We present a precise characterization of the TOI-561 planetary system obtained by combining previously published data with TESS and CHEOPS photometry, and a new set of \(62\) HARPS-N radial ...velocities (RVs). Our joint analysis confirms the presence of four transiting planets, namely TOI-561 b (\(P = 0.45\) d, \(R = 1.42\) R\(_\oplus\), \(M = 2.0\) M\(_\oplus\)), c (\(P = 10.78\) d, \(R = 2.91\) R\(_\oplus\), \(M = 5.4\) M\(_\oplus\)), d (\(P = 25.7\) d, \(R = 2.82\) R\(_\oplus\), \(M = 13.2\) M\(_\oplus\)) and e (\(P = 77\) d, \(R = 2.55\) R\(_\oplus\), \(M = 12.6\) M\(_\oplus\)). Moreover, we identify an additional, long-period signal (\(>450\) d) in the RVs, which could be due to either an external planetary companion or to stellar magnetic activity. The precise masses and radii obtained for the four planets allowed us to conduct interior structure and atmospheric escape modelling. TOI-561 b is confirmed to be the lowest density (\(\rho_{\rm b} = 3.8 \pm 0.5\) g cm\(^{-3}\)) ultra-short period (USP) planet known to date, and the low metallicity of the host star makes it consistent with the general bulk density-stellar metallicity trend. According to our interior structure modelling, planet b has basically no gas envelope, and it could host a certain amount of water. In contrast, TOI-561 c, d, and e likely retained an H/He envelope, in addition to a possibly large water layer. The inferred planetary compositions suggest different atmospheric evolutionary paths, with planets b and c having experienced significant gas loss, and planets d and e showing an atmospheric content consistent with the original one. The uniqueness of the USP planet, the presence of the long-period planet TOI-561 e, and the complex architecture make this system an appealing target for follow-up studies.
The ultracool dwarf star TRAPPIST-1 hosts seven Earth-size transiting planets, some of which could harbour liquid water on their surfaces. UV observations are essential to measure their high-energy ...irradiation, and to search for photodissociated water escaping from their putative atmospheres. Our new observations of TRAPPIST-1 Ly-\(\alpha\) line during the transit of TRAPPIST-1c show an evolution of the star emission over three months, preventing us from assessing the presence of an extended hydrogen exosphere. Based on the current knowledge of the stellar irradiation, we investigated the likely history of water loss in the system. Planets b to d might still be in a runaway phase, and planets within the orbit of TRAPPIST-1g could have lost more than 20 Earth oceans after 8 Gyr of hydrodynamic escape. However, TRAPPIST-1e to h might have lost less than 3 Earth oceans if hydrodynamic escape stopped once they entered the habitable zone. We caution that these estimates remain limited by the large uncertainty on the planet masses. They likely represent upper limits on the actual water loss because our assumptions maximize the XUV-driven escape, while photodissociation in the upper atmospheres should be the limiting process. Late-stage outgassing could also have contributed significant amounts of water for the outer, more massive planets after they entered the habitable zone. While our results suggest that the outer planets are the best candidates to search for water with the JWST, they also highlight the need for theoretical studies and complementary observations in all wavelength domains to determine the nature of the TRAPPIST-1 planets, and their potential habitability.
We present sixteen occultation and three transit light curves for the ultra-short period hot Jupiter WASP-103 b, in addition to five new radial velocity measurements. We combine these observations ...with archival data and perform a global analysis of the resulting extensive dataset, accounting for the contamination from a nearby star. We detect the thermal emission of the planet in both the \(z'\) and \(K_{\mathrm{S}}\)-bands, the measured occultation depths being 699\(\pm\)110 ppm (6.4-\(\sigma\)) and \(3567_{-350}^{+400}\) ppm (10.2-\(\sigma\)), respectively. We use these two measurements together with recently published HST/WFC3 data to derive joint constraints on the properties of WASP-103 b's dayside atmosphere. On one hand, we find that the \(z'\)-band and WFC3 data are best fit by an isothermal atmosphere at 2900 K or an atmosphere with a low H\(_2\)O abundance. On the other hand, we find an unexpected excess in the \(K_{\mathrm{S}}\)-band measured flux compared to these models, which requires confirmation with additional observations before any interpretation can be given. From our global data analysis, we also derive a broad-band optical transmission spectrum that shows a minimum around 700 nm and increasing values towards both shorter and longer wavelengths. This is in agreement with a previous study based on a large fraction of the archival transit light curves used in our analysis. The unusual profile of this transmission spectrum is poorly matched by theoretical spectra and is not confirmed by more recent observations at higher spectral resolution. Additional data, both in emission and transmission, are required to better constrain the atmospheric properties of WASP-103 b.
We present 17 transit light curves of seven known warm-Jupiters observed with the CHaracterising ExOPlanet Satellite (CHEOPS). The light curves have been collected as part of the CHEOPS Guaranteed ...Time Observation (GTO) program that searches for transit-timing variation (TTV) of warm-Jupiters induced by a possible external perturber to shed light on the evolution path of such planetary systems. We describe the CHEOPS observation process, from the planning to the data analysis. In this work we focused on the timing performance of CHEOPS, the impact of the sampling of the transit phases, and the improvement we can obtain combining multiple transits together. We reached the highest precision on the transit time of about 13-16 s for the brightest target (WASP-38, G = 9.2) in our sample. From the combined analysis of multiple transits of fainter targets with G >= 11 we obtained a timing precision of about 2 min. Additional observations with CHEOPS, covering a longer temporal baseline, will further improve the precision on the transit times and will allow us to detect possible TTV signals induced by an external perturber.
Context: Transmission spectroscopy has proven to be a useful tool for the study of exoplanet atmospheres, and has lead to the detection of a small number of elements and molecules (Na, K, H\(_2\)O), ...but also revealed that many planets show flat transmission spectra consistent with the presence of opaque high-altitude hazes or clouds. Aims: We apply this technique to the \(M_P=0.38 M_{jup}\), \(R_p=1.12 R_{jup}\), \(P=2.78d\) planet WASP-49b, aiming to characterize its transmission spectrum between 0.73 and 1 \(\mathrm{\mu}\)m and search for the features of K and H\(_2\)O. Methods: Three transits of WASP-49b have been observed with the FORS2 instrument installed at the VLT/UT1 telescope at the ESO Paranal site. We used FORS2 in MXU mode with grism GRIS_600z, producing simultaneous multiwavelength transit lightcurves throughout the i' and z' bands. We combined these data with independent broadband photometry from the Euler and TRAPPIST telescopes to obtain a good measurement of the transit shape. Strong correlated noise structures are present in the FORS2 lightcurves, which are due to rotating flat-field structures that are introduced by inhomogeneities of the linear atmospheric dispersion corrector's transparency. We accounted for these structures by constructing common noise models from the residuals of lightcurves bearing the same noise structures, and used them together with simple parametric models to infer the transmission spectrum. Results: We present three independent transmission spectra of WASP-49b between 0.73 and 1.02 \(\mu m\), as well as a transmission spectrum between 0.65 and 1.02 \(\mu m\) from the combined analysis of FORS2 and broadband data. The results obtained from the three individual epochs agree well. The transmission spectrum of WASP-49b is best fit by atmospheric models containing a cloud deck at pressure levels of 1 mbar or lower.
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.
The Astronomical Journal, Volume 156, Number 5, Published 2018
October 22 The TRAPPIST-1 planetary system represents an exceptional opportunity for the
atmospheric characterization of temperate ...terrestrial exoplanets with the
upcoming James Webb Space Telescope (JWST). Assessing the potential impact of
stellar contamination on the planets' transit transmission spectra is an
essential precursor step to this characterization. Planetary transits
themselves can be used to scan the stellar photosphere and to constrain its
heterogeneity through transit depth variations in time and wavelength. In this
context, we present our analysis of 169 transits observed in the optical from
space with K2 and from the ground with the SPECULOOS and Liverpool telescopes.
Combining our measured transit depths with literature results gathered in the
mid/near-IR with Spitzer/IRAC and HST/WFC3, we construct the broadband
transmission spectra of the TRAPPIST-1 planets over the 0.8-4.5 $\mu$m spectral
range. While planets b, d, and f spectra show some structures at the 200-300ppm
level, the four others are globally flat. Even if we cannot discard their
instrumental origins, two scenarios seem to be favored by the data: a stellar
photosphere dominated by a few high-latitude giant (cold) spots, or,
alternatively, by a few small and hot (3500-4000K) faculae. In both cases, the
stellar contamination of the transit transmission spectra is expected to be
less dramatic than predicted in recent papers. Nevertheless, based on our
results, stellar contamination can still be of comparable or greater order than
planetary atmospheric signals at certain wavelengths. Understanding and
correcting the effects of stellar heterogeneity therefore appears essential to
prepare the exploration of TRAPPIST-1's with JWST.
We present here the detection of a system of four low-mass planets around the bright (V=5.5) and close-by (6.5 pc) star HD219134. This is the first result of the Rocky Planet Search program with ...HARPS-N on the TNG in La Palma. The inner planet orbits the star in 3.0937 +/-0.0004 days, on a quasi-circular orbit with a semi-major axis of 0.0382 +/- 0.0003 AU. Spitzer observations allowed us to detect the transit of the planet in front of the star making HD219134b the nearest known transiting planet to date. From the amplitude of the radial-velocity variation (2.33 +/- 0.24 m/s) and observed depth of the transit (359 +/- 38 ppm), the planet mass and radius are estimated to be 4.46 +/- 0.47 M_{\oplus} and 1.606 +/- 0.086 R_{\oplus} leading to a mean density of 5.89 +/- 1.17 g/cc, suggesting a rocky composition. One additional planet with minimum mass of 2.67 +/- 0.59 M_{\oplus} moves on a close-in, quasi-circular orbit with a period of 6.765 +/- 0.005 days. The third planet in the system has a period of 46.78 +/- 0.16 days and a minimum mass of 8.7 +/- 1.1 M{\oplus}, at 0.234 +/- 0.002 AU from the star. Its eccentricity is 0.32 +/- 0.14. The period of this planet is close to the rotational period of the star estimated from variations of activity indicators (42.3 +/- 0.1 days). The planetary origin of the signal is, however, the preferred solution as no indication of variation at the corresponding frequency is observed for activity-sensitive parameters. Finally, a fourth additional longer-period planet of mass of 62 +/- 6 M_{\oplus} orbits the star in 1190 days, on an eccentric orbit (e=0.27 +/- 0.11) at a distance of 2.14 +/- 0.27 AU.
