SN2025aico: An Interesting Case Of 56Ni Mixing, Ejecta Asymmetries, and Dust Formation in a Type IIb Supernova
Abstract
Stripped-envelope supernovae provide a window into how massive stars lose their layers, mix radioactive material, produce dust, and explode asymmetrically. We present optical, near-infrared (NIR), and mid-infrared (MIR) observations of SN~2025aico, a Type~IIb supernova in LEDA~35384. Our spectroscopic sequence, spanning +1 to +167 d after explosion, follows its evolution from a photospheric phase exhibiting both hydrogen and helium features to prominent helium emission and, ultimately, nebular-phase ejecta. Using He I $1.083$ and 2.0581 μm transitions, we investigated the kinematics and geometry of the helium-rich material. Both transitions exhibit a three-phase, non-monotonic velocity evolution: an initial rapid decline, a subsequent increase, and an eventual plateau. We interpret this behavior as evidence for limited outward mixing of 56Ni, such that radioactive energy deposition reaches the outer helium-rich ejecta progressively as the ejecta expand, producing the non-thermal electrons responsible for helium excitation. After ∼100 d, both NIR He I transitions develop double-peaked emission profiles. Similar structure in the oxygen emission indicates ejecta asymmetry. Comparison with other supernovae suggests a tentative connection between this structure and explosion energy, potentially linked to the delay between core collapse and explosion. Serendipitous JWST observations at +124.4d reveal an infrared excess. Modeling favors warm (∼800--$1500$K) carbon dust newly formed in the ejecta, together with cooler carbon or silicate dust likely associated with pre-existing circumstellar material. SN~2025aico demonstrates how continuous optical-to-MIR observations can connect progenitor evolution, explosion physics, ejecta geometry, and dust production.
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BibTeX
@misc{davis2026sn2025aico,
title = {{SN2025aico: An Interesting Case Of $^56$Ni Mixing, Ejecta Asymmetries, and Dust Formation in a Type IIb Supernova}},
author = {Grace Davis and Kyle Medler and Chris Ashall and Willem B. Hoogendam and Cameron Pfeffer and David O. Jones and Shunsaku Horiuchi and Tyco Mera and Benjamin Shappee and Charlotte Ward and Grace Showerman},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.26935},
eprint = {2609.26935},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.26935},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - SN2025aico: An Interesting Case Of ^56Ni Mixing, Ejecta Asymmetries, and Dust Formation in a Type IIb Supernova
AU - Grace Davis
AU - Kyle Medler
AU - Chris Ashall
AU - Willem B. Hoogendam
AU - Cameron Pfeffer
AU - David O. Jones
AU - Shunsaku Horiuchi
AU - Tyco Mera
AU - Benjamin Shappee
AU - Charlotte Ward
AU - Grace Showerman
PY - 2026
DA - 2026/09/22
PB - arXiv
DO - 10.48550/arxiv.2609.26935
UR - https://arxiv.org/abs/2609.26935
AB - Stripped-envelope supernovae provide a window into how massive stars lose their layers, mix radioactive material, produce dust, and explode asymmetrically. We present optical, near-infrared (NIR), and mid-infrared (MIR) observations of SN~2025aico, a Type~IIb supernova in LEDA~35384. Our spectroscopic sequence, spanning +1 to +167 d after explosion, follows its evolution from a photospheric phase exhibiting both hydrogen and helium features to prominent helium emission and, ultimately, nebular-phase ejecta. Using He I $1.083$ and 2.0581 μm transitions, we investigated the kinematics and geometry of the helium-rich material. Both transitions exhibit a three-phase, non-monotonic velocity evolution: an initial rapid decline, a subsequent increase, and an eventual plateau. We interpret this behavior as evidence for limited outward mixing of ^56Ni, such that radioactive energy deposition reaches the outer helium-rich ejecta progressively as the ejecta expand, producing the non-thermal electrons responsible for helium excitation. After ∼100 d, both NIR He I transitions develop double-peaked emission profiles. Similar structure in the oxygen emission indicates ejecta asymmetry. Comparison with other supernovae suggests a tentative connection between this structure and explosion energy, potentially linked to the delay between core collapse and explosion. Serendipitous JWST observations at +124.4d reveal an infrared excess. Modeling favors warm (∼800--$1500$K) carbon dust newly formed in the ejecta, together with cooler carbon or silicate dust likely associated with pre-existing circumstellar material. SN~2025aico demonstrates how continuous optical-to-MIR observations can connect progenitor evolution, explosion physics, ejecta geometry, and dust production.
ER -