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Register a new userThe TESS-Keck Survey II: An Ultra-Short Period Rocky Planet and its Siblings Transiting the Galactic Thick-Disk Star TOI-561
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We report the discovery of TOI-561, a multi-planet system in the galactic thick disk that contains a rocky, ultra-short period planet (USP). This bright ($V=10.2$) star hosts three small transiting planets identified in photometry from the NASA TESS mission: TOI-561 b (TOI-561.02, P=0.44 days, $R_b = 1.45pm0.11,R_oplus$), c (TOI-561.01, P=10.8 days, $R_c=2.90pm0.13,R_oplus$), and d (TOI-561.03, P=16.3 days, $R_d=2.32pm0.16,R_oplus$). The star is chemically ([Fe/H]$=-0.41pm0.05$, [$alpha$/H]$=+0.23pm0.05$) and kinematically consistent with the galactic thick disk population, making TOI-561 one of the oldest ($10pm3,$Gyr) and most metal-poor planetary systems discovered yet. We dynamically confirm planets b and c with radial velocities from the W. M. Keck Observatory High Resolution Echelle Spectrometer. Planet b has a mass and density of $3.2pm0.8,M_oplus$ and $5.5^{+2.0}_{-1.6},$g$,$cm$^{-3}$, consistent with a rocky composition. Its lower-than-average density is consistent with an iron-poor composition, although an Earth-like iron-to-silicates ratio is not ruled out. Planet c is $7.0pm2.3,M_oplus$ and $1.6pm0.6,$g$,$cm$^{-3}$, consistent with an interior rocky core overlaid with a low-mass volatile envelope. Several attributes of the photometry for planet d (which we did not detect dynamically) complicate the analysis, but we vet the planet with high-contrast imaging, ground-based photometric follow-up and radial velocities. TOI-561 b is the first rocky world around a galactic thick-disk star confirmed with radial velocities and one of the best rocky planets for thermal emission studies.
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We report the first discovery of a thick-disk planet, LHS 1815b (TOI-704b, TIC 260004324), detected in the TESS survey. LHS 1815b transits a bright (V = 12.19 mag, K = 7.99 mag) and quiet M dwarf located $ 29.87pm0.02 pc$ away with a mass of $0.502pm0.015 M_{odot}$ and a radius of $0.501pm0.030 R_{odot}$. We validate the planet by combining space and ground-based photometry, spectroscopy, and imaging. The planet has a radius of $1.088pm 0.064 R_{oplus}$ with a $3 sigma$ mass upper-limit of $8.7 M_{oplus}$. We analyze the galactic kinematics and orbit of the host star LHS1815 and find that it has a large probability ($P_{thick}/P_{thin} = 6482$) to be in the thick disk with a much higher expected maximal height ($Z_{max} = 1.8 kpc$) above the Galactic plane compared with other TESS planet host stars. Future studies of the interior structure and atmospheric properties of planets in such systems using for example the upcoming James Webb Space Telescope (JWST), can investigate the differences in formation efficiency and evolution for planetary systems between different Galactic components (thick and thin disks, and halo).
Based on HARPS-N radial velocities (RVs) and TESS photometry, we present a full characterisation of the planetary system orbiting the late G dwarf TOI-561. After the identification of three transiting candidates by TESS, we discovered two additional external planets from RV analysis. RVs cannot confirm the outer TESS transiting candidate, which would also make the system dynamically unstable. We demonstrate that the two transits initially associated with this candidate are instead due to single transits of the two planets discovered using RVs. The four planets orbiting TOI-561 include an ultra-short period (USP) super-Earth (TOI-561 b) with period $P_{rm b} = 0.45$ d, mass $M_{rm b} =1.59 pm 0.36$ M$_oplus$ and radius $R_{rm b}=1.42 pm 0.07$ R$_oplus$, and three mini-Neptunes: TOI-561 c, with $P_{rm c} = 10.78$ d, $M_{rm c} = 5.40 pm 0.98$ M$_oplus$, $R_{rm c}= 2.88 pm 0.09$ R$_oplus$; TOI-561 d, with $P_{rm d} = 25.6$ d, $M_{rm d} = 11.9 pm 1.3$ M$_oplus$, $R_{rm d} = 2.53 pm 0.13$ R$_oplus$; and TOI-561 e, with $P_{rm e} = 77.2$ d, $M_{rm e} = 16.0 pm 2.3$ M$_oplus$, $R_{rm e} = 2.67 pm 0.11$ R$_oplus$. Having a density of $3.0 pm 0.8$ g cm$^{-3}$, TOI-561 b is the lowest density USP planet known to date. Our N-body simulations confirm the stability of the system and predict a strong, anti-correlated, long-term transit time variation signal between planets d and e. The unusual density of the inner super-Earth and the dynamical interactions between the outer planets make TOI-561 an interesting follow-up target.
Dynamical histories of planetary systems, as well as atmospheric evolution of highly irradiated planets, can be studied by characterizing the ultra-short-period planet population, which the TESS mission is particularly well suited to discover. Here, we report on the follow-up of a transit signal detected in the TESS sector 19 photometric time series of the M3.0 V star TOI-1685 (2MASS J04342248+4302148). We confirm the planetary nature of the transit signal, which has a period of P_b=0.6691403+0.0000023-0.0000021 d, using precise radial velocity measurements taken with the CARMENES spectrograph. From the joint photometry and radial velocity analysis, we estimate the following parameters for TOI-1685 b: a mass of M_b=3.78+/-0.63 M_Earth, a radius of R_b=1.70+/-0.07 R_Earth, which together result in a bulk density of rho_b=4.21+0.95-0.82 g/cm3, and an equilibrium temperature of Teq_b=1069+/-16 K. TOI-1685 b is the least dense ultra-short period planet around an M dwarf known to date. TOI-1685 b is also one of the hottest transiting Earth-size planets with accurate dynamical mass measurements, which makes it a particularly attractive target for thermal emission spectroscopy. Additionally, we report a further non-transiting planet candidate in the system, TOI-1685[c], with an orbital period of P_[c]=9.02+0.10-0.12 d.
We report the detection of the first circumbinary planet found by TESS. The target, a known eclipsing binary, was observed in sectors 1 through 12 at 30-minute cadence and in sectors 4 through 12 at two-minute cadence. It consists of two stars with masses of 1.1 MSun and 0.3 MSun on a slightly eccentric (0.16), 14.6-day orbit, producing prominent primary eclipses and shallow secondary eclipses. The planet has a radius of ~6.9 REarth and was observed to make three transits across the primary star of roughly equal depths (~0.2%) but different durations -- a common signature of transiting circumbinary planets. Its orbit is nearly circular (e ~ 0.09) with an orbital period of 95.2 days. The orbital planes of the binary and the planet are aligned to within ~1 degree. To obtain a complete solution for the system, we combined the TESS photometry with existing ground-based radial-velocity observations in a numerical photometric-dynamical model. The system demonstrates the discovery potential of TESS for circumbinary planets, and provides further understanding of the formation and evolution of planets orbiting close binary stars.
Ultra-short period (USP) planets are a class of exoplanets with periods shorter than one day. The origin of this sub-population of planets is still unclear, with different formation scenarios highly dependent on the composition of the USP planets. A better understanding of this class of exoplanets will, therefore, require an increase in the sample of such planets that have accurate and precise masses and radii, which also includes estimates of the level of irradiation and information about possible companions. Here we report a detailed characterization of a USP planet around the solar-type star HD 80653 $equiv$ EP 251279430 using the K2 light curve and 108 precise radial velocities obtained with the HARPS-N spectrograph, installed on the Telescopio Nazionale Galileo. From the K2 C16 data, we found one super-Earth planet ($R_{b}=1.613pm0.071 R_{oplus}$) transiting the star on a short-period orbit ($P_{rm b}=0.719573pm0.000021$ d). From our radial velocity measurements, we constrained the mass of HD 80653 b to $M_{b}=5.60pm0.43 M_{oplus}$. We also detected a clear long-term trend in the radial velocity data. We derived the fundamental stellar parameters and determined a radius of $R_{star}=1.22pm0.01 R_{odot}$ and mass of $M_{star}=1.18pm0.04 M_{odot}$, suggesting that HD 80653, has an age of $2.7pm1.2$ Gyr. The bulk density ($rho_{b} = 7.4 pm 1.1$ g cm$^{-3}$) of the planet is consistent with an Earth-like composition of rock and iron with no thick atmosphere. Our analysis of the K2 photometry also suggests hints of a shallow secondary eclipse with a depth of 8.1$pm$3.7 ppm. Flux variations along the orbital phase are consistent with zero. The most important contribution might come from the day-side thermal emission from the surface of the planet at $Tsim3480$ K.
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