S. Bagnulo
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View article: Polarimetric and spectropolarimetric observations with FoReRo2: Instrument overview and standard stars monitoring
Polarimetric and spectropolarimetric observations with FoReRo2: Instrument overview and standard stars monitoring Open
In this paper, we present a description and characterisation of the 2-Channel Focal Reducer Rozhen (FoReRo2), with an emphasis on its polarimetric and spectropolarimetric observation modes. FoReRo2 is a multimode instrument mounted at the …
View article: Rapid-response characterization of near-Earth asteroid 2024 YR4 during a Torino Scale 3 alert
Rapid-response characterization of near-Earth asteroid 2024 YR4 during a Torino Scale 3 alert Open
On 27 December 2024, near-Earth object (NEO) 2024 YR$_4$ was discovered by the ATLAS survey and identified as a virtual impactor. A few weeks later, it eventually reached level 3 on the Torino Scale and was the first and only asteroid to b…
View article: Research Hypothesis: Continuous Regeneration of a Nickel Shell on 3I/ATLAS - Most Probable Option
Research Hypothesis: Continuous Regeneration of a Nickel Shell on 3I/ATLAS - Most Probable Option Open
RESEARCH HYPOTHESIS: This study presents a technical hypothesis exploring the possibility that a nickel shell on the interstellar object 3I/ATLAS could be continuously regenerated by micro-cells operating in closed-loop. Based on 2025 obse…
View article: Extreme Negative Polarization of New Interstellar Comet 3I/ATLAS
Extreme Negative Polarization of New Interstellar Comet 3I/ATLAS Open
We present the first polarimetric observations of the third discovered interstellar object (ISO), 3I/ATLAS (C/2025 N1, or 3I), obtained preperihelion with FORS2 at the Very Large Telescope, ALFOSC at the Nordic Optical Telescope, and FoReR…
View article: JWST Detection of a Carbon-dioxide-dominated Gas Coma Surrounding Interstellar Object 3I/ATLAS
JWST Detection of a Carbon-dioxide-dominated Gas Coma Surrounding Interstellar Object 3I/ATLAS Open
3I/ATLAS is the third confirmed interstellar object to visit our solar system and only the second to display a clear coma. Infrared spectroscopy with the James Webb Space Telescope (JWST) provides the opportunity to measure its coma compos…
View article: Planet Earth in reflected and polarized light
Planet Earth in reflected and polarized light Open
Earthshine observations offer a unique opportunity to study Earth as an exoplanet seen from the Moon. As the Sun-Earth-Moon geometry changes, Earth can be observed as a spatially unresolved exoplanet at different phase angles, providing im…
View article: Planet Earth in reflected and polarized light -- III. Modeling and analysis of a decade-long catalog of Earthshine observations
Planet Earth in reflected and polarized light -- III. Modeling and analysis of a decade-long catalog of Earthshine observations Open
Earthshine observations offer a unique opportunity to study Earth as an exoplanet seen from the Moon. As the Sun-Earth-Moon geometry changes, Earth can be observed as a spatially unresolved exoplanet at different phase angles, providing im…
View article: Extreme Negative Polarisation of New Interstellar Comet 3I/ATLAS
Extreme Negative Polarisation of New Interstellar Comet 3I/ATLAS Open
We present the first polarimetric observations of the third discovered interstellar object, 3I/ATLAS (C/2025 N1), obtained pre-perihelion with FORS2/VLT, ALFOSC/NOT, and FoReRo2/RCC, over a phase angle range of 7.7-22.4°. This marks the se…
View article: Investigating Surface Variability of Main-Belt Asteroid (203) Pompeja through Spectropolarimetry
Investigating Surface Variability of Main-Belt Asteroid (203) Pompeja through Spectropolarimetry Open
Main-belt asteroid (203) Pompeja exhibits unusual and variable spectral behaviour. Observations during its 2021 apparition revealed an extremely steep red spectral slope in the visible and near-infrared, closely resembling trans-Neptunian …
View article: Planet Earth in reflected and polarized light
Planet Earth in reflected and polarized light Open
The characterization of nearby rocky exoplanets will become feasible with the next generation of telescopes, such as the Extremely Large Telescope (ELT) and the mission concept Habitable Worlds Observatory (HWO). Using an improved model se…
View article: Characterization of the DART Ejecta Using Computer Modeling of the Ground-based and HST Photopolarimetric Data
Characterization of the DART Ejecta Using Computer Modeling of the Ground-based and HST Photopolarimetric Data Open
Among the published observations of the DART ejecta, we have identified a set of quasi-simultaneous data acquired on 2022 October 4–5, using different but complementary techniques: polarimetry (FORS2 at the Very Large Telescope (VLT)), spe…
View article: Planet Earth in reflected and polarized light
Planet Earth in reflected and polarized light Open
Future ground- and space-based telescopes will enable the characterization of rocky exoplanets in reflected light, allowing for the observation of their albedo, which depends on surface, cloud, and atmospheric properties. Identifying key a…
View article: The EnVisS fish-eye camera for the Comet Interceptor ESA mission: design and performance
The EnVisS fish-eye camera for the Comet Interceptor ESA mission: design and performance Open
Publisher Copyright: © 2025 ESA and CNES.
View article: Strong magnetic fields of old white dwarfs are symmetric about the stellar rotation axes
Strong magnetic fields of old white dwarfs are symmetric about the stellar rotation axes Open
Many magnetic white dwarfs exhibit a polarised spectrum that periodically varies as the star rotates because the magnetic field is not symmetric about the rotation axis. In this work, we report the discovery that while weakly magnetic whit…
View article: Strong magnetic fields of old white dwarfs are symmetric about the stellar rotation axes
Strong magnetic fields of old white dwarfs are symmetric about the stellar rotation axes Open
Many magnetic white dwarfs exhibit a polarised spectrum that periodically varies as the star rotates because the magnetic field is not symmetric about the rotation axis. In this work, we report the discovery that while weakly magnetic whit…
View article: The Pre-perihelion Evolution of the Activity of Comet C/2017 K2 (Pan-STARRS) during the Water Ice-line Crossover
The Pre-perihelion Evolution of the Activity of Comet C/2017 K2 (Pan-STARRS) during the Water Ice-line Crossover Open
Comets, relics from the early solar system, consist of dust and ice. The ice sublimates as comets approach the Sun, ejecting dust from their nuclei seen as activity. Different volatiles sublimate at different Sun–comet distances and eject …
View article: Searching for magnetic fields in featureless white dwarfs with the DIPOL-UF polarimeter at the Nordic Optical Telescope
Searching for magnetic fields in featureless white dwarfs with the DIPOL-UF polarimeter at the Nordic Optical Telescope Open
About 20% of the white dwarfs possess a magnetic field that may be detected by the splitting and/or polarization of their spectral lines. As they cool, the effective temperatures of the white dwarfs becomes so low that no spectral lines ca…
View article: Searching for magnetic fields in featureless white dwarfs with the DIPOL-UF polarimeter at the Nordic Optical Telescope
Searching for magnetic fields in featureless white dwarfs with the DIPOL-UF polarimeter at the Nordic Optical Telescope Open
About 20% of the white dwarfs possess a magnetic field that may be detected by the splitting and/or polarization of their spectral lines. As they cool, the effective temperatures of the white dwarfs become so low that no spectral lines can…
View article: The pre-perihelion evolution of the activity of comet C/2017 K2 (PANSTARRS) during the water ice-line crossover
The pre-perihelion evolution of the activity of comet C/2017 K2 (PANSTARRS) during the water ice-line crossover Open
Comets, relics from the early solar system, consist of dust and ice. The ice sublimates as comets approach the Sun, ejecting dust from their nuclei seen as activity. Different volatiles sublimate at different Sun-comet distances and eject …
View article: Atmospheric heating and magnetism driven by <sup>22</sup>Ne distillation in isolated white dwarfs
Atmospheric heating and magnetism driven by <sup>22</sup>Ne distillation in isolated white dwarfs Open
The origin of atmospheric heating in the cool, magnetic white dwarf GD 356 remains unsolved nearly 40 years after its discovery. This once idiosyncratic star with T eff ≈ 7500 K, yet Balmer lines in Zeeman-split emission is now part of a g…
View article: Metal accretion scars may be common on magnetic, polluted white dwarfs
Metal accretion scars may be common on magnetic, polluted white dwarfs Open
More than 30% of white dwarfs exhibit atmospheric metals, which are understood to be from recent or ongoing accretion of circumstellar debris. In cool white dwarfs, surface motions should rapidly homogenise photospheric abundances, and the…
View article: Modeling linear polarization of the Didymos-Dimorphos system before and after the DART impact
Modeling linear polarization of the Didymos-Dimorphos system before and after the DART impact Open
The NASA Double Asteroid Redirection Test (DART) impacted the smaller component, Dimorphos, of the Didymos binary system on 2022 September 26 (Daly et al. 2023). The planetary defense test successfully and clearly changed the orbit o…
View article: VSTPOL: making the VST a large survey telescope for optical polarimetry
VSTPOL: making the VST a large survey telescope for optical polarimetry Open
Since the start of operations in 2011, the VLT Survey Telescope (VST) has been one of the most efficient wide-field imagers in the optical bands. However, in the next years the Vera C. Rubin Observatory Legacy Survey of Space and Time (LSS…
View article: Coma and tail of Comet 67P/Churyumov–Gerasimenko during the 2021–2022 apparition
Coma and tail of Comet 67P/Churyumov–Gerasimenko during the 2021–2022 apparition Open
We present results on the global activity of comet 67P/Churyumov–Gerasimenko (67P), the ROSETTA target, during its first perihelion passage after the mission and after an encounter with planet Jupiter. 67P was observed by broad-band filter…
View article: Imaging Polarimetry of Comet 67P/Churyumov-Gerasimenko: Homogeneous Distribution of Polarisation and its Implications
Imaging Polarimetry of Comet 67P/Churyumov-Gerasimenko: Homogeneous Distribution of Polarisation and its Implications Open
Comet 67P/Churyumov-Gerasimenko (67P) become observable for the first time in 2021 since the Rosetta rendezvous in 2014--16. Here, we present pre-perihelion polarimetric measurements of 67P from 2021 performed with the Very Large Telescope…
View article: Imaging polarimetry of comet 67 P/Churyumov–Gerasimenko: homogeneous distribution of polarization and its implications
Imaging polarimetry of comet 67 P/Churyumov–Gerasimenko: homogeneous distribution of polarization and its implications Open
Comet 67P/Churyumov–Gerasimenko (67P) become observable for the first time in 2021 since the Rosetta rendezvous in 2014–2016. Here, we present pre-perihelion polarimetric measurements of 67P from 2021 performed with the Very Large Telescop…
View article: Discovery of Magnetically Guided Metal Accretion onto a Polluted White Dwarf
Discovery of Magnetically Guided Metal Accretion onto a Polluted White Dwarf Open
Dynamically active planetary systems orbit a significant fraction of white dwarf stars. These stars often exhibit surface metals accreted from debris disks, which are detected through infrared excess or transiting structures. However, the …
View article: Rotation plays a role in the generation of magnetic fields in single white dwarfs
Rotation plays a role in the generation of magnetic fields in single white dwarfs Open
Recent surveys of close white dwarf binaries as well as single white dwarfs have provided evidence for the late appearance of magnetic fields in white dwarfs, and a possible generation mechanism, a crystallization and rotation-driven dynam…
View article: Rotation plays a role in the generation of magnetic fields in single white dwarfs
Rotation plays a role in the generation of magnetic fields in single white dwarfs Open
Recent surveys of close white dwarf binaries as well as single white dwarfs have provided evidence for the late appearance of magnetic fields in white dwarfs, and a possible generation mechanism a crystallization and rotation-driven dynamo…
View article: The Comet Interceptor Mission
The Comet Interceptor Mission Open