arXiv subjects

Arianna Nigioni

Publications and source records attributed to Arianna Nigioni.

6 recordsLinked to original sources

arXiv2026

Mind the Companion : Demographics of Transiting S-type Exoplanets

Exoplanet demographic studies rely on large and homogeneous catalogues, yet stellar multiplicity remains incompletely characterised in many planet samples. We update the PlanetS catalogue of transiting exoplanets by systematically identifying gravitationally bound stellar companions using Gaia data release 3 (DR3), constructing a matched control sample of single hosts to mitigate selection and observational biases. Using this curated dataset of 860 transiting exoplanets including 133 S-type planets, we perform a comparative demographic analysis as a function of host multiplicity, stellar mass, and binary separation. We find a binary fraction of 19.4% relative to the control sample, consistent with previous estimates but derived from a larger and more homogeneous dataset. In the giant planet regime, less affected by observational biases, planets in binaries tend to be more massive than their single-star counterparts and orbit closer to their host stars, making their radii more inflated. In particular, 53% of giant planets orbiting M-dwarfs reside in binary systems with separations < 1000 AU, a 2.6σ excess compared to FGK-type hosts, suggesting that stellar multiplicity plays a key role in the formation or survival of giant planets around low-mass stars.

astro-ph.EP↗

arXiv2026

TIC-65910228 b / NGTS-38 b, a 180 day transiting warm super-Jupiter

We present the discovery of TIC-65910228 b / NGTS-38 b, a giant exoplanet with a radius of $1.081\pm0.047$ R$_\text{J}$ and a mass of $4.78_{-0.37}^{+0.39}$ M$_\text{J}$ on a long-period ($180.52797\pm0.00036$ day), moderately eccentric ($e=0.3086\pm0.010$) orbit transiting a bright (V=$10.230\pm0.020$ mag) metal rich ([Fe/H]=$0.33\pm0.09$, 'dex') F6V-F7V type host star. The planet was initially detected from a single transit in TESS Sector 33. A photometric monitoring campaign of 228 nights with NGTS detected a transit egress of the planet, which together with spectroscopic radial velocity monitoring with CORALIE and HARPS identified an orbital period of ~180.5,d. These radial velocity measurements also showed the mass of the companion to be planetary. Additional transit observations coordinated by the TESS follow-up observing program allowed further confirmation and refinement of this period. With its relatively cool equilibrium temperature of $457\pm11$ K, NGTS-38 b joins a small but growing population of well characterised transiting warm-Jupiters and has one of the longest periods of any discovered to date. The target is situated in the LOPS2 field of the upcoming PLATO mission which will allow for greater refinement of the system parameters and potential for the discovery of additional companions too small and/or too long-period to be seen by TESS or NGTS. NGTS-38 b's bright host star and wide orbital separation make it an attractive target for further study, including potential measurement of its spin-orbit alignment or targeted exomoon/ring searches.

astro-ph.EP↗

arXiv2026

The PAIRS project: a global formation model for planets in binaries. I. Effect of disc truncation on the growth of S-type planets

Binary stars are as common as single stars. The number of detected planets orbiting binaries is rapidly increasing thanks to the synergy between transit surveys, Gaia and high-resolution direct imaging campaigns. However, global planet formation models around binary stars are still underdeveloped, which limits the theoretical understanding of planets orbiting binary star systems. Hereby we introduce the PAIRS project, which aims at building a global planet formation model for planets in binaries, and to produce planet populations synthesis to statistically compare theory and observations. In this first paper, we present the adaptation of the circumstellar disc to simulate the formation of S-type planets. The presence of a secondary star tidally truncates and heats the outer part of the circumprimary disc (and vice-versa for the circumsecondary disc), limiting the material to form planets. We implement and quantify this effect for a range of binary parameters by adapting the Bern Model of planet formation in its pebble-based form and for in-situ planet growth. We find that the disc truncation has a strong impact on reducing the pebble supply for core growth, steadily suppressing planet formation for binary separations below 160 au, when considering all the formed planets more massive than Mars. We find as well that S-type planets tend to form close to the central star with respect to the binary separation and disc truncation radius. Our newly developed model will be the basis of future S-type planet population synthesis studies.

astro-ph.EP↗

arXiv2026

The PAIRS project: a global formation model for planets in binaries. II. Gravitational perturbation effects from secondary stars

Roughly half of Sun-like stars have at least one stellar companion, whereas it is widely assumed that most known exoplanets orbit single stars, largely due to observational biases. However, astrometric surveys, direct imaging, and speckle interferometry are steadily increasing the number of confirmed exoplanets in binaries. A stellar companion introduces additional effects, such as circumstellar disk truncation and gravitational perturbations, which can strongly impact planet formation. While global planet formation models, for example the Bern model, have been broadly applied to single stars, modeling S-type binaries requires key modifications to capture these effects. This study extends the Bern model by incorporating the gravitational influence of a stellar companion into its N-body integrator, allowing us to quantify how this perturbation affects planetary formation and final system architecture across a range of binary configurations. By comparing binary and single-star systems under identical initial conditions, we can assess the specific impact of binary-induced dynamics. We ran three sets of simulations: (i) a grid of in situ single-embryo cases to quantify gravitational effects; (ii) formation simulations with and without migration to compare outcomes with single-star analogs; and (iii) multi-embryo runs to evaluate impacts on multi-planetary systems. Planets forming beyond half the host star's Hill radius are much more likely to become unbound especially in systems with high binary eccentricity. Even within stable zones, growth is suppressed by both reduced material availability and increased eccentricity from stellar perturbations. Both disk truncation and stellar perturbations must be included to model planet formation in S-type binaries accurately. Neglecting either one will end up misrepresenting planetary growth and survival.

astro-ph.EP↗

arXiv2025

The quest for Magrathea planets. II. Orbital stability of exoplanets formed around double white dwarfs

Planetary formation might occur at different stages of the stellar evolution of compact binaries. In recent years, the formation of second-generation planets has been tested in circumbinary discs formed by the ejection of stellar material from double white dwarf (DWD) binaries. In these environments, planets ranging from sub-Neptunian to giant masses can form and migrate to within 1 au of the central binary. Nevertheless, studies on the orbital stability of such systems have yet to be undertaken. In this work, we use N-body simulations to study the stability of multi-planet systems formed around compact DWDs in both resonant and non-resonant configurations over timescales of a few million years. We track the occurrence of catastrophic events and employ a variety of metrics, e.g., orbital spacing, centre-of-mass variations and Normalized Angular Momentum Deficit, to explore the outcomes of their evolution. Furthermore, we evaluate the potential for detecting these systems in their final configurations with the Laser Interferometer Space Antenna (LISA) mission by measuring the overall gravitational-wave frequency shift amplitude induced by their planets. Our results show that planets orbiting DWDs can be stable over the studied timescales. While planetary systems starting with two-planets are more likely to survive unaltered, planetary systems with three, four or five planets, experience catastrophic events that cause them to lose some of their original planets, ending up hosting only two surviving planets in the majority of cases. This increases the number of two-planet systems by 122% with respect to their initial abundance and creates a single-planet population amounting to 7% of the totality of systems. The majority of these single-planet systems are potential candidates for LISA. Concerning multi-planet systems, a handful of systems could be detected.

astro-ph.EP↗

arXiv2024

NGTS-33b: A Young Super-Jupiter Hosted by a Fast Rotating Massive Hot Star

In the last few decades planet search surveys have been focusing on solar type stars, and only recently the high-mass regimes. This is mostly due to challenges arising from the lack of instrumental precision, and more importantly, the inherent active nature of fast rotating massive stars. Here we report NGTS-33b (TOI-6442b), a super-Jupiter planet with mass, radius and orbital period of 3.6 $\pm$ 0.3 M$_{\rm jup}$, 1.64 $\pm$ 0.07 R$_{\rm jup}$ and $2.827972 \pm 0.000001$ days, respectively. The host is a fast rotating ($0.6654 \pm 0.0006$ day) and hot (T$_{\rm eff}$ = 7437 $\pm$ 72 K) A9V type star, with a mass and radius of 1.60 $\pm$ 0.11 M$_{\odot}$ and 1.47 $\pm$ 0.06 R$_{\odot}$, respectively. Planet structure and Gyrochronology models shows that NGTS-33 is also very young with age limits of 10-50 Myr. In addition, membership analysis points towards the star being part of the Vela OB2 association, which has an age of $\sim$ 20-35 Myr, thus providing further evidences about the young nature of NGTS-33. Its low bulk density of 0.19$\pm$0.03 g cm$^{-3}$ is 13$\%$ smaller than expected when compared to transiting hot Jupiters with similar masses. Such cannot be solely explained by its age, where an up to 15$\%$ inflated atmosphere is expected from planet structure models. Finally, we found that its emission spectroscopy metric is similar to JWST community targets, making the planet an interesting target for atmospheric follow-up. Therefore, NGTS-33b's discovery will not only add to the scarce population of young, massive and hot Jupiters, but will also help place further strong constraints on current formation and evolution models for such planetary systems.

astro-ph.EP↗