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Brandeker, A., Lendl, M., Patel, J. A. & Olofsson, G. (2023). 55 Cancri e's occultation captured with CHEOPS. Astronomy and Astrophysics, 669, Article ID A64.
Open this publication in new window or tab >>55 Cancri e's occultation captured with CHEOPS
2023 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 669, article id A64Article in journal (Refereed) Published
Abstract [en]

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 ± 3 ppm. We derive a corresponding 2σ upper limit on the geometric albedo of Ag < 0.55 once decontaminated from the thermal emission measured by Spitzer at 4.5 µm. 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.

Keywords
planets and satellites: individual: 55 Cnc e, techniques: photometric, methods: observational
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:su:diva-215723 (URN)10.1051/0004-6361/202244894 (DOI)000927949800004 ()2-s2.0-85146369927 (Scopus ID)
Available from: 2023-03-27 Created: 2023-03-27 Last updated: 2023-03-27Bibliographically approved
Morgado, B. E., Brandeker, A., Florén, H. G., Olofsson, G. & de Wit, J. (2023). A dense ring of the trans-Neptunian object Quaoar outside its Roche limit. Nature, 614(7947), 239-243
Open this publication in new window or tab >>A dense ring of the trans-Neptunian object Quaoar outside its Roche limit
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2023 (English)In: Nature, ISSN 0028-0836, E-ISSN 1476-4687, Vol. 614, no 7947, p. 239-243Article in journal (Refereed) Published
Abstract [en]

In our efforts to characterize Quaoar’s shape and search for putative material around it, we have predicted and observed several stellar occultations by this body. Following a report from Australia of a Neptune-like ring detected during a 2021 occultation and independently suspected in 2019, we have identified secondary events in previous occultations observed between 2018 and 2020. They are consistent with a circular ring centred on the body, with two possible mirror solutions for the ring orientation. Both solutions have radii close to 4,100 km, or roughly 7.4 Quaoar radii. One solution has a ring pole that presents a large mismatch with Weywot’s orbital pole, whereas the other solution is consistent with a ring coplanar with Weywot’s orbit. This is our preferred solution, as a primordial collisional system surrounding Quaoar is expected to settle in a disc that subsequently forms both the ring and Weywot.

National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:su:diva-216054 (URN)10.1038/s41586-022-05629-6 (DOI)000941028700001 ()36755175 (PubMedID)2-s2.0-85147724719 (Scopus ID)
Available from: 2023-03-31 Created: 2023-03-31 Last updated: 2023-03-31Bibliographically approved
Ehrenreich, D., Olofsson, G., Brandeker, A., Florén, H. G. & Walton, N. A. (2023). A full transit of v2 Lupi d and the search for an exomoon in its Hill sphere with CHEOPS. Astronomy and Astrophysics, 671, Article ID A154.
Open this publication in new window or tab >>A full transit of v2 Lupi d and the search for an exomoon in its Hill sphere with CHEOPS
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2023 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 671, article id A154Article in journal (Refereed) Published
Abstract [en]

The planetary system around the naked-eye star v2 Lupi (HD 136352; TOI-2011) is composed of three exoplanets with masses of 4.7, 11.2, and 8.6 Earth masses (M). 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 M exoplanet v2 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 = 107.1361−0.0022+0.0019 days and Tc = 2459009.7759−0.0096+0.0101 BJDTDB, 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 v2 Lup d transits will warrant a comprehensive search for a moon around this outstanding exoplanet.

Keywords
planets and satellites: detection, planets and satellites: individual: HD 136352, planets and satellites: general
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:su:diva-220589 (URN)10.1051/0004-6361/202244790 (DOI)000982504800001 ()2-s2.0-85150788165 (Scopus ID)
Available from: 2023-08-31 Created: 2023-08-31 Last updated: 2023-08-31Bibliographically approved
Brandeker, A. & Olofsson, G. (2023). A new dynamical modeling of the WASP-47 system with CHEOPS observations star. Astronomy and Astrophysics, 673, Article ID A42.
Open this publication in new window or tab >>A new dynamical modeling of the WASP-47 system with CHEOPS observations star
2023 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 673, article id A42Article in journal (Refereed) Published
Abstract [en]

Among the hundreds of known hot Jupiters (HJs), only five have been found to have companions on short-period orbits. Within this rare class of multiple planetary systems, the architecture of WASP-47 is unique, hosting an HJ (planet-b) with both an inner and an outer sub-Neptunian mass companion (-e and -d, respectively) as well as an additional non-transiting, long-period giant (-c). The small period ratio between planets -b and -d boosts the transit time variation (TTV) signal, making it possible to reliably measure the masses of these planets in synergy with the radial velocity (RV) technique. In this paper, we present new space- and ground-based photometric data of WASP-47b and WASP-47-d, including 11 unpublished light curves from the ESA mission CHaracterising ExOPlanet Satellite (CHEOPS). We analyzed the light curves in a homogeneous way together with all the publicly available data to carry out a global N-body dynamical modeling of the TTV and RV signals. We retrieved, among other parameters, a mass and density for planet -d of Md = 15.5 ± 0.8 M and ρd = 1.69 ± 0.22 g cm−3, which is in good agreement with the literature and consistent with a Neptune-like composition. For the inner planet (-e), we found a mass and density of Me = 9.0 ± 0.5 M and ρe = 8.1 ± 0.5 g cm−3, suggesting an Earth-like composition close to other ultra-hot planets at similar irradiation levels. Though this result is in agreement with previous RV plus TTV studies, it is not in agreement with the most recent RV analysis (at 2.8σ), which yielded a lower density compatible with a pure silicate composition. This discrepancy highlights the still unresolved issue of suspected systematic offsets between RV and TTV measurements. In this paper, we also significantly improve the orbital ephemerides of all transiting planets, which will be crucial for any future follow-up.

Keywords
techniques : photometric, planets and satellites : detection, planets and satellites : general
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:su:diva-219592 (URN)10.1051/0004-6361/202245486 (DOI)000983106000011 ()2-s2.0-85159559703 (Scopus ID)
Available from: 2023-07-26 Created: 2023-07-26 Last updated: 2023-07-26Bibliographically approved
Oddo, D., Dragomir, D., Brandeker, A., Osborn, H. P., Collins, K., Stassun, K. G., . . . Ziegler, C. (2023). Characterization of a Set of Small Planets with TESS and CHEOPS and an Analysis of Photometric Performance. Astronomical Journal, 165(3), Article ID 134.
Open this publication in new window or tab >>Characterization of a Set of Small Planets with TESS and CHEOPS and an Analysis of Photometric Performance
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2023 (English)In: Astronomical Journal, ISSN 0004-6256, E-ISSN 1538-3881, Vol. 165, no 3, article id 134Article in journal (Refereed) Published
Abstract [en]

The radius valley carries implications for how the atmospheres of small planets form and evolve, but this feature is visible only with highly precise characterizations of many small planets. We present the characterization of nine planets and one planet candidate with both NASA TESS and ESA CHEOPS observations, which adds to the overall population of planets bordering the radius valley. While five of our planets—TOI 118 b, TOI 262 b, TOI 455 b, TOI 560 b, and TOI 562 b—have already been published, we vet and validate transit signals as planetary using follow-up observations for four new TESS planets, including TOI 198 b, TOI 244 b, TOI 444 b, and TOI 470 b. While a three times increase in primary mirror size should mean that one CHEOPS transit yields an equivalent model uncertainty in transit depth as about nine TESS transits in the case that the star is equally as bright in both bands, we find that our CHEOPS transits typically yield uncertainties equivalent to between two and 12 TESS transits, averaging 5.9 equivalent transits. Therefore, we find that while our fits to CHEOPS transits provide overall lower uncertainties on transit depth and better precision relative to fits to TESS transits, our uncertainties for these fits do not always match expected predictions given photon-limited noise. We find no correlations between number of equivalent transits and any physical parameters, indicating that this behavior is not strictly systematic, but rather might be due to other factors such as in-transit gaps during CHEOPS visits or nonhomogeneous detrending of CHEOPS light curves.

Keywords
Exoplanet astronomy, Extrasolar rocky planets, Mini Neptunes
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:su:diva-216055 (URN)10.3847/1538-3881/acb4e3 (DOI)000943362700001 ()2-s2.0-85149476352 (Scopus ID)
Available from: 2023-04-03 Created: 2023-04-03 Last updated: 2023-04-03Bibliographically approved
Patel, J. A., Brandeker, A., Olofsson, G. & Walton, N. A. (2023). CHEOPS and TESS view of the ultra-short-period super-Earth TOI-561 b. Astronomy and Astrophysics, 679, Article ID A92.
Open this publication in new window or tab >>CHEOPS and TESS view of the ultra-short-period super-Earth TOI-561 b
2023 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 679, article id A92Article in journal (Refereed) Published
Abstract [en]

Context. Ultra-short-period planets (USPs) are a unique class of super-Earths with an orbital period of less than a day, and hence they are subject to intense radiation from their host star. These planets cannot retain a primordial H/He atmosphere, and most of them are indeed consistent with being bare rocky cores. A few USPs, however, show evidence for a heavyweight envelope, which could be a water layer resilient to evaporation or a secondary metal-rich atmosphere sustained by outgassing of the molten volcanic surface. Much thus remains to be learned about the nature and formation of USPs. Aims. The prime goal of the present work is to refine the bulk planetary properties of the recently discovered TOI-561 b through the study of its transits and occultations. This is crucial in order to understand the internal structure of this USP and to assess the presence of an atmosphere. Methods. We obtained ultra-precise transit photometry of TOI-561 b with CHEOPS, and performed a joint analysis of these data along with three archival visits from CHEOPS and four TESS sectors. Results. Our analysis of TOI-561 b transit photometry put strong constraints on its properties. In particular, we restrict the uncertainties on the planetary radius at similar to 2% retrieving R-p = 1.42 +/- 0.02 R-circle plus. This result informs our internal structure modelling of the planet, which shows that the observations are consistent with a negligible H/He atmosphere; however, other lighter materials are required, in addition to a pure iron core and a silicate mantle, to explain the observed density. We find that this can be explained by the inclusion of a water layer in our model. Additionally, we ran a grid of forward models with a water-enriched atmosphere to explain the transit radius. We searched for variability in the measured R-p/R-star over time, which could trace changes in the structure of the planetary envelope. However, no temporal variations are recovered within the present data precision. In addition to the transit event, we tentatively detect an occultation signal in the TESS data with an eclipse depth L = 27.40(-11.35)(+10.87) ppm. We use models of outgassed atmospheres from the literature to explain this eclipse signal. We find that the thermal emission from the planet can mostly explain the observation. Based on this, we predict that near- to mid-infrared observations with the James Webb Space Telescope should be able to detect silicate species in the atmosphere of the planet. This could also reveal important clues about the planetary interior and help disentangle planet formation and evolution models.

Keywords
techniques: photometric, planets and satellites: terrestrial planets, planets and satellites: composition, planets and satellites: atmospheres, planets and satellites: individual: TOI-561 b
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:su:diva-225820 (URN)10.1051/0004-6361/202244946 (DOI)001107280500001 ()2-s2.0-85181986100 (Scopus ID)
Available from: 2024-01-23 Created: 2024-01-23 Last updated: 2024-01-23Bibliographically approved
Brandeker, A. & Olofsson, G. (2023). Connecting photometric and spectroscopic granulation signals with CHEOPS and ESPRESSO. Astronomy and Astrophysics, 670, Article ID A24.
Open this publication in new window or tab >>Connecting photometric and spectroscopic granulation signals with CHEOPS and ESPRESSO
2023 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 670, article id A24Article in journal (Refereed) Published
Abstract [en]

Context. Stellar granulation generates fluctuations in photometric and spectroscopic data whose properties depend on the stellar type, composition, and evolutionary state. Characterizing granulation is key for understanding stellar atmospheres and detecting planets.

Aims. 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.

Methods. For the first time, we observed two bright stars (Teff = 5833 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 dataset. We compared them to Kepler observations and 3D hydrodynamic models. While isolating the granulation-induced changes by attenuating and filtering the p-mode oscillation signals, we studied the relationship between photometric and spectroscopic observables.

Results. 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 versus radial velocities, RV) and with specific spectroscopic observables (shape of the cross-correlation functions) are however difficult to isolate due to S/N dependent variations.

Conclusions. 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.

Keywords
methods: data analysis, Sun: granulation, stars: atmospheres, techniques: photometric, techniques: radial velocities
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:su:diva-215724 (URN)10.1051/0004-6361/202244223 (DOI)000928269900004 ()2-s2.0-85147676859 (Scopus ID)
Available from: 2023-03-24 Created: 2023-03-24 Last updated: 2023-03-24Bibliographically approved
Florén, H. G., Brandeker, A. & Olofsson, G. (2023). Discovery of TOI-1260d and the characterization of the multiplanet system. Monthly notices of the Royal Astronomical Society, 519(1), 1437-1451
Open this publication in new window or tab >>Discovery of TOI-1260d and the characterization of the multiplanet system
2023 (English)In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 519, no 1, p. 1437-1451Article in journal (Refereed) Published
Abstract [en]

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 d, respectively. The nature of the third transiting planet with a 16.6-d 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 and TOI-1260c are 2.36±0.06R⊕2.36±0.06R⊕⁠, 2.82±0.08R⊕2.82±0.08R⊕⁠, respectively while the newly discovered third planet has a radius of 3.09±0.09R⊕3.09±0.09R⊕⁠. The radius uncertainties are in the range of 3 per cent, 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.

Keywords
techniques: photometric, techniques: radial velocities, planets and satellites: composition, planets and satellites: detection, planets and satellites: individual: TOI-1260b, c, d, stars: individual: TOI-1260
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:su:diva-215721 (URN)10.1093/mnras/stac3639 (DOI)000927884000010 ()
Available from: 2023-03-27 Created: 2023-03-27 Last updated: 2023-03-27Bibliographically approved
Florén, H. G., Brandeker, A. & Olofsson, G. (2023). Examining the orbital decay targets KELT-9 b, KELT-16 b, and WASP-4 b, and the transit-timing variations of HD 97658 b. Astronomy and Astrophysics, 669, Article ID A124.
Open this publication in new window or tab >>Examining the orbital decay targets KELT-9 b, KELT-16 b, and WASP-4 b, and the transit-timing variations of HD 97658 b
2023 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 669, article id A124Article in journal (Refereed) Published
Abstract [en]

Context. Tidal orbital decay is suspected to occur for hot Jupiters in particular, with the only observationally confirmed case of this being WASP-12b. 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 the kinetic energy of the planet is dissipated within the star. This can provide information about the interior of the star.

Aims. In this study, we aim to improve constraints on the tidal decay of the KELT-9, KELT-16, and WASP-4 systems in order to find evidence for or against the presence of tidal orbital decay. With this, we want to constrain the Q* value for each star. In addition, we 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.

Methods. Making use of newly acquired photometric observations from CHEOPS (CHaracterising ExOplanet Satellite) and TESS (Transiting Exoplanet Survey Satellite), combined with archival transit and occultation data, we use Markov chain Monte Carlo (MCMC) algorithms to fit three models to the data, namely a constant-period model, an orbital-decay model, and an apsidal-precession model.

Results. 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 σ being a possible solution as well. A Keplerian orbit model with a constant orbital period provides the best fit to the transit timings of KELT-16 b because of the scatter and scale of their error bars. The WASP-4 system is best represented by an orbital decay model at a 5 σ 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.

Keywords
planets and satellites, dynamical evolution and stability, planet-star interactions, techniques, photometric
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:su:diva-215725 (URN)10.1051/0004-6361/202244529 (DOI)000921718300001 ()2-s2.0-85147138880 (Scopus ID)
Available from: 2023-03-27 Created: 2023-03-27 Last updated: 2023-03-27Bibliographically approved
Boldog, Á., Brandeker, A., Olofsson, G. & Walton, N. A. (2023). Glancing through the debris disk: Photometric analysis of DE Boo with CHEOPS star. Astronomy and Astrophysics, 671, Article ID A127.
Open this publication in new window or tab >>Glancing through the debris disk: Photometric analysis of DE Boo with CHEOPS star
2023 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 671, article id A127Article in journal (Refereed) Published
Abstract [en]

Aims. 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.

Methods. 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.

Results. 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.

Conclusions. 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.

Keywords
techniques: photometric, methods: data analysis, stars: flare, starspots, circumstellar matter
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:su:diva-216983 (URN)10.1051/0004-6361/202245101 (DOI)000953843800003 ()2-s2.0-85150786885 (Scopus ID)
Available from: 2023-05-09 Created: 2023-05-09 Last updated: 2023-05-09Bibliographically approved
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Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0002-7201-7536

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