We report the discovery of a transiting, temperate, Neptune-sized exoplanet orbiting the nearby (d = 27.5 pc), M3V star TOI-1231 (NLTT 24399, L 248-27, 2MASS J10265947-5228099). The planet was ...detected using photometric data from the Transiting Exoplanet Survey Satellite and followed up with observations from the Las Cumbres Observatory and the Antarctica Search for Transiting ExoPlanets program. Combining the photometric data sets, we find that the newly discovered planet has a radius of 3.65 +0.16 −0.15 R ⊕ , and an orbital period of 24.246 days. Radial velocity measurements obtained with the Planet Finder Spectrograph on the Magellan Clay telescope confirm the existence of the planet and lead to a mass measurement of 15.5±3.3 M ⊕. With an equilibrium temperature of just 330K TOI-1231 b is one of the coolest small planets accessible for atmospheric studies thus far, and its host star's bright NIR brightness (J=8.88, K s =8.07) make it an exciting target for HST and JWST. Future atmospheric observations would enable the first comparative planetology efforts in the 250-350 K temperature regime via comparisons with K2-18 b. Furthermore, TOI-1231's high systemic radial velocity (70.5 km s −1) may allow for the detection of low-velocity hydrogen atoms escaping the planet by Doppler shifting the H I Ly-alpha stellar emission away from the geocoronal and ISM absorption features.
Small Solar system bodies serve as pristine records that have been minimally
altered since their formation. Their observations provide valuable information
regarding the formation and evolution of ...our Solar system. Interstellar objects
(ISOs) can also provide insight on the formation of exoplanetary systems and
planetary system evolution as a whole. In this work, we present the application
of our framework to search for small Solar system bodies in exoplanet transit
survey data collected by the Antarctic Search for Transiting ExoPlanets (ASTEP)
project. We analysed data collected during the Austral winter of 2021 by the
ASTEP 400 telescope located at the Concordia Station, at Dome C, Antarctica. We
identified 20 known objects from dynamical classes ranging from Inner Main-belt
asteroids to one comet. Our search recovered known objects down to a magnitude
of $V$ = 20.4 mag, with a retrieval rate of $\sim$80% for objects with $V \le $
20 mag. Future work will apply the pipeline to archival ASTEP data that
observed fields for periods of longer than a few hours to treat them as
deep-drilling datasets and reach fainter limiting magnitudes for slow-moving
objects, on the order of $V\approx $ 23-24 mag.
Ongoing ground-based radial-velocity observations seeking to detect circumbinary planets focus on single-lined binaries even though over nine in every ten binary systems in the solar-neighbourhood ...are double-lined. Double-lined binaries are on average brighter, and should in principle yield more precise radial-velocities. However, as the two stars orbit one another, they produce a time-varying blending of their weak spectral lines. This makes an accurate measure of radial velocities difficult, producing a typical scatter of 10-15m/s. This extra noise prevents the detection of most orbiting circumbinary planets. We develop two new data-driven approaches to disentangle the two stellar components of a double-lined binary, and extract accurate and precise radial-velocities. Both approaches use a Gaussian Process regression, with the first one working in the spectral domain, whereas the second works on cross-correlated spectra. We apply our new methods to TIC 172900988, a proposed circumbinary system with a double-lined binary, and detect a circumbinary planet with an orbital period of 150 days, different than previously proposed. We also measure a significant residual scatter, which we speculate is caused by stellar activity. We show that our two data-driven methods outperform the traditionally used TODCOR and TODMOR, for that particular binary system.
In the hunt for Earth-like exoplanets it is crucial to have reliable host star parameters, as they have a direct impact on the accuracy and precision of the inferred parameters for any discovered ...exoplanet. For stars with masses between 0.35 and 0.5 \({\rm M_{\odot}}\) an unexplained radius inflation is observed relative to typical stellar models. However, for fully convective objects with a mass below 0.35 \({\rm M_{\odot}}\) it is not known whether this radius inflation is present as there are fewer objects with accurate measurements in this regime. Low-mass eclipsing binaries present a unique opportunity to determine empirical masses and radii for these low-mass stars. Here we report on such a star, EBLM J2114-39\,B. We have used HARPS and FEROS radial-velocities and \textit{TESS} photometry to perform a joint fit of the data, and produce one of the most precise estimates of a very low mass star's parameters. Using a precise and accurate radius for the primary star using {\it Gaia} DR3 data, we determine J2114-39 to be a \(M_1 = 0.998 \pm 0.052\)~\({\rm M_{\odot}}\) primary star hosting a fully convective secondary with mass \(M_2~=~0.0986~\pm 0.0038~\,\mathrm{M_{\odot}}\), which lies in a poorly populated region of parameter space. With a radius \(R_2 =~0.1275~\pm0.0020~\,\mathrm{R_{\odot}}\), similar to TRAPPIST-1, we see no significant evidence of radius inflation in this system when compared to stellar evolution models. We speculate that stellar models in the regime where radius inflation is observed might be affected by how convective overshooting is treated.
Colour-Magnitude Diagrams provide a convenient way of comparing populations of similar objects. When well populated with precise measurements, they allow quick inferences to be made about the bulk ...properties of an astronomic object simply from its proximity on a diagram to other objects. We present here a Python toolkit which allows a user to produce colour-magnitude diagrams of transiting exoplanets, comparing planets to populations of ultra-cool dwarfs, of directly imaged exoplanets, to theoretical models of planetary atmospheres, and to other transiting exoplanets. Using a selection of near- and mid-infrared colour-magnitude diagrams, we show how outliers can be identified for further investigation, and how emerging sub-populations can be identified. Additionally, we present evidence that observed differences in the \textit{Spitzer}'s 4.5\mu m flux, between irradiated Jupiters, and field brown dwarfs, might be attributed to phosphine, which is susceptible to photolysis. The presence of phosphine in low irradiation environments may negate the need for thermal inversions to explain eclipse measurements. We speculate that the anomalously low 4.5\mu m flux flux of the nightside of HD 189733b and the daysides of GJ 436b and GJ 3470b might be caused by phosphine absorption. Finally, we use our toolkit to include \textit{Hubble} WFC3 spectra, creating a new photometric band called the `Water band' (\textit{W\(_{JH}\)}-band) in the process. We show that the colour index \textit{W\(_{JH}\)-H} can be used to constrain the C/O ratio of exoplanets, showing that future observations with \textit{JWST} and \textit{Ariel} will be able to distinguish these populations if they exist, and select members for future follow-up.
Planets orbiting binary systems are relatively unexplored compared to those
around single stars. Detections of circumbinary planets and planetary systems
offer a first detailed view into our ...understanding of circumbinary planet
formation and dynamical evolution. The BEBOP (Binaries Escorted by Orbiting
Planets) radial velocity survey plays a special role in this adventure as it
focuses on eclipsing single-lined binaries with an FGK dwarf primary and M
dwarf secondary allowing for the highest-radial velocity precision using the
HARPS and SOPHIE spectrographs. We obtained 4512 high-resolution spectra for
the 179 targets in the BEBOP survey which we used to derive the stellar
atmospheric parameters using both equivalent widths and spectral synthesis. We
furthermore derive stellar masses, radii, and ages for all targets. With this
work, we present the first homogeneous catalogue of precise stellar parameters
for these eclipsing single-lined binaries.
M-dwarfs are the most abundant stars in the galaxy and popular targets for exoplanet searches. However, their intrinsic faintness and complex spectra inhibit precise characterisation. We only know of ...dozens of M-dwarfs with fundamental parameters of mass, radius and effective temperature characterised to better than a few per cent. Eclipsing binaries remain the most robust means of stellar characterisation. Here we present two targets from the Eclipsing Binary Low Mass (EBLM) survey that were observed with K2: EBLM J0055-00 and EBLM J2217-04. Combined with HARPS and CORALIE spectroscopy, we measure M-dwarf masses with precisions better than 5%, radii better than 3% and effective temperatures on order 1%. However, our fits require invoking a model to derive parameters for the primary star. By investigating three popular models, we determine that the model uncertainty is of similar magnitude to the statistical uncertainty in the model fits. Therefore, whilst these can be considered benchmark M-dwarfs, we caution the community to consider model uncertainty when pushing the limits of precise stellar characterisation.
We report on the discovery of Gliese 12 b, the nearest transiting temperate, Earth-sized planet found to date. Gliese 12 is a bright (\(V=12.6\) mag, \(K=7.8\) mag) metal-poor M4V star only ...\(12.162\pm0.005\) pc away from the Solar System with one of the lowest stellar activity levels known for an M-dwarf. A planet candidate was detected by TESS based on only 3 transits in sectors 42, 43, and 57, with an ambiguity in the orbital period due to observational gaps. We performed follow-up transit observations with CHEOPS and ground-based photometry with MINERVA-Australis, SPECULOOS, and Purple Mountain Observatory, as well as further TESS observations in sector 70. We statistically validate Gliese 12 b as a planet with an orbital period of \(12.76144\pm0.00006\) days and a radius of \(1.0\pm{0.1}\) R\(_\oplus\), resulting in an equilibrium temperature of \(\sim\)315K. Gliese 12 b has excellent future prospects for precise mass measurement, which may inform how planetary internal structure is affected by the stellar compositional environment. Gliese 12 b also represents one of the best targets to study whether Earth-like planets orbiting cool stars can retain their atmospheres, a crucial step to advance our understanding of habitability on Earth and across the Galaxy.
On December 2021, a new camera box for two-colour simultaneous visible photometry was successfully installed on the ASTEP telescope at the Concordia station in Antarctica. The new focal box offers ...increased capabilities for the ASTEP+ project. The opto-mechanical design of the camera was described in a previous paper. Here, we focus on the laboratory tests of each of the two cameras, the low-temperature behaviour of the focal box in a thermal chamber, the on-site installation and alignment of the new focal box on the telescope, the measurement of the turbulence in the tube and the operation of the telescope equipped with the new focal box. We also describe the data acquisition and the telescope guiding procedure and provide a first assessment of the performances reached during the first part of the 2022 observation campaign. Observations of the WASP19 field, already observed previously with ASTEP, demonstrates an improvement of the SNR by a factor 1.7, coherent with an increased number of photon by a factor of 3. The throughput of the two cameras is assessed both by calculation of the characteristics of the optics and quantum efficiency of the cameras, and by direct observations on the sky. We find that the ASTEP+ two-colour transmission curves (with a dichroic separating the fluxes at 690nm) are similar to those of GAIA in the blue and red channels, but with a lower transmission in the ASTEP+ red channel leading to a 1.5 magnitude higher B-R value compared to the GAIA B-R value. With this new setting, the ASTEP+ telescope will ensure the follow-up and the characterization of a large number of exoplanetary transits in the coming years in view of the future space missions JWST and Ariel.
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