PREDNASAJUCI / LECTURER :

Oleksandra Ivanova

(1) Astronomical Institute, Slovak Academy of Sciences,
059 60 Tatranská Lomnica

NAZOV / TITLE :

Quasi-simultaneous photometric, polarimetric, and spectral
observations of interstellar comet 3I/ATLAS

ABSTRAKT / ABSTRACT :

We present a comprehensive study of the interstellar comet 3I/ATLAS
based on photometric, spectroscopic, and polarimetric observations
obtained before and after perihelion. The dataset combines multi-band
photometry, spectroscopy, and post-perihelion polarimetry, allowing
us to trace the evolution of the comet’s activity and dust properties.
We find that the comet exhibits unusually high linear polarization
(7.4% at 30° phase angle), making 3I/ATLAS the most highly polarized
comet observed to date. Light-scattering modeling indicates that the
dust is dominated by aggregated particles composed of organics mixed
with silicates, with possible minor water ice content. The comet shows
a gradual increase in dust activity and reddening of the spectral slope,
with no gas emission detected until CN appeared in mid-August 2025.
Post-perihelion spectra reveal a carbon-chain-depleted composition,
with CN, C2, C3, and NH2 detected at low abundances. We derive that
the coma morphology is relatively simple, dominated by a persistent
sunward jet observed both before and after perihelion. Modeling
suggests activity from high-latitude regions near opposite poles,
consistent with a rotation period near 16.2 h. The stability of the
jet indicates long-lived active regions and a relatively simple
nucleus geometry. These results provide new constraints on interstellar
cometary dust and demonstrate the diagnostic power of polarimetry for
characterizing extrasolar small bodies.