arXiv subjects

M. G. Scott

Publications and source records attributed to M. G. Scott.

8 recordsLinked to original sources

arXiv2026

TOI-1080 b: a temperate, rocky planet orbiting a quiet M4V host

We present the detection and validation of a small, temperate transiting exoplanet orbiting TOI-1080 every 3.9652482$^{+0.0000014}_{-0.0000015}$ days. The host is a quiet M4V star at 25.6 pc. The planet signal was first detected by TESS and validated using TESS and ground-based observations. By fitting the available light curves, the planet radius is measured to be 1.200+- 0.058 Rearth and its equilibrium temperature of 368$^{+12}_{-10}$ K. With NIRPS radial velocities, we are able to place a 3-sigma upper limit on the mass of TOI-1080 b of 10.7 Mearth. Our injection-recovery tests enable us to discard additional transiting planets in the TOI-1080 system with radii down to 0.9 Rearth and periods between 0.5 and 7.7 days, and planets with radii larger than 1.4 Rearth for periods up to 19 days. We demonstrate that it is highly amenable to characterisation of its mass and putative atmosphere. In particular, we find that TOI-1080 b is an exceptional target for the ongoing JWST+HST Rocky Worlds DDT programme, having a priority score that is higher than four out of nine targets currently being investigated by the programme. TOI-1080 b can be added to the sample of nearby benchmark planets accessible for detailed study with JWST.

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arXiv2026

Hidden Gems in TESS: sherlock finds two new rocky planets around nearby M dwarfs

The Hidden Gems project searches the TESS data for additional planets transiting low-mass stars in confirmed systems. Our goal is to identify planet candidates that are below the detection threshold set by the SPOC and QLP pipelines using sherlock, a specialized pipeline for robust detection and vetting of transit signals in TESS data. We present the discovery of two inner rocky planets in the TOI-237 and TOI-4336 A systems, confirmed with ground-based photometry from the TRAPPIST, SPECULOOS, ExTrA, and LCO facilities. TOI-237 c has a radius of 1.21 +/- 0.04Re, orbits its mid-M host star every 1.74 days, and is close to a 3:1 mean-motion resonance with TOI-237 b. TOI-4336 A c has a radius of 1.17 +/- 0.06Re, and orbits with a period of 7.58 days an M3.5 host star which is part of a hierarchical triple system. We performed model comparison to search for non-zero eccentricities, and found that the circular transit models are statistically favored. Dynamical simulations show that both systems are in stable configurations, and the TTVs expected for the TOI-237 system are of the order of seconds. TOI-237 c and TOI-4336 A c join the high-interest population of warm likely super-Earths below the so-called "radius valley". In particular, TOI-237 c is a good candidate for phase curve observations with JWST/MIRI thanks to the small radius of the host star and its short period.

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arXiv2025

MANGOS II: Five new giant planets orbiting low-mass stars

Giant planets orbiting low-mass stars on short orbits present a conundrum, as in the most extreme cases their existence cannot be reconciled with current models of core accretion. Therefore, surveys dedicated to finding these rare planets have a key role to play by growing the sample to overcome small number statistics. In this work we present MANGOS, a programme dedicated to the search for giant objects (planets, brown dwarfs, and low-mass stars) orbiting M dwarfs. We report on the discovery of five new giant planets (TOI-3288 Ab, TOI-4666 b, TOI-5007 b, TOI-5292 Ab, TOI-5916 b) first detected by TESS, and confirmed using ground-based photometry and spectroscopy. The five planets have radii in the range 0.99-1.12 $\mathrm{R_{Jup}}$, masses between 0.49--1.69~$\mathrm{M_{Jup}}$, and orbital periods between 1.43 and 2.91 days. We reveal that TOI-3288 and TOI-5292 are wide binaries, and in the case of TOI-5292 we are able to characterise both stellar components. We demonstrate that the planets presented are suitable for further characterisation of their obliquities and atmospheres. We detect a small but significant eccentricity for TOI-5007 b, although for this to be more robust, more observations are needed to fully sample the orbit. Finally, we reveal a correlation between stellar metallicity and planet bulk density for giant planets orbiting low-mass stars.

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arXiv2025

ATREIDES I. Embarking on a trek across the exo-Neptunian landscape with the TOI-421 system

The distribution of close-in exoplanets is shaped by the interplay between atmospheric and dynamical processes. The Neptunian Desert, Ridge, and Savanna illustrate the sensitivity of these worlds to such processes, making them ideal to disentangle their roles. Determining how many Neptunes were brought close-in by early disk-driven migration (DDM; maintaining primordial spin-orbit alignment) or late high-eccentricity migration (HEM; generating large misalignments) is essential to understand how much atmosphere they lost. We propose a unified view of the Neptunian landscape to guide its exploration, speculating that the Ridge is a hot spot for evolutionary processes. Low-density Neptunes would mainly undergo DDM, getting fully eroded at shorter periods than the Ridge, while denser Neptunes would be brought to the Ridge and Desert by HEM. We embark on this exploration via ATREIDES, which relies on spectroscopy and photometry of 60 close-in Neptunes, their reduction with robust pipelines, and their interpretation through internal structure, atmospheric, and evolutionary models. We carried out a systematic RM census with VLT/ESPRESSO to measure the distribution of 3D spin-orbit angles, correlate its shape with system properties and thus relate the fraction of aligned-misaligned systems to DDM, HEM, and atmospheric erosion. Our first target, TOI-421c, lies in the Savanna with a neighboring sub-Neptune TOI-421b. We measured their 3D spin-orbit angles (Psib = 57+11-15 deg; Psic = 44.9+4.4-4.1 deg). Together with the eccentricity and possibly large mutual inclination of their orbits, this hints at a chaotic dynamical origin that could result from DDM followed by HEM. ATREIDES will provide the community with a wealth of constraints for formation and evolution models. We welcome collaborations that will contribute to pushing our understanding of the Neptunian landscape forward.

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arXiv2025

Two warm Earth-sized exoplanets and an Earth-sized candidate in the M5V-M6V binary system TOI-2267

We report two warm Earth-sized exoplanets orbiting the close binary TOI-2267 (M5+M6, separation ~8 au). Data from TESS and ground-based facilities confirm the planets, but we cannot determine which star they orbit. The planets have radii of 1.00+/-0.11 R_Earth (TOI-2267 b, P=2.28 d) and 1.14+/-0.13 R_Earth (TOI-2267 c, P=3.49 d) if around TOI-2267A, or 1.22+/-0.29 R_Earth and 1.36+/-0.33 R_Earth if around TOI-2267B. TESS also shows a candidate signal (TOI-2267.02, P=2.03 d, 0.95+/-0.12 or 1.13+/-0.30 R_Earth). Dynamical analysis shows all three cannot orbit one star; the most stable configuration has planets b and c (near a 3:2 resonance) orbiting one star and the candidate the other. This scenario would make TOI-2267 the most compact binary system known to host planets, with both components harbouring transiting worlds, offering a unique benchmark for studying planet formation and evolution in compact binary.

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arXiv2025

EBLM XV -- Revised dynamical masses for the circumbinary planet host Kepler-16 AB, using the SOPHIE spectrograph

Eclipsing binaries are perfect laboratories to measure precise, accurate and model-independent stellar radii and stellar masses, so long as both components are spectroscopically resolved. Resolving both components is difficult in high-contrast binaries, for instance, those composed of an FGK main-sequence star with an M-type companion. In those cases, the secondary can contribute <1% of the total flux in optical wavelengths. This makes measuring dynamical masses challenging and has typically only been attempted with large-aperture telescopes (8-10-m). The High-Resolution Cross-Correlation Spectroscopy (HRCCS) method was developed to extract weak emission and transmission spectra for exoplanet atmospheres. This method was recently adapted and applied to measure dynamical masses in high-contrast binaries. In this work, we apply the HRCCS method to optical spectra of the high-contrast binary and circumbinary planet host Kepler-16AB, obtained with the SOPHIE spectrograph at the 1.93-m telescope at the Observatoire de Haute-Provence. The secondary, which has a contrast ratio of ~ 6 x 10-3, is resolved with a detection significance of 9.5-sigma. We derive dynamical masses with a precision of 1.5% and 0.9% for the primary and secondary respectively. These are comparable, but slightly higher (within 2-7%) to previous mass-measurements, which has -- within the uncertainties -- no implication for the mass of the known circumbinary planet. This work demonstrates that dynamical mass measurements of high-contrast binaries can be done with 2-m class telescopes. We also investigate different analysis protocols to ensure we derive robust uncertainties for dynamical masses.

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arXiv2025

A transiting rocky super-Earth and a non-transiting sub-Neptune orbiting the M dwarf TOI-771

The origin and evolution of the sub-Neptune population is a highly debated topic in the exoplanet community. With the advent of JWST, atmospheric studies can now put unprecedented constraints on the internal composition of this population. In this context, the THIRSTEE project aims to investigate the population properties of sub-Neptunes with a comprehensive and demographic approach, providing a homogeneous sample of precisely characterised sub-Neptunes across stellar spectral types. We present here the precise characterisation of the planetary system orbiting one of the THIRSTEE M-dwarf targets, TOI-771 (V = 14.9 mag), known to host one planet, TOI-771 b, which has been statistically validated using TESS observations. We use TESS, SPECULOOS, TRAPPIST and M-Earth photometry together with 31 high-precision ESPRESSO radial velocities to derive the orbital parameters and investigate the internal composition of TOI-771 b, as well as exploring the presence of additional companions in the system. We derive precise mass and radius for TOI-771 b, a super-Earth with R_b = 1.36 +/- 0.10 R_e and M_b = 2.47 +/- 0.32 M_e orbiting at 2.3 d. Its composition is consistent with an Earth-like planet, and it adds up to the rocky population of sub-Neptunes lying below the density gap identified around M dwarfs. With a 13% precision in mass, a 7% radius precision, and a warm equilibrium temperature of T_eq= 543 K, TOI-771 b is a particularly interesting target for atmospheric characterisation, and it is indeed one of the targets under consideration for the Rocky World DDT program. Additionally, we discover the presence of a second, non-transiting planet, TOI-771 c, with a period of 7.6 d and a minimum mass of Mp sin(i) = 2.9 +/- 0.4 M_e. Even though the inclination is not directly constrained, the planet likely belongs to the temperate sub-Neptune population, with an equilibrium temperature of 365 K.

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arXiv2025

TOI-6508b: A massive transiting brown dwarf orbiting a low-mass star

We report the discovery of a transiting brown dwarf orbiting a low-mass star, TOI-6508b. Today, only ~50 transiting brown dwarfs have been discovered. TOI-6508b was first detected with data from the Transiting Exoplanet Survey Satellite (TESS) in Sectors 10, 37, and 63. Ground-based follow-up photometric data were collected with the SPECULOOS-South and LCOGT-1.0m telescopes, and RV measurements were obtained with the Near InfraRed Planet Searcher (NIRPS) spectrograph. We find that TOI-6508b has a mass of Mp=72.5+7.6-5.1MJup and a radius of Rp=1.03+/-0.03RJup. Our modeling shows that the data are consistent with an eccentric orbit of 19day and an eccentricity of e=0.28+0.09-0.08. TOI-6508b has a mass ratio of M_BD/Ms=0.40, makes it the second highest mass ratio brown dwarf that transits a low-mass star. The host has a mass of Ms=0.174+/-0.004M_Sun, a radius of Rs=0.205+/-0.006R_Sun, an effective temperature of Teff=2930+/-70K, and a metallicity of [Fe/H]=-0.22+/-0.08. This makes TOI-6508b an interesting discovery that has come to light in a region still sparsely populated.

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