| 1. |
- Luque, R., et al.
(författare)
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A resonant sextuplet of sub-Neptunes transiting the bright star HD 110067
- 2023
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Ingår i: Nature. - 0028-0836 .- 1476-4687. ; 623:7989, s. 932-937
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Tidskriftsartikel (refereegranskat)abstract
- 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 1,2. However, their composition, formation and evolution remain poorly understood 3. 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.
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| 2. |
- Bluhm, P., et al.
(författare)
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Precise mass and radius of a transiting super-Earth planet orbiting the M dwarf TOI-1235: a planet in the radius gap?
- 2020
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 639
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Tidskriftsartikel (refereegranskat)abstract
- We report the confirmation of a transiting planet around the bright weakly active M0.5 V star TOI-1235 (TYC 4384-1735-1, V ≈ 11.5 mag), whose transit signal was detected in the photometric time series of sectors 14, 20, and 21 of the TESS space mission. We confirm the planetary nature of the transit signal, which has a period of 3.44 d, by using precise RV measurements with the CARMENES, HARPS-N, and iSHELL spectrographs, supplemented by high-resolution imaging and ground-based photometry. A comparison of the properties derived for TOI-1235 b with theoretical models reveals that the planet has a rocky composition, with a bulk density slightly higher than that of Earth. In particular, we measure a mass of Mp = 5.9 ± 0.6 M⊕ and a radius of Rp = 1.69 ± 0.08 R⊕, which together result in a density of ρp = 6.7- 1.1+ 1.3 g cm-3. When compared with other well-characterized exoplanetary systems, the particular combination of planetary radius and mass places our discovery in the radius gap, which is a transition region between rocky planets and planets with significant atmospheric envelopes. A few examples of planets occupying the radius gap are known to date. While the exact location of the radius gap for M dwarfs is still a matter of debate, our results constrain it to be located at around 1.7 R⊕ or larger at the insolation levels received by TOI-1235 b (~60 S⊕). This makes it an extremely interesting object for further studies of planet formation and atmospheric evolution.
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| 3. |
- Gandolfi, D., et al.
(författare)
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The Transiting Multi-planet System HD15337: Two Nearly Equal-mass Planets Straddling the Radius Gap
- 2019
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Ingår i: Astrophysical Journal Letters. - : American Astronomical Society. - 2041-8213 .- 2041-8205. ; 876:2
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Tidskriftsartikel (refereegranskat)abstract
- We report the discovery of a super-Earth and a sub-Neptune transiting the star HD 15337 (TOI-402, TIC 120896927), a bright (V = 9) K1 dwarf observed by the Transiting Exoplanet Survey Satellite (TESS) in Sectors 3 and 4. We combine the TESS photometry with archival High Accuracy Radial velocity Planet Searcher spectra to confirm the planetary nature of the transit signals and derive the masses of the two transiting planets. With an orbital period of 4.8 days, a mass of {7.51}-1.01+1.09 {M}\oplus and a radius of 1.64 ± 0.06 R ⊕, HD 15337 b joins the growing group of short-period super-Earths known to have a rocky terrestrial composition. The sub-Neptune HD 15337 c has an orbital period of 17.2 days, a mass of {8.11}-1.69+1.82 {{{M}}}\oplus , and a radius of 2.39 ± 0.12 R ⊕, suggesting that the planet might be surrounded by a thick atmospheric envelope. The two planets have similar masses and lie on opposite sides of the radius gap, and are thus an excellent testbed for planet formation and evolution theories. Assuming that HD 15337 c hosts a hydrogen-dominated envelope, we employ a recently developed planet atmospheric evolution algorithm in a Bayesian framework to estimate the history of the high-energy (extreme ultraviolet and X-ray) emission of the host star. We find that at an age of 150 Myr, the star possessed on average between 3.7 and 127 times the high-energy luminosity of the current Sun.
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| 4. |
- Nielsen, L. D., et al.
(författare)
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Mass determinations of the three mini-Neptunes transiting TOI-125
- 2020
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Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 492:4, s. 5399-5412
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Tidskriftsartikel (refereegranskat)abstract
- The Transiting Exoplanet Survey Satellite, TESS, is currently carrying out an all-sky search for small planets transiting bright stars. In the first year of the TESS survey, a steady progress was made in achieving the mission's primary science goal of establishing bulk densities for 50 planets smaller than Neptune. During that year, the TESS's observations were focused on the southern ecliptic hemisphere, resulting in the discovery of three mini-Neptunes orbiting the star T01-125, a V = 11,0 KO dwarf. We present intensive HARPS radial velocity observations, yielding precise mass measurements for TO1-125b, TOI-125c, and TOI-125d. TOI-125b has an orbital period of 4,65 d, a radius of 2,726 + 0,075 RE, a mass of 9,50 0,88 ME, and is near the 2:1 mean motion resonance with TOI-125c at 9.15 d. TOI-125c has a similar radius of 2,759 0.10 RE and a mass of 6,63 + 0,99 ME, being the puffiest of the three planets. T01-125d has an orbital period of 19,98 d and a radius of 2.93 + 0,17 RE and mass 13,6 1,2 ME, For T01-125b and d, we find unusual high eccentricities of 0.19 0.04 and 0.17+(c):(!,(, respectively. Our analysis also provides upper mass limits for the two low-SNR planet candidates in the system; for T01-125.04 (Rp = 1.36 RE, P = 0.53 d), we find a 2a upper mass limit of 1.6 ME, whereas T01-125.05 (RP = 4.2-'2E44 RE, P = 13.28 d) is unlikely a viable planet candidate with an upper mass limit of 2.7 ME. We discuss the internal structure of the three confirmed planets, as well as dynamical stability and system architecture for this intriguing exoplanet system.
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| 5. |
- Barragán, O., et al.
(författare)
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K2-139 b: a low-mass warm Jupiter on a 29-d orbit transiting an active K0 V star
- 2018
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Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 475:2, s. 1765-1776
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Tidskriftsartikel (refereegranskat)abstract
- We announce the discovery of K2-139 b (EPIC 218916923 b), a transiting warm-Jupiter (Teq = 547 ± 25 K) on a 29-d orbit around an active (log R'_HK = -4.46 ± 0.06) K0V star in K2 Campaign 7. We derive the system's parameters by combining the K2 photometry with ground-based follow-up observations. With a mass of 0.387_-0.075^+0.083 M_J and radius of 0.808_-0.033^+0.034 R_J, K2-139 b is one of the transiting warm Jupiters with the lowest mass known to date. The planetary mean density of 0.91_-0.20^+0.24 g/cm^3 can be explained with a core of ~50 M⊕. Given the brightness of the host star (V = 11.653 mag), the relatively short transit duration (~5 h), and the expected amplitude of the Rossiter-McLaughlin effect (~25m/s), K2-139 is an ideal target to measure the spin-orbit angle of a planetary system hosting a warm Jupiter.
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| 6. |
- Esposito, M., et al.
(författare)
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HD 219666 b: a hot-Neptune from TESS Sector 1
- 2019
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 623:623
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Tidskriftsartikel (refereegranskat)abstract
- We report on the confirmation and mass determination of a transiting planet orbiting the old and inactive G7 dwarf star HD219666 (M-star = 0.92 +/- 0.03 M-circle dot, R-star = 1.03 +/- 0.03 R-circle dot, tau(star) = 10 +/- 2 Gyr). With a mass of M-b = 16.6 +/- 1.3 M-circle plus, a radius of R-b = 4.71 +/- 0.17 R-circle plus, and an orbital period of P-orb similar or equal to 6 days, HD219666 b is a new member of a rare class of exoplanets: the hot-Neptunes. The Transiting Exoplanet Survey Satellite (TESS) observed HD219666 (also known as TOI-118) in its Sector 1 and the light curve shows four transit-like events, equally spaced in time. We confirmed the planetary nature of the candidate by gathering precise radial-velocity measurements with the High Accuracy Radial velocity Planet Searcher (HARPS) at ESO 3.6 m. We used the co-added HARPS spectrum to derive the host star fundamental parameters (T-eff = 5527 +/- 65 K, log g(star) = 4.40 +/- 0.11 (cgs), [Fe/H] = 0.04 +/- 0.04 dex, log R-HK' = -5.07 +/- 0.03), as well as the abundances of many volatile and refractory elements. The host star brightness (V = 9.9) makes it suitable for further characterisation by means of in-transit spectroscopy. The determination of the planet orbital obliquity, along with the atmospheric metal-to-hydrogen content and thermal structure could provide us with important clues on the formation mechanisms of this class of objects.
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| 7. |
- Hidalgo, D., et al.
(författare)
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Three planets transiting the evolved star EPIC 249893012: a hot 8.8-Mearth super-Earth and two warm 14.7 and 10.2-Mearth sub-Neptunes
- 2020
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 636
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Tidskriftsartikel (refereegranskat)abstract
- We report the discovery of a new planetary system with three transiting planets, one super-Earth and two sub-Neptunes, that orbit EPIC 249893012, a G8 IV-V evolved star (M⋆ = 1.05 ± 0.05 M☉, R⋆ = 1.71 ± 0.04 R☉, Teff = 5430 ± 85 K). The star is just leaving the main sequence. We combined K2 photometry with IRCS adaptive-optics imaging and HARPS, HARPS-N, and CARMENES high-precision radial velocity measurements to confirm the planetary system, determine the stellar parameters, and measure radii, masses, and densities of the three planets. With an orbital period of 3.5949-0.0007+0.0007days, a mass of 8.75-1.08+1.09 M⊕, and a radius of 1.95-0.08+0.09 R⊕, the inner planet b is compatible with nickel-iron core and a silicate mantle (ρb = 6.39-1.04+1.19 g cm-3). Planets c and d with orbital periods of 15.624-0.001+0.001 and 35.747-0.005+0.005 days, respectively, have masses and radii of 14.67-1.89+1,84 M⊕ and 3.67-0.14+0.17 R⊕ and 10.18-2.42+2.46 M⊕ and 3.94-0.12+0.13 R⊕, respectively, yielding a mean density of 1.62-0.29+0.30 and 0.91-0.23+0.25 g cm-3, respectively. The radius of planet b lies in the transition region between rocky and gaseous planets, but its density is consistent with a rocky composition. Its semimajor axis and the corresponding photoevaporation levels to which the planet has been exposed might explain its measured density today. In contrast, the densities and semimajor axes of planets c and d suggest a very thick atmosphere. The singularity of this system, which orbits a slightly evolved star that is just leaving the main sequence, makes it a good candidate for a deeper study from a dynamical point of view.
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| 8. |
- Dai, F., et al.
(författare)
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The Discovery and Mass Measurement of a New Ultra-short-period Planet: K2-131
- 2017
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Ingår i: Astronomical Journal. - : American Astronomical Society. - 1538-3881 .- 0004-6256. ; 154:6, s. 226-
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Tidskriftsartikel (refereegranskat)abstract
- We report the discovery of a new ultra-short-period planet and summarize the properties of all such planets for which the mass and radius have been measured. The new planet, EPIC 228732031b, was discovered in K2 Campaign 10. It has a radius of 1.81-0.12+0.16 R_Earth and orbits a G dwarf with a period of 8.9 hr. Radial velocities obtained with Magellan/PFS and TNG/HARPS-N show evidence for stellar activity along with orbital motion. We determined the planetary mass using two different methods: (1) the “floating chunk offset” method, based only on changes in velocity observed on the same night; and (2) a Gaussian process regression based on both the radial velocity and photometric time series. The results are consistent and lead to a mass measurement of 6.5+/- 1.6 M_Earth and a mean density of 6.0-2.7+3.0 g cm‑3.
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| 9. |
- Guenther, E. W., et al.
(författare)
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K2-106, a system containing a metal-rich planet and a planet of lower density
- 2017
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 608, s. 93-
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Tidskriftsartikel (refereegranskat)abstract
- Planets in the mass range from 2 to 15 M_Earth are very diverse. Some of them have low densities, while others are very dense. By measuring the masses and radii, the mean densities, structure, and composition of the planets are constrained. These parameters also give us important information about their formation and evolution, and about possible processes for atmospheric loss.We determined the masses, radii, and mean densities for the two transiting planets orbiting K2-106. The inner planet has an ultra-short period of 0.57 days. The period of the outer planet is 13.3 days. Although the two planets have similar masses, their densities are very different. For K2-106b we derive Mb=8.36-0.94+0.96 M_Earh, Rb=1.52+/-0.16 R_Earth, and a high density of 13.1-3.6+5.4 g/cm^3. For K2-106c, we find Mc=5.8-3.0+3.3 M_Earth, Rc=2.50-0.26+0.27 R_Earth and a relatively low density of 2.0-1.1+1.6 g/cm^3.Since the system contains two planets of almost the same mass, but different distances from the host star, it is an excellent laboratory to study atmospheric escape. In agreement with the theory of atmospheric-loss processes, it is likely that the outer planet has a hydrogen-dominated atmosphere. The mass and radius of the inner planet is in agreement with theoretical models predicting an iron core containing 80+20-30% of its mass. Such a high metal content is surprising, particularly given that the star has an ordinary (solar) metal abundance. We discuss various possible formation scenarios for this unusual planet.
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| 10. |
- Nespral, D., et al.
(författare)
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Mass determination of K2-19b and K2-19c from radial velocities and transit timing variations
- 2017
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 601, s. Article Number: A128-
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Tidskriftsartikel (refereegranskat)abstract
- We present radial velocity follow-up observations of K2-19, a compact planetary system hosting three planets, of which the two larger ones, K2-19b and K2-19c, are close to the 3: 2 mean motion resonance. An analysis considering only the radial velocity measurements detects K2-19b, the larger and more massive planet in the system, with a mass of 54.8 +/- 7.5 M-circle plus and provides a marginal detection of K2-19c, with a mass of M-c = 5.9(-4.3)(+7.6) M-circle plus. We also used the TRADES code to simultaneously model both our RV measurements and the existing transit timing measurements. We derived a mass of 54.4 +/- 8.9 M-circle plus for K2-19b and of 7.5(-1.4)(+3.0) M-circle plus for K2-19c. For K2-19b, these masses are consistent with a previous determination that was principally based on a photodynamical analysis of the K2-19 light curve. Differences remain mainly in the mass determination of the more lightweight planet, driven likely by the limited precision of the RV measurements and possibly some as yet unrecognized systematics.
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