arXiv subjects

Rodrigo F. Díaz

Publications and source records attributed to Rodrigo F. Díaz.

At least 19 recordsLinked to original sources

arXiv2026

Weighing the mass of LHS 3844 b

Context: LHS 3844 b (TOI-136 b) is a ultra short-period, Earth-size exoplanet detected by TESS. It is one of the most favourable object for atmospheric characterisation and the study of its surface with the James Webb Space Telescope. However, the dynamical mass of this planet has not been measured yet. Aims: We aim to determine the mass of LHS 3844 b using high-precision radial velocity (RV) measurements and assess the robustness of the inferred signal across different noise and orbital modelling assumptions. Methods: We analyse 25 ESPRESSO RV observations within a fully Bayesian framework. We explore 15 competing RV models that differ in their treatment of correlated stellar variability (through different Gaussian Process kernels) and long-term drifts. Marginal likelihoods are computed for all models and used for Bayesian model comparison and evidence-weighted parameter estimation. Results: The RV planetary signal is robustly detected across all models, and the inferred semi-amplitude remains stable under all tested noise and drift prescriptions. From the evidence-weighted posterior samples we derive a planetary mass of $2.27 \pm 0.23$ M$_\oplus$ and a bulk density of $5.67 \pm 0.65$ gcm$^{-3}$, consistent with a predominantly rocky composition. Model comparison favours GP kernels including periodic or quasi-periodic components associated with stellar rotation and disfavors models with additional long-term drifts. Using interior-structure inference, we find that the core mass fraction is comparable to (or slightly smaller than) Earth's and only trace amounts of water are permitted, supporting a dry, terrestrial interior. We also investigate a tentative additional signal near $\sim 6.9$ days, but Bayesian model comparison does not provide conclusive support for its planetary interpretation.

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arXiv2026

Demographics of Close-In TESS Exoplanets Orbiting FGK Main-sequence Stars

Understanding the demographics of close-in planets is crucial for insights into exoplanet formation and evolution. We present a detailed analysis of occurrence rates for close-in (0.5-16 day) planets with radii between 2 and 20$\,R_{\oplus}$ around FGK main-sequence stars. Our study uses a comprehensive sample from four years of TESS Science Processing Operations Center full-frame image data cross-matched with Gaia, analysed through our rigorous detection, vetting, and validation pipeline. Using high-confidence planet candidates, we apply a hierarchical Bayesian model to determine occurrence rates in the two-dimensional orbital period-radius plane. Our results are presented using 10-by-10 bins across the period-radius parameter space, offering unprecedented resolution and statistical precision. We find an overall occurrence rate of $9.4^{+0.7}_{-0.6}\%$. When using identical binning, our occurrence rate posteriors distributions align with Kepler's but have a magnitude smaller uncertainties on average. For hot Jupiters, we estimate the overall occurrence rate of $0.39^{+0.03}_{-0.02}\%$. This value is consistent with the previous Kepler FGK-type result within $1σ$. We find an overall occurrence rate of Neptunian desert planets of $0.08\pm0.01\%$, to our knowledge the first such determination. Additionally, in a volume-limited Gaia subsample within 100 pc in the same parameter region, we measure an overall planet occurrence rate of $15.4^{+1.6}_{-1.5}\%$ and a hot Jupiter occurrence rate of $0.42^{+0.16}_{-0.12}\%$. Our results establishes an improved foundation for constraining theoretical models of exoplanet populations.

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arXiv2025

RAVEN: RAnking and Validation of ExoplaNets

We present RAVEN, a newly developed vetting and validation pipeline for TESS exoplanet candidates. The pipeline employs a Bayesian framework to derive the posterior probability of a candidate being a planet against a set of False Positive (FP) scenarios, through the use of a Gradient Boosted Decision Tree and a Gaussian Process classifier, trained on comprehensive synthetic training sets of simulated planets and 8 astrophysical FP scenarios injected into TESS lightcurves. These training sets allow large scale candidate vetting and performance verification against individual FP scenarios. A Non-Simulated FP training set consisting of real TESS candidates caused primarily by stellar variability and systematic noise is also included. The machine learning derived probabilities are combined with scenario specific prior probabilities, including the candidates' positional probabilities, to compute the final posterior probabilities. Candidates with a planetary posterior probability greater than 99% against each FP scenario and whose implied planetary radius is less than 8$R_{\oplus}$ are considered to be statistically validated by the pipeline. In this first version, the pipeline has been developed for candidates with a lightcurve released from the TESS Science Processing Operations Centre, an orbital period between 0.5 and 16 days and a transit depth greater than 300ppm. The pipeline obtained area-under-curve (AUC) scores > 97% on all FP scenarios and > 99% on all but one. Testing on an independent external sample of 1361 pre-classified TOIs, the pipeline achieved an overall accuracy of 91%, demonstrating its effectiveness for automated ranking of TESS candidates. For a probability threshold of 0.9 the pipeline reached a precision of 97% with a recall score of 66% on these TOIs. The RAVEN pipeline is publicly released as a cloud-hosted app, making it easily accessible to the community.

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arXiv2025

Exploring the Neptunian Desert: Insights from a Homogeneous Planetary Sample

In this paper, we present a homogeneous analysis of close-in Neptune planets. To do this, we compile a sample of TESS-observed planets using a ranking criterion which takes into account the planet's period, radius, and the visual magnitude of its host star. We use archival and new HARPS data to ensure every target in this sample has precise radial velocities. This yields a total of 64 targets, 46 of which are confirmed planets and 18 of which show no significant radial velocity signal. We explore the mass-radius distribution, planetary density, stellar host metallicity, and stellar and planetary companions of our targets. We find 26$\%$ of our sample are in multi-planet systems, which are typically seen for planets located near the lower edge of the Neptunian desert. We define a 'gold' subset of our sample consisting of 33 confirmed planets with planetary radii between 2$R_{\oplus}$ and 10$R_{\oplus}$. With these targets, we calculate envelope mass fractions (EMF) using the GAS gianT modeL for Interiors (GASTLI). We find a clear split in EMF between planets with equilibrium temperatures below and above 1300~K, equivalent to an orbital period of $\sim$3.5~days. Below this period, EMFs are consistent with zero, while above they typically range from 20$\%$ to 40$\%$, scaling linearly with the planetary mass. The orbital period separating these two populations coincides with the transition between the Neptunian desert and the recently identified Neptunian ridge, further suggesting that different formation and/or evolution mechanisms are at play for Neptune planets across different close-in orbital regions.

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arXiv2024

TOI-2374 b and TOI-3071 b: two metal-rich sub-Saturns well within the Neptunian desert

We report the discovery of two transiting planets detected by the Transiting Exoplanet Survey Satellite (TESS), TOI-2374 b and TOI-3071 b, orbiting a K5V and an F8V star, respectively, with periods of 4.31 and 1.27 days, respectively. We confirm and characterize these two planets with a variety of ground-based and follow-up observations, including photometry, precise radial velocity monitoring and high-resolution imaging. The planetary and orbital parameters were derived from a joint analysis of the radial velocities and photometric data. We found that the two planets have masses of $(57 \pm 4)$ $M_\oplus$ or $(0.18 \pm 0.01)$ $M_J$, and $(68 \pm 4)$ $M_\oplus$ or $(0.21 \pm 0.01)$ $M_J$, respectively, and they have radii of $(6.8 \pm 0.3)$ $R_\oplus$ or $(0.61 \pm 0.03)$ $R_J$ and $(7.2 \pm 0.5)$ $R_\oplus$ or $(0.64 \pm 0.05)$ $R_J$, respectively. These parameters correspond to sub-Saturns within the Neptunian desert, both planets being hot and highly irradiated, with $T_{\rm eq} \approx 745$ $K$ and $T_{\rm eq} \approx 1812$ $K$, respectively, assuming a Bond albedo of 0.5. TOI-3071 b has the hottest equilibrium temperature of all known planets with masses between $10$ and $300$ $M_\oplus$ and radii less than $1.5$ $R_J$. By applying gas giant evolution models we found that both planets, especially TOI-3071 b, are very metal-rich. This challenges standard formation models which generally predict lower heavy-element masses for planets with similar characteristics. We studied the evolution of the planets' atmospheres under photoevaporation and concluded that both are stable against evaporation due to their large masses and likely high metallicities in their gaseous envelopes.

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arXiv2023

TOI-332 b: a super dense Neptune found deep within the Neptunian desert

To date, thousands of planets have been discovered, but there are regions of the orbital parameter space that are still bare. An example is the short period and intermediate mass/radius space known as the Neptunian desert, where planets should be easy to find but discoveries remain few. This suggests unusual formation and evolution processes are responsible for the planets residing here. We present the discovery of TOI-332 b, a planet with an ultra-short period of $0.78$ d that sits firmly within the desert. It orbits a K0 dwarf with an effective temperature of $5251 \pm 71$ K. TOI-332 b has a radius of $3.20^{+0.16}_{-0.12}$ R$_{\oplus}$, smaller than that of Neptune, but an unusually large mass of $57.2 \pm 1.6$ M$_{\oplus}$. It has one of the highest densities of any Neptune-sized planet discovered thus far at $9.6^{+1.1}_{-1.3}$ gcm$^{-3}$. A 4-layer internal structure model indicates it likely has a negligible hydrogen-helium envelope, something only found for a small handful of planets this massive, and so TOI-332 b presents an interesting challenge to planetary formation theories. We find that photoevaporation cannot account for the mass loss required to strip this planet of the Jupiter-like envelope it would have been expected to accrete. We need to look towards other scenarios, such as high-eccentricity migration, giant impacts, or gap opening in the protoplanetary disc, to try and explain this unusual discovery.

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arXiv2023

TOI-908: a planet at the edge of the Neptune desert transiting a G-type star

We present the discovery of an exoplanet transiting TOI-908 (TIC-350153977) using data from TESS sectors 1, 12, 13, 27, 28 and 39. TOI-908 is a T = 10.7 mag G-dwarf ($T_{eff}$ = 5626 $\pm$ 61 K) solar-like star with a mass of 0.950 $\pm$ 0.010 $M_{\odot}$ and a radius of 1.028 $\pm$ 0.030 $R_{\odot}$. The planet, TOI-908 b, is a 3.18 $\pm$ 0.16 $R_{\oplus}$ planet in a 3.18 day orbit. Radial velocity measurements from HARPS reveal TOI-908 b has a mass of approximately 16.1 $\pm$ 4.1 $M_{\oplus}$ , resulting in a bulk planetary density of 2.7+0.2-0.4 g cm-3. TOI-908 b lies in a sparsely-populated region of parameter space known as the Neptune desert. The planet likely began its life as a sub-Saturn planet before it experienced significant photoevaporation due to X-rays and extreme ultraviolet radiation from its host star, and is likely to continue evaporating, losing a significant fraction of its residual envelope mass.

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arXiv2021

GJ 367b: A dense ultra-short period sub-Earth planet transiting a nearby red dwarf star

Ultra-short-period (USP) exoplanets have orbital periods shorter than one day. Precise masses and radii of USPs could provide constraints on their unknown formation and evolution processes. We report the detection and characterization of the USP planet GJ 367b using high precision photometry and radial velocity observations. GJ 367b orbits a bright (V-band magnitude = 10.2), nearby, red (M-type) dwarf star every 7.7 hours. GJ 367b has a radius of $0.718 \pm 0.054$ Earth-radii, a mass of $0.546 \pm 0.078$ Earth-masses, making it a sub-Earth. The corresponding bulk density is $8.106 \pm 2.165$ g cm$^-3$, close to that of iron. An interior structure model predicts the planet has an iron core radius fraction of $86 \pm 5\%$, similar to Mercury's interior.

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arXiv2021

TOI-431/HIP 26013: a super-Earth and a sub-Neptune transiting a bright, early K dwarf, with a third RV planet

We present the bright (V$_{mag} = 9.12$), multi-planet system TOI-431, characterised with photometry and radial velocities. We estimate the stellar rotation period to be $30.5 \pm 0.7$ days using archival photometry and radial velocities. TOI-431b is a super-Earth with a period of 0.49 days, a radius of 1.28 $\pm$ 0.04 R$_{\oplus}$, a mass of $3.07 \pm 0.35$ M$_{\oplus}$, and a density of $8.0 \pm 1.0$ g cm$^{-3}$; TOI-431d is a sub-Neptune with a period of 12.46 days, a radius of $3.29 \pm 0.09$ R$_{\oplus}$, a mass of $9.90^{+1.53}_{-1.49}$ M$_{\oplus}$, and a density of $1.36 \pm 0.25$ g cm$^{-3}$. We find a third planet, TOI-431c, in the HARPS radial velocity data, but it is not seen to transit in the TESS light curves. It has an $M \sin i$ of $2.83^{+0.41}_{-0.34}$ M$_{\oplus}$, and a period of 4.85 days. TOI-431d likely has an extended atmosphere and is one of the most well-suited TESS discoveries for atmospheric characterisation, while the super-Earth TOI-431b may be a stripped core. These planets straddle the radius gap, presenting an interesting case-study for atmospheric evolution, and TOI-431b is a prime TESS discovery for the study of rocky planet phase curves.

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arXiv2020

A remnant planetary core in the hot-Neptune desert

The interiors of giant planets remain poorly understood. Even for the planets in the Solar System, difficulties in observation lead to large uncertainties in the properties of planetary cores. Exoplanets that have undergone rare evolutionary processes provide a route to understanding planetary interiors. Planets found in and near the typically barren hot-Neptune 'desert' (a region in mass-radius space that contains few planets) have proved to be particularly valuable in this regard. These planets include HD149026b, which is thought to have an unusually massive core, and recent discoveries such as LTT9779b and NGTS-4b, on which photoevaporation has removed a substantial part of their outer atmospheres. Here we report observations of the planet TOI-849b, which has a radius smaller than Neptune's but an anomalously large mass of $39.1^{+2.7}_{-2.6}$ Earth masses and a density of $5.2^{+0.7}_{-0.8}$ grams per cubic centimetre, similar to Earth's. Interior structure models suggest that any gaseous envelope of pure hydrogen and helium consists of no more than $3.9^{+0.8}_{-0.9}$ per cent of the total planetary mass. The planet could have been a gas giant before undergoing extreme mass loss via thermal self-disruption or giant planet collisions, or it could have avoided substantial gas accretion, perhaps through gap opening or late formation. Although photoevaporation rates cannot account for the mass loss required to reduce a Jupiter-like gas giant, they can remove a small (a few Earth masses) hydrogen and helium envelope on timescales of several billion years, implying that any remaining atmosphere on TOI-849b is likely to be enriched by water or other volatiles from the planetary interior. We conclude that TOI-849b is the remnant core of a giant planet.

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arXiv2020

A pair of TESS planets spanning the radius valley around the nearby mid-M dwarf LTT 3780

We present the confirmation of two new planets transiting the nearby mid-M dwarf LTT 3780 (TIC 36724087, TOI-732, $V=13.07$, $K_s=8.204$, $R_s$=0.374 R$_{\odot}$, $M_s$=0.401 M$_{\odot}$, d=22 pc). The two planet candidates are identified in a single TESS sector and are validated with reconnaissance spectroscopy, ground-based photometric follow-up, and high-resolution imaging. With measured orbital periods of $P_b=0.77$ days, $P_c=12.25$ days and sizes $r_{p,b}=1.33\pm 0.07$ R$_{\oplus}$, $r_{p,c}=2.30\pm 0.16$ R$_{\oplus}$, the two planets span the radius valley in period-radius space around low mass stars thus making the system a laboratory to test competing theories of the emergence of the radius valley in that stellar mass regime. By combining 63 precise radial-velocity measurements from HARPS and HARPS-N, we measure planet masses of $m_{p,b}=2.62^{+0.48}_{-0.46}$ M$_{\oplus}$ and $m_{p,c}=8.6^{+1.6}_{-1.3}$ M$_{\oplus}$, which indicates that LTT 3780b has a bulk composition consistent with being Earth-like, while LTT 3780c likely hosts an extended H/He envelope. We show that the recovered planetary masses are consistent with predictions from both photoevaporation and from core-powered mass loss models. The brightness and small size of LTT 3780, along with the measured planetary parameters, render LTT 3780b and c as accessible targets for atmospheric characterization of planets within the same planetary system and spanning the radius valley.

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arXiv2019

Quantifying the Bayesian Evidence for a Planet in Radial Velocity Data

We present results from a data challenge posed to the radial velocity (RV) community: namely, to quantify the Bayesian "evidence" for n={0,1,2,3} planets in a set of synthetically generated RV datasets containing a range of planet signals. Participating teams were provided the same likelihood function and set of priors to use in their analysis. They applied a variety of methods to estimate Z, the marginal likelihood for each n-planet model, including cross-validation, the Laplace approximation, importance sampling, and nested sampling. We found the dispersion in Z across different methods grew with increasing n-planet models: ~3 for 0-planets, ~10 for 1-planet, ~100-1000 for 2-planets, and >10,000 for 3-planets. Most internal estimates of uncertainty in Z for individual methods significantly underestimated the observed dispersion across all methods. Methods that adopted a Monte Carlo approach by comparing estimates from multiple runs yielded plausible uncertainties. Finally, two classes of numerical algorithms (those based on importance and nested samplers) arrived at similar conclusions regarding the ratio of Zs for n and (n+1)-planet models. One analytic method (the Laplace approximation) demonstrated comparable performance. We express both optimism and caution: we demonstrate that it is practical to perform rigorous Bayesian model comparison for <=3-planet models, yet robust planet discoveries require researchers to better understand the uncertainty in Z and its connections to model selection.

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arXiv2017

Models of radial velocities and transit light curves

Research in extrasolar-planet science is data-driven. With the advent of radial-velocity instruments like HARPS and HARPS-N, and transit space missions like Kepler, our ability to discover and characterise extrasolar planets is no longer limited by instrumental precision but by our ability to model the data accurately. This chapter presents the models that describe radial-velocity measurements and transit light curves. I begin by deriving the solution of the two-body problem and from there, the equations describing the radial velocity of a planet-host star and the distance between star and planet centres, necessary to model transit light curves. Stochastic models are then presented and I delineate how they are used to model complex physical phenomena affecting the exoplanet data sets, such as stellar activity. Finally, I give a brief overview of the processes of Bayesian inference, focussing on the construction of likelihood functions and prior probability distributions. In particular, I describe different methods to specify ignorance priors.

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arXiv2017

The SOPHIE search for northern extrasolar planets - XII. Three giant planets suitable for astrometric mass determination with Gaia

We present new radial velocity measurements for three low-metallicity solar-like stars observed with the SOPHIE spectrograph and its predecessor ELODIE, both installed at the 193 cm telescope of the Haute-Provence Observatory, allowing the detection and characterization of three new giant extrasolar planets in intermediate periods of 1.7 to 3.7 years. All three stars, HD17674, HD42012 and HD29021 present single giant planetary companions with minimum masses between 0.9 and 2.5 MJup. The range of periods and masses of these companions, along with the distance of their host stars, make them good targets to look for astrometric signals over the lifetime of the new astrometry satellite Gaia. We discuss the preliminary astrometric solutions obtained from the first Gaia data release.

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arXiv2015

One of the closest exoplanet pairs to the 3:2 Mean Motion Resonance: K2-19b \& c

The K2 mission has recently begun to discover new and diverse planetary systems. In December 2014 Campaign 1 data from the mission was released, providing high-precision photometry for ~22000 objects over an 80 day timespan. We searched these data with the aim of detecting further important new objects. Our search through two separate pipelines led to the independent discovery of K2-19b \& c, a two-planet system of Neptune sized objects (4.2 and 7.2 $R_\oplus$), orbiting a K dwarf extremely close to the 3:2 mean motion resonance. The two planets each show transits, sometimes simultaneously due to their proximity to resonance and alignment of conjunctions. We obtain further ground based photometry of the larger planet with the NITES telescope, demonstrating the presence of large transit timing variations (TTVs), and use the observed TTVs to place mass constraints on the transiting objects under the hypothesis that the objects are near but not in resonance. We then statistically validate the planets through the \texttt{PASTIS} tool, independently of the TTV analysis.

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arXiv2015

SOPHIE velocimetry of Kepler transit candidates XVI. Tomographic measurement of the low obliquity of KOI-12b, a warm Jupiter transiting a fast rotator

We present the detection and characterization of the transiting warm Jupiter KOI-12b, first identified with Kepler with an orbital period of 17.86 days. We combine the analysis of Kepler photometry with Doppler spectroscopy and line-profile tomography of time-series spectra obtained with the SOPHIE spectrograph to establish its planetary nature and derive its properties. To derive reliable estimates for the uncertainties on the tomographic model parameters, we devised an empirical method to calculate statistically independent error bars on the time-series spectra. KOI-12b has a radius of 1.43$\pm$0.13$ R_\mathrm{Jup}$ and a 3$σ$ upper mass limit of 10$M_\mathrm{Jup}$. It orbits a fast-rotating star ($v$sin$i_{\star}$ = 60.0$\pm$0.9 km s$^{-1}$) with mass and radius of 1.45$\pm$0.09 $M_\mathrm{Sun}$ and 1.63$\pm$0.15 $R_\mathrm{Sun}$, located at 426$\pm$40 pc from the Earth. Doppler tomography allowed a higher precision on the obliquity to be reached by comparison with the analysis of the Rossiter-McLaughlin radial velocity anomaly, and we found that KOI-12b lies on a prograde, slightly misaligned orbit with a low sky-projected obliquity $λ$ = 12.6$\stackrel{+3.0}{_{-2.9}}^\circ$. The properties of this planetary system, with a 11.4 magnitude host-star, make of KOI-12b a precious target for future atmospheric characterization.

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arXiv2014

PASTIS: Bayesian extrasolar planet validation. I. General framework, models, and performance

A large fraction of the smallest transiting planet candidates discovered by the Kepler and CoRoT space missions cannot be confirmed by a dynamical measurement of the mass using currently available observing facilities. To establish their planetary nature, the concept of planet validation has been advanced. This technique compares the probability of the planetary hypothesis against that of all reasonably conceivable alternative false-positive (FP) hypotheses. The candidate is considered as validated if the posterior probability of the planetary hypothesis is sufficiently larger than the sum of the probabilities of all FP scenarios. In this paper, we present PASTIS, the Planet Analysis and Small Transit Investigation Software, a tool designed to perform a rigorous model comparison of the hypotheses involved in the problem of planet validation, and to fully exploit the information available in the candidate light curves. PASTIS self-consistently models the transit light curves and follow-up observations. Its object-oriented structure offers a large flexibility for defining the scenarios to be compared. The performance is explored using artificial transit light curves of planets and FPs with a realistic error distribution obtained from a Kepler light curve. We find that data support for the correct hypothesis is strong only when the signal is high enough (transit signal-to-noise ratio above 50 for the planet case) and remains inconclusive otherwise. PLATO shall provide transits with high enough signal-to-noise ratio, but to establish the true nature of the vast majority of Kepler and CoRoT transit candidates additional data or strong reliance on hypotheses priors is needed.

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arXiv2013

SOPHIE velocimetry of Kepler transit candidates. VIII. KOI-205 b: a brown-dwarf companion to a K-type dwarf

We report the discovery of a transiting brown dwarf companion to KOI-205, a K0 main-sequence star, in a 11.720125-day period orbit. The transits were detected by the Kepler space telescope, and the reflex motion of the star was measured using radial velocity observations obtained with the SOPHIE spectrograph. The atmospheric parameters of the host stars were determined from the analysis of high-resolution, high signal-to-noise ratio ESPaDOns spectra obtained for this purpose. Together with spectrophotometric measurements recovered from the literature, these spectra indicate that the star is a mildly metallic K0 dwarf with Teff 5237 $\pm$ 60 K. The mass of the companion is 39.9 $\pm$ 1.0 MJup and its radius is 0.81 $\pm$ 0.02 RJup, in agreement with current theoretical predictions. This is the first time a bona fide brown dwarf companion is detected in orbit around a star of this type. The formation and orbital evolution of brown dwarf companions is briefly discussed in the light of this new discovery.

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