arXiv subjects

Rosario Brunetto

Publications and source records attributed to Rosario Brunetto.

4 recordsLinked to original sources

arXiv2026

Tracing the source of carbon oxides on the large moons of Uranus

The Uranian moons Ariel, Umbriel, Titania, and Oberon are enriched in CO2 mixed with CO, but the origin(s) of these carbon oxides, be they primarily native or radiolytic, remains uncertain. Using data collected by NIRSpec on the James Webb Space Telescope (JWST), we measured the spectral signature of CO2 and other carbon oxides to help disentangle these hypotheses. Through comparison to laboratory data, we find that many of the detected spectral features are consistent with CO2 ice, including 12CO2 scattering peaks (4.15 - 4.26 microns), multi-lobe 13CO2 bands (4.35 - 4.43 microns), and CO2 biphonon and triphonon modes (4.80 - 5.25 microns). Our measurements show that CO2 and CO are concentrated on the trailing hemispheres of the inner moons Ariel and Umbriel, potentially supporting a radiolytic production hypothesis, consistent with prior ground-based results. However, many of the identified spectral features are only observed in thick crystalline ice deposits measured in the laboratory, which may be difficult to form via radiolysis of carbon-bearing material mixed in icy regoliths. Similarly, the data exhibit weak 4.02 microns and 4.40 microns bands, hinting at the presence of carbonate minerals and 13CO2 clathrates, respectively, possibly formed in the interiors of these moons. Furthermore, JWST has revealed that CO2 is widespread at Uranus, present in its system of rings, ring moons, and irregular satellites, consistent with its largest moons accreting CO2 and other carbon oxides from the Uranian subnebula. We conclude that exposed carbon oxides are potentially native, with their surface distributions shaped by charged particle irradiation and seasonal sublimation-condensation cycles.

astro-ph.EP↗

arXiv2026

JWST reveals anomalously enhanced methane outgassing from below Chiron's water ice and carbon dioxide bearing surface

Centaurs are inward-scattered Kuiper belt objects, with some exhibiting comet-like activity. The physical mechanisms powering this activity remain poorly understood, with carbon monoxide (CO) sublimation or the crystallization of amorphous water ice commonly invoked as the dominant drivers. Here we present high-resolution JWST spectroscopy of 2060 Chiron, one of the largest known Centaurs, revealing methane and carbon dioxide gas emission with distinct coma spatial morphologies and production rates of $Q_{\rm CH_4}=(1.55\pm0.04)\times10^{27}$ molecules s$^{-1}$ and $Q_{\rm CO_2}=(1.01\pm0.06)\times10^{26}$ molecules s$^{-1}$. The surface spectrum displays spectral signatures attributed to water ice, carbon dioxide, CO, and refractory organic-rich material, while lacking detectable methane ice absorption bands. These findings suggest that carbon dioxide production is sustained by direct surface sublimation, whereas methane originates from the subsurface. The absence of measurable CO emission despite the presence of solid-state CO implies that any surviving primordial CO reservoir remains thermally inaccessible at greater depth below the methane, while irradiation-produced near-surface CO may be inefficiently released from the surface matrix. This inferred volatile stratification may result from long-term thermal evolution or potentially partial differentiation. Chiron differs markedly from other active small bodies, where CO production typically dominates over methane, indicating that Centaur activity may be driven by a broader range of volatile and thermophysical processes than predicted by canonical models.

astro-ph.EP↗

arXiv2025

JWST/NIRSpec Observations of Salacia-Actaea and Máni: Exploring Population-level Trends among Water-ice-rich Kuiper Belt Objects

We present observations of the midsized Kuiper Belt objects (KBOs) Salacia$-$Actaea and Máni, obtained with the Near-Infrared Spectrograph on JWST. The satellite Actaea was fully blended with Salacia at the spatial resolution of the integral field unit, and we extracted the combined spectrum. The 0.7$-$5.1 $μ$m reflectance spectra of Salacia$-$Actaea and Máni display prominent water-ice absorption bands at 1.5, 2, 3, and 4$-$5 $μ$m. The $ν_{3}$ fundamental vibrational band of carbon dioxide ice at 4.25 $μ$m is present in both spectra. From a quantitative band-depth analysis of the entire current JWST spectroscopic sample of water-ice-rich KBOs, we find strong evidence for a positive covariance between relative water-ice abundance and size, which may indicate the emergent impacts of internal differentiation and cryovolcanic production of surface water ice on midsized KBOs. A detailed look at the distribution of 2 and 3 $μ$m band depths suggests additional sources of variability, such as different water-ice grain sizes. In addition, we report an apparent transition in the carbon dioxide band depth at object diameters of roughly 300$-$500 km, with larger objects showing systematically weaker absorptions, although selection effects within the sample do not allow us to confidently distinguish between a size-dependent phenomenon and a correlation with dynamical class.

astro-ph.EP↗

arXiv2025

Rotational Dynamics in Pulsational Pair-Instability Supernovae: Implications for Mass-Loss and Transient Events

Pulsational pair-instability supernovae (PPISNe) are transient events occurring in progenitor stars with helium cores of approximately 32-65 solar masses, where rapid electron-positron pair production induces pressure loss, collapse, and pulsations driving episodic mass loss. The number, strength, and duration of these pulses can lead to shell collisions that produce shock-powered transients, potentially explaining some of the most luminous events, such as superluminous supernovae, and other rare transients. Rapid progenitor rotation lowers the PPISN mass threshold and influences the dynamics, energetics, and chemical composition of PPISN-driven pulses. In this study, we computed 1D evolutionary models of massive, rotating PPISN progenitor stars with zero-age main-sequence masses of 85-140 solar masses and solar metallicity and 10% solar metallicity. Our analysis reveals strong correlations between PPISN ejected mass and total energy as well as between ejected mass and peak ejected shell velocity. Additionally, moderate correlations indicate that higher initial PPISN progenitor mass leads to greater mass ejection and energy release, while negative correlations show that rapid rotation appears to reduce mass ejection and kinetic energy of the shells. Subsequent pulses lead to hydrogen-poor, carbon- and oxygen-enriched ejected shells, indicating the effect of rotationally-induced chemical mixing in PPISN-driven episodic mass loss with implications for their transients. We model the light curve and synthetic spectra that arise from the collision of two H-poor shells for one of our models using the radiation transport code SuperLite. We find that shock-heated H-poor PPISN shell collisions from rapidly rotating progenitors can lead to moderately luminous H-poor transients that share some similarities with observed SLSN-I events.

astro-ph.HE↗