55 research outputs found
An Earth-sized Planet around an M5 Dwarf Star at 22 pc
We report on the discovery of an Earth-sized transiting planet (R p = 1.015 ± 0.051 R â) in a P = 4.02 day orbit around K2-415 (EPIC 211414619), an M5V star at 22 pc. The planet candidate was first identified by analyzing the light-curve data obtained by the K2 mission, and it is here shown to exist in the most recent data from TESS. Combining the light curves with the data secured by our follow-up observations, including high-resolution imaging and near-infrared spectroscopy with IRD, we rule out false-positive scenarios, finding a low false-positive probability of 2 Ă 10â4. Based on IRDâs radial velocities of K2-415, which were sparsely taken over three years, we obtain a planet mass of 3.0 ± 2.7 M â (M p < 7.5 M â at 95% confidence) for K2-415b. Being one of the lowest-mass stars (â0.16 M â) known to host an Earth-sized transiting planet, K2-415 will be an interesting target for further follow-up observations, including additional radial velocity monitoring and transit spectroscopy
High-Contrast Imaging of Intermediate-Mass Giants with Long-Term Radial Velocity Trends
A radial velocity (RV) survey for intermediate-mass giants has been operated for over a decade at Okayama Astrophysical Observatory (OAO). The OAO survey has revealed that some giants show long-term linear RV accelerations (RV trends), indicating the presence of outer companions. Direct imaging observations can help clarify what objects generate these RV trends. We present the results of high-contrast imaging observations of six intermediate-mass giants with long-term RV trends using the Subaru Telescope and HiCIAO camera. We detected co-moving companions to gamma Hya B (0.61+0.12 0.14 Stellar Mass), HD 5608 B (0.10 +/- 0.01 Stellar Mass), and HD 109272 B (0.28 +/- 0.06 Stellar Mass). For the remaining targets( Dra, 18 Del, and HD 14067) we exclude companions more massive than 30-60 M(sub Jup) at projected separations of 1-7. We examine whether these directly imaged companions or unidentified long-period companions can account for the RV trends observed around the six giants. We find that the Kozai mechanism can explain the high eccentricity of the inner planets Dra b, HD 5608 b, and HD 14067 b
Validation and atmospheric exploration of the sub-Neptune TOI-2136b around a nearby M3 dwarf
Context. The NASA space telescope TESS is currently in the extended mission of its all-sky search for new transiting planets. Of the thousands of candidates that TESS is expected to deliver, transiting planets orbiting nearby M dwarfs are particularly interesting targets since they provide a great opportunity to characterize their atmospheres by transmission spectroscopy. Aims. We aim to validate and characterize the new sub-Neptune-sized planet candidate TOI-2136.01 orbiting a nearby M dwarf (d = 33.36 +/- 0.02 pc, T-eff = 3373 +/- 108 K) with an orbital period of 7.852 days. Methods. We use TESS data, ground-based multicolor photometry, and radial velocity measurements with the InfraRed Doppler (IRD) instrument on the Subaru Telescope to validate the planetary nature of TOI-2136.01, and estimate the stellar and planetary parameters. We also conduct high-resolution transmission spectroscopy to search for helium in its atmosphere. Results. We confirm that TOI-2136.01 (now named TOI-2136b) is a bona fide planet with a planetary radius of R-p = 2.20 +/- 0.07 R-circle plus and a mass of M-p = 4.7(-2.6)(+3.1) M-circle plus. We also search for helium 10830 angstrom absorption lines and place an upper limit on the equivalent width of <7.8 m angstrom and on the absorption signal of <1.44% with 95% confidence. Conclusions. TOI-2136b is a sub-Neptune transiting a nearby and bright star (J = 10.8 mag), and is a potentially hycean planet, which is a new class of habitable planets with large oceans under a H-2-rich atmosphere, making it an excellent target for atmospheric studies to understand the formation, evolution, and habitability of the small planets
Mass and density of the transiting hot and rocky super-Earth LHS 1478 b (TOI-1640 b)
One of the main objectives of the Transiting Exoplanet Survey Satellite
({TESS}) mission is the discovery of small rocky planets around relatively
bright nearby stars. Here, we report the discovery and characterization of the
transiting super-Earth planet orbiting LHS~1478 (TOI-1640). The star is an
inactive red dwarf (\,mag and spectral type m3\,V) with mass and
radius estimates of \, and \,,
respectively, and an effective temperature of \,K.It was observed by
\tess in four sectors. These data revealed a transit-like feature with a period
of 1.949 days. We combined the TESS data with three ground-based transit
measurements, 57 radial velocity (RV) measurements from CARMENES, and 13 RV
measurements from IRD, determining that the signal is produced by a planet with
a mass of \, and a radius of
\,. The resulting bulk density of this planet
is 6.67\,g\,cm, which is consistent with a rocky planet with an Fe- and
MgSiO-dominated composition. Although the planet would be too hot to
sustain liquid water on its surface (its equilibrium temperature is about
595\,K, suggesting a Venus-like atmosphere), spectroscopic metrics based
on the capabilities of the forthcoming James Webb Space Telescope and the fact
that the host star is rather inactive indicate that this is one of the most
favorable known rocky exoplanets for atmospheric characterization.Comment: 14 pages, 10 figures, 6 tables, accepted for publication in A&
Zodiacal Exoplanets in Time. X. The Orbit and Atmosphere of the Young "Neptune Desert"-Dwelling Planet K2-100b
We obtained high-resolution infrared spectroscopy and short-cadence
photometry of the 600-800 Myr Praesepe star K2-100 during transits of its
1.67-day planet. This Neptune-size object, discovered by the NASA K2 mission,
is an interloper in the "desert" of planets with similar radii on short period
orbits. Our observations can be used to understand its origin and evolution by
constraining the orbital eccentricity by transit fitting, measuring the
spin-orbit obliquity by the Rossiter-McLaughlin effect, and detecting any
extended, escaping hydrogen-helium envelope with the 10830A line of neutral
helium in the 2s3S triplet state. Transit photometry with 1-min cadence was
obtained by the K2 satellite during Campaign 18 and transit spectra were
obtained with the IRD spectrograph on the Subaru telescope. While the elevated
activity of K2-100 prevented us from detecting the Rossiter-McLaughlin effect,
the new photometry combined with revised stellar parameters allowed us to
constrain the eccentricity to e < 0.15/0.28 with 90%/99% confidence. We modeled
atmospheric escape as an isothermal, spherically symmetric Parker wind, with
photochemistry driven by UV radiation that we estimate by combining the
observed spectrum of the active Sun with calibrations from observations of
K2-100 and similar young stars in the nearby Hyades cluster. Our non-detection
(<5.7mA) of a transit-associated He I line limits mass loss of a
solar-composition atmosphere through a T<10000K wind to <0.3Me/Gyr. Either
K2-100b is an exceptional desert-dwelling planet, or its mass loss is occurring
at a lower rate over a longer interval, consistent with a core
accretion-powered scenario for escape.Comment: Accepted to MNRA
The discovery and follow-up of four transiting short-period sub-Neptunes orbiting M dwarfs
Sub-Neptunes with radii of 2â3 Râ are intermediate in size between rocky planets and Neptune-sized planets. The orbital properties and bulk compositions of transiting sub-Neptunes provide clues to the formation and evolution of close-in small planets. In this paper, we present the discovery and follow-up of four sub-Neptunes orbiting M dwarfs (TOI-782, TOI-1448, TOI-2120, and TOI-2406), three of which were newly validated by ground-based follow-up observations and statistical analyses. TOI-782 b, TOI-1448 b, TOI-2120 b, and TOI-2406 b have radii of Rp = 2.740 +0.082-0.079 Râ, 2.769+0.073-0.068 Râ, 2.120 ± 0.067 Râ, and 2.830+0.068-0.066 Râ and orbital periods of P = 8.02, 8.11, 5.80, and 3.08 days, respectively. Doppler monitoring with the Subaru/InfraRed Doppler instrument led to 2Ï upper limits on the masses of <19.1 Mâ, <19.5 Mâ, <6.8 Mâ, and <15.6 Mâ for TOI-782 b, TOI-1448 b, TOI-2120 b, and TOI-2406 b, respectively. The massâradius relationship of these four sub-Neptunes testifies to the existence of volatile material in their interiors. These four sub-Neptunes, which are located above the so-called "radius valley," are likely to retain a significant atmosphere and/or an icy mantle on the core, such as a water world. We find that at least three of the four sub-Neptunes (TOI-782 b, TOI-2120 b, and TOI-2406 b), orbiting M dwarfs older than 1 Gyr, are likely to have eccentricities of e ⌠0.2â0.3. The fact that tidal circularization of their orbits is not achieved over 1 Gyr suggests inefficient tidal dissipation in their interiors.Peer reviewe
Quantifying the Influence of Jupiter on the Earth's Orbital Cycles
A wealth of Earth-sized exoplanets will be discovered in the coming years,
proving a large pool of candidates from which the targets for the search for
life beyond the Solar system will be chosen. The target selection process will
require the leveraging of all available information in order to maximise the
robustness of the target list and make the most productive use of follow-up
resources. Here, we present the results of a suite of -body simulations that
demonstrate the degree to which the orbital architecture of the Solar system
impacts the variability of Earth's orbital elements. By varying the orbit of
Jupiter and keeping the initial orbits of the other planets constant, we
demonstrate how subtle changes in Solar system architecture could alter the
Earth's orbital evolution -- a key factor in the Milankovitch cycles that alter
the amount and distribution of solar insolation, thereby driving periodic
climate change on our planet. The amplitudes and frequencies of Earth's modern
orbital cycles fall in the middle of the range seen in our runs for all
parameters considered -- neither unusually fast nor slow, nor large nor small.
This finding runs counter to the `Rare Earth' hypothesis, which suggests that
conditions on Earth are so unusual that life elsewhere is essentially
impossible. Our results highlight how dynamical simulations of newly discovered
exoplanetary systems could be used as an additional means to assess the
potential targets of biosignature searches, and thereby help focus the search
for life to the most promising targets.Comment: 19 pages; 11 figures; accepted for publication in the Astronomical
Journal Version 2 - incorporates typo corrections and minor changes noted at
the proofing stage, after acceptanc
Two temperate super-Earths transiting a nearby late-type M dwarf
peer reviewedIn the age of JWST, temperate terrestrial exoplanets transiting nearby late-type M dwarfs provide unique opportunities for characterising their atmospheres, as well as searching for biosignature gases. We report here the discovery and validation of two temperate super-Earths transiting LP 890-9 (TOI-4306, SPECULOOS-2), a relatively low-activity nearby (32 pc) M6V star. The inner planet, LP 890-9b, was first detected by TESS (and identified as TOI-4306.01) based on four sectors of data. Intensive photometric monitoring of the system with the SPECULOOS Southern Observatory then led to the discovery of a second outer transiting planet, LP 890-9c (also identified as SPECULOOS-2c), previously undetected by TESS. The orbital period of this second planet was later confirmed by MuSCAT3 follow-up observations. With a mass of 0.118±0.002 Mâ, a radius of 0.1556±0.0086 Râ, and an effective temperature of 2850±75 K, LP 890-9 is the second-coolest star found to host planets, after TRAPPIST-1. The inner planet has an orbital period of 2.73 d, a radius of 1.320+0.053â0.027 Râ, and receives an incident stellar flux of 4.09±0.12 Sâ. The outer planet has a similar size of 1.367+0.055â0.039 Râ and an orbital period of 8.46 d. With an incident stellar flux of 0.906 ± 0.026 Sâ, it is located within the conservative habitable zone, very close to its inner limit. Although the masses of the two planets remain to be measured, we estimated their potential for atmospheric characterisation via transmission spectroscopy using a mass-radius relationship and found that, after the TRAPPIST-1 planets, LP 890-9c is the second-most favourable habitable-zone terrestrial planet known so far. The discovery of this remarkable system offers another rare opportunity to study temperate terrestrial planets around our smallest and coolest neighbours
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