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Bonfanti, A., Brandeker, A., Olofsson, G. & Zingales, T. (2024). Characterising TOI-732 b and c: New insights into the M-dwarf radius and density valley. Astronomy and Astrophysics, 682, Article ID A66.
Open this publication in new window or tab >>Characterising TOI-732 b and c: New insights into the M-dwarf radius and density valley
2024 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 682, article id A66Article in journal (Refereed) Published
Abstract [en]

Context

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-732b is an ultrashort-period planet (P = 0.76837931-0.00000042+0.0000039 days) with a radius Rb = 1.325-0.058+0.057R, a mass Mb = 2.46 ± 0.19 M, and thus a mean density ρb = 5.8-0.8+1.0 g cm-3, while the outer planet at P = 12.252284 ± 0.000013 days has Rc = 2.39-0.11+0.10RMc = 8.04-0.48+0.50M, and thus ρc = 3.24-0.43+0.55 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 logP = -0.065-0.013+0.024, 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 ρ^valley / d log P = -0.02-0.04+0.12.

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.

Keywords
techniques: photometric, techniques: radial velocities, planets and satellites: fundamental parameters, stars: fundamental parameters
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:su:diva-227978 (URN)10.1051/0004-6361/202348180 (DOI)001158428600006 ()2-s2.0-85184519282 (Scopus ID)
Available from: 2024-04-05 Created: 2024-04-05 Last updated: 2024-04-05Bibliographically approved
Pagano, I., Brandeker, A., Olofsson, G. & Walton, N. A. (2024). Constraining the reflective properties of WASP-178 b using CHEOPS photometry. Astronomy and Astrophysics, 682, Article ID A102.
Open this publication in new window or tab >>Constraining the reflective properties of WASP-178 b using CHEOPS photometry
2024 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 682, article id A102Article in journal (Refereed) Published
Abstract [en]

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.

Keywords
planets and satellites: individual: wasp-178 b, techniques: photometric, planets and satellites: detection, planets and satellites: gaseous planets, planets and satellites: atmospheres
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:su:diva-228318 (URN)10.1051/0004-6361/202346705 (DOI)001188262400001 ()2-s2.0-85185216038 (Scopus ID)
Available from: 2024-04-12 Created: 2024-04-12 Last updated: 2024-04-12Bibliographically approved
Swayne, M. I., Olofsson, G., Brandeker, A. & Wilson, T. G. (2024). The EBLM Project- XI. Mass, radius, and effective temperature measurements for 23 M-dwarf companions to solar-type stars observed with CHEOPS. Monthly notices of the Royal Astronomical Society, 528(4), 5703-5722
Open this publication in new window or tab >>The EBLM Project- XI. Mass, radius, and effective temperature measurements for 23 M-dwarf companions to solar-type stars observed with CHEOPS
2024 (English)In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 528, no 4, p. 5703-5722Article in journal (Refereed) Published
Abstract [en]

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.

Keywords
techniques: photometric, techniques: spectroscopic, binaries: eclipsing, stars: fundamental parameters, stars: low-mass
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:su:diva-227979 (URN)10.1093/mnras/stad3866 (DOI)001164781800001 ()2-s2.0-85180478235 (Scopus ID)
Available from: 2024-04-05 Created: 2024-04-05 Last updated: 2024-04-05Bibliographically approved
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
Luque, R., Brandeker, A., Olofsson, G. & Zingales, T. (2023). A resonant sextuplet of sub-Neptunes transiting the bright star HD 110067. Nature, 623(7989), 932-937
Open this publication in new window or tab >>A resonant sextuplet of sub-Neptunes transiting the bright star HD 110067
2023 (English)In: Nature, ISSN 0028-0836, E-ISSN 1476-4687, Vol. 623, no 7989, p. 932-937Article in journal (Refereed) Published
Abstract [en]

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. However, their composition, formation and evolution remain poorly understood3. 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.

National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:su:diva-227977 (URN)10.1038/s41586-023-06692-3 (DOI)001169044100007 ()38030780 (PubMedID)2-s2.0-85178181432 (Scopus ID)
Available from: 2024-04-05 Created: 2024-04-05 Last updated: 2024-04-05Bibliographically 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
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0002-7201-7536

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