Author 1: N. Kiselev (Crimean Astrophysical Observatory (CrAO), Institute of Astronomy of the Russian Academy of Sciences (INASAN)); Shcherbina (INASAN), D. Petrov (CrAO), E. Zhuzhulina (CrAO), M. Chazov (SAO RAS), N. Karpov (INASAN), A. Shein (INASAN), A. Salakhotdinova (INASAN), I. Sokolov (INASAN), D. Andreev (INASAN), N. Kapitanov (INASAN), and G. Dyachenko (CrAO)

Title 1: Polarimetric and Photometric Characteristics of the Interstellar Comet 3I/ATLAS: Key Features

Abstracts:

A major milestone in the direct study of small bodies originating from other planetary systems was the discovery and investigation of the first interstellar objects: the asteroid 1I/‘Oumuamua in 2017 and the comet 2I/Borisov in 2019.

The existence of interstellar comets had been proposed as early as the time of Laplace (1813), although he believed that all comets in the Solar System were of interstellar origin.

The first two detected interstellar objects have already demonstrated that this population may be physically diverse. The object 1I/‘Oumuamua showed no clear evidence of strong cometary activity. However, it exhibited nongravitational acceleration, which was interpreted as a possible manifestation of weak cometary activity. In contrast, 2I/Borisov behaved as an active comet with pronounced dust and gas emission. The discovery of the third interstellar object, 3I/ATLAS, therefore provided an opportunity to obtain new information about this class of objects.

We present the results of polarimetric and photometric observations of the interstellar comet 3I/ATLAS conducted between 18 November 2025 and 26 January 2026. The observations were performed using the POLSHAKH polarimeters mounted on the 2-m Zeiss-2000 telescope of the INASAN Terskol Observatory and the 2.6-m telescope of the Crimean Astrophysical Observatory, as well as the SCORPIO-2 focal reducer mounted on the 6-m BTA telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences. The observations were obtained using broadband BVRI, SDSS g, and SDSS r filters, together with dedicated narrowband cometary filters.

The aim of this study was to determine the polarimetric and photometric characteristics of the interstellar comet 3I/2025 N1 (ATLAS) and to model the physical properties of its coma particles.

The observations and subsequent analysis yielded the following results:

1. Comet 3I/ATLAS exhibited an exceptionally high degree of polarization, both in terms of the absolute value of its negative polarization and in the positive polarization branch. The negative polarization branch is strongly asymmetric, with a minimum polarization of a phase angle of  inversion angle of , and a polarimetric slope of  In the positive polarization branch, the polarization of 3I/ATLAS exceeds that measured for all previously observed comets.
2. In the visible spectral range, 3I/ATLAS showed a weaker increase in polarization with wavelength, than the average value of observed for Solar System comets.
3. In November 2025, the reflectance gradient of the comet between the V and R bands was A pronounced depression was observed in the blue spectral region, with
4. The (B-V), (V-R), and (R-I) color indices were approximately 0.4 mag, while (g-r=0.71) mag.
5. The parameter, which characterizes the comet’s dust production, was ( cm in the SDSS r band for a projected coma diameter of 22,696 km on 27 November 2025, when the comet was at a heliocentric distance of 1.710 au.
6. The best agreement with the observed phase dependence of polarization was obtained using an Sh-matrix model of conjugated random Gaussian particles with surface roughness  and a mixture composed of 95% amorphous carbon, 4.5% Mg-rich silicates, and 0.5% water ice

These distinctive properties of 3I/ATLAS will be discussed in comparison with the typical characteristics of Solar System comets.

Author 2: M. Shcherbina (Institute of Astronomy of the Russian Academy of Sciences (INASAN)); Kiselev N. (CrAO, INASAN)

Title 2: A New Asteroid Polarimetric Database: Structure, Content, and Functionality

Abstracts:

This contribution presents a new database of asteroid polarimetric observations that combines previously published measurements with unique new observational data obtained using telescopes of the Crimean Astrophysical Observatory and the INASAN Terskol Observatory. The primary objective of the project is to create a unified open-access resource for the storage, retrieval, visualization, and analysis of the polarimetric characteristics of small Solar System bodies.

The resource is based on data from the Asteroid Polarimetric Database (APD), which was last updated in 2022. As part of the present project, the database was supplemented with new measurements published in the scientific literature between 2022 and 2026, as well as with the results of our own observations.

The website was developed as a web application using Django and PostgreSQL and provides open access to the observational catalogue. Its functionality includes:

• filtering data by asteroid, phase-angle range, observational band, taxonomic classification, and asteroid family;
• exporting selected data in Excel and TSV formats;
• individual pages for each asteroid;
• interactive visualization of polarization–phase-angle dependences;
• integration of bibliographic references and information on the observational instruments used.

Particular attention was paid to combining observations obtained in different photometric systems and spectral ranges. For each asteroid, the database provides the covered phase-angle ranges and lists the filters used in the observations.

The presentation will include a demonstration of the database and its full range of available functions.