George Dransfield

Abstract:

We identify two large-radius planets around the F-type star HD 114082 as the longest-period young transiting exoplanets known. From the first transit, detected by NASA’s Transiting Exoplanet Survey Satellite (TESS), and a second dip, spotted by the Next-Generation Transit Survey (NGTS), we predicted midtransit times for HD 114082 b (planet b). We pinpoint its orbit (period Pb = 225.5504 ± 0.0004 days) from a third transit captured with the ESA’s CHaracterising ExOplanet Satellite and the upgraded Antarctic Search for Transiting ExoPlanets telescope (ASTEP+), alongside orbit-discriminating observations. Another dimming partly covered by ASTEP+ completes the four-transit series. We support with dynamical evidence the planetary nature of a deeper transit detected with TESS and NGTS, identifying planet c. Additionally, we reexamine the debris disk, fitting its excess emission with two dust components. Fundamental stellar parameters are inferred from stellar evolution models, while a joint modeling of photometric and radial velocity time series yields the planetary parameters, with masses further constrained using an N-body code. For planet b, the semimajor axis ab = 0.791 ± 0.008 au, eccentricity eb ≈0, inclination ib = 89 (Formula presented) .° 791 ±0.014, radius Rb = 1.046 ± 0.014 RJ, and 95% confidence upper limit on its mass M95%,b = 1.6 MJ. For planet c, ac = 0.99 (Formula presented) −0.04+0.03 au, ec ≈0, ic = 89 (Formula presented) .° 701 ±0.011, Rc = 1.36±0.03 RJ, and M95%,c = 2.0 MJ (0.24 MJ if adding transit-timing-variation constraints). They seem to be moderate-to-low-mass giants in nearly resonant, coplanar, circular orbits that formed in situ, or beyond the snow line, and migrated inward, shaping the disk.

Abstract:

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 of 0.99–1.12 , masses between 0.49 and 1.69 , and orbital periods between 1.43 and 2.91 d. We reveal that TOI-3288 and TOI-5292 are wide binaries, and in the case of TOI-5292, we are able to characterize both stellar components. We demonstrate that the planets presented are suitable for further characterization 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.

Abstract:

We present the detection and validation of a small, temperate transiting exoplanet orbiting TOI-1080 every 3.9652482 d. The host is a quiet M4V star at 25.6 pc. The planet signal was first detected by the Transiting Exoplanet Survey Satellite (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 R and its equilibrium temperature of K. With Near Infra Red Planet Searcher (NIRPS) radial velocities, we are able to place a 3 upper limit on the mass of TOI-1080 b of 10.7 M. Our injection-recovery tests enable us to discard additional transiting planets in the TOI-1080 system with radii down to 0.9 R and periods between 0.5 and 7.7 d, and planets with radii larger than 1.4 R for periods up to 19 d. We demonstrate that it is highly amenable to characterization 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.

Abstract:

As the diversity of exoplanets continues to grow, it is important to revisit assumptions about habitability and classical HZ definitions. In this work, we introduce an expanded ’temperate’ zone, defined by instellation fluxes between 0.1 < S/S⊕ < 5, thus encompassing a broader range of potentially habitable worlds. We also introduce the TEMPOS survey, which aims to produce a catalogue of precise radii for temperate planets orbiting M dwarfs with Teff ≤ 3400 K. This work reports the discovery and characterisation of two planets in this temperate regime orbiting mid-type M dwarfs: TOI-6716 b, a Rb = 0.98 ± 0.07 R⊕ planet orbiting its M4 host star (R⋆ = 0.231 ± 0.015R ⊙, M⋆ = 0.223 ± 0.011 M ⊙, Teff = 3110 ± 80 K) with a period $P=4.7185898^{+0.0000054}_{-0.0000041}\, \mathrm{d}$ , and TOI-7384 b, a Rb = 3.56 ± 0.21 R⊕ planet orbiting an M4 (R⋆ = 0.319 ± 0.018R ⊙, M⋆ = 0.318 ± 0.016 M ⊙, Teff = 3185 ± 75 K) star every $P=6.2340258^{+0.0000034}_{-0.0000036}\, \mathrm{d}$ . The radii of TOI-6716 b and TOI-7384 b have precisions of 6.8 % and 5.9 % respectively. We validate these planets with multi-band ground-based photometric observations, high-resolution imaging and statistical analyses. We find these planets to have instellation fluxes close to the inner (hotter) edge of the temperate zone, with Sb = 4.4 ± 1.1 S⊕ and Sb = 4.9 ± 1.1 S⊕ for TOI-6716 b and TOI-7384 b respectively. Also, with a predicted TSM similar to the TRAPPIST-1 planets, TOI-6716 b is likely to be a good rocky-world JWST target, should it have retained its atmosphere.

Abstract:

We report the discovery of TOI-4507 b, a transiting sub-Saturn with a density <0.2 g cm−3 on a 105 days prograde orbit around a 700 Myr old F star. The transits were detected using data from TESS as well as the Antarctic telescope ASTEP. A joint analysis of the light curves and radial velocities from HARPS, FEROS, and CORALIE confirmed the planetary nature of the signal, by limiting the mass to be below 20 M⊕ at 95% confidence. The radial velocities also exhibit the Rossiter–McLaughlin effect and imply that the planet orbits the star in a prograde orbit with a sky-projected obliquity λ=−15−44+50 ° (∣λ∣ < 80° at 3σ). With these characteristics, TOI-4507 is one of the longest-period systems for which the stellar obliquity has been measured, and the planet is among the longest-period and youngest “superpuff” planets yet discovered.