| 1. |
- Delrez, Laetitia, et al.
(author)
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Transit detection of the long-period volatile-rich super-Earth nu(2) Lupi d with CHEOPS
- 2021
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In: Nature Astronomy. - : Springer Science and Business Media LLC. - 2397-3366. ; :5, s. 775-787
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Journal article (peer-reviewed)abstract
- Exoplanets transiting bright nearby stars are key objects for advancing our knowledge of planetary formation and evolution. The wealth of photons from the host star gives detailed access to the atmospheric, interior and orbital properties of the planetary companions. nu(2) Lupi (HD 136352) is a naked-eye (V = 5.78) Sun-like star that was discovered to host three low-mass planets with orbital periods of 11.6, 27.6 and 107.6 d via radial-velocity monitoring(1). The two inner planets (b and c) were recently found to transit(2), prompting a photometric follow-up by the brand new Characterising Exoplanets Satellite (CHEOPS). Here, we report that the outer planet d is also transiting, and measure its radius and mass to be 2.56 +/- 0.09 R-circle plus and 8.82 +/- 0.94 M-circle plus, respectively. With its bright Sun-like star, long period and mild irradiation (similar to 5.7 times the irradiation of Earth), nu(2) Lupi d unlocks a completely new region in the parameter space of exoplanets amenable to detailed characterization. We refine the properties of all three planets: planet b probably has a rocky mostly dry composition, while planets c and d seem to have retained small hydrogen-helium envelopes and a possibly large water fraction. This diversity of planetary compositions makes the nu(2) Lupi system an excellent laboratory for testing formation and evolution models of low-mass planets.
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| 2. |
- Akinsanmi, B., et al.
(author)
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The tidal deformation and atmosphere of WASP-12 b from its phase curve
- 2024
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In: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 685
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Journal article (peer-reviewed)abstract
- Context. Ultra-hot Jupiters present a unique opportunity to understand the physics and chemistry of planets, their atmospheres, and interiors at extreme conditions. WASP-12 b stands out as an archetype of this class of exoplanets, with a close-in orbit around its star that results in intense stellar irradiation and tidal effects. Aims. The goals are to measure the planet's tidal deformation, atmospheric properties, and also to refine its orbital decay rate. Methods. We performed comprehensive analyses of the transits, occultations, and phase curves of WASP-12b by combining new CHEOPS observations with previous TESS and Spitzer data. The planet was modeled as a triaxial ellipsoid parameterized by the second-order fluid Love number of the planet, h2, which quantifies its radial deformation and provides insight into the interior structure. Results. We measured the tidal deformation of WASP-12b and estimated a Love number of h2 = 1.55- 0.49+0.45 (at 3.2σ) from its phase curve. We measured occultation depths of 333 ± 24 ppm and 493 ± 29 ppm in the CHEOPS and TESS bands, respectively, while the nightside fluxes are consistent with zero, and also marginal eastward phase offsets. Our modeling of the dayside emission spectrum indicates that CHEOPS and TESS probe similar pressure levels in the atmosphere at a temperature of ~2900 K. We also estimated low geometric albedos of Ag = 0.086 ± 0.017 and Ag = 0.01 ± 0.023 in the CHEOPS and TESS passbands, respectively, suggesting the absence of reflective clouds in the high-temperature dayside of the planet. The CHEOPS occultations do not show strong evidence for variability in the dayside atmosphere of the planet at the median occultation depth precision of 120 ppm attained. Finally, combining the new CHEOPS timings with previous measurements refines the precision of the orbital decay rate by 12% to a value of - 30.23 ± 0.82 ms yr- 1, resulting in a modified stellar tidal quality factor of Q′∗ = 1.70 ± 0.14 × 105. Conclusions. WASP-12 b becomes the second exoplanet, after WASP-103b, for which the Love number has been measured from the effect of tidal deformation in the light curve. However, constraining the core mass fraction of the planet requires measuring h2 with a higher precision. This can be achieved with high signal-to-noise observations with JWST since the phase curve amplitude, and consequently the induced tidal deformation effect, is higher in the infrared.
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| 3. |
- Alonso, R., et al.
(author)
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No random transits in CHEOPS observations of HD 139139 *,**
- 2023
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In: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 680
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Journal article (peer-reviewed)abstract
- Context . The star HD 139139 (a.k.a. ‘the Random Transiter’) is a star that exhibited enigmatic transit-like features with no apparent periodicity in K2 data. The shallow depth of the events (-200 ppm - equivalent to transiting objects with radii of -1.5 R⊕ in front of a Sun-like star) and their non-periodicity constitute a challenge for the photometric follow-up of this star. Aims . The goal of this study is to confirm with independent measurements the presence of shallow, non-periodic transit-like features on this object. Methods . We performed observations with CHEOPS for a total accumulated time of 12.75 days, distributed in visits of roughly 20 h in two observing campaigns in years 2021 and 2022. The precision of the data is sufficient to detect 150 ppm features with durations longer than 1.5 h. We used the duration and times of the events seen in the K2 curve to estimate how many events should have been detected in our campaigns, under the assumption that their behaviour during the CHEOPS observations would be the same as in the K2 data of 2017. Results . We do not detect events with depths larger than 150 ppm in our data set. If the frequency, depth, and duration of the events were the same as in the K2 campaign, we estimate the probability of having missed all events due to our limited observing window would be 4.8%. Conclusions . We suggest three different scenarios to explain our results: 1) Our observing window was not long enough, and the events were missed with the estimated 4.8% probability. 2) The events recorded in the K2 observations were time critical, and the mechanism producing them was either not active in the 2021 and 2022 campaigns or created shallower events under our detectability level. 3) The enigmatic events in the K2 data are the result of an unidentified and infrequent instrumental noise in the original data set or its data treatment.
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| 4. |
- Benz, W., et al.
(author)
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The CHEOPS mission
- 2021
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In: Experimental Astronomy. - : Springer Science and Business Media LLC. - 0922-6435 .- 1572-9508. ; 51:1, s. 109-151
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Journal article (peer-reviewed)abstract
- The CHaracterising ExOPlanet Satellite (CHEOPS) was selected on October 19, 2012, as the first small mission (S-mission) in the ESA Science Programme and successfully launched on December 18, 2019, as a secondary passenger on a Soyuz-Fregat rocket from Kourou, French Guiana. CHEOPS is a partnership between ESA and Switzerland with important contributions by ten additional ESA Member States. CHEOPS is the first mission dedicated to search for transits of exoplanets using ultrahigh precision photometry on bright stars already known to host planets. As a follow-up mission, CHEOPS is mainly dedicated to improving, whenever possible, existing radii measurements or provide first accurate measurements for a subset of those planets for which the mass has already been estimated from ground-based spectroscopic surveys. The expected photometric precision will also allow CHEOPS to go beyond measuring only transits and to follow phase curves or to search for exo-moons, for example. Finally, by unveiling transiting exoplanets with high potential for in-depth characterisation, CHEOPS will also provide prime targets for future instruments suited to the spectroscopic characterisation of exoplanetary atmospheres. To reach its science objectives, requirements on the photometric precision and stability have been derived for stars with magnitudes ranging from 6 to 12 in the V band. In particular, CHEOPS shall be able to detect Earth-size planets transiting G5 dwarf stars (stellar radius of 0.9R⊙) in the magnitude range 6 ≤ V ≤ 9 by achieving a photometric precision of 20 ppm in 6 hours of integration time. In the case of K-type stars (stellar radius of 0.7R⊙) of magnitude in the range 9 ≤ V ≤ 12, CHEOPS shall be able to detect transiting Neptune-size planets achieving a photometric precision of 85 ppm in 3 hours of integration time. This precision has to be maintained over continuous periods of observation for up to 48 hours. This precision and stability will be achieved by using a single, frame-transfer, back-illuminated CCD detector at the focal plane assembly of a 33.5 cm diameter, on-axis Ritchey-Chrétien telescope. The nearly 275 kg spacecraft is nadir-locked, with a pointing accuracy of about 1 arcsec rms, and will allow for at least 1 Gbit/day downlink. The sun-synchronous dusk-dawn orbit at 700 km altitude enables having the Sun permanently on the backside of the spacecraft thus minimising Earth stray light. A mission duration of 3.5 years in orbit is foreseen to enable the execution of the science programme. During this period, 20% of the observing time is available to the wider community through yearly ESA call for proposals, as well as through discretionary time approved by ESA’s Director of Science. At the time of this writing, CHEOPS commissioning has been completed and CHEOPS has been shown to fulfill all its requirements. The mission has now started the execution of its science programme.
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| 5. |
- Bonfanti, A., et al.
(author)
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Characterising TOI-732 b and c: New insights into the M-dwarf radius and density valley ★,★★
- 2024
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In: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 682
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Journal article (peer-reviewed)abstract
- TOI-732 is an M dwarf hosting two transiting planets that are located on the two opposite sides of the radius valley. Inferring a reliable demographics for this type of systems is key to understanding their formation and evolution mechanisms. Aims. By doubling the number of available space-based observations and increasing the number of radial velocity (RV) measurements, we aim at refining the parameters of TOI-732 b and c. We also use the results to study the slope of the radius valley and the density valley for a well-characterised sample of M-dwarf exoplanets. Methods. We performed a global Markov chain Monte Carlo analysis by jointly modelling ground-based light curves and CHEOPS and TESS observations, along with RV time series both taken from the literature and obtained with the MAROON-X spectrograph. The slopes of the M-dwarf valleys were quantified via a support vector machine (SVM) procedure. Results. TOI-732 b is an ultrashort-period planet (P = 0.76837931−+000000004200000039 days) with a radius Rb = 1.325+−00057058 R☉, a mass Mb = 2.46 ± 0.19 M☉, and thus a mean density ρb = 5.8+−1008 g cm−3, while the outer planet at P = 12.252284 ± 0.000013 days has Rc = 2.39+−001011 R☉, Mc = 8.04+−005048 M☉, and thus ρc = 3.24+−005543 g cm−3. Even with respect to the most recently reported values, this work yields uncertainties on the transit depths and on the RV semi-amplitudes that are smaller up to a factor of ∼1.6 and ∼2.4 for TOI-732 b and c, respectively. Our calculations for the interior structure and the location of the planets in the mass-radius diagram lead us to classify TOI-732 b as a super-Earth and TOI-732 c as a mini-Neptune. Following the SVM approach, we quantified d log Rp,valley/d log P = −0.065+−00024013, which is flatter than for Sun-like stars. In line with former analyses, we note that the radius valley for M-dwarf planets is more densely populated, and we further quantify the slope of the density valley as d log ρ̂valley/d log P = −0.02+−001204. Conclusions. Compared to FGK stars, the weaker dependence of the position of the radius valley on the orbital period might indicate that the formation shapes the radius valley around M dwarfs more strongly than the evolution mechanisms.
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| 6. |
- Bonfanti, A., et al.
(author)
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CHEOPS observations of the HD 108236 planetary system: A fifth planet, improved ephemerides, and planetary radii
- 2021
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In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 646
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Journal article (peer-reviewed)abstract
- Context. The detection of a super-Earth and three mini-Neptunes transiting the bright (V = 9.2 mag) star HD 108236 (also known as TOI-1233) was recently reported on the basis of TESS and ground-based light curves. Aims. We perform a first characterisation of the HD 108236 planetary system through high-precision CHEOPS photometry and improve the transit ephemerides and system parameters. Methods. We characterise the host star through spectroscopic analysis and derive the radius with the infrared flux method. We constrain the stellar mass and age by combining the results obtained from two sets of stellar evolutionary tracks. We analyse the available TESS light curves and one CHEOPS transit light curve for each known planet in the system. Results. We find that HD 108236 is a Sun-like star with R? = 0.877 ± 0.008 R? , M? = 0.869-0.048+0.050 M? , and an age of 6.7-5.1+4.0 Gyr. We report the serendipitous detection of an additional planet, HD 108236 f, in one of the CHEOPS light curves. For this planet, the combined analysis of the TESS and CHEOPS light curves leads to a tentative orbital period of about 29.5 days. From the light curve analysis, we obtain radii of 1.615 ± 0.051, 2.071 ± 0.052, 2.539-0.065+0.062, 3.083 ± 0.052, and 2.017-0.057+0.052 R? for planets HD 108236 b to HD 108236 f, respectively. These values are in agreement with previous TESS-based estimates, but with an improved precision of about a factor of two. We perform a stability analysis of the system, concluding that the planetary orbits most likely have eccentricities smaller than 0.1. We also employ a planetary atmospheric evolution framework to constrain the masses of the five planets, concluding that HD 108236 b and HD 108236 c should have an Earth-like density, while the outer planets should host a low mean molecular weight envelope. Conclusions. The detection of the fifth planet makes HD 108236 the third system brighter than V = 10 mag to host more than four transiting planets. The longer time span enables us to significantly improve the orbital ephemerides such that the uncertainty on the transit times will be of the order of minutes for the years to come. A comparison of the results obtained from the TESS and CHEOPS light curves indicates that for a V - 9 mag solar-like star and a transit signal of -500 ppm, one CHEOPS transit light curve ensures the same level of photometric precision as eight TESS transits combined, although this conclusion depends on the length and position of the gaps in the light curve.
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| 7. |
- Bourrier, V., et al.
(author)
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A CHEOPS-enhanced view of the HD 3167 system
- 2022
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In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 668
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Journal article (peer-reviewed)abstract
- Much remains to be understood about the nature of exoplanets smaller than Neptune, most of which have been discovered in compact multi-planet systems. With its inner ultra-short period planet b aligned with the star and two larger outer planets d-c on polar orbits, the multi-planet system HD 3167 features a peculiar architecture and offers the possibility to investigate both dynamical and atmospheric evolution processes. To this purpose we combined multiple datasets of transit photometry and radial velocimetry (RV) to revise the properties of the system and inform models of its planets. This effort was spearheaded by CHEOPS observations of HD 3167b, which appear inconsistent with a purely rocky composition despite its extreme irradiation. Overall the precision on the planetary orbital periods are improved by an order of magnitude, and the uncertainties on the densities of the transiting planets b and c are decreased by a factor of 3. Internal structure and atmospheric simulations draw a contrasting picture between HD 3167d, likely a rocky super-Earth that lost its atmosphere through photo-evaporation, and HD 3167c, a mini-Neptune that kept a substantial primordial gaseous envelope. We detect a fourth, more massive planet on a larger orbit, likely coplanar with HD 3167d-c. Dynamical simulations indeed show that the outer planetary system d-c-e was tilted, as a whole, early in the system history, when HD 3167b was still dominated by the star influence and maintained its aligned orbit. RV data and direct imaging rule out that the companion that could be responsible for the present-day architecture is still bound to the HD 3167 system. Similar global studies of multi-planet systems will tell how many share the peculiar properties of the HD 3167 system, which remains a target of choice for follow-up observations and simulations.
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| 8. |
- Brandeker, Alexis, et al.
(author)
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CHEOPS geometric albedo of the hot Jupiter HD 209458 b
- 2022
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In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 659
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Journal article (peer-reviewed)abstract
- We report the detection of the secondary eclipse of the hot Jupiter HD 209458 b in optical/visible light using the CHEOPS space telescope. Our measurement of 20.4+3.2-3.3 parts per million translates into a geometric albedo of Ag = 0.096 ± 0.016. The previously estimated dayside temperature of about 1500 K implies that our geometric albedo measurement consists predominantly of reflected starlight and is largely uncontaminated by thermal emission. This makes the present result one of the most robust measurements of Ag for any exoplanet. Our calculations of the bandpass-integrated geometric albedo demonstrate that the measured value of Ag is consistent with a cloud-free atmosphere, where starlight is reflected via Rayleigh scattering by hydrogen molecules, and the water and sodium abundances are consistent with stellar metallicity. We predict that the bandpass-integrated TESS geometric albedo is too faint to detect and that a phase curve of HD 209458 b observed by CHEOPS would have a distinct shape associated with Rayleigh scattering if the atmosphere is indeed cloud free.
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| 9. |
- Bruno, G., et al.
(author)
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Detailed cool star flare morphology with CHEOPS and TESS
- 2024
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In: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 686
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Journal article (peer-reviewed)abstract
- Context. White-light stellar flares are proxies for some of the most energetic types of flares, but their triggering mechanism is still poorly understood. As they are associated with strong X and ultraviolet emission, their study is particularly relevant to estimate the amount of high-energy irradiation onto the atmospheres of exoplanets, especially those in their stars’ habitable zone. Aims. We used the high-cadence, high-photometric capabilities of the CHEOPS and TESS space telescopes to study the detailed morphology of white-light flares occurring in a sample of 130 late-K and M stars, and compared our findings with results obtained at a lower cadence. Methods. We employed dedicated software for the reduction of 3 s cadence CHEOPS data, and adopted the 20 s cadence TESS data reduced by their official processing pipeline. We developed an algorithm to separate multi-peak flare profiles into their components, in order to contrast them to those of single-peak, classical flares. We also exploited this tool to estimate amplitudes and periodicities in a small sample of quasi-periodic pulsation (QPP) candidates. Results. Complex flares represent a significant percentage (≳30%) of the detected outburst events. Our findings suggest that high-impulse flares are more frequent than suspected from lower-cadence data, so that the most impactful flux levels that hit close-in exoplanets might be more time-limited than expected. We found significant differences in the duration distributions of single and complex flare components, but not in their peak luminosity. A statistical analysis of the flare parameter distributions provides marginal support for their description with a log-normal instead of a power-law function, leaving the door open to several flare formation scenarios. We tentatively confirmed previous results about QPPs in high-cadence photometry, report the possible detection of a pre-flare dip, and did not find hints of photometric variability due to an undetected flare background. Conclusions. The high-cadence study of stellar hosts might be crucial to evaluate the impact of their flares on close-in exoplanets, as their impulsive phase emission might otherwise be incorrectly estimated. Future telescopes such as PLATO and Ariel, thanks to their high-cadence capability, will help in this respect. As the details of flare profiles and of the shape of their parameter distributions are made more accessible by continuing to increase the instrument precision and time resolution, the models used to interpret them and their role in star-planet interactions might need to be updated constantly.
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| 10. |
- Cabrera, J., et al.
(author)
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The planetary system around HD 190622 (TOI-1054): Measuring the gas content of low-mass planets orbiting F-stars
- 2023
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In: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 675
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Journal article (peer-reviewed)abstract
- Context. Giant planets are known to dominate the long-term stability of planetary systems due to their prevailing gravitational interactions, but they are also thought to play an important role in planet formation. Observational constraints improve our understanding of planetary formation processes such as the delivery of volatile-rich planetesimals from beyond the ice line into the inner planetary system. Additional constraints may come from studies of the atmosphere, but almost all such studies of the atmosphere investigate the detection of certain species, and abundances are not routinely quantitatively measured. Aims. Accurate measurements of planetary bulk parameters-that is, mass and density-provide constraints on the inner structure and chemical composition of transiting planets. This information provides insight into properties such as the amounts of volatile species, which in turn can be related to formation and evolution processes. Methods. The Transiting Exoplanet Survey Satellite (TESS) reported a planetary candidate around HD 190622 (TOI-1054), which was subsequently validated and found to merit further characterization with photometric and spectroscopic facilities. The KESPRINT collaboration used data from the High Accuracy Radial Velocity Planet Searcher (HARPS) to independently confirm the planetary candidate, securing its mass, and revealing the presence of an outer giant planet in the system. The CHEOPS consortium invested telescope time in the transiting target in order to reduce the uncertainty on the radius, improving the characterization of the planet. Results. We present the discovery and characterization of the planetary system around HD 190622 (TOI-1054). This system hosts one transiting planet, which is smaller than Neptune (3.087-0.053+0.058REarth, 7.7 ± 1.0 MEarth) but has a similar bulk density (1.43 ± 0.21 g cm-3) and an orbital period of 16 days; and a giant planet, not known to be transiting, with a minimum mass of 227.0 ± 6.7 MEarth in an orbit with a period of 315 days. Conclusions. Our measurements constrain the structure and composition of the transiting planet. HD 190622b has singular properties among the known population of transiting planets, which we discuss in detail. Among the sub-Neptune-sized planets known today, this planet stands out because of its large gas content.
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| 11. |
- Delrez, L., et al.
(author)
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Refining the properties of the TOI-178 system with CHEOPS and TESS
- 2023
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In: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 678
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Journal article (peer-reviewed)abstract
- Context. The TOI-178 system consists of a nearby late K-dwarf transited by six planets in the super-Earth to mini-Neptune regime, with radii ranging from -1.1 to 2.9 R and orbital periods between 1.9 and 20.7 days. All planets but the innermost one form a chain of Laplace resonances. Mass estimates derived from a preliminary radial velocity (RV) dataset suggest that the planetary densities do not decrease in a monotonic way with the orbital distance to the star, contrary to what one would expect based on simple formation and evolution models. Aims. To improve the characterisation of this key system and prepare for future studies (in particular with JWST), we performed a detailed photometric study based on 40 new CHEOPS visits, one new TESS sector, and previously published CHEOPS, TESS, and NGTS data. Methods. First we updated the parameters of the host star using the new parallax from Gaia EDR3. We then performed a global analysis of the 100 transits contained in our data to refine the physical and orbital parameters of the six planets and study their transit timing variations (TTVs). We also used our extensive dataset to place constraints on the radii and orbital periods of potential additional transiting planets in the system. Results. Our analysis significantly refines the transit parameters of the six planets, most notably their radii, for which we now obtain relative precisions of -3%, with the exception of the smallest planet, b, for which the precision is 5.1%. Combined with the RV mass estimates, the measured TTVs allow us to constrain the eccentricities of planets c to g, which are found to be all below 0.02, as expected from stability requirements. Taken alone, the TTVs also suggest a higher mass for planet d than that estimated from the RVs, which had been found to yield a surprisingly low density for this planet. However, the masses derived from the current TTV dataset are very prior-dependent, and further observations, over a longer temporal baseline, are needed to deepen our understanding of this iconic planetary system.
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| 12. |
- Demangeon, O., et al.
(author)
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Asymmetry in the atmosphere of the ultra-hot Jupiter WASP-76 b***
- 2024
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In: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 684
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Journal article (peer-reviewed)abstract
- Context. WASP-76 b has been a recurrent subject of study since the detection of a signature in high-resolution transit spectroscopy data indicating an asymmetry between the two limbs of the planet. The existence of this asymmetric signature has been confirmed by multiple studies, but its physical origin is still under debate. In addition, it contrasts with the absence of asymmetry reported in the infrared (IR) phase curve. Aims. We provide a more comprehensive dataset of WASP-76 b with the goal of drawing a complete view of the physical processes at work in this atmosphere. In particular, we attempt to reconcile visible high-resolution transit spectroscopy data and IR broadband phase curves. Methods. We gathered 3 phase curves, 20 occultations, and 6 transits for WASP-76 b in the visible with the CHEOPS space telescope. We also report the analysis of three unpublished sectors observed by the TESS space telescope (also in the visible), which represents 34 phase curves. Results. WASP-76 b displays an occultation of 260 ± 11 and 152 ± 10 ppm in TESS and CHEOPS bandpasses respectively. Depending on the composition assumed for the atmosphere and the data reduction used for the IR data, we derived geometric albedo estimates that range from 0.05 ± 0.023 to 0.146 ± 0.013 and from <0.13 to 0.189 ± 0.017 in the CHEOPS and TESS bandpasses, respectively. As expected from the IR phase curves, a low-order model of the phase curves does not yield any detectable asymmetry in the visible either. However, an empirical model allowing for sharper phase curve variations offers a hint of a flux excess before the occultation, with an amplitude of ∼40 ppm, an orbital offset of ∼−30◦, and a width of ∼20◦. We also constrained the orbital eccentricity of WASP-76 b to a value lower than 0.0067, with a 99.7% confidence level. This result contradicts earlier proposed scenarios aimed at explaining the asymmetry observed in high-resolution transit spectroscopy. Conclusions. In light of these findings, we hypothesise that WASP-76 b could have night-side clouds that extend predominantly towards its eastern limb. At this limb, the clouds would be associated with spherical droplets or spherically shaped aerosols of an unknown species, which would be responsible for a glory effect in the visible phase curves.
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| 13. |
- Garai, Z., et al.
(author)
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Refined parameters of the HD 22946 planetary system and the true orbital period of planet d
- 2023
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In: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 674
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Journal article (peer-reviewed)abstract
- Context. Multi-planet systems are important sources of information regarding the evolution of planets. However, the long-period planets in these systems often escape detection. These objects in particular may retain more of their primordial characteristics compared to close-in counterparts because of their increased distance from the host star. HD 22946 is a bright (G = 8.13 mag) late F-type star around which three transiting planets were identified via Transiting Exoplanet Survey Satellite (TESS) photometry, but the true orbital period of the outermost planet d was unknown until now. Aims. We aim to use the Characterising Exoplanet Satellite (CHEOPS) space telescope to uncover the true orbital period of HD 22946d and to refine the orbital and planetary properties of the system, especially the radii of the planets. Methods. We used the available TESS photometry of HD 22946 and observed several transits of the planets b, c, and d using CHEOPS. We identified two transits of planet d in the TESS photometry, calculated the most probable period aliases based on these data, and then scheduled CHEOPS observations. The photometric data were supplemented with ESPRESSO (Echelle SPectrograph for Rocky Exoplanets and Stable Spectroscopic Observations) radial velocity data. Finally, a combined model was fitted to the entire dataset in order to obtain final planetary and system parameters. Results. Based on the combined TESS and CHEOPS observations, we successfully determined the true orbital period of the planet d to be 47.42489 ± 0.00011 days, and derived precise radii of the planets in the system, namely 1.362 ± 0.040 R, 2.328 ± 0.039 R, and 2.607 ± 0.060 R for planets b, c, and d, respectively. Due to the low number of radial velocities, we were only able to determine 3σ upper limits for these respective planet masses, which are 13.71 M, 9.72 M, and 26.57 M. We estimated that another 48 ESPRESSO radial velocities are needed to measure the predicted masses of all planets in HD 22946. We also derived stellar parameters for the host star. Conclusions. Planet c around HD 22946 appears to be a promising target for future atmospheric characterisation via transmission spectroscopy. We can also conclude that planet d, as a warm sub-Neptune, is very interesting because there are only a few similar confirmed exoplanets to date. Such objects are worth investigating in the near future, for example in terms of their composition and internal structure.
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| 14. |
- Hooton, M.J., et al.
(author)
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Spi-OPS: Spitzer and CHEOPS confirm the near-polar orbit of MASCARA-1 b and reveal a hint of dayside reflection
- 2022
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In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 658
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Journal article (peer-reviewed)abstract
- Context. The light curves of tidally locked hot Jupiters transiting fast-rotating, early-type stars are a rich source of information about both the planet and star, with full-phase coverage enabling a detailed atmospheric characterisation of the planet. Although it is possible to determine the true spin-orbit angle ψ-a notoriously difficult parameter to measure-from any transit asymmetry resulting from gravity darkening induced by the stellar rotation, the correlations that exist between the transit parameters have led to large disagreements in published values of ψ for some systems. Aims. We aimed to study these phenomena in the light curves of the ultra-hot Jupiter MASCARA-1 b, which is characteristically similar to well-studied contemporaries such as KELT-9 b and WASP-33 b. Methods. We obtained optical CHaracterising ExOPlanet Satellite (CHEOPS) transit and occultation light curves of MASCARA-1 b, and analysed them jointly with a Spitzer/IRAC 4.5 μm full-phase curve to model the asymmetric transits, occultations, and phase-dependent flux modulation. For the latter, we employed a novel physics-driven approach to jointly fit the phase modulation by generating a single 2D temperature map and integrating it over the two bandpasses as a function of phase to account for the differing planet-star flux contrasts. The reflected light component was modelled using the general ab initio solution for a semi-infinite atmosphere. Results. When fitting the CHEOPS and Spitzer transits together, the degeneracies are greatly diminished and return results consistent with previously published Doppler tomography. Placing priors informed by the tomography achieves even better precision, allowing a determination of ψ = 72.1-2.4+2.5 deg. From the occultations and phase variations, we derived dayside and nightside temperatures of 3062-68+66 K and 1720 ± 330 K, respectively.Our retrieval suggests that the dayside emission spectrum closely follows that of a blackbody. As the CHEOPS occultation is too deep to be attributed to blackbody flux alone, we could separately derive geometric albedo Ag = 0.171-0.068+0.066 and spherical albedo As = 0.266-0.100+0.097 from the CHEOPS data, and Bond albedoAB = 0.057-0.101+0.083 from the Spitzer phase curve.Although small, the Ag and As indicate that MASCARA-1 b is more reflective than most other ultra-hot Jupiters, where H- absorption is expected to dominate. Conclusions. Where possible, priors informed by Doppler tomography should be used when fitting transits of fast-rotating stars, though multi-colour photometry may also unlock an accurate measurement of ψ. Our approach to modelling the phase variations at different wavelengths provides a template for how to separate thermal emission from reflected light in spectrally resolved James Webb Space Telescope phase curve data.
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| 15. |
- Hoyer, S., et al.
(author)
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Characterization of the HD 108236 system with CHEOPS and TESS Confirmation of a fifth transiting planet
- 2022
-
In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 668
-
Journal article (peer-reviewed)abstract
- Context. The HD 108236 system was first announced with the detection of four small planets based on TESS data. Shortly after, the transit of an additional planet with a period of 29.54 d was serendipitously detected by CHEOPS. In this way, HD 108236 (V = 9.2) became one of the brightest stars known to host five small transiting planets (Rp < 3 Ro˙). Aims. We characterize the planetary system by using all the data available from CHEOPS and TESS space missions. We use the flexible pointing capabilities of CHEOPS to follow up the transits of all the planets in the system, including the fifth transiting body. Methods. After updating the host star parameters by using the results from Gaia eDR3, we analyzed 16 and 43 transits observed by CHEOPS and TESS, respectively, to derive the planets' physical and orbital parameters. We carried out a timing analysis of the transits of each of the planets of HD 108236 to search for the presence of transit timing variations. Results. We derived improved values for the radius and mass of the host star (R∗ = 0.876 ± 0.007 R0 and M∗ = 0.867-0.046+0.047M). We confirm the presence of the fifth transiting planet f in a 29.54 d orbit. Thus, the HD 108236 system consists of five planets of Rb = 1.587±0.028, Rc = 2.122±0.025, Rd = 2.629 ± 0.031, Re = 3.008 ± 0.032, and Rf = 1.89 ± 0.04 [Ro˙]. We refine the transit ephemeris for each planet and find no significant transit timing variations for planets c, d, and e. For planets b and f, instead, we measure significant deviations on their transit times (up to 22 and 28 min, respectively) with a non-negligible dispersion of 9.6 and 12.6 min in their time residuals. Conclusions. We confirm the presence of planet f and find no significant evidence for a potential transiting planet in a 10.9 d orbital period, as previously suggested. Further monitoring of the transits, particularly for planets b and f, would confirm the presence of the observed transit time variations. HD 108236 thus becomes a key multi-planetary system for the study of formation and evolution processes. The reported precise results on the planetary radii - together with a profuse RV monitoring - will allow for an accurate characterization of the internal structure of these planets.
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| 16. |
- Leleu, A., et al.
(author)
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Six transiting planets and a chain of Laplace resonances in TOI-178
- 2021
-
In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 649
-
Journal article (peer-reviewed)abstract
- Determining the architecture of multi-planetary systems is one of the cornerstones of understanding planet formation and evolution. Resonant systems are especially important as the fragility of their orbital configuration ensures that no significant scattering or collisional event has taken place since the earliest formation phase when the parent protoplanetary disc was still present. In this context, TOI-178 has been the subject of particular attention since the first TESS observations hinted at the possible presence of a near 2:3:3 resonant chain. Here we report the results of observations from CHEOPS, ESPRESSO, NGTS, and SPECULOOS with the aim of deciphering the peculiar orbital architecture of the system. We show that TOI-178 harbours at least six planets in the super-Earth to mini-Neptune regimes, with radii ranging from 1.152 to 2.87 Earth radii and periods of 1.91, 3.24, 6.56, 9.96, 15.23, and 20.71 days. All planets but the innermost one form a 2:4:6:9:12 chain of Laplace resonances, and the planetary densities show important variations from planet to planet, jumping from 1.02 to 0.177 times the Earth's density between planets c and d. Using Bayesian interior structure retrieval models, we show that the amount of gas in the planets does not vary in a monotonous way, contrary to what one would expect from simple formation and evolution models and unlike other known systems in a chain of Laplace resonances. The brightness of TOI-178 (H = 8.76 mag, J = 9.37 mag, V = 11.95 mag) allows for a precise characterisation of its orbital architecture as well as of the physical nature of the six presently known transiting planets it harbours. The peculiar orbital configuration and the diversity in average density among the planets in the system will enable the study of interior planetary structures and atmospheric evolution, providing important clues on the formation of super-Earths and mini-Neptunes. -0.070 -0.13 -0.23 -0.061 +0.073 +0.14 +0.28 +0.055
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| 17. |
- Lendl, M., et al.
(author)
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The hot dayside and asymmetric transit of WASP-189 b seen by CHEOPS
- 2020
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In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 643
-
Journal article (peer-reviewed)abstract
- The CHEOPS space mission dedicated to exoplanet follow-up was launched in December 2019, equipped with the capacity to perform photometric measurements at the 20 ppm level. As CHEOPS carries out its observations in a broad optical passband, it can provide insights into the reflected light from exoplanets and constrain the short-wavelength thermal emission for the hottest of planets by observing occultations and phase curves. Here, we report the first CHEOPS observation of an occultation, namely, that of the hot Jupiter WASP-189 b, a MP ≈ 2MJ planet orbiting an A-type star. We detected the occultation of WASP-189 b at high significance in individual measurements and derived an occultation depth of dF = 87.9 ± 4.3 ppm based on four occultations. We compared these measurements to model predictions and we find that they are consistent with an unreflective atmosphere heated to a temperature of 3435 ± 27 K, when assuming inefficient heat redistribution. Furthermore, we present two transits of WASP-189 b observed by CHEOPS. These transits have an asymmetric shape that we attribute to gravity darkening of the host star caused by its high rotation rate. We used these measurements to refine the planetary parameters, finding a ~25% deeper transit compared to the discovery paper and updating the radius of WASP-189 b to 1.619 ± 0.021RJ. We further measured the projected orbital obliquity to be λ = 86.4-4.4+2.9°, a value that is in good agreement with a previous measurement from spectroscopic observations, and derived a true obliquity of ψ = 85.4 ± 4.3°. Finally, we provide reference values for the photometric precision attained by the CHEOPS satellite: for the V = 6.6 mag star, and using a 1-h binning, we obtain a residual RMS between 10 and 17 ppm on the individual light curves, and 5.7 ppm when combining the four visits.
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| 18. |
- Luque, R., et al.
(author)
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A resonant sextuplet of sub-Neptunes transiting the bright star HD 110067
- 2023
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In: Nature. - 0028-0836 .- 1476-4687. ; 623:7989, s. 932-937
-
Journal article (peer-reviewed)abstract
- Planets with radii between that of the Earth and Neptune (hereafter referred to as ‘sub-Neptunes’) are found in close-in orbits around more than half of all Sun-like stars 1,2. However, their composition, formation and evolution remain poorly understood 3. The study of multiplanetary systems offers an opportunity to investigate the outcomes of planet formation and evolution while controlling for initial conditions and environment. Those in resonance (with their orbital periods related by a ratio of small integers) are particularly valuable because they imply a system architecture practically unchanged since its birth. Here we present the observations of six transiting planets around the bright nearby star HD 110067. We find that the planets follow a chain of resonant orbits. A dynamical study of the innermost planet triplet allowed the prediction and later confirmation of the orbits of the rest of the planets in the system. The six planets are found to be sub-Neptunes with radii ranging from 1.94R ⊕ to 2.85R ⊕. Three of the planets have measured masses, yielding low bulk densities that suggest the presence of large hydrogen-dominated atmospheres.
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| 19. |
- Meier Valdes, E., et al.
(author)
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Investigating the visible phase-curve variability of 55 Cnc e
- 2023
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In: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 677
-
Journal article (peer-reviewed)abstract
- Context. 55 Cnc e is an ultra-short period super-Earth transiting a Sun-like star. Previous observations in the optical range detected a time-variable flux modulation that is phased with the planetary orbital period, whose amplitude is too large to be explained by reflected light and thermal emission alone. Aims. The goal of the study is to investigate the origin of the variability and timescale of the phase-curve modulation in 55 Cnc e. To this end, we used the CHaracterising ExOPlanet Satellite (CHEOPS), whose exquisite photometric precision provides an opportunity to characterise minute changes in the phase curve from one orbit to the next. Methods. CHEOPS observed 29 individual visits of 55 Cnc e between March 2020 and February 2022. Based on these observations, we investigated the different processes that could be at the origin of the observed modulation. In particular, we built a toy model to assess whether a circumstellar torus of dust driven by radiation pressure and gravity might match the observed flux variability timescale. Results. We find that the phase-curve amplitude and peak offset of 55 Cnc e do vary between visits. The sublimation timescales of selected dust species reveal that silicates expected in an Earth-like mantle would not survive long enough to explain the observed phase-curve modulation. We find that silicon carbide, quartz, and graphite are plausible candidates for the circumstellar torus composition because their sublimation timescales are long. Conclusions. The extensive CHEOPS observations confirm that the phase-curve amplitude and offset vary in time. We find that dust could provide the grey opacity source required to match the observations. However, the data at hand do not provide evidence that circumstellar material with a variable grain mass per unit area causes the observed variability. Future observations with the James Webb Space Telescope (JWST) promise exciting insights into this iconic super-Earth.
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| 20. |
- Pagano, I., et al.
(author)
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Constraining the reflective properties of WASP-178 b using CHEOPS photometry
- 2024
-
In: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 682
-
Journal article (peer-reviewed)abstract
- Context. Multiwavelength photometry of the secondary eclipses of extrasolar planets is able to disentangle the reflected and thermally emitted light radiated from the planetary dayside. Based on this, we can measure the planetary geometric albedo Ag, which is an indicator of the presence of clouds in the atmosphere, and the recirculation efficiency ϵ, which quantifies the energy transport within the atmosphere. Aims. We measure Ag and ϵ for the planet WASP-178 b, a highly irradiated giant planet with an estimated equilibrium temperature of 2450 K. Methods. We analyzed archival spectra and the light curves collected by CHEOPS and TESS to characterize the host WASP-178, refine the ephemeris of the system, and measure the eclipse depth in the passbands of the two telescopes. Results. We measured a marginally significant eclipse depth of 70 ± 40 ppm in the TESS passband, and a statistically significant depth of 70 ± 20 ppm in the CHEOPS passband. Conclusions. Combining the eclipse-depth measurement in the CHEOPS (λeff = 6300 Å) and TESS (λeff = 8000 Å) passbands, we constrained the dayside brightness temperature of WASP-178 b in the 2250-2800 K interval. The geometric albedo 0.1< Ag<0.35 generally supports the picture that giant planets are poorly reflective, while the recirculation efficiency ϵ >0.7 makes WASP-178 b an interesting laboratory for testing the current heat-recirculation models.
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| 21. |
- Parviainen, H., et al.
(author)
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CHEOPS finds KELT-1b darker than expected in visible light: Discrepancy between the CHEOPS and TESS eclipse depths
- 2022
-
In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 668
-
Journal article (peer-reviewed)abstract
- Recent studies based on photometry from the Transiting Exoplanet Survey Satellite (TESS) have suggested that the dayside of KELT-1b, a strongly irradiated brown dwarf, is significantly brighter in visible light than what would be expected based on Spitzer observations in the infrared. We observed eight eclipses of KELT-1b with CHaracterising ExOPlanet Satellite (CHEOPS) to measure its dayside brightness temperature in the bluest passband observed so far, and we jointly modelled the CHEOPS photometry with the existing optical and near-infrared photometry from TESS, LBT, CFHT, and Spitzer. Our modelling has led to a self-consistent dayside spectrum for KELT-1b covering the CHEOPS, TESS, H, Ks, and Spitzer IRAC 3.6 and 4.5 μm bands, where our TESS, H, Ks, and Spitzer band estimates largely agree with the previous studies. However, we discovered a strong discrepancy between the CHEOPS and TESS bands. The CHEOPS observations yield a higher photometric precision than the TESS observations, but they do not show a significant eclipse signal, while a deep eclipse is detected in the TESS band. The derived TESS geometric albedo of 0.36-0.13+0.12 is difficult to reconcile with a CHEOPS geometric albedo that is consistent with zero because the two passbands have considerable overlap. Variability in cloud cover caused by the transport of transient nightside clouds to the dayside could provide an explanation for reconciling the TESS and CHEOPS geometric albedos, but this hypothesis needs to be tested by future observations.
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| 22. |
- Psaridi, A., et al.
(author)
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Discovery of two warm mini-Neptunes with contrasting densities orbiting the young K3V star TOI-815
- 2024
-
In: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 685
-
Journal article (peer-reviewed)abstract
- We present the discovery and characterization of two warm mini-Neptunes transiting the K3V star TOI-815 in a K–M binary system. Analysis of its spectra and rotation period reveal the star to be young, with an age of 200+−400200 Myr. TOI-815b has a 11.2-day period and a radius of 2.94 ± 0.05 R+ with transits observed by TESS, CHEOPS, ASTEP, and LCOGT. The outer planet, TOI-815c, has a radius of 2.62 ± 0.10 R+, based on observations of three nonconsecutive transits with TESS; targeted CHEOPS photometry and radial velocity follow-up with ESPRESSO were required to confirm the 35-day period. ESPRESSO confirmed the planetary nature of both planets and measured masses of 7.6 ± 1.5 M+ (ρP = 1.64+−003331 g cm−3) and 23.5 ± 2.4 M+ (ρP = 7.2+−1110 g cm−3), respectively. Thus, the planets have very different masses, which is unusual for compact multi-planet systems. Moreover, our statistical analysis of mini-Neptunes orbiting FGK stars suggests that weakly irradiated planets tend to have higher bulk densities compared to those undergoing strong irradiation. This could be ascribed to their cooler atmospheres, which are more compressed and denser. Internal structure modeling of TOI-815b suggests it likely has a H-He atmosphere that constitutes a few percent of the total planet mass, or higher if the planet is assumed to have no water. In contrast, the measured mass and radius of TOI-815c can be explained without invoking any atmosphere, challenging planetary formation theories. Finally, we infer from our measurements that the star is viewed close to pole-on, which implies a spin-orbit misalignment at the 3σ level. This emphasizes the peculiarity of the system’s orbital architecture, and probably hints at an eventful dynamical history.
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| 23. |
- Scandariato, Gaetano, et al.
(author)
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Phase curve and geometric albedo of WASP-43b measured with CHEOPS, TESS, and HST WFC3/UVIS
- 2022
-
In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 668
-
Journal article (peer-reviewed)abstract
- Context. Observations of the phase curves and secondary eclipses of extrasolar planets provide a window onto the composition and thermal structure of the planetary atmospheres. For example, the photometric observations of secondary eclipses lead to the measurement of the planetary geometric albedo, Ag, which is an indicator of the presence of clouds in the atmosphere. Aims. In this work, we aim to measure the Ag in the optical domain of WASP-43b, a moderately irradiated giant planet with an equilibrium temperature of ~1400 K. Methods. For this purpose, we analyzed the secondary eclipse light curves collected by CHEOPS together with TESS along with observations of the system and the publicly available photometry obtained with HST WFC3/UVIS. We also analyzed the archival infrared observations of the eclipses and retrieve the thermal emission spectrum of the planet. By extrapolating the thermal spectrum to the optical bands, we corrected for the optical eclipses for thermal emission and derived the optical Ag. Results. The fit of the optical data leads to a marginal detection of the phase-curve signal, characterized by an amplitude of 160 ± 60 ppm and 80a-? 50+60 ppm in the CHEOPS and TESS passbands, respectively, with an eastward phase shift of ~50 (1.5Ï ? detection). The analysis of the infrared data suggests a non-inverted thermal profile and solar-like metallicity. The combination of the optical and infrared analyses allows us to derive an upper limit for the optical albedo of Ag< 0.087, with a confidence of 99.9%. Conclusions. Our analysis of the atmosphere of WASP-43b places this planet in the sample of irradiated hot Jupiters, with monotonic temperature-pressure profile and no indication of condensation of reflective clouds on the planetary dayside.
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| 24. |
- Singh, V., et al.
(author)
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CHEOPS observations of KELT-20 b/MASCARA-2 b: An aligned orbit and signs of variability from a reflective day side
- 2024
-
In: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 683
-
Journal article (peer-reviewed)abstract
- Context. Occultations are windows of opportunity to indirectly peek into the dayside atmosphere of exoplanets. High-precision transit events provide information on the spin-orbit alignment of exoplanets around fast-rotating hosts. Aims. We aim to precisely measure the planetary radius and geometric albedo of the ultra-hot Jupiter (UHJ) KELT-20 b along with the spin-orbit alignment of the system. Methods. We obtained optical high-precision transits and occultations of KELT-20 b using CHEOPS observations in conjunction with simultaneous TESS observations. We interpreted the occultation measurements together with archival infrared observations to measure the planetary geometric albedo and dayside temperatures. We further used the host star's gravity-darkened nature to measure the system's obliquity. Results. We present a time-averaged precise occultation depth of 82 ± 6 ppm measured with seven CHEOPS visits and 131-7+8 from the analysis of all available TESS photometry. Using these measurements, we precisely constrain the geometric albedo of KELT-20 b to 0.26 ± 0.04 and the brightness temperature of the dayside hemisphere to 2566-80+77 K. Assuming Lambertian scattering law, we constrain the Bond albedo to 0.36-0.05+0.04 along with a minimal heat transfer to the night side (Ïμ = 0.14-0.10+0.13). Furthermore, using five transit observations we provide stricter constraints of 3 9 ± 1 1 deg on the sky-projected obliquity of the system. Conclusions. The aligned orbit of KELT-20 b is in contrast to previous CHEOPS studies that have found strongly inclined orbits for planets orbiting other A-type stars. The comparably high planetary geometric albedo of KELT-20 b corroborates a known trend of strongly irradiated planets being more reflective. Finally, we tentatively detect signs of temporal variability in the occultation depths, which might indicate variable cloud cover advecting onto the planetary day side.
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| 25. |
- Swayne, M.I., et al.
(author)
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The EBLM Project– XI. Mass, radius, and effective temperature measurements for 23 M-dwarf companions to solar-type stars observed with CHEOPS
- 2024
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In: Monthly Notices of the Royal Astronomical Society. - 0035-8711 .- 1365-2966. ; 528:4, s. 5703-5722
-
Journal article (peer-reviewed)abstract
- Observations of low-mass stars have frequently shown a disagreement between observed stellar radii and radii predicted by theoretical stellar structure models. This ‘radius inflation’ problem could have an impact on both stellar and exoplanetary science. We present the final results of our observation programme with the CHaracterising ExOPlanet Satellite (CHEOPS) to obtain high-precision light curves of eclipsing binaries with low-mass stellar companions (EBLMs). Combined with the spectroscopic orbits of the solar-type companions, we can derive the masses, radii, and effective temperatures of 23 M-dwarf stars. We use the PYCHEOPS data analysis software to analyse their primary and secondary occultations. For all but one target, we also perform analyses with Transiting Exoplanet Survey Satellite (TESS) light curves for comparison. We have assessed the impact of starspot-induced variation on our derived parameters and account for this in our radius and effective temperature uncertainties using simulated light curves. We observe trends in inflation with both metallicity and orbital separation. We also observe a strong trend in the difference between theoretical and observational effective temperatures with metallicity. There is no such trend with orbital separation. These results are not consistent with the idea that the observed inflation in stellar radius combines with lower effective temperature to preserve the luminosity predicted by low-mass stellar models. Our EBLM systems provide high-quality and homogeneous measurements that can be used in further studies of radius inflation.
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| 26. |
- Szabó, G.M., et al.
(author)
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The changing face of AU Mic b: Stellar spots, spin-orbit commensurability, and transit timing variations as seen by CHEOPS and TESS
- 2021
-
In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 654
-
Journal article (peer-reviewed)abstract
- AU Mic is a young planetary system with a resolved debris disc showing signs of planet formation and two transiting warm Neptunes near mean-motion resonances. Here we analyse three transits of AU Mic b observed with the CHaracterising ExOPlanet Satellite (CHEOPS), supplemented with sector 1 and 27 Transiting Exoplanet Survey Satellite (TESS) photometry, and the All-Sky Automated Survey from the ground. The refined orbital period of AU Mic b is 8.462995 ± 0.000003 d, whereas the stellar rotational period is Prot = 4.8367 ± 0.0006 d. The two periods indicate a 7:4 spin-orbit commensurability at a precision of 0.1%. Therefore, all transits are observed in front of one of the four possible stellar central longitudes. This is strongly supported by the observation that the same complex star-spot pattern is seen in the second and third CHEOPS visits that were separated by four orbits (and seven stellar rotations). Using a bootstrap analysis we find that flares and star spots reduce the accuracy of transit parameters by up to 10% in the planet-to-star radius ratio and the accuracy on transit time by 3-4 min. Nevertheless, occulted stellar spot features independently confirm the presence of transit timing variations (TTVs) with an amplitude of at least 4 min. We find that the outer companion, AU Mic c, may cause the observed TTVs.
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| 27. |
- Ulmer-Moll, S., et al.
(author)
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TOI-5678b: A 48-day transiting Neptune-mass planet characterized with CHEOPS and HARPS
- 2023
-
In: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 674
-
Journal article (peer-reviewed)abstract
- Context. A large sample of long-period giant planets has been discovered thanks to long-term radial velocity surveys, but only a few dozen of these planets have a precise radius measurement. Transiting gas giants are crucial targets for the study of atmospheric composition across a wide range of equilibrium temperatures and, more importantly, for shedding light on the formation and evolution of planetary systems. Indeed, compared to hot Jupiters, the atmospheric properties and orbital parameters of cooler gas giants are unaltered by intense stellar irradiation and tidal effects. Aims. We aim to identify long-period planets in the Transiting Exoplanet Survey Satellite (TESS) data as single or duo-transit events. Our goal is to solve the orbital periods of TESS duo-transit candidates with the use of additional space-based photometric observations and to collect follow-up spectroscopic observations in order to confirm the planetary nature and measure the mass of the candidates. Methods. We use the CHaracterising ExOPlanet Satellite (CHEOPS) to observe the highest-probability period aliases in order to discard or confirm a transit event at a given period. Once a period is confirmed, we jointly model the TESS and CHEOPS light curves along with the radial velocity datasets to measure the orbital parameters of the system and obtain precise mass and radius measurements. Results. We report the discovery of a long-period transiting Neptune-mass planet orbiting the G7-type star TOI-5678. Our spectroscopic analysis shows that TOI-5678 is a star with a solar metallicity. The TESS light curve of TOI-5678 presents two transit events separated by almost two years. In addition, CHEOPS observed the target as part of its Guaranteed Time Observation program. After four non-detections corresponding to possible periods, CHEOPS detected a transit event matching a unique period alias. Follow-up radial velocity observations were carried out with the ground-based high-resolution spectrographs CORALIE and HARPS. Joint modeling reveals that TOI-5678 hosts a 47.73 day period planet, and we measure an orbital eccentricity consistent with zero at 2σ. The planet TOI-5678 b has a mass of 20 ± 4 Earth masses (M) and a radius of 4.91 ± 0.08 R Using interior structure modeling, we find that TOI-5678 b is composed of a low-mass core surrounded by a large H/He layer with a mass of 3.2±1.7-1.3 M. Conclusions. TOI-5678 b is part of a growing sample of well-characterized transiting gas giants receiving moderate amounts of stellar insolation (11 S). Precise density measurement gives us insight into their interior composition, and the objects orbiting bright stars are suitable targets to study the atmospheric composition of cooler gas giants.
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| 28. |
- Van Grootel, V., et al.
(author)
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A search for transiting planets around hot subdwarfs: I. Methods and performance tests on light curves from Kepler, K2, TESS, and CHEOPS
- 2021
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In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 650
-
Journal article (peer-reviewed)abstract
- Context. Hot subdwarfs experienced strong mass loss on the red giant branch (RGB) and are now hot and small He-burning objects. These stars constitute excellent opportunities for addressing the question of the evolution of exoplanetary systems directly after the RGB phase of evolution. Aims. In this project we aim to perform a transit survey in all available light curves of hot subdwarfs from space-based telescopes (Kepler, K2, TESS, and CHEOPS) with our custom-made pipeline SHERLOCK in order to determine the occurrence rate of planets around these stars as a function of orbital period and planetary radius. We also aim to determine whether planets that were previously engulfed in the envelope of their red giant host star can survive, even partially, as a planetary remnant. Methods. For this first paper, we performed injection-and-recovery tests of synthetic transits for a selection of representative Kepler, K2, and TESS light curves to determine which transiting bodies in terms of object radius and orbital period we will be able to detect with our tools. We also provide estimates for CHEOPS data, which we analyzed with the pycheops package. Results. Transiting objects with a radius ≤ 1.0 R⊕ can be detected in most of the Kepler, K2, and CHEOPS targets for the shortest orbital periods (1 d and shorter), reaching values as low as ∼0.3 R⊕ in the best cases. Sub-Earth-sized bodies are only reached for the brightest TESS targets and for those that were observed in a significant number of sectors. We also give a series of representative results for larger planets at greater distances, which strongly depend on the target magnitude and on the length and quality of the data. Conclusions. The TESS sample will provide the most important statistics for the global aim of measuring the planet occurrence rate around hot subdwarfs. The Kepler, K2, and CHEOPS data will allow us to search for planetary remnants, that is, very close and small (possibly disintegrating) objects.
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