arXiv subjects

C. Guerra

Publications and source records attributed to C. Guerra.

3 recordsLinked to original sources

arXiv2026

The GAPS programme at TNG: LXXVI. TOI-1533: a compact system hosting a super-Neptune-mass pair with disparate radii

The present-day architecture of planetary systems contains information about their formation and migration histories. The origin of hot Jupiters (HJs, P $\lesssim$ 10 d, $R_{\rm p} > 8 R_\oplus$) has long been a matter of debate. While most of them are found to be ``lonely'', there is a rare population of HJs hosting small companions on inner orbits (eight known as of May 2026). Their peculiar architecture suggests a gentle disc-migration mechanism. In this study, we present the discovery and characterisation of the multi-planet system TOI-1533, comprising an inner sub-Neptune (TOI-1533 b, $P_{\rm orb} = 3.63$ d, $R_{\rm p} = 3.15 R_\oplus$) and an outer hot giant planet (TOI-1533 c, $P_{\rm orb} = 8.06$ d, $R_{\rm p} > 7.5 R_\oplus$) with substantial H/He by mass ($\rho_{\rm p} < 0.48$ g cm$^{-3}$), both transiting an active K-dwarf star ($T_{\rm eff} \approx$ 5130 K; $V$ (mag) $\approx$ 11). Our joint modelling of stellar activity and planetary signals from radial velocities (HARPS-N) and transits (TESS) allows us to detect their Keplerian signals (approximately $10~\sigma$) and to isolate the stellar modulation. The inclusion of simultaneous photometry in the multi-dimensional Gaussian processes formalism was a fundamental addition to the spectroscopic activity indicators, enabling the disentanglement of stellar activity from planetary signals. The mass ratio of the two confirmed planets ($M_{\rm b} / M_{\rm c}$ about 0.8), together with the super-Neptune mass of the large outer companion ($M_{\rm c} \approx 40 M_\oplus$), makes this system unusual compared to the other few HJs with low-mass inner companions.

astro-ph.EP↗

arXiv2025

Superoxide anion (O$_{2}\negthinspace^{-}$) collisions with CO$_{2}$ molecules in the energy range 50-950 eV

A novel gas-phase molecular scattering study is reported for O$_{2}\negthinspace^{-}$ colliding with CO$_{2}$ for impact energies ranging from 50 to 950 eV. The absolute total electron detachment, relative total and partial ionization cross sections have been measured within this energy range and the positive ion yield of those produced during the collisions has been obtained. The primary anionic beam projectile is produced in a pulsed hollow cathode discharge induced plasma, and its interactions with the neutral molecular target occur in a gas cell at a well-known constant pressure. For impact energies above 500 eV high mass (m $>$ 44 u) charged complexes have been detected. With the aid of a theoretical study, using ab initio methods, we propose a mechanism to infer on the formation of these cationic species, which have been assigned as projectile-target stable compounds (CO$_{3}\negthinspace^{+}$ and CO$_{4}\negthinspace^{+}$).

physics.chem-ph↗

arXiv2024

Hydrodynamical simulations of wind interaction in spider systems : A step toward understanding transitional millisecond pulsars

The detected population of "spiders" has significantly grown in the past decade thanks to multiwavelength follow-up investigations of unidentified Fermi sources. These systems consist of low-mass stellar companions orbiting rotation-powered millisecond pulsars in short periods of a few hours up to day. Among them, a subset of intriguing objects called transitional millisecond pulsars (tMSPs) has been shown to exhibit a remarkable behavior, transitioning between pulsar-binary and faint low-mass X-ray binary states over a span of a few years. Our objective is to study the interaction of stellar winds in tMSPs in order to understand their observational properties. To this end we focus on the parameter range that places the system near Roche-lobe overflow. Employing the adaptative mesh refinement (AMR) AMRVAC 2.0 code, we performed 2D hydrodynamical (HD) simulations of the interaction between the flows from both stars, accounting for the effects of gravity and orbital motion. By studying the mass loss and launch speed of the winds, we successfully recreated two phenomenologically distinct regimes: the accretion stream and the radio pulsar state. We also identified the tipping point that marks the sharp transition between these two states. In the pulsar state, we reconstructed the corresponding X-ray light curves of the system that produces the characteristic double-peak pattern of these systems. The position of the peaks is shifted due to orbital motion and the leading peak is weaker due to eclipsing by the companion. We suggest that a smaller leading peak in X-rays is indicative of a nearly edge-on system. This study highlights the importance of gravity and orbital motion in the interaction between the companion and pulsar winds. Our setup allows the study of the complex interaction between the pulsar wind and an accretion stream during mass transfer.

astro-ph.HE↗