ALLIK Mohamed Lamine: Contribution of Amateur Astronomers from Bejaia to the Observation of Stellar Occultation by Asteroids in Algeria

Since their first participation in the First Algerian Meeting on Occultations in December 2016 in Algiers, amateur astronomers from Bejaia have gradually established themselves in the field of stellar occultation observations by small Solar System bodies. Notably, they organized the second edition of this meeting in Tichy (Bejaia) in August 2017, on the occasion of the stellar occultation by asteroid (5247) Kyrlov. Their involvement continued through regular participation in national meetings held in Relizane (2018), Laghouat (2019 and 2020), and Ghardaia (2022). Despite sometimes unfavorable conditions (cloudy skies, technical issues, or negative observations) positive results were nevertheless obtained, including some by naked-eye observation. Their progress culminated in two major international contributions: the observation of the occultation of the star Betelgeuse by asteroid (319) Leona on December 12, 2023, in Alicante (Spain), and the total solar eclipse on April 8, 2024, in Dallas (USA), during which successful imaging of Baily’s beads was achieved. This work outlines the main stages of this progression and highlights the significant achievements of the Béjaïa amateur astronomers in the study and observation of occultations.

BABA AISSA Djounai: The observation of quadruple-chords stellar occultation on February 18th, 2025 by the transneptunian object (468861) 2013 LU28 in the far southern of Algeria

The celestial body (468861) 2013 LU28, is an enigmatic Trans- Neptunian object classified as centaur/damocloid due to its elliptical, highly eccentric, and retrograde orbit, was discovered on June 8, 2013, by the Mount Lemmon Survey (Arizona, USA). Until recently, stellar occultations by this TNO had eluded confirmed observations. On January 30, 2025, David Dunham & al. from the IOTA organization successfully observed this occultation in Maryland (USA) and obtained the first multi-chords. Consequently, by incorporating the results obtained by the American team, the Lucky Star team from Paris Observatory, in collaboration with the Institute of Astrophysics in Granada team, refined swiftly their calculations with new astrometric data, to improve the prediction of the occultation event February 18, 2025 in the far southern of Algeria. A scientific expedition led by Algerian researchers from CRAAG (ex Algiers Observatory), in collaboration with amateur astronomers and local teams, achieved Algeria’s first four positive observations of this event. These results represent a major milestone in the study of Trans-Neptunian Objects, paving the way for better understanding the orbital and physical parameters of 2013 LU28 and distant icy bodies in the Solar System.

BURZYŃSKI Wojciech: The beginning of observations occultation events at University of Białystok Astronomical Observatory

The main focus of the University of Białystok Astronomical Observatory is photometric observations within the BHTOM system. Black Hole Target and Observation Manager is a web-based system for managing and coordinating astrophysical observations, enabling researchers to efficiently track, prioritize, and monitor a wide range of transient and variable phenomena. We successfully observe quasars, active galactic nuclei, variable stars: novae, symbiotic, and cataclysmic, the effects of gravitational microlensing, tidal disruption events and X-ray binaries.

A secondary, but equally important, observational goals are occultation events – starting in the fall of 2024 we have observed many asteroidal and lunar double stars occultations.

BOUDIBA Ghoulam Imad Eddine et al: Preliminary results of four stellar occultation bu the Trojan (4709) Ennomos

Jupiter’s Trojans are pristine objects (most likely trans-neptunian objects, TNOs) that were captured by Jupiter, during the planetary migration. These Trojans are captured in Jupiter’s Lagrange points L4 and L5.
This work aims to conduct a study of the Trojan (4709) Ennomos through stellar occultation in order to deduce its shape, size and geometrical albedo. Stellar occultations provide an accurate estimate of the size and the shape of the asteroid’s limb and the astrometric object position at the time of the occultation.
Two distinct observation campaigns were conducted to study stellar occultations by the Trojan Ennomos. The first campaign, carried out between 2018 and 2020, was led by the Occult Watcher team, which predicted the occultations and coordinated the observations. Data with positive chord measurements was directly provided by participating observers. The second campaign, conducted from 2020 to 2023, was organized by the Lucky Star team. The Lucky Star team successfully predicted and observed stellar occultations from the US and Europe. The data were managed through the Occultation Portal website. A total of four occultation events were observed with positives chords. We develop a python code to perform aperture photometry and use SORA python package to fit the ellipses at the times of the occultations.
We fit Ennomos’ projected ellipse for the four occultations events, on February 2018 and April 2020 in Australia, on November 2021 in US and on August 2022 in Europe. Obtaining the size parameter for each ellipse as primer result. The equatorial radius and the oblateness were in the range of a = 59.06^{+29.68}_{-8.22} and ϵ = 0.25^{+0.36}_{-0.19} respectively. which correspond to an apparent equivalent radius in the order of 50.01^{+2.67}_{-4.29} with a geometrical albedo between 5.8% and 7.8%.

CHOUKROUN Antoine et al: Asteroid sizes constrained by thermophysical model and stellar occultations

Context
Reliable asteroid diameter estimates are crucial for deriving physical parameters
such as density or thermal inertia. Yet, many literature values suffer from
significant uncertainties due to simplistic modelling assumptions or sparse data.
Stellar occultations, when resulting in multiple chords, offer a nearly direct
and highly accurate method to determine asteroid sizes. However, these events
remain rare due to strong observational constraints.
Aims
We aim to demonstrate that multi-chord stellar occultations remain the gold
standard for asteroid diameter determination. Our goal was to determine precise
diameters for fifteen slowly rotating, low-amplitude main-belt asteroids using
occultation fitting, and to compare them with values obtained through advanced
thermophysical modelling (see Choukroun et al. 2025).
Methods
We derive convex 3D shape and spin models from dense, multi-apparition pho
tometric lightcurves using lightcurve inversion. These shape models are then
scaled using multi-chord stellar occultations with shape model silhouettes pro
jected and fitted to the observed chords in the fundamental plane. The occultation
based diameters are compared with values obtained from thermophysical mod
elling (CITPM), allowing us to assess residuals and check consistency.
Results
For all fifteen targets, occultation-based diameters agree with CITPM-derived
values within 5% in most cases. Larger discrepancies are found only for poorly
covered events (few chords or asymmetric coverage of the body). These re
sults confirm the robustness of the occultation-fitting method and its continued
importance for validating and constraining asteroid size estimates obtained by
indirect means.
Conclusions
Despite the improving quality of thermal data and modelling techniques, multi
chord stellar occultations remain a critical benchmark for size determinations.
Our results prove their use as a reference for model validation and provide high
quality input for future studies on asteroid densities and internal structures.

GÄHRKEN Bernd: Occultation by Psyche in Algeria at Oct. 8. 2025

On October 8, 2025, the minor planet Psyche occulted a 6-magnitude star in Algeria. In the same night, Neptune’s rings occulted an 11-magnitude star. Since the minor planet Psyche is the target of a space mission, the Algerian amateurs organized a large-scale observation campaign near the desert town of Laghouat. This talk will provide impressions of the trip and explore the conditions during the 2027 solar eclipse.

GäHRKEN Bernd,KATTENTIDT Björn: Grazing Occultation of Maia at April 1. 2025

Maia is one of the main stars of the Pleiades. It is an interesting quadruple star whose nearby component, ‘Ab,’ was discovered in 1988 through a grazing occultation. Since it was not possible to calculate its distance in 1988, it is interesting to take another look. We used two Seestar Smartscopes for the occultation. This talk will present some of the results and demonstrate the capabilities of the Seestar-S50 in occultation projects.

GUHL Konrad, SCHAFFER Frank: Improvement in VAMOR process

In 2023 the authors presented the project VAMOR CAD – Validation of Asteroid
Models by Occultation Results for the spatial representation of occultation
observation events on the 3D-model. The process was complemented with a
“drawing” or “design” method for more irregular bodies, especially. This
method has been tested on the very precisely known (22) Kalliope model. The
simpler method, developed first for bodies that are more regular, is compared
with the further developed method and the results, using the examples (357)
Ninia and (22) Kalliope, compared with each other.

GUTEKUNST Martin: Optimal exposure time regarding the detectability of big dips (>1.5mag)
Length about 20 min

The lecture deals with the question of which exposure time or S/N ratio is optimal for an event with a given brightness and event duration for a given equipment
The talk also shows a method for finding the optimum exposure time.

GUTEKUNST Martin: Optimal exposure time regarding the detectability of small dips (<1.5mag)
Length about 20 min

A method is presented how to check whether the event is observable for a given brightness, signal dip and event duration for a given equipment.
For a positive answer a procedure is presented to determine the optimal exposure time.

HANUš Josef: Stellar Occultations by Asteroids Observed with the Unistellar Network: The Case of (16583) Oersted

We present results from the stellar occultation by asteroid (16583) Oersted observed on March 3, 2024. The event was recorded by fifteen stations across the Czech Republic and Latvia, including one chord contributed by the Unistellar citizen science network. The resulting multi-chord dataset enabled precise reconstruction of Oersted’s silhouette, which we combined with archival sparse photometry and thermal infrared measurements to derive its shape, spin state, and surface thermal properties. Our analysis demonstrates that Unistellar data can reach the quality needed for high-precision shape scaling and offers a new path to robust asteroid characterization when integrated with professional datasets. We discuss the implications of this result for future occultation campaigns and the growing role of citizen science in planetary research.

KATTENTIDT Björn: Grazing lunar occultation on 1. May 2025 near Regensburg using 3 different optical systems by comparison

A lunar occultation has been observed very successful recording 3 chords with 3(4) different astronomical equipment. The results are presented and compared with prediction by GRAZPREP and analysis by Mitsuru Soma (if available). The 3 optical systems and mounts as well as recording systems are compared one against another concerning effort of installation, system cost and pros vs. cons.

KRETLOW Mike: A comparison of radiometric and occultation-derived diameters of TNOs

Trans-Neptunian Objects (TNOs) are fundamental to understanding the formation and evolution of the outer Solar System. To date, most diameter estimates for TNOs and Centaurs come from radiometric techniques, primarily based on thermal data from ESA’s Herschel Space Observatory. These are typically interpreted using the Standard Thermal Model (STM) or the Near-Earth Asteroid Thermal Model (NEATM), the latter also widely used in infrared surveys such as IRAS, WISE/NEOWISE, Spitzer, and AKARI.

Stellar occultations provide (apparent) size measurements of TNOs with kilometer-scale precision and can reveal their shape, binarity and rings. Combined with absolute magnitudes, they also enable accurate albedo estimates. In recent years, collaborative (pro-am) efforts have significantly expanded the sample of occultation-based sizes, allowing robust comparison with radiometric results.

Our analysis shows good overall agreement in diameters, with a mean weighted normalized orthogonal distance of 11.8%, which is consistent with similar studies of main-belt and near-Earth asteroids. However, albedo estimates show more variation, primarily due to uncertainties in absolute magnitude (H). Occultations play a key role in validating and refining thermal models, especially for non-spherical or complex bodies. Larger discrepancies, typically when radiometric diameters exceed occultation values by more than ~12%, may indicate unresolved companions or ring systems contributing excess thermal flux.

MIDAVAINE Thierry (ZOOM): The Ganymede III occultation on the 14th of October

The Ganymede III occultation on the 14th of octobre.
This is a call for a European wide campaign to meet three targets attached to this event.
The occulted star is magnitude 7 giving us a nice opportunity to run at high rate our instrumental setup.

NIKOŁAJUK Marek: Eclipsing X-ray binaries

X-ray binary systems contain two components. One is an ordinary star, and the other is a neutron star (NS) or black hole (BH). True to their name, they emit X-ray radiation. It originates from the matter of the accretion disk, which falls on the compact star. In this short lecture, I would like to focus on the systems that show eclipses.

PERŁA Julia, MARCINIAK Anna: Expanding Results from Asteroid Shape Modelling Driven by Archival Stellar Occultation Data

Stellar occultation databases gather many high-quality, multichord results of occultation phenomena
(Herald et al. 2024, SODIS). This data is a great foundation for determining physical properties of
asteroids, such as size and shape (Herald et al. 2020). In order to determine an asteroid size, it is possible to fit a sphere, ellipsoid, or spin and shape model to chords from a stellar occultation campaign (Durech et al. 2011, Herald et al. 2020). As is known from multiple space missions,
asteroid shapes are mostly irregular. Therefore, the most accurate method for determining asteroid
sizes is through the fitting of complex shape models, rather than ellipsoids. Accurate diameters in
turn allow, for instance, better density constraints (Carry 2012).

Aims:
There is a significant number of asteroids with valuable stellar occultation data, but no shape model. The primary reason for the absence of a spin and shape model is typically an insufficient amount of photometric data. Therefore, we conducted an observing campaign to collect rotational lighcurves in additional apparitions of these targets.

Methods:
Asteroids were modelled using the convex inversion method (Kaasalainen, Torppa 2001,
Kaasalainen et al. 2001) and then scaled with rich stellar occultation data (Durech et al. 2011).

Results:
We modelled spins and shapes of a few main belt asteroids. This permitted the precise determination of the asteroid diameters, narrowing the range of diameters determined by the infrared studies. Moreover, for some targets we resolved the mirror-pole ambiguity.

References:
Herald D., et al. 2024. Asteroid Occultations V4.0. NASA Planetary Data System
Stellar Occultation Data Input System (SODIS), https://sodis.iota-es.de
Durech, J., Kaasalainen, M., Herald, D., et al. 2011, Icarus, 214, 652
Herald, D., Gault, D., Anderson, R., et al. 2020, MNRAS, 499, 4570
Carry B. 2012. Planet. Space Sci., 73, 98
Kaasalainen, M. & Torppa, J. 2001, Icarus, 153, 24
Kaasalainen, M., Torppa, J., & Muinonen, K. 2001, Icarus, 153, 37

PRATT Alex: Lunar Occultations of Double Stars

High-cadence video photometry (>50 fps) of lunar occultations of close double stars allows us to estimate the magnitudes, position angle and separation of double star components. This talk gives an overview of how to obtain predictions, record an event, analyse the data, and share your observations. It summarises the history of worldwide observing programmes and mentions new developments such as the OLED project.

PURVINSKIS Robert: Path shifts

The shifting of an asteroid occultation path away from an observer is a frustrating experience. This talk aims to define what a path shift is, and possible causes. Some examples are presented, including recent non-observations by IOTA observers.

SAOULI Andane et al: Scientific Achievements of Suhail Astronomy Association in Laghouat in Observing Stellar Occultations by Asteroids in Algeria

The Suhail Association for Astronomy and Space Sciences, based in Laghouat, Algeria, has been actively engaged since 2016 in astronomy outreach and citizen science, with a particular focus on stellar occultations by asteroids. Initially centered on visual observations, the association’s members have gradually developed technical expertise that has significantly improved the precision and quality of their data. The organization of the 8th, 9th, and 12th national meetings on asteroid occultations has further consolidated its role as a key player in this field within Algeria. Notably, the 9th meeting, held in October 2020, set a national record with the participation of 120 amateur astronomers from across the country, using a total of 54 telescopes. Among its major scientific contributions is the observation of the stellar occultation by asteroid (283) Emma in November 24, 2020, which led to the discovery of a binary star system with the widest angular separation ever recorded, recognized by the International Occultation Timing Association (IOTA). The association has also taken part in international campaigns, including the observation of the occultation of the star Betelgeuse by asteroid (319) Leona on December 12, 2023, in Alicante, Spain, and the total solar eclipse in Dallas, United States, in 2024, during which high-resolution images of Bailey’s Beads were captured. Finally, observations of the near-Earth asteroid (2212) Hephaistos in November 08, 2024, and the trans-Neptunian object 2013 LU28 (in Adrar, Algeria) in February 18, 2025, have provided valuable data to the international scientific community, with results currently under review for publication in peer-reviewed journals.

SCHNABEL Carles: Spanish TSE 2026 from the edges

Next year’s eclipse will cross the Iberian Peninsula from NW to E. I would like to suggest and give some guidelines for observing the event from both edges: north and south.

SOUAMI Damya: The best 2026 occultation opportunities by Didymos before the arrival of Hera (ESA) mission April 16th (France, Sardinia …) and May 4th (Algeria)

Although the use of occultations to characterise NEAs [K10] have been expected 15 years ago; it has only become recently feasible thanks to the Gaia DR3 stellar catalogues [G23] which have revolutionised the use of stellar occultations to the point of successfully predicting occultations by sub-km sized NEAs. This began with the occultation by (99 942) Apophis [D23], followed by a series of occultation by the Didymos-Dimorphos system [S23, T24] target of the DART (NASA) and Hera (ESA) planetary defence missions.

We present here the last good occultation opportunity by the Didymos system on April 16th, 2026 UT which will be observable in Europe, from France and Sardinia; as well as the May 4th UT event which will be observable from Algeria.

This talk is meant to alert the IOTA community at large and in particular the IOTA-ES community of the importance of these two events.

References:
[K10] Koschny, D., Drolshagen, J., and Bobrinsky, N.: 2010, Cosmic Research 48, 403. doi:10.1134/S0010952510050059.
[G23] Gaia Collaboration, Vallenari, A., Brown, A.G.A., Prusti, T., de Bruijne, J.H.J., Arenou, F., et al.: 2023, Astronomy and Astrophysics 674, A1. doi:10.1051/0004-6361/202243940.
[D23] Desmars, J., Souami, D., Vavilov, D., Hsu, H.M., De Pater, I., and Hestroffer, D.: 2023, Asteroids, Comets, Meteors Conference 2851, 2376.
[S23] Souami, D.: 2023, Sky and Telescope 145, 8.
[T24] Tanga, P., Souami, D., Tsiganis, K., Siakas, A., Ferreira, J., Tsardaridis, S., et al.: 2024, European Planetary Science Congress, EPSC2024-1019. doi:10.5194/epsc2024-1019.
[S25] Souami, D., Sfair, R., Renner, S., and El Moutamid, M.: 2025, Philosophical Transactions of the Royal Society of London Series A 383, 20240202.

STOLZEN Peter: Observation of the partial solar eclipse on March 29, 2025 on La Palma

Photographic observation of the partial solar eclipse on March 29, 2025, on La Palma using a 500mm telephoto lens, converter, and digital camera. Presentation of a slide show. Description of the technique, recording data, and methodology.

VELASCO Enrique: OLED Project – Lunar occultations of double star

In this talk we will present the OLED project, a collaborative initiative between Spanish and French observers focused on measuring lunar occultations of double stars. The project places particular emphasis on close binaries and unresolved stars known to be double. We will share the results obtained to date, discuss future prospects, explore potential technical improvements, and extend an invitation for collaboration.

WILAND Janusz: 48 years of my occultation observations

I will present the history of my occultation observations since 1978. I will show the optical equipment used for these observations and the electronic devices for precise time measurement. Almost all of these devices were made by me or under my supervision.

ZAWILSKI Marek: Historical occultation phenomena observed from the Greater Poland region

Over the centuries, the region of Greater Poland  has witnessed many interesting occultation phenomena. The total solar eclipse of October 29, 878 probably was observed, but no written document about it has survived.We only have such evidence from the 15^th century, when an anonymous priest from the vicinity of Trzemeszno wrote down his impressions of the deep solar eclipses of June 16, 1406, June 7, 1415, and June 26, 1424 (the latter is the only description of a total phase on a European scale).The next great solar eclipse of May 12, 1706 was recorded in Poznań, Zbąszyń, Słupca, Międzychód and Wałcz. Unfortunately, the circumstances of the phenomenon (the Great Northern War) prevented more precise observations. The partial solar eclipse on April 1, 1764 was observed by Józef Rogaliński at Poznań.During the total solar eclipse of August 19, 1887, the weather was terrible and only a short great darkness was seen in the overcast morning.

In 1919, after the establishment of an astronomical observatory in Poznań, the situation changed radically. Many local astronomers regularly performed observations of lunar occultations, including Józef Witkowski (the first director), Stanisław Andruszewski and Jerzy Sławski, and later also Ferdynand Koebcke, Hieronim Hurnik, Janusz Pagaczewski and several others. In total, over 800 such phenomena were recorded in the period 1923-1959. Astronomers from the Poznań Observatory also took part in several expeditions to total solar eclipses around the world.

Prof. Witkowski also dealt with the theory of occultation phenomena, aspects of their observation and the study of changes in the position of the Earth’s rotation axis. His habilitation thesis concerned the analysis of the occultation of the star 6G.Lib by Jupiter and its satellite Ganymedes in 1911 (what was predicted by Prof. Tadeusz Banachiewicz, the promotor of Witkowski, and observed in Australia, China and South America, respectively).

In 1974-1975 amateur observations of lunar occultations were continued at Poznań by Zbigniew Rzepka. Finally, a valuable contribution to the observations of the grazing occultation of Aldebaran on April 28,  1998 was made at two stations in Poznańby Krzysztof Kamiński and Jan Nowicki.

Posters:

Name	Title
Haymes Tim	Magnitude Calibration in TANGRA and Occult 4 – some tips
O’Connell Michael	Remote Observations of Stellar Occultations
Marciniak Anna, Durech Josef, Choukroun Antoine, Perła Julia	Asteroid sizes determined with stellar occultations