| 1. |
- Alonso, R., et al.
(författare)
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No random transits in CHEOPS observations of HD 139139
- 2023
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Ingår i: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 680
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Tidskriftsartikel (refereegranskat)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 (similar to 200 ppm - equivalent to transiting objects with radii of similar to 1.5 R-circle plus 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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| 2. |
- Cabrera, J., et al.
(författare)
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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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Ingår i: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 675
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Tidskriftsartikel (refereegranskat)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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| 3. |
- Sicardy, B., et al.
(författare)
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Constraints on the evolution of the Triton atmosphere from occultations : 1989-2022
- 2024
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Ingår i: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 682
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Tidskriftsartikel (refereegranskat)abstract
- Context. In about 2000, the south pole of Triton experienced an extreme summer solstice that occurs every ∼650 years, when the subsolar latitude reached about 50°S. Bracketing this epoch, a few occultations probed the Triton atmosphere in 1989, 1995, 1997, 2008, and 2017. A recent ground-based stellar occultation observed on 6 October 2022 provides a new measurement of the atmospheric pressure on Triton. This is presented here.Aims. The goal is to constrain the volatile transport models (VTMs) of the Triton atmosphere. The atmosphere is basically in vapor pressure equilibrium with the nitrogen ice at its surface.Methods. Fits to the occultation light curves yield the atmospheric pressure of Triton at the reference radius 1400 km, from which the surface pressure is deduced.Results. The fits provide a pressure p1400 = 1.211 ± 0.039 μbar at radius 1400 km (47 km altitude), from which a surface pressure of psurf = 14.54 ± 0.47 μbar is deduced (1σ error bars). To within the error bars, this is identical to the pressure derived from the previous occultation of 5 October 2017, p1400 = 1.18 ± 0.03 μbar and psurf = 14.1 ± 0.4 μbar, respectively. Based on recent models of the volatile cycles of Triton, the overall evolution of the surface pressure over the last 30 years is consistent with N2 condensation taking place in the northern hemisphere. However, models typically predict a steady decrease in the surface pressure for the period 2005-2060, which is not confirmed by this observation. Complex surface-atmosphere interactions, such as ice albedo runaway and formation of local N2 frosts in the equatorial regions of Triton, could explain the relatively constant pressure between 2017 and 2022.
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