Context. Measurements of the occultation of an exoplanet at visible wavelengths allow us to determine the reflective properties of a planetary atmosphere. The observed occultation depth can be ...translated into a geometric albedo. This in turn aids in characterising the structure and composition of an atmosphere by providing additional information on the wavelength-dependent reflective qualities of the aerosols in the atmosphere. Aims. Our aim is to provide a precise measurement of the geometric albedo of the gas giant HD 189733b by measuring the occultation depth in the broad optical bandpass of CHEOPS (350 - 1100 nm). Methods. We analysed 13 observations of the occultation of HD 189733b performed by CHEOPS utilising the Python package PyCHEOPS. The resulting occultation depth is then used to infer the geometric albedo accounting for the contribution of thermal emission from the planet. We also aid the analysis by refining the transit parameters combining observations made by the TESS and CHEOPS space telescopes. Results. We report the detection of an \(24.7 \pm 4.5\) ppm occultation in the CHEOPS observations. This occultation depth corresponds to a geometric albedo of \(0.076 \pm 0.016\). Our measurement is consistent with models assuming the atmosphere of the planet to be cloud-free at the scattering level and absorption in the CHEOPS band to be dominated by the resonant Na doublet. Taking into account previous optical-light occultation observations obtained with the Hubble Space Telescope, both measurements combined are consistent with a super-stellar Na elemental abundance in the dayside atmosphere of HD 189733b. We further constrain the planetary Bond albedo to between 0.013 and 0.42 at 3\(\sigma\) confidence.
HD\(\,\)172555 is a young (\(\sim\)20\(\,\)Myr) A7V star surrounded by a 10\(\,\)au wide debris disk suspected to be replenished partly by collisions between large planetesimals. Small evaporating ...transiting bodies, exocomets, have also been detected in this system by spectroscopy. After \(\beta\,\)Pictoris, this is another example of a system possibly witnessing a phase of heavy bombardment of planetesimals. In such system, small bodies trace dynamical evolution processes. We aim at constraining their dust content by using transit photometry. We performed a 2-day-long photometric monitoring of HD\(\,\)172555 with the CHEOPS space telescope in order to detect shallow transits of exocomets with a typical expected duration of a few hours. The large oscillations in the lightcurve indicate that HD\(\,\)172555 is a \(\delta\,\)Scuti pulsating star. Once removing those dominating oscillations, we find a hint for a transient absorption. If fitted with an exocomet transit model, it corresponds to an evaporating body passing near the star at a distance of \(6.8\pm1.4\,\)R\(_\star\) (or \(0.05\pm 0.01\,\)au) with a radius of 2.5 km. These properties are comparable to those of the exocomets already found in this system using spectroscopy, as well as those found in the \(\beta\,\)Pic system. The nuclei of solar system's Jupiter family comets, with radii of 2-6\(\,\)km, are also comparable in size. This is the first evidence for an exocomet photometric transit detection in the young system of HD\(\,\)172555.
DE Boo is a unique system, with an edge-on view through the debris disk around the star. The disk, which is analogous to the Kuiper belt in the Solar System, was reported to extend from 74 to 84 AU ...from the central star. The high photometric precision of the Characterising Exoplanet Satellite (CHEOPS) provided an exceptional opportunity to observe small variations in the light curve due to transiting material in the disk. This is a unique chance to investigate processes in the debris disk. Photometric observations of DE Boo of a total of four days were carried out with CHEOPS. Photometric variations due to spots on the stellar surface were subtracted from the light curves by applying a two-spot model and a fourth-order polynomial. The photometric observations were accompanied by spectroscopic measurements with the 1m RCC telescope at Piszkéstető and with the SOPHIE spectrograph in order to refine the astrophysical parameters of DE Boo. We present a detailed analysis of the photometric observation of DE Boo. We report the presence of nonperiodic transient features in the residual light curves with a transit duration of 0.3-0.8 days. We calculated the maximum distance of the material responsible for these variations to be 2.47 AU from the central star, much closer than most of the mass of the debris disk. Furthermore, we report the first observation of flaring events in this system. We interpreted the transient features as the result of scattering in an inner debris disk around DE Boo. The processes responsible for these variations were investigated in the context of interactions between planetesimals in the system.
Stellar granulation generates fluctuations in photometric and spectroscopic data whose properties depend on the stellar type, composition, and evolutionary state. In this study, we aim to detect the ...signatures of stellar granulation, link spectroscopic and photometric signatures of convection for main-sequence stars, and test predictions from 3D hydrodynamic models. For the first time, we observed two bright stars (Teff = 5833 K and 6205 K) with high-precision observations taken simultaneously with CHEOPS and ESPRESSO. We analyzed the properties of the stellar granulation signal in each individual data set. We compared them to Kepler observations and 3D hydrodynamic models. While isolating the granulation-induced changes by attenuating the p-mode oscillation signals, we studied the relationship between photometric and spectroscopic observables. The signature of stellar granulation is detected and precisely characterized for the hotter F star in the CHEOPS and ESPRESSO observations. For the cooler G star, we obtain a clear detection in the CHEOPS dataset only. The TESS observations are blind to this stellar signal. Based on CHEOPS observations, we show that the inferred properties of stellar granulation are in agreement with both Kepler observations and hydrodynamic models. Comparing their periodograms, we observe a strong link between spectroscopic and photometric observables. Correlations of this stellar signal in the time domain (flux vs RV) and with specific spectroscopic observables (shape of the cross-correlation functions) are however difficult to isolate due to signal-to-noise dependent variations. In the context of the upcoming PLATO mission and the extreme precision RV surveys, a thorough understanding of the properties of the stellar granulation signal is needed. The CHEOPS and ESPRESSO observations pave the way for detailed analyses of this stellar process.
A&A 671, A154 (2023) The planetary system around the naked-eye star $\nu^2$ Lupi (HD 136352;
TOI-2011) is composed of three exoplanets with masses of 4.7, 11.2, and 8.6
Earth masses. The TESS and ...CHEOPS missions revealed that all three planets are
transiting and have radii straddling the radius gap separating volatile-rich
and volatile-poor super-earths. Only a partial transit of planet d had been
covered so we re-observed an inferior conjunction of the long-period 8.6
Earth-mass exoplanet $\nu^2$ Lup d with the CHEOPS space telescope. We
confirmed its transiting nature by covering its whole 9.1 h transit for the
first time. We refined the planet transit ephemeris to P = 107.1361
(+0.0019/-0.0022) days and Tc = 2,459,009.7759 (+0.0101/-0.0096) BJD_TDB,
improving by ~40 times on the previously reported transit timing uncertainty.
This refined ephemeris will enable further follow-up of this outstanding
long-period transiting planet to search for atmospheric signatures or explore
the planet's Hill sphere in search for an exomoon. In fact, the CHEOPS
observations also cover the transit of a large fraction of the planet's Hill
sphere, which is as large as the Earth's, opening the tantalising possibility
of catching transiting exomoons. We conducted a search for exomoon signals in
this single-epoch light curve but found no conclusive photometric signature of
additional transiting bodies larger than Mars. Yet, only a sustained follow-up
of $\nu^2$ Lup d transits will warrant a comprehensive search for a moon around
this outstanding exoplanet.
We present the Young Exoplanet Transit Initiative (YETI), in which we use several 0.2 to 2.6m telescopes around the world to monitor continuously young (< 100 Myr), nearby (< 1 kpc) stellar clusters ...mainly to detect young transiting planets (and to study other variability phenomena on time-scales from minutes to years). The telescope network enables us to observe the targets continuously for several days in order not to miss any transit. The runs are typically one to two weeks long, about three runs per year per cluster in two or three subsequent years for about ten clusters. There are thousands of stars detectable in each field with several hundred known cluster members, e.g. in the first cluster observed, Tr-37, a typical cluster for the YETI survey, there are at least 469 known young stars detected in YETI data down to R=16.5 mag with sufficient precision of 50 milli-mag rms (5 mmag rms down to R=14.5 mag) to detect transits, so that we can expect at least about one young transiting object in this cluster. If we observe 10 similar clusters, we can expect to detect approximately 10 young transiting planets with radius determinations. The precision given above is for a typical telescope of the YETI network, namely the 60/90-cm Jena telescope (similar brightness limit, namely within +/-1 mag, for the others) so that planetary transits can be detected. For planets with mass and radius determinations, we can calculate the mean density and probe the internal structure. We aim to constrain planet formation models and their time-scales by discovering planets younger than 100 Myr and determining not only their orbital parameters, but also measuring their true masses and radii, which is possible so far only by the transit method. Here, we present an overview and first results. (Abstract shortened)
Past occultation and phase-curve observations of the ultra-short period super-Earth 55 Cnc e obtained at visible and infrared wavelengths have been challenging to reconcile with a planetary ...reflection and emission model. In this study, we analyse a set of 41 occultations obtained over a two-year timespan with the CHEOPS satellite. We report the detection of 55 Cnc e's occultation with an average depth of \(12\pm3\) ppm. We derive a corresponding 2-\(\sigma\) upper limit on the geometric albedo of \(A_g < 0.55\) once decontaminated from the thermal emission measured by Spitzer at 4.5\(\mu\)m. CHEOPS's photometric performance enables, for the first time, the detection of individual occultations of this super-Earth in the visible and identifies short-timescale photometric corrugations likely induced by stellar granulation. We also find a clear 47.3-day sinusoidal pattern in the time-dependent occultation depths that we are unable to relate to stellar noise, nor instrumental systematics, but whose planetary origin could be tested with upcoming JWST occultation observations of this iconic super-Earth.
We report the discovery of a third planet transiting the star TOI-1260, previously known to host two transiting sub-Neptune planets with orbital periods of 3.127 and 7.493 days, respectively. The ...nature of the third transiting planet with a 16.6-day orbit is supported by ground-based follow-up observations, including time-series photometry, high-angular resolution images, spectroscopy, and archival imagery. Precise photometric monitoring with CHEOPS allows to improve the constraints on the parameters of the system, improving our knowledge on their composition. The improved radii of TOI-1260b, TOI-1260c are \(2.36 \pm 0.06 \rm R_{\oplus}\), \(2.82 \pm 0.08 \rm R_{\oplus}\), respectively while the newly discovered third planet has a radius of \(3.09 \pm 0.09 \rm R_{\oplus}\). The radius uncertainties are in the range of 3\%, allowing a precise interpretation of the interior structure of the three planets. Our planet interior composition model suggests that all three planets in the TOI-1260 system contains some fraction of gas. The innermost planet TOI-1260b has most likely lost all of its primordial hydrogen-dominated envelope. Planets c and d were also likely to have experienced significant loss of atmospheric through escape, but to a lesser extent compared to planet b.
Tidal orbital decay is suspected to occur especially for hot Jupiters, with the only observationally confirmed case of this being WASP-12 b. By examining this effect, information on the properties of ...the host star can be obtained using the so-called stellar modified tidal quality factor \(Q_*'\), which describes the efficiency with which kinetic energy of the planet is dissipated within the star. This can help to get information about the interior of the star. In this study, we aim to improve constraints on the tidal decay of the KELT-9, KELT-16 and WASP-4 systems, to find evidence for or against the presence of this particular effect. With this, we want to constrain each star's respective \(Q_*'\) value. In addition to that, we also aim to test the existence of the transit timing variations (TTVs) in the HD 97658 system, which previously favoured a quadratic trend with increasing orbital period. Making use of newly acquired photometric observations from CHEOPS and TESS, combined with archival transit and occultation data, we use Markov chain Monte Carlo (MCMC) algorithms to fit three models, a constant period model, an orbital decay model, and an apsidal precession model, to the data. We find that the KELT-9 system is best described by an apsidal precession model for now, with an orbital decay trend at over 2 \(\sigma\) being a possible solution as well. A Keplerian orbit model with a constant orbital period fits the transit timings of KELT-16 b the best due to the scatter and scale of their error bars. The WASP-4 system is represented the best by an orbital decay model at a 5 \(\sigma\) significance, although apsidal precession cannot be ruled out with the present data. For HD 97658 b, using recently acquired transit observations, we find no conclusive evidence for a previously suspected strong quadratic trend in the data.
Observations of the phase curves and secondary eclipses of extrasolar planets provide a window on 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 \(A_g\), which is an indicator of the presence of clouds in the atmosphere. In this work we aim to measure the \(A_g\) in the optical domain of WASP-43b, a moderately irradiated giant planet with an equilibrium temperature of \(\sim\)1400~K. To this purpose, we analyze the secondary eclipse light curves collected by CHEOPS, together with TESS observations of the system and the publicly available photometry obtained with HST WFC3/UVIS. We also analyze 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 correct the optical eclipses for thermal emission and derive the optical \(A_g\). The fit of the optical data leads to a marginal detection of the phase curve signal, characterized by an amplitude of \(160\pm60\)~ppm and 80\(^{+60}_{-50}\)~ppm in the CHEOPS and TESS passband respectively, with an eastward phase shift of \(\sim50^\circ\) (1.5\(\sigma\) detection). The analysis of the infrared data suggests a non-inverted thermal profile and solar-like metallicity. The combination of optical and infrared analysis allows us to derive an upper limit for the optical albedo of \(A_g<0.087\) with a confidence of 99.9\%. 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.
