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  • 1
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    Hot planets around cool stars – two short-period mini-Neptunes transiting the late K-dwarf TOI-1260
    Oxford University Press (OUP) ; 2021
    In:  Monthly Notices of the Royal Astronomical Society Vol. 505, No. 4 ( 2021-06-25), p. 4684-4701
    Details
    In: Monthly Notices of the Royal Astronomical Society, Oxford University Press (OUP), Vol. 505, No. 4 ( 2021-06-25), p. 4684-4701
    Abstract: We present the discovery and characterization of two sub-Neptunes in close orbits, as well as a tentative outer planet of a similar size, orbiting TOI-1260 – a low metallicity K6 V dwarf star. Photometry from Transiting Exoplanet Survey Satellite(TESS) yields radii of Rb = 2.33 ± 0.10 and Rc = 2.82 ± 0.15 R⊕, and periods of 3.13 and 7.49 d for TOI-1260 b and TOI-1260 c, respectively. We combined the TESS data with a series of ground-based follow-up observations to characterize the planetary system. From HARPS-N high-precision radial velocities we obtain Mb = $8.6 _{ - 1.5 } ^ { + 1.4 }$ and Mc = $11.8 _{ - 3.2 } ^ { + 3.4 }$ M⊕. The star is moderately active with a complex activity pattern, which necessitated the use of Gaussian process regression for both the light-curve detrending and the radial velocity modelling, in the latter case guided by suitable activity indicators. We successfully disentangle the stellar-induced signal from the planetary signals, underlining the importance and usefulness of the Gaussian process approach. We test the system’s stability against atmospheric photoevaporation and find that the TOI-1260 planets are classic examples of the structure and composition ambiguity typical for the 2–3 R⊕ range.
    Type of Medium: Online Resource
    ISSN: 0035-8711 , 1365-2966
    URL: Article
    DOI: 10.1093/mnras/stab1464
    Language: English
    Publisher: Oxford University Press (OUP)
    Publication Date: 2021
    detail.hit.zdb_id: 2016084-7
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  • 2
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    A planetary system with two transiting mini-Neptunes near the radius valley transition around the bright M dwarf TOI-776
    EDP Sciences ; 2021
    In:  Astronomy & Astrophysics Vol. 645 ( 2021-1), p. A41-
    Details
    In: Astronomy & Astrophysics, EDP Sciences, Vol. 645 ( 2021-1), p. A41-
    Abstract: We report the discovery and characterization of two transiting planets around the bright M1 V star LP 961-53 (TOI-776, J = 8.5 mag, M = 0.54 ± 0.03 M ⊙ ) detected during Sector 10 observations of the Transiting Exoplanet Survey Satellite (TESS). Combining the TESS photometry with HARPS radial velocities, as well as ground-based follow-up transit observations from the MEarth and LCOGT telescopes, for the inner planet, TOI-776 b, we measured a period of P b = 8.25 d, a radius of R b = 1.85 ± 0.13 R ⊕ , and a mass of M b = 4.0 ± 0.9 M ⊕ ; and for the outer planet, TOI-776 c, a period of P c = 15.66 d, a radius of R c = 2.02 ± 0.14 R ⊕ , and a mass of M c = 5.3 ± 1.8 M ⊕ . The Doppler data shows one additional signal, with a period of ~34 d, associated with the rotational period of the star. The analysis of fifteen years of ground-based photometric monitoring data and the inspection of different spectral line indicators confirm this assumption. The bulk densities of TOI-776 b and c allow for a wide range of possible interior and atmospheric compositions. However, both planets have retained a significant atmosphere, with slightly different envelope mass fractions. Thanks to their location near the radius gap for M dwarfs, we can start to explore the mechanism(s) responsible for the radius valley emergence around low-mass stars as compared to solar-like stars. While a larger sample of well-characterized planets in this parameter space is still needed to draw firm conclusions, we tentatively estimate that the stellar mass below which thermally-driven mass loss is no longer the main formation pathway for sculpting the radius valley is between 0.63 and 0.54 M ⊙ . Due to the brightness of the star, the TOI-776 system is also an excellent target for the James Webb Space Telescope, providing a remarkable laboratory in which to break the degeneracy in planetary interior models and to test formation and evolution theories of small planets around low-mass stars.
    Type of Medium: Online Resource
    ISSN: 0004-6361 , 1432-0746
    URL: Article
    DOI: 10.1051/0004-6361/202039455
    RVK:
    UA 1000
    RVK:
    US 1090
    Language: English
    Publisher: EDP Sciences
    Publication Date: 2021
    detail.hit.zdb_id: 1458466-9
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  • 3
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    Masses and compositions of three small planets orbiting the nearby M dwarf L231-32 (TOI-270) and the M dwarf radius valley
    Oxford University Press (OUP) ; 2021
    In:  Monthly Notices of the Royal Astronomical Society
    Details
    In: Monthly Notices of the Royal Astronomical Society, Oxford University Press (OUP)
    Abstract: We report on precise Doppler measurements of L231-32 (TOI-270), a nearby M dwarf (d = 22 pc, M⋆ = 0.39 M⊙, R⋆ = 0.38 R⊙), which hosts three transiting planets that were recently discovered using data from the Transiting Exoplanet Survey Satellite (TESS). The three planets are 1.2, 2.4, and 2.1 times the size of Earth and have orbital periods of 3.4, 5.7, and 11.4 days. We obtained 29 high-resolution optical spectra with the newly commissioned Echelle Spectrograph for Rocky Exoplanet and Stable Spectroscopic Observations (ESPRESSO) and 58 spectra using the High Accuracy Radial velocity Planet Searcher (HARPS). From these observations, we find the masses of the planets to be 1.58 ± 0.26, 6.15 ± 0.37, and 4.78 ± 0.43 M⊕, respectively. The combination of radius and mass measurements suggests that the innermost planet has a rocky composition similar to that of Earth, while the outer two planets have lower densities. Thus, the inner planet and the outer planets are on opposite sides of the ‘radius valley’ — a region in the radius-period diagram with relatively few members, which has been interpreted as a consequence of atmospheric photo-evaporation. We place these findings into the context of other small close-in planets orbiting M dwarf stars, and use support vector machines to determine the location and slope of the M dwarf (Teff & lt; 4000 K) radius valley as a function of orbital period. We compare the location of the M dwarf radius valley to the radius valley observed for FGK stars, and find that its location is a good match to photo-evaporation and core-powered mass loss models. Finally, we show that planets below the M dwarf radius valley have compositions consistent with stripped rocky cores, whereas most planets above have a lower density consistent with the presence of a H-He atmosphere.
    Type of Medium: Online Resource
    ISSN: 0035-8711 , 1365-2966
    URL: Article
    DOI: 10.1093/mnras/stab2143
    Language: English
    Publisher: Oxford University Press (OUP)
    Publication Date: 2021
    detail.hit.zdb_id: 2016084-7
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  • 4
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    TOI-220  b : a warm sub-Neptune discovered by TESS
    Oxford University Press (OUP) ; 2021
    In:  Monthly Notices of the Royal Astronomical Society Vol. 505, No. 3 ( 2021-06-17), p. 3361-3379
    Details
    In: Monthly Notices of the Royal Astronomical Society, Oxford University Press (OUP), Vol. 505, No. 3 ( 2021-06-17), p. 3361-3379
    Abstract: In this paper, we report the discovery of TOI-220 b, a new sub-Neptune detected by the Transiting Exoplanet Survey Satellite (TESS) and confirmed by radial velocity follow-up observations with the HARPS spectrograph. Based on the combined analysis of TESS transit photometry and high precision radial velocity measurements, we estimate a planetary mass of 13.8 ± 1.0 M⊕ and radius of 3.03 ± 0.15 R⊕, implying a bulk density of 2.73 ± 0.47 $\rm {g\,cm}^{-3}$. TOI-220 b orbits a relative bright (V= 10.4) and old (10.1 ± 1.4 Gyr) K dwarf star with a period of ∼10.69 d. Thus, TOI-220 b is a new warm sub-Neptune with very precise mass and radius determinations. A Bayesian analysis of the TOI-220 b internal structure indicates that due to the strong irradiation it receives, the low density of this planet could be explained with a steam atmosphere in radiative–convective equilibrium and a supercritical water layer on top of a differentiated interior made of a silicate mantle and a small iron core.
    Type of Medium: Online Resource
    ISSN: 0035-8711 , 1365-2966
    URL: Article
    DOI: 10.1093/mnras/stab1427
    Language: English
    Publisher: Oxford University Press (OUP)
    Publication Date: 2021
    detail.hit.zdb_id: 2016084-7
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  • 5
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    The young HD 73583 (TOI-560) planetary system: two 10-M⊕ mini-Neptunes transiting a 500-Myr-old, bright, and active K dwarf
    Oxford University Press (OUP) ; 2022
    In:  Monthly Notices of the Royal Astronomical Society Vol. 514, No. 2 ( 2022-06-11), p. 1606-1627
    Details
    In: Monthly Notices of the Royal Astronomical Society, Oxford University Press (OUP), Vol. 514, No. 2 ( 2022-06-11), p. 1606-1627
    Abstract: We present the discovery and characterization of two transiting planets observed by TESS in the light curves of the young and bright (V = 9.67) star HD73583 (TOI-560). We perform an intensive spectroscopic and photometric space- and ground-based follow-up in order to confirm and characterize the system. We found that HD73583 is a young (∼500 Myr) active star with a rotational period of 12.08 ± 0.11  d, and a mass and radius of 0.73 ± 0.02 M⊙ and 0.65 ± 0.02 R⊙, respectively. HD 73583 b (Pb = $6.3980420 _{ - 0.0000062 } ^ { + 0.0000067 }$ d) has a mass and radius of $10.2 _{ - 3.1 } ^ { + 3.4 }$ M⊕ and 2.79 ± 0.10 R⊕, respectively, which gives a density of $2.58 _{ - 0.81 } ^ { + 0.95 }$ ${\rm g\, cm^{-3}}$. HD 73583 c (Pc = $18.87974 _{ - 0.00074 } ^ { + 0.00086 }$ d) has a mass and radius of $9.7 _{ - 1.7 } ^ { + 1.8 }$ M⊕ and $2.39 _{ - 0.09 } ^ { + 0.10 }$ R⊕, respectively, which translates to a density of $3.88 _{ - 0.80 } ^ { + 0.91 }$ ${\rm g\, cm^{-3}}$. Both planets are consistent with worlds made of a solid core surrounded by a volatile envelope. Because of their youth and host star brightness, they both are excellent candidates to perform transmission spectroscopy studies. We expect ongoing atmospheric mass-loss for both planets caused by stellar irradiation. We estimate that the detection of evaporating signatures on H and He would be challenging, but doable with present and future instruments.
    Type of Medium: Online Resource
    ISSN: 0035-8711 , 1365-2966
    URL: Article
    DOI: 10.1093/mnras/stac638
    Language: English
    Publisher: Oxford University Press (OUP)
    Publication Date: 2022
    detail.hit.zdb_id: 2016084-7
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  • 6
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    Precise mass determination for the keystone sub-Neptune planet transiting the mid-type M dwarf G 9-40
    EDP Sciences ; 2022
    In:  Astronomy & Astrophysics Vol. 666 ( 2022-10), p. A154-
    Details
    In: Astronomy & Astrophysics, EDP Sciences, Vol. 666 ( 2022-10), p. A154-
    Abstract: Context. Despite being a prominent subset of the exoplanet population discovered in the past three decades, the nature and provenance of sub-Neptune-sized planets is still one of the open questions in exoplanet science. Aims. For planets orbiting bright stars, precisely measuring the orbital and planet parameters of the system is the best approach to distinguish between competing theories regarding their formation and evolution. Methods. We obtained 69 new radial velocity observations of the mid-M dwarf G 9–40 with the CARMENES instrument to measure for the first time the mass of its transiting sub-Neptune planet, G 9–40 b, discovered in data from the K2 mission. Results. Combined with new observations from the TESS mission during Sectors 44, 45, and 46, we are able to measure the radius of the planet to an uncertainty of 3.4% ( R b = 1.900 ± 0.065 R ⊕ ) and determine its mass with a precision of 16% ( M b = 4.00 ± 0.63 M ⊕ ). The resulting bulk density of the planet is inconsistent with a terrestrial composition and suggests the presence of either a water-rich core or a significant hydrogen-rich envelope. Conclusions. G 9–40 b is referred to as a keystone planet due to its location in period-radius space within the radius valley. Several theories offer explanations for the origin and properties of this population and this planet is a valuable target for testing the dependence of those models on stellar host mass. By virtue of its brightness and small size of the host, it joins L 98-59 d as one of the two best warm ( T eq ~ 400 K) sub-Neptunes for atmospheric characterization with JWST, which will probe cloud formation in sub-Neptune-sized planets and break the degeneracies of internal composition models.
    Type of Medium: Online Resource
    ISSN: 0004-6361 , 1432-0746
    URL: Article
    DOI: 10.1051/0004-6361/202244426
    RVK:
    UA 1000
    RVK:
    US 1090
    Language: English
    Publisher: EDP Sciences
    Publication Date: 2022
    detail.hit.zdb_id: 1458466-9
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  • 7
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    HD 20329b: An ultra-short-period planet around a solar-type star found by TESS
    EDP Sciences ; 2022
    In:  Astronomy & Astrophysics Vol. 668 ( 2022-12), p. A158-
    Details
    In: Astronomy & Astrophysics, EDP Sciences, Vol. 668 ( 2022-12), p. A158-
    Abstract: Context. Ultra-short-period (USP) planets are defined as planets with orbital periods shorter than one day. This type of planets is rare, highly irradiated, and interesting because their formation history is unknown. Aims. We aim to obtain precise mass and radius measurements to confirm the planetary nature of a USP candidate found by the Transiting Exoplanet Survey Satellite (TESS). These parameters can provide insights into the bulk composition of the planet candidate and help to place constraints on its formation history. Methods. We used TESS light curves and HARPS-N spectrograph radial velocity measurements to establish the physical properties of the transiting exoplanet candidate found around the star HD 20329 (TOI-4524). We performed a joint fit of the light curves and radial velocity time series to measure the mass, radius, and orbital parameters of the candidate. Results. We confirm and characterize HD 20329b, a USP planet transiting a solar-type star. The host star (HD 20329, V = 8.74 mag, J = 7.5 mag) is characterized by its G5 spectral type with M * = 0.90 ± 0.05 M ⊙ , R * = 1.13 ± 0.02 R ⊙ , and T eff = 5596 ± 50 K; it is located at a distance d = 63.68 ± 0.29 pc. By jointly fitting the available TESS transit light curves and follow-up radial velocity measurements, we find an orbital period of 0.9261 ± (0.5 × 10 −4 ) days, a planetary radius of 1.72 ± 0.07 R ⊗ , and a mass of 7.42 ± 1.09 M ⊗ , implying a mean density of ρ p = 8.06 ± 1.53 g cm −3 . HD 20329b joins the ~30 currently known USP planets with radius and Doppler mass measurements.
    Type of Medium: Online Resource
    ISSN: 0004-6361 , 1432-0746
    URL: Article
    DOI: 10.1051/0004-6361/202244459
    RVK:
    UA 1000
    RVK:
    US 1090
    Language: English
    Publisher: EDP Sciences
    Publication Date: 2022
    detail.hit.zdb_id: 1458466-9
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  • 8
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    Radial velocity confirmation of a hot super-Neptune discovered by TESS with a warm Saturn–mass companion
    Oxford University Press (OUP) ; 2023
    In:  Monthly Notices of the Royal Astronomical Society Vol. 519, No. 4 ( 2023-01-17), p. 5637-5655
    Details
    In: Monthly Notices of the Royal Astronomical Society, Oxford University Press (OUP), Vol. 519, No. 4 ( 2023-01-17), p. 5637-5655
    Abstract: We report the discovery and confirmation of the planetary system TOI-1288. This late G dwarf harbours two planets: TOI-1288 b and TOI-1288 c. We combine TESS space-borne and ground-based transit photometry with HARPS-N and HIRES high-precision Doppler measurements, which we use to constrain the masses of both planets in the system and the radius of planet b. TOI-1288 b has a period of $2.699835^{+0.000004}_{-0.000003}$ d, a radius of 5.24 ± 0.09 R⊕, and a mass of 42 ± 3 M⊕, making this planet a hot transiting super-Neptune situated right in the Neptunian desert. This desert refers to a paucity of Neptune-sized planets on short period orbits. Our 2.4-yr-long Doppler monitoring of TOI-1288 revealed the presence of a Saturn–mass planet on a moderately eccentric orbit ($0.13^{+0.07}_{-0.09}$) with a minimum mass of 84 ± 7 M⊕ and a period of $443^{+11}_{-13}$ d. The five sectors worth of TESS data do not cover our expected mid-transit time for TOI-1288 c, and we do not detect a transit for this planet in these sectors.
    Type of Medium: Online Resource
    ISSN: 0035-8711 , 1365-2966
    URL: Article
    DOI: 10.1093/mnras/stac3684
    Language: English
    Publisher: Oxford University Press (OUP)
    Publication Date: 2023
    detail.hit.zdb_id: 2016084-7
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  • 9
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    The planetary system around HD 190622 (TOI-1054) : Measuring the gas content of low-mass planets orbiting F-stars
    EDP Sciences ; 2023
    In:  Astronomy & Astrophysics Vol. 675 ( 2023-7), p. A183-
    Details
    In: Astronomy & Astrophysics, EDP Sciences, Vol. 675 ( 2023-7), p. A183-
    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 +0.058 R Earth , 7.7 ± 1.0 M Earth ) 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 M Earth 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.
    Type of Medium: Online Resource
    ISSN: 0004-6361 , 1432-0746
    URL: Article
    DOI: 10.1051/0004-6361/202245774
    RVK:
    UA 1000
    RVK:
    US 1090
    Language: English
    Publisher: EDP Sciences
    Publication Date: 2023
    detail.hit.zdb_id: 1458466-9
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  • 10
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    K2-99 revisited: a non-inflated warm Jupiter, and a temperate giant planet on a 522-d orbit around a subgiant
    Oxford University Press (OUP) ; 2022
    In:  Monthly Notices of the Royal Astronomical Society Vol. 510, No. 4 ( 2022-01-20), p. 5035-5049
    Details
    In: Monthly Notices of the Royal Astronomical Society, Oxford University Press (OUP), Vol. 510, No. 4 ( 2022-01-20), p. 5035-5049
    Abstract: We report new photometric and spectroscopic observations of the K2-99 planetary system. Asteroseismic analysis of the short-cadence light curve from K2’s Campaign 17 allows us to refine the stellar properties. We find K2-99 to be significantly smaller than previously thought, with R⋆ = 2.55 ± 0.02 R⊙. The new light curve also contains four transits of K2-99 b, which we use to improve our knowledge of the planetary properties. We find the planet to be a non-inflated warm Jupiter, with Rb = 1.06 ± 0.01 $\mathrm{R_{\rm Jup}}$. 60 new radial velocity measurements from HARPS, HARPS-N, and HIRES enable the determination of the orbital parameters of K2-99 c, which were previously poorly constrained. We find that this outer planet has a minimum mass Mcsin ic = 8.4 ± 0.2 $\mathrm{M_{\rm Jup}}$, and an eccentric orbit (ec = 0.210 ± 0.009) with a period of 522.2 ± 1.4 d. Upcoming TESS observations in 2022 have a good chance of detecting the transit of this planet, if the mutual inclination between the two planetary orbits is small.
    Type of Medium: Online Resource
    ISSN: 0035-8711 , 1365-2966
    URL: Article
    DOI: 10.1093/mnras/stab3497
    Language: English
    Publisher: Oxford University Press (OUP)
    Publication Date: 2022
    detail.hit.zdb_id: 2016084-7
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