which yielded a light path equivalent to 6.9 zenithal
atmospheres. Scintillation effects are worsened by a low angularelevation in the sky, and by local thermal instabilities in theatmosphere. Scintillation is partially alleviated by high elevation
above sea level and by larger telescope apertures, but perhaps
surprisingly, it is nearly independent of wavelength [8]. Most
observers have limited ability to adjust the variables that affectscintillation when making occultation observations, but weencourage the use of the largest aperture available when making
an observation in which scintillation may be a factor.
Our judgement of the likelihood that a drop in brightness isdue to an occultation is based on the statistical probability thata brightness excursion of the same depth and duration could becaused by chance due to the random variations in the light curvethat we call noise. If the false event probability is measurably
greater than zero, then it may be useful to have some confirmationsuch as a second chord, or some peculiar circumstance of theobservation that can serve as confirmation.
When making this analysis, we generally include the full
expanse of the noise rather than filtering out a small area of thelight curve that has a lesser amount of noise. There is no currently
accepted, scientifically justified method of selecting a brief area of alight curve for analysis by virtue of a local area of lower noise. In
Venable's April 9th observation, he was able to find his suspected
event at the predicted time because there was a moment of lessnoise at that time. This may have been a real occultation, but inview of the overall noise of the light curve, the feature may havebeen caused by scintillation. There is no known way to prove
either hypothesis. The point here is that a very brief event with a
non-zero brightness nadir, such as can be expected in some

Figure 4. Part of Venable's light curve at 380 frames per second, centred on the predicted event time of the 2022 April 9
occultation by (99942) Apophis. This shows approximately 2 seconds of data. For further explanation, see text.

JOURNAL FOR OCCULTATION ASTRONOMY I 2022- 4

15

occultations by NEAs, may not meet the requirement of statisticalprobability that demonstrates that the event is real, even whenlight curve features such as diffraction effects are suspected in
the light curve.
It could be argued that the presence of each of the featuresthat Venable hoped to find, listed above, is so unusual that an
occultation is confirmed. In response, David Herald points out
two ideas. First, if it is an occultation, adding the astrometric point
to the database will not improve the orbit model, since the orbit
and the purported event correspond so well. Second, if it is not
an occultation, then adding the astrometric point to the database
will degrade the orbit with a new, bad astrometric point. Thus,
no astrometric point should be derived from the observation(David Herald, personal communication). This wisdom illustrates
pitfall #5: Though these events can be exciting and challenging,it can all be for naught.

Future Work
Since most digital cameras do not place a GPS time stamp on
each frame, some other accurate means of assessing the time isneeded. Aart Olsen has developed a GPS flasher device using
an Arduino together with an attached GPS "shield" that receives
GPS signals [9]. With this device, the timing of an event can bemeasured by interpolating the frame times between the known

times of the flashes. A potential problem with such a device isthat it does not indicate the possible presence of dropped frames.
Therefore, each camera model must be tested by some otherstandard to ascertain whether it will drop frames at the frame
rate that is desired. Further, it should be tested to discover what
settings, if any, will cause it to drop frames. The stability of the
exposure duration should also be tested.
Scintillation noise does not appear random when evaluated ona sufficiently short time interval to manifest its autocorrelation.
Instead of the random-appearing up and downs that we see withlow frame rates, a high frame rate can reveal relatively smooth
curves of ups and downs, with each such curve defined by many
points (see Figure 5). The higher the frame rate, the greater the
autocorrelation of the scintillation noise. (Of course, thisautocorrelation will be more evident when the scintillation is lesssevere than that shown in Figure 4.) In the context of smoothly
varying brightness values, the pattern of a very brief occultation
may be identifiable by virtue of its interruption of the
autocorrelation, or by a spike in a graph of autoregression withdifferencing. Variations in autocorrelation, like the variations inbrightness by which we currently judge the occurrences ofoccultations, are subject to statistical analysis. It remains to be seen
whether such analysis can identify brief events that would be
hidden amid the scintillation noise if analysed solely by themethods that are currently in use.

Figure 5. A 1.1-second duration part of a light curve made by recording 7.7 magnitude HIP 96083 on 2022 June 14 at 07:42 UT when thestar was at an altitude of 86 degrees. The recording was made at 996 frames per second using a ZWO ASI290MM camera, 2x2 pixel
binning, and a region of interest of only 80x60 (equivalent to 160x120 pixels unbinned). A runs test on the entire 29,989 frames (about 30
seconds) reveals the longest run above median to be 75, with many runs longer than 21, while a single longest run of 21 would besignificant at the p < 0.01 level. This means that the brightness values are not normally distributed. In general, the autocorrelation ofbrightness values increases with faster frame rates, and such autocorrelation can cause a non-Gaussian distribution. One can plainly seethat there are two different types of noise in the light curve: a frame to frame instrumental noise, and a slower, rolling scintillation noise.
The presence of two types of noise may be another contributor to the non-normality of the distribution. (The sky background was notblack, and the normalized cross-correlation of aperture and background values is 0.010, indicating that the variations in brightness values
are not due to variations in exposure duration.) The frame rate is fast enough to reveal the details of the scintillation effects, so that, forvery brief occultation events, the instrumental noise of this camera may be more important than the scintillation noise. The camera is notcooled, and a cooled version of the camera would presumably show less instrumental noise. We expect continuing reductions in
instrumental noise as camera technology develops, so our ability to detect brief events amid the scintillation will be improved.

162022- 4 I JOURNAL FOR OCCULTATION ASTRONOMYJournal for

Occultation Astronomy

Digital cameras are capable of higher frame rates than video
cameras, and therefore will be able to record briefer events
than video can. Since brief events are likely to show the featuresof diffraction and stellar size, higher frame rates can help toidentify an occultation by revealing those features. Thus, higher
frame rates may be able to mitigate the problem of scintillationnoise by enabling the identification of an event by patternrecognition. Pattern recognition is what we do now to identify
occultations by main-belt asteroids: We look for a pattern ofsudden disappearance, a flat bottom, and a sudden reappearance.
As discussed here, the pattern may be different for very brief
events, and high frame rates are the way to show such patterns.
Future digital cameras will have higher quantum efficiency, lesselectronic noise, and faster maximum useful frame rates. Already,some cameras enable the observer to distinguish between
scintillation noise and instrumental noise in some recordings (seeFigure 5). With cooling, the camera used for Figure 5's light curve
would presumably have reduced instrumental noise. One of us(Venable) is experimenting with frame rates up to 4,000 frames per
second using only a small region of interest in the CMOS chip, andJonathan Bradshaw has made lunar occultation observations witha frame rate of 1,000 frames per second [10]. Though currently
available cameras appear excellent, users should keep in mind thata halving of even a small amount of instrumental noise will resultin a doubling of the signal-to-noise ratio. (Signal-to-noise ratio isequivalent to sensitivity.) With cameras of the future that have lessinstrumental noise, brief occultations with smaller drops inbrightness will be detectable. We shall be looking for opportunities
to stretch our capabilities in the detection of occultations by NEAs.

Summary
Since the first detection of occultations by (3200) Phaethon in
2019, interest in occultations by NEAs has increased, andcampaigns to observe them have been under way, with somesuccess. These efforts have started for each object with acampaign involving a larger than usual number of observers, bywhich a successful observation has been used to significantly
improve the asteroid's orbital model, enabling more modest
efforts for confirmatory observations. Due to the very narrow
shadow paths made by these small asteroids, observers musttravel to the paths, which requires the observer's plans andequipment to be prepared for mobile observing. Occultations by
NEAs are very brief, so that some such observations will require
high camera frame rates, which in turn may require relatively large
apertures in order to obtain adequate video signal. The light
curves of such events may be peculiar in several ways. Diffraction
effects may be prominent, including momentary brightness
increases immediately before the disappearance and after the
reappearance, and brightening in the middle of the event
consistent with a Poisson's spot, and a non-zero event bottom
even when the asteroid is very faint. Large subtended diameters of
occulted stars will affect the light curve by creating frames ofintermediate brightness that may appear to shorten an alreadybrief event, and may cause a non-zero event bottom. Large
stellar diameters can appear to affect the light curves of such
brief events much more than they appear to affect light curves of
longer duration events. Rapid atmospheric scintillation can mimic
an occultation event, and to some extent the use of a high frame
rate can mitigate the scintillation effect. With improved camera
technology, it is likely that more difficult occultations by NEAs will
be within range of amateur observers. The use of new mathematical methods to detect such events should be investigated. We
are currently at a historically special time at which NEAs can bestudied by occultation means

References[1] Wikipedia. "3200 Phaethon." Accessed May 24, 2022.
Available at https://en.wikipedia.org/wiki/3200_Phaethon .
[2] Dunham D., Dunham J., Buie M., et al (2019). "(3200) Phaethon, firstsuccessful observations of occultations by a small near-Earth object."Paper no. 2062 at conference, Asteroid Science in the Age of Hayabusa2
and OSIRIS-REx, Tucson, Arizona.
[3] Dunham, D. (2022). "Precise astrometry for occultations of stars by
Didymos and Dimorphos." Paper presented online at conference, Small
Bodies Assessment Group #26, Jan. 2022.
https://occultations.org/publications/rasc/2022/
DunhamDidymosOccultationsNew.pdf[4] Buie, M. (2019) "Small body science with occultations." Presentation
at meeting of Small Bodies Assessment Group.
https://www.lpi.usra.edu/sbag/meetings/jan2019/presentations/
Tuesday-AM/Buie.pdf[5] Dunham, D., Dunham, J., Buie, M., et al (2021). "Accurate NEA orbits
from occultation observations." Paper at 7th IAA Planetary Defense
Conference, Vienna, Austria.
[6] Roques, F., Moncuquet, M., Sicardy, B. (1987). "Stellar occultations bysmall bodies: diffraction effects." Astron J 93(6):1549-1558.
[7] Siraj, A., Loeb, A, (2020). "Detecting interstellar objects throughstellar occultations." arXiv:2001.026891v2 [astro-ph.EP] 11 Feb 2020.
[8] Young, A, (1967). "Photometric error analysis. VI. Confirmation ofReiger's theory of scintillation." Astron J 72(6): 747-753.
[9] Olsen, A (2021). "Aart's Arduino Timers." A folder of files with
explanations, available at https://groups.io/g/IOTAoccultations/files/
Aart's Arduino Timers . Access requires login to IOTAoccultations
message list on groups.io .
[10] Bradshaw, J. (2022). "Total lunar occultations with the high speed
174 chip camera." Presentation at 16th Trans-Tasman Symposium on
Occultations, 2022 July 2.
Video vailable on line at https://www.youtube.com/watch?v=2wQ7w49YeNIJOURNAL FOR OCCULTATION ASTRONOMY I 2022- 4

17Beyond Jupiter

The World of Distant Minor Planets

Since the downgrading of Pluto in 2006 by the IAU, the planet
Neptune marks the end of the zone of planets. Beyond Neptune,
the world of icy large and small bodies, with and without anatmosphere (called Trans-Neptunian Objects or TNOs) starts. This
zone between Jupiter and Neptune is also host to mysterious
objects, namely the Centaurs and the Neptune Trojans. All of thesegroups are summarised as ”distant minor planets”. Occultation
observers investigate these members of our solar system, without
ever using a spacecraft. The sheer number of these minor planets
is huge. As of 2022 September 30, the Minor Planet Center listed
1451 Centaurs and 2934 TNOs.
In the coming years, JOA wants to portray a member of this worldin every issue; needless to say not all of them will get an article
here. The table shows you where to find the objects presented
in former JOA issues. (KG)18
20

In thisIssue:(174567) Varda
Konrad Guhl · IOTA/ES . Berlin ·Germany · kguhl@astw.de

ABSTRACT: The minor planet (341520) Mors-Somnus was
discovered in 2007 and with an orbital period of 248 years,
is in resonance with Neptune and so belongs to the Plutinoclass of trans-Neptunian objects. The elliptical orbit has its
perihelion just inside the perihelion distance of Neptune. It
was found to be a double asteroid, with each body having
approximately the same size, roughly 120 km across.

No. Name

No.

Name

AuthorLink to Issue

AuthorLink to Issue

944

HidalgoOliver Klös

JOA 1 2019

54598

BienorKonrad Guhl

JOA 3 2018

2060

ChironMike Kretlow

JOA 2 2020

55576

AmycusKonrad Guhl

JOA 1 2021

5145

PholusKonrad Guhl

JOA 2 2016

60558

Echeclus

Oliver Klös

JOA 4 2017

8405

Asbolus

Oliver Klös

JOA 3 2016

90377

Sedna

Mike Kretlow

JOA 3 2020

10370

Hylonome

Konrad Guhl

JOA 3 2021

90482

Orcus

Konrad Guhl

JOA 3 2017

10199

Chariklo

Mike Kretlow

JOA 1 2017120347

Salacia

Andrea Guhl

JOA 4 2016

15760

AlbionNikolai Wünsche

JOA 4 2019134340

Pluto

Andre Knöfel

JOA 2 2019

15810

Awran

Konrad Guhl

JOA 4 2021

136108

HaumeaMike Kretlow

JOA 3-2019

20000

VarunaAndre Knöfel

JOA 2 2017

136199Eris

Andre Knöfel

JOA 1 2018

28728

Ixion

Nikolai Wünsche

JOA 2 2018136472

Makemake

Christoph Bittner

JOA 4 2018

38628

Huya

Christian Weber

JOA 2-2021

174567

Varda

Christian Weber

JOA 2 2022

47171

Lempo

Oliver Klös

JOA 4 2020

208996

2003 AZ84

Sven Andersson

JOA 3 2022

50000

QuaoarMike Kretlow

JOA 1 2020-2004 XR190

Carles Schnabel

JOA 1 2022

20224 I JOURNAL FOR OCCULTATION ASTRONOMY
2019-1

Journal for

Occultation Astronomy

The Discovery
the stars and constellations.  She also set the vessels of the Sun Figure 1. The 8.3-m Subaru Telescope.
Credit: National Astronomical Observatory of Japan

Figure 2. The 6.5 m Magellan Telescope.
Credit: Carnegie Science

Figure 3. The dome of the Gemini North
Telescope. Credit: NOIRLab

JOURNAL FOR OCCULTATION ASTRONOMY I 2022- 4

19

The Name
8) Haumea in only 6 years [12].

Orbit and Classification

Physical Characteristics

Figure 4. Hypnos or Sleep, (267), British Museum. Dept. of
Greek and Roman Antiquities; Walters, Select bronzes, Greek,
Roman, and Etruscan, in the departments of antiquities, 1915,
Henry Beauchamp (1867-1944), Public domain, copyright
expired.

Figure 5. Orbit diagram and position for 2022 November 15.
(Source: https://ssd.jpl.nasa.gov/tools/sbdb_lookup.html#/?sstr=341520&view=VOSPD)

20

2022- 4 I JOURNAL FOR OCCULTATION ASTRONOMYJournal for

Occultation Astronomy

The orbital eccentricity is accordingly 0.153 ± 0.003, and theorbital plane of the two components is inclined 15.7 ± 0.2° withrespect to the Ecliptic. With knowledge of the orbitalparameters, the total mass of the system can be found to be
7.9_±_0.2_×_1017_kg. Calculated from the typical albedo for such
ultra-red TNOs, the radius of both bodies is calculated to beabout 60 km. Reference [7] comprises a good review article on
the properties of this binary system and how it compares with
TNOs in general.

References[1] Minor Planet Electronic Circulars MPEC 2008-M38, 2008 June 25
https://www.minorplanetcenter.net/mpec/K08/K08M38.html[2] IAU Circular 8962, 2008 August 1
http://www.cbat.eps.harvard.edu/iauc/08900/08962.html[3] Minor Planet Circulars MPC 94392, 2015 June 2
https://www.minorplanetcenter.net/iau/ECS/MPCArchive/2015/
MPC_20150602.pdf[4] JPL Small-Body Database
https://ssd.jpl.nasa.gov/tools/sbdb_lookup.html#/?
sstr=341520&view=OPDA[5] Thirouin, A., Noll, K.S., Ortiz, J.L., and Morales, N, “Rotational
properties of the binary and non-binary populations in the transNeptunian belt”, Astronomy & Astrophysics, Vol 569, A3 (20pp), 2014
September
https://doi.org/10.1051/0004-6361/201423567[6] Minor Planet Light Curve Database (LCDB) Query
https://minplanobs.org/mpinfo/php/lcdb.php[7] Sheppard, Scott S., Ragozzine, Darin and Trujillo, Chadwick: “2007TY430: A COLD CLASSICAL KUIPER BELT TYPE BINARY IN THE PLUTINO
POPULATION”, Astronomical Journal, 143(3), 58 (13pp), 2012 Marchhttps://iopscience.iop.org/article/10.1088/0004-6256/143/3/58/pdf[8] Buie, Marc “Research and Education Collaborative Occultation
Network” (RECON) at http://tnorecon.net/ and Global TNO event
candidate list https://www.boulder.swri.edu/~buie/recon/allevents.html

Further Reading
Figure 6. Both components of the binary system separated
by 0.7” can be seen in this image taken with the GMOS
instrument on the Gemini North telescope in December
2007 at a maximum separation of only 0.7 arcsecond on
the sky. Credit: International Gemini Observatory/NOIRLab/
NSF/AURA“The Trans-Neptunian Solar System” edited by D. Prialnik, M.A. Barucci
and L.A. Young, Elsevier Science, 478pp., (2019)

Future Stellar Occultations
To date, no occultation by this body has been successfully
observed. In the Research and Education Collaborative Occultation
Network (RECON) candidate list, a potential occultation is predicted
for 2022 October 14 10:20 UT, which involves the Gaia cataloguestar, GA1020:00353908 (G=16.6 mag) [8]. Unfortunately, themajority of the occultation zone will be over water.

Figure 7.
Map for the event on
2022 Oct 14.
The predicted path willcross central America
before dawn.
Credit: RECON [8]JOURNAL FOR OCCULTATION ASTRONOMY I 2022- 4

21

The International Occultation Timing
Association’s 40th Annual Meeting,2022 August 13-14 via Zoom Online
Richard Nugent · IOTA · Dripping Springs, Texas · USA · RNugent@wt.net
ABSTRACT: IOTA’s 2022 Annual Meeting was held via Zoom online on 2022 August 13-14. Numerous
presentations were made by members of the IOTA community worldwide. More than 70 attendees
participated in the meeting.
The 40th annual meeting of the International Occultation Timing
Association was held on Saturday and Sunday 2022 August 13-14
via Zoom online. The meeting schedule and agenda are locatedon the IOTA web site [1].
Video recordings of the session are available on YouTube [2].

in North America. More efforts led by her have resulted in 9
successful occultations worldwide through 2021 of small objects
down to 6 km diameter in size. Among them, the occultation on
2021_Oct 3 in Japan was a great success, with 18 sites positive (7sites misses, the other 11 sites failed) by a 36-site observing party
led by her.

Saturday 13th August 2022 - Day 1
IOTA’s Vice President Roger Venable opened and welcomed
everyone to the meeting.

Business Meeting
Treasurer Joan Dunham presented IOTA’s financials andmembership status.
Executive Secretary Richard Nugent presented the election
results of the IOTA's Officers. All officers were re-elected.
A full report of the business meeting is available [3].

AwardsRichard Nugent then presented IOTA’s Homer F. Daboll,David E. Laird and the Lifetime Achievement Awards. The Homer
F. DaBoll Award is given to recognize significant contributions to
the field of occultation science and to the work of IOTA.
Figure 1. Homer F. Daboll Award: Fumi Yoshida
This year's recipient is Fumi Yoshida from Japan. Fumi Yoshidais the member of DESTINY+(DDemonstration and Experiment ofSpace Technology for INterplanetary voY
Yage with Phaethon flyby
and dust science) project with plans to observe (3200) Phaethon
through spacecraft flyby mission by JAXA and PERC. Phaethon is
the special active asteroid also known as the parent body of theGeminid meteor shower. Her team has made and will continue tomake preliminary ground-based observations for (3200) Phaethon
to ensure the success of the mission. Yoshida is in charge of theseground observations. In cooperation with NASA, SwRI and IOTA,
she asked observers around the worldwide to observe occultationsby (3200) Phaethon starting from 2018, and organized her own
observation team composed of professional researchers andamateur observers. Right after that, the first successful observation
was made. The fantastic 2019 July 29 result observed in the western
USA was organized because of what her team requested to IOTA

22

2022 - 4 I JOURNAL FOR OCCULTATION ASTRONOMY

Fumi sent the following message upon her notification of theaward:
Thank you very much for the wonderful news. Mr. Hayamizu
gave me the details of the award, and I am truly honored toreceive this very prestigious award from IOTA. I am also attachinga photo as requested in your previous e-mail. I would like to thankthe many amateur astronomers who helped me with the Phaethon
occultation observations. There were no professional researchers
around me who specialize in occultation observation, so I finallysucceeded in the observation while asking for help from amateurs.
I am truly grateful for everyone's cooperation. When amateurs
and professionals work together, we can indeed accomplish greatthings. Just like small radio telescopes connected and working asa huge telescope. IAU has recently established a Working GroupJournal for

Occultation Astronomy

eclipses [5].

honour.

Figure 2. David E. Laird Award: Marek Zawislki

JOURNAL FOR OCCULTATION ASTRONOMY I 2022 - 4

23webpage [6].

Phil showed a video of Titan occulting a double star taken withthe 200-inch telescope on 2001 Dec 20.
Here's a screen shot from that video:

Figure 4. Titan occults a double star on 2001 Dec 20. Screenshot
of a video recorded with the 200" telescope at Palomar.

Figure 3. IOTA Lifetime Achievement Award:
John Broughton

The 2022 July 9 event had a low 0.66 SNR ratio, due to the small
magnitude diffrerence between the target star and Titan. Thirtysix observers participated in the event in the USA and Canada
including Filipp Romanov from Russia who used a remotetelescope in New Mexico using itelescope.net. D and R times
were poorly defined due to the gradual decline of brightness ofthe target star due to Titan's atmosphere. Following an analysisof the light curves, Phil deduced an approximate height of theatmosphere from Peter Ceravolo's chord. Peter's chord grazed
the upper levels of the atmosphere implying its effect extends toapproximately 500 km.

Vice President of Planetary Occultation Services John Moore
presented recent well observed North American asteroid
occultations during the past 12 months. John showed sky plane
profiles and in some cases 3D-profiles of events from the DAMIT
shape models. Most occultation chords and the DAMIT shapemodels had excellent agreement. Events shown:Technical Sessions

24

2022 - 4 I JOURNAL FOR OCCULTATION ASTRONOMY# (957) Camelia: 2021-09-15# (780) Armenia: 2021-11-09# (535) Montague: 2021-11-10# (84522) 2002 TC302: 2021-11-11# (308) Polyxo: 2021-12-05# (877) Walkure: 2022-02-15# (22) Kalliope: 2022-03-02# (17) Thetis: 2022-05-04# (617) Patroclus/Menoetius a two-body binary asteroid:2022-06-04# (90) Antiope another 2-body system: 2022-08-08.

Journal for

Occultation Astronomy

Figures 5a-c.
Sky plane profiles measured during
the occultations by (22) Kalliope on2022 Mar 3, (617) Patroclus/Menoetius
on 2022 Jun 4 and (90) Antiope on2022 Aug 8(from top).

JOURNAL FOR OCCULTATION ASTRONOMY I 2022 - 425

Figure 6. Profiles for (15094) Polymele and its satellite at the sky plane. Graphic courtesy of M. Buie, SwRI.
Tony George presented the discovery of a satellite of the
Trojan asteroid (15094) Polymele. The occultation occured on 2022
March_27. 26 observers participated on this expedition arrangedby the SwRI. Polymele is one of seven asteroids scheduled to beobserved by the LUCY mission - six Trojans and one main-belt
object. LUCY was launched in October 2021 and is expected toreach Polymele on 2027 September 15. Tony's site was near Salina,
Kansas - a 7-hour drive from his house. The predicted time of theevent at his site was predicted to +/-0.1 s accuracy, but his event
was 6 seconds late. The occultation results showed a normal sizefor the asteroid and then Tony's event occured 6 seconds later
which turns out to be the discovery of a small moon of Polymele(Figure 6).
The unofficial name of the moon chosen by Tony is "Shaun".
Hopefully the LUCY spacecraft will confirm this exciting discovery
when it reaches Polymele in September 2027. Congratulations
Tony !!

Table 1. Number of asteroidal occultations by region for 2021.

26

2022 - 4 I JOURNAL FOR OCCULTATION ASTRONOMYJohn Moore talked about the rapid growth in the number ofasteroid observations and review of the teamwork associated withthe reductions. Worldwide events for sky plane profiles of North
American observers with 20 or more observations in 2021: Bill
Hanna, Paul Maley and Roger Venable led the list. Several reasonsfor the large increasing number of observations are due to theGaia data plus Dave Herald's and Hristo Pavlov's enhancements
to Occult [7] and Occult Watcher [8] (Table 1).
And let's not forget the reduction programs PyOTE [9], PyMovie[10], Tangra [11] and AOTA [7]. John gave special thanks to his
team of persons that help reduce the observations: Jerry Bardecker,
Norm Carlson, Bob Dunford, Ernie Iverson, Steve Messner, Tony
George (IOTA's difficult event genius) plus Johnny Barton andDave Eisfeldt - for Tangra support. Many comments from themeeting attendees praised John for the outstanding work he andthe group has done.

Journal for

Occultation Astronomyytage versus simply increasing the integration setting. If the sky isbright (twilight, nearby bright moon, light pollution), it may be
impossible to increase the integration setting without saturating
the pixels. In this case, what is needed is not to sum the brightness,but instead average it over a longer time interval. For longer
events, this could still capture the actuality of an occultation but
which might fail the usual tests with the standard PyMovie/PyOTE
procedures. By averaging frames, the random bright sky pixels
include the darkness which is not the case with the star’s pixels.

Figure 9. Example of an occultation at the edge of detection shown
during the lecture.
Figure 7. 3D-printed carrier for the Run Cam Eagle (left).

Further, PyMovie already has coding to construct finders andthen adjust the brightness/contrast to better show the star against
the sky. If PyMovie can be induced to create a new video from an
automated assembly of “finders”, or even perhaps “finders” which
overlap in time, this would be useful. If the finder is optimallysignificantly longer than the integration exposure setting, then
the time resolution can be improved closer to the original setting
versus the longer “finder” setting. PyOTE and PyMovie would
require new coding to accommodate this.
He illustrated this technique with a 1 minute series of “finders”
for the 2022 Aug 8 occultation by (50000) Quaoar, a high rank
event with high probability the occultation seen is real. This is a15.3 magnitude target only 12 degrees from a 90% Moon, seenin an 8” telescope at 16x Watec integration. He also showed the
PyOTE reductions by standard means, for both Kirk Bender andhis data. Rick's PowerPoint talk is available [12].

Figure 8. Heat sink mounted on the camera.

Tony George presented two new functions of PyOTE: 1)
Evaluation of detectability and 2) Analysis of a single point
event. The Single-point Event Tool can analyze a single-point
event to determine if it is statistically distinct from baseline noisein the light curve. A Monte Carlo simulation of correlated noise
equivalent to the light curve noise added to a straight line 50,000
times is used to determine if any noise spikes are representativeof the single-point event. If the single point passes the test, it isstatistically significant at the equivalent 4-sigma level and can befurther investigated as a potential event. If it does not pass thetest, the event should be considered to be due to noise, except
if there are corroborating chords nearby to evaluate the validityof the single-point event.

JOURNAL FOR OCCULTATION ASTRONOMY I 2022 - 4

27

Next was the Event Detectability tool. This tool can be used todetermine if an event was detectable, in the event an observer
believes there was a miss. If the test indicates that an event of acertain mag drop and duration was detectable, and no such event
was observed, then the observer can reliably claim there was aqualified miss for any event longer than the detectability limit. Also,it was demonstrated how the tool could be used to process any
light curve, with or without an embedded event, to use for futureplanning of observation sessions. Users were encouraged to record
a variety of light curves for different cameras and integration
settings, as well as at different altitudes and observing seasons touse for planning for future events. Then when a future event
presents itself, the recorded light curve that would approximate theequivalent camera/settings/altitude/seasonal noise could be used
to see if the upcoming event would be detectable given theupcoming mag drop and duration. Roger Venable suggested that
open galactic clusters could be used to record a variety of star
magnitudes at the same time.

Sunday 14th August 2022 - Day 2
Technical Sessions
Vice President Roger Venable talked about making unattended
remote observations. He showed example locations for good sites
using Google Earth and how he sets up just off highways. He
recommended painting your equipment black so as not to bevisible from passing cars. In setting up a pre-point station, he usesa small piece of wood for the tripod legs to rest on so they don't
sink into the ground. Dew shields are also advised especially inhumid climates. He also leaves a note on the equipment for
onlookers requesting that they "DO NOT TOUCH" with an
explanation of what the equipment is for. Care must be taken
when setting up telecopes so as not to break any laws such as
trespassing, going past or opening gates to a fence, setting upon
private lands without permission, etc. A group discussion followedwith experiences of observers dealing with Police, landowners andidentifying equipment parts in the dark such as battery terminals.

Dave Herald talked about the use of the double star function
in Occult. An important point is to treat the observer's identificationof the brighter/fainter star with scepticism if the magnitudedifferences aren't great. This is a major issue in matching events
to components. He described the basic process of fitting theobservations using least squares to generate a position angle andseparation. Light curves are also encouraged to be submitted todetermine the magnitude drop for step events on the D and R
sides of the occultation. Smaller step events are sometimes difficult
to verify compared to the noise in the data.
Double star events can result in more than one solution forthe position angle and separation. With a unique solution - youknow where the asteroid is relative to both stars. Double solution- you know where the asteroid is relative to one star, but the fit
is ambiguous for the other star. In this case, one observer mightrecord both step events and a second observer might only record
one step event. A four solution case - the asteroid location is
ambiguous for both stars.
An astrometry issue: occultation discovered double stars are
not usually resolved in the Gaia data. The issue here is to match
the photo-centre of the event to the Gaia position. Dave showed
how Occult does this with the double and 4 solution cases.
Occult has a database of double star discoveries by asteroid
occultations - as of today's date there are 199 discoveries. To geta discovery of a new double star into the Washington Double
Star Catalog (WDS), the USNO requests that the discovery mustbe published - they will not accept a direct notification. The
Journal of Double Star Observations [13] is the preferred journal
for announcing the discovery.
The Meeting formerly ended at 0:50 UT August 14th. Discussions
continued among the attendees.

28

2022 - 4 I JOURNAL FOR OCCULTATION ASTRONOMY

Figure 10. Roger Venable at a remote station witha 5" Celestron SC. The laptop for recording is stored
in the box.
Roger Venable next talked about the appearance of light
curves of near-Earth asteroid events. For faint main-belt objects
at occultation time the brightness usually drops to zero (as theasteroid is usually not visible with our equipment) and the D and
R are usually instantaneous. He showed a few light curves of near
Earth objects and some common features of the light curves.
Spikes in the light curves can be caused by Fresnel and diffraction
effects and by the star's diameter. Sometimes a central spike
appears on a light curve of an asteroid - this is a diffraction effect(wavelength dependent) due to the size of the asteroid and not
due to a non-existent atmosphere. Diffaction spikes can occur

Journal for

Occultation Astronomy

depending on what part of the asteroid is occulted (centre oredge) from the ground position of the observer. A high recording
frame rate can help identify diffraction spikes. Diffraction, frame
duration and star diameter can affect the occultation timings ofsmall objects such as Apophis (~500 ft size) compared to larger
main-belt objects of 20 km and larger.

President Steve Preston next presented the best asteroid
occultations opportunities in North America for 2023. The eventswere of stars down to magnitude m = +10 and he showed the
Occult path maps for each one. The best one is when (319) Leonaoccults Betelguese on 2023 December 12 over south Florida,
Mexico plus Europe. If visible, this should be a spectacular naked
eye event with the maximum duration of up to 11 seconds.

Trojans occultations for 2023:• (617) Patroclus - has the moon Menoetius• (624) Hektor• (911) Agamemnon• (1143) Odysseus• (1173) Anchises• (2241) Alcathous• (3548) Eurybates - has a small 1 km moon Queta discovered by
HST.
• (11351) Leucus - LUCY mission target• (15094) Polymele - has a 5 km moon 200 km away
• (21900) Orus
• (58931) Palmys
Special main-belt asteroids in 2023 (Figure 12):

Breaking News

FigureFigure 11. The highlight of 2023. Asteroid (319) Leona occults
Betelgeuse on Dec 12. Note: Path may shift based on revised
position for Betelgeuse.

David Dunham talked about near-Earth asteroid events inthe coming year. These include:• (433) Eros• (1620) Geographos• (1866) Sisyphus• (2102) Tantalus• (3122) Florence• (3200) Phaethon• (4179) Toutatis• (29886) Randytung• (65803) Didymos - has 160m moon 1.2 km away
• (95802) Francismuir• (99942) Apophis• (10995) Bennu• (163693) Atira - has an approx 1 km size moon 6 km away

• (16) Psyche• (90) Antiope• (26) Kleopatra - has 2 small moons• (234) Barbara - possible contact binary asteroid• (253) Mathilde• (319) Leona• (513) Centesima• (762) Pulcova- has a 15 km Moon
• (957) Camelia• (2258) Viipuri - may have a 5 km moon
• (4337)Arecibo - Binary discovered in 2021 confirmed by Gaia
• (4552) Nabelek• (33074) 1997 WP21 - might have a 9 km moon
• (52246) Donaldjohanson - LUCY
• (172376) 2002 YE25 - possible binary asteroid
David then showed a list of (50000) Quaoar (size ~ 550 km)
and Weywot (moon of Quaoar, size ~ 170km) occultations forthe remainder of 2022 and 2023. He then showed a map ofoccultation stars brighter than m = +9.0 for North America he isworking on for the RASC Handbook.

David Dunham next talked about the (65803) Didymos events
for the rest of 2022 and 2023. Didymos is the target of the DART
mission to impact it and test the planetary deflection techniqueof a non-hazardous asteroid. Following the impact, the orbit willchange slightly. Events in 2022 with stars down to m = +12.0 are
numerous - major ones are: Aug 17, Aug 23, Aug 24 and Aug 25,
Sep 3, Oct 2, Oct 8, Oct 10, Oct 12, Oct 15, Oct 17.
Didymos opportunities for 2023: Jan 1, Jan 3, Jan 5, Jan 5, Jan6, Jan 9, Jan 10, Jan 12, Jan 16, Jan 18, Jan 21, Jan 23, Jan 28, Mar
2, Mar 20, Apr 9, Apr 25, May 4.

JOURNAL FOR OCCULTATION ASTRONOMY I 2022 - 4

29

Figure 12. Occultations by special main-belt asteroids across North America in 2023. (source: Occult 4.2022.8.18)

Figure 13. Occultations by (65803) Didymos across N. America from 2022 Oct 18 to 2023 Jan 1. (source: Occult 4.2022.4.11)302022 - 4 I JOURNAL FOR OCCULTATION ASTRONOMYJournal for

Occultation Astronomy

Dave Herald talked about issues to think about regarding light
curve analysis. Event time accuracy - should we aim for highest
time precision? When is sub-frame timing desireable? Fact is 95%
of occultation astrometry has an uncertainty of >1.0 mas. Shaperesolution depends on the number of chords. Single chord events
have no shape info, the more chords (with good spacing) the
better in determining the shape. With a better shape the "centre of
figure" can be determined resulting in a more accurate astrometricposition for orbit updating. Then he discussed dealing withbackground subtraction. The purpose of background subtraction isto set the zero level of the light curve to zero light. He showed 3
light curves of the (718) Erida event 2022 Jun 24 recorded by
Richard Nolthenius. The light curves were made by PyMovie andTangra with usual and average background subtraction in AOTA.
Background subtraction results in a more distinguishable eventfrom the data points compared to not using it.

He then showed an Occult demo of (433) Eros rotating basedon shape and axis models.
Figures 14a,b.
While the chords fit theDAMIT model 5705 ofasteroid (713) Luscinia(left), there is no matchwith model 5706 (below).
(Source: Occult4.2022.8.14)

Magnitude drops - realistically with our video equipment
mag drops can be measured down to 0.1 mag precision. Noisein the event can influence this. Some observers have reported
mag drops to 0.001 mag! This is not credible or sensible - Davesuggested we report mag drops as a percentage of full light.
Gamma function - On our video cameras the gamma functionchanges the vertical response in a non-linear manner. It should
always be set to 1. With instantaneous events the non-linear
vertical response has a minimal effect to event time. Gamma set
to less than 1 affects magnitude changes. Magnitude changes are
generally poorly determined from our 8-bit light curves. However
if adjusting Gamma enables one to make an observation, by allmeans do it.

Dave Gault talked about time stamping delays associated withthe computer. There are acquisition delays, delays from VTI tocamera and internal camera processing delays to the computer.
More delays are within the PC's used for timing. Questions are:does anyone test their system for these delays? And correct theirtimes for this delay? Delays can be 53 - 68 ms. Hristo Pavlov andDave Gault wrote an article on this problem in the Journal for
Occultation Astronomy (JOA) issue 2020-02 [14].

Dave Herald next talked about shape model analysis with Occult.
Shape models provide the shape, not size of the asteroid. The
shape provides a volume-equivalent diameter to be measured.
Well observed events can help locate the centre of mass and not
the centre of figure. Dave showed sample Occult plots overlaid
with DAMIT shape models and location for the centre of figure(Figures 14a, b). The centre of figure point is used to determine
the astrometric position for MPC reporting. Multiple occultations
by the same asteroid can also be used to get the axis of rotation.
With the axis of rotation known, the asteroid can be rotated toshow different orientations.

The meeting ended at 00:10 UT August 15th.

References[1] Agenda on IOTA Meeting 2022 http://occultations.org/community/
meetingsconferences/na/ 2022-iota-annual-meeting/[2] Playlist of recordings of IOTA Meeting 2022
https://www.youtube.com/playlist?
list=PLPYvLiLF-6zsX6YPcT4WohWtdOMfHIplR[3] IOTA's Business Meeting 2022
http://www.poyntsource.com/Richard/IOTAMeeting2022.htm[4] https://www.iau.org/science/scientific_bodies/working_groups/330/[5] https://www.youtube.com/watch?v=t7sYab_EKmQ[6] http://www.asteroidoccultations.com/observations/Awards/IOTA
Awards.htm[7] Herald, D., Occult V4
http://www.lunar-occultations.com/iota/occult4.htm[8] Pavlov, H., Occult Watcher software https://www.occultwatcher.net/[9] Anderson, B., PyOTE software
https://occultations.org/observing/software/pymovie/[10] Anderson, B., PyMOVIE software
https://occultations.org/observing/software/pymovie/[11] Pavlov, H., Tangra software, http://www.hristopavlov.net/Tangra3/[12] https://www.dr-ricknolthenius.com/Apowers/
IOTANewTechniqueFaint.pdf[13] Journal of Double Star Observations http://www.jdso.org/[14] Pavlov, H., Gault, D., Using the Window's Clock with Network Time
Protocol (NTP) for Occultation Timing, Journal for Occultation
Astronomy, No. 2020-02, p 10-19.

JOURNAL FOR OCCULTATION ASTRONOMY I 2022 - 4

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Journal for

Occultation
Astronomy
IOTA’s Mission
The International Occultation Timing Association, Inc was established to encourage and facilitate theobservation of occultations and eclipses It provides predictions for grazing occultations of stars by the Moonand predictions for occultations of stars by asteroids and planets, information on observing equipment andtechniques, and reports to the members of observations made.

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The Journal for Occultation Astronomy (JOA) is published on behalf of IOTA, IOTA/ES and RASNZ andfor the worldwide occultation astronomy community.

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Submission Deadline for JOA 2023-1: November 15

IOTA maintains the following web sites for yourinformation and rapid notification of events:

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These sites contain information about the organisation known as IOTA and provide information
about joining.
The main page of occultations.org provides links
to IOTA’s major technical sites, as well as to themajor IOTA sections, including those in Europe,
Middle East, Australia/New Zealand, and SouthAmerica.
The technical sites hold definitions and information
about all issues of occultation methods. It contains
also results for all different phenomena. Occultations by the Moon, by planets, asteroids and TNOs
are presented. Solar eclipses as a special kind of
occultation can be found there as well results ofother timely phenomena such as mutual events ofsatellites and lunar meteor impact flashes.
IOTA and IOTA/ES have an on-line archive of allissues of Occultation Newsletter, IOTA’S predecessor to JOA.
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