96 research outputs found
The host stars of Kepler's habitable exoplanets : superflares, rotation and activity
We embark on a detailed study of the light curves of Kepler's most Earth-like exoplanet host stars using the full length of Kepler data. We derive rotation periods, photometric activity indices, flaring energies, mass-loss rates, gyrochronological ages, X-ray luminosities and consider implications for the planetary magnetospheres and habitability. Furthermore, we present the detection of superflares in the light curve of Kepler-438, the exoplanet with the highest Earth Similarity Index to date. Kepler-438b orbits at a distance of 0.166 au to its host star, and hence may be susceptible to atmospheric stripping. Our sample is taken from the Habitable Exoplanet Catalogue, and consists of the stars Kepler-22, Kepler-61, Kepler-62, Kepler-174, Kepler-186, Kepler-283, Kepler-296, Kepler-298, Kepler-438, Kepler-440, Kepler-442, Kepler-443 and KOI-4427, between them hosting 15 of the most habitable transiting planets known to date from Kepler
Single transit candidates from K2 : detection and period estimation
Photometric surveys such as Kepler have the precision to identify exoplanet and eclipsing binary candidates from only a single transit. K2, with its 75 d campaign duration, is ideally suited to detect significant numbers of single-eclipsing objects. Here we develop a Bayesian transit-fitting tool (‘Namaste: An Mcmc Analysis of Single Transit Exoplanets’) to extract orbital information from single transit events. We achieve favourable results testing this technique on known Kepler planets, and apply the technique to seven candidates identified from a targeted search of K2 campaigns 1, 2 and 3. We find EPIC203311200 to host an excellent exoplanet candidate with a period, assuming zero eccentricity, of 540+410 −230 d and a radius of 0.51 ± 0.05RJup. We also find six further transit candidates for which more follow-up is required to determine a planetary origin. Such a technique could be used in the future with TESS, PLATO and ground-based photometric surveys such as NGTS, potentially allowing the detection of planets in reach of confirmation by Gaia
One of the closest exoplanet pairs to the 3:2 Mean Motion Resonance: K2-19b \& c
The K2 mission has recently begun to discover new and diverse planetary
systems. In December 2014 Campaign 1 data from the mission was released,
providing high-precision photometry for ~22000 objects over an 80 day timespan.
We searched these data with the aim of detecting further important new objects.
Our search through two separate pipelines led to the independent discovery of
K2-19b \& c, a two-planet system of Neptune sized objects (4.2 and 7.2
), orbiting a K dwarf extremely close to the 3:2 mean motion
resonance. The two planets each show transits, sometimes simultaneously due to
their proximity to resonance and alignment of conjunctions. We obtain further
ground based photometry of the larger planet with the NITES telescope,
demonstrating the presence of large transit timing variations (TTVs), and use
the observed TTVs to place mass constraints on the transiting objects under the
hypothesis that the objects are near but not in resonance. We then
statistically validate the planets through the \texttt{PASTIS} tool,
independently of the TTV analysis.Comment: 18 pages, 10 figures, accepted to A&A, updated to match published
versio
TESS Duotransit Candidates from the Southern Ecliptic Hemisphere
Discovering transiting exoplanets with long orbital periods allows us to
study warm and cool planetary systems with temperatures similar to the planets
in our own Solar system. The TESS mission has photometrically surveyed the
entire Southern Ecliptic Hemisphere in Cycle 1 (August 2018 - July 2019), Cycle
3 (July 2020 - June 2021) and Cycle 5 (September 2022 - September 2023). We use
the observations from Cycle 1 and Cycle 3 to search for exoplanet systems that
show a single transit event in each year - which we call duotransits. The
periods of these planet candidates are typically in excess of 20 days, with the
lower limit determined by the duration of individual TESS observations. We find
85 duotransit candidates, which span a range of host star brightnesses between
8 < < 14, transit depths between 0.1 per cent and 1.8 per cent, and
transit durations between 2 and 10 hours with the upper limit determined by our
normalisation function. Of these candidates, 25 are already known, and 60 are
new. We present these candidates along with the status of photometric and
spectroscopic follow-up.Comment: 25 pages, 16 figures, submitted to Monthly Notices of the Royal
Astronomical Societ
KELT-9 b's Asymmetric TESS Transit Caused by Rapid Stellar Rotation and Spin-Orbit Misalignment
KELT-9 b is an ultra hot Jupiter transiting a rapidly rotating, oblate
early-A-type star in a polar orbit. We model the effect of rapid stellar
rotation on KELT-9 b's transit light curve using photometry from the Transiting
Exoplanet Survey Satellite (\tess) to constrain the planet's true spin-orbit
angle and to explore how KELT-9 b may be influenced by stellar gravity
darkening. We constrain the host star's equatorial radius to be
times as large as its polar radius and its local surface brightness to vary by
\% between its hot poles and cooler equator. We model the stellar
oblateness and surface brightness gradient and find that it causes the transit
light curve to lack the usual symmetry around the time of minimum light. We
take advantage of the light curve asymmetry to constrain KELT-9 b's true spin
orbit angle (), agreeing with
\citet{gaudi2017giant} that KELT-9 b is in a nearly polar orbit. We also apply
a gravity darkening correction to the spectral energy distribution model from
\citet{gaudi2017giant} and find that accounting for rapid rotation gives a
better fit to available spectroscopy and yields a more reliable estimate for
the star's polar effective temperature.Comment: Accepted for Publication in ApJ. arXiv admin note: text overlap with
arXiv:1911.0502
Photodynamical mass determination of the multiplanetary system K2-19
K2-19 is the second multiplanetary system discovered with K2 observations. The system is composed of two Neptune size planets close to the 3:2 mean-motion resonance. To better characterize the system we obtained two additional transit observations of K2-19b and five additional radial velocity observations. These were combined with K2 data and fitted simultaneously with the system dynamics (photodynamical model) which increases the precision of the transit time measurements. The higher transit time precision allows us to detect the chopping signal of the dynamic interaction of the planets that in turn permits to uniquely characterize the system. Although the reflex motion of the star was not detected, dynamic modelling of the system allowed us to derive planetary masses of Mb = 44 ± 12  M⊕ and Mc = 15.9 ± 7.0  M⊕ for the inner and the outer planets, respectively, leading to densities close to Uranus. We also show that our method allows the derivation of mass ratios using only the 80 d of observations during the first campaign of K2
TESS Hunt for Young and Maturing Exoplanets (THYME) IX: a 27 Myr extended population of Lower-Centaurus Crux with a transiting two-planet system
We report the discovery and characterization of a nearby (~ 85 pc), older (27
+/- 3 Myr), distributed stellar population near Lower-Centaurus-Crux (LCC),
initially identified by searching for stars co-moving with a candidate
transiting planet from TESS (HD 109833; TOI 1097). We determine the association
membership using Gaia kinematics, color-magnitude information, and rotation
periods of candidate members. We measure it's age using isochrones,
gyrochronology, and Li depletion. While the association is near known
populations of LCC, we find that it is older than any previously found LCC
sub-group (10-16 Myr), and distinct in both position and velocity. In addition
to the candidate planets around HD 109833 the association contains four
directly-imaged planetary-mass companions around 3 stars, YSES-1, YSES-2, and
HD 95086, all of which were previously assigned membership in the younger LCC.
Using the Notch pipeline, we identify a second candidate transiting planet
around HD 109833. We use a suite of ground-based follow-up observations to
validate the two transit signals as planetary in nature. HD 109833 b and c join
the small but growing population of <100 Myr transiting planets from TESS. HD
109833 has a rotation period and Li abundance indicative of a young age (< 100
Myr), but a position and velocity on the outskirts of the new population, lower
Li levels than similar members, and a CMD position below model predictions for
27 Myr. So, we cannot reject the possibility that HD 109833 is a young field
star coincidentally nearby the population.Comment: 23 pages, 15 figures, Accepted for publication in A
Discovery and characterisation of two Neptune-mass planets orbiting HD 212729 with TESS
We report the discovery of two exoplanets orbiting around HD 212729
(TOI\,1052, TIC 317060587), a K star with V=9.51 observed by
TESS in Sectors 1 and 13. One exoplanet, TOI-1052b, is Neptune-mass and
transits the star, and an additional planet TOI-1052c is observed in radial
velocities but not seen to transit. We confirm the planetary nature of
TOI-1052b using precise radial velocity observations from HARPS and determined
its parameters in a joint RV and photometry analysis. TOI-1052b has a radius of
R, a mass of M, and
an orbital period of 9.14 days. TOI-1052c does not show any transits in the
TESS data, and has a minimum mass of M and an
orbital period of 35.8 days, placing it just interior to the 4:1 mean motion
resonance. Both planets are best fit by relatively high but only marginally
significant eccentricities of for planet b and
for planet c. We perform a dynamical analysis and
internal structure model of the planets as well as deriving stellar parameters
and chemical abundances. The mean density of TOI-1052b is g
cm consistent with an internal structure similar to Neptune. A nearby
star is observed in Gaia DR3 with the same distance and proper motion as
TOI-1052, at a sky projected separation of ~1500AU, making this a potential
wide binary star system.Comment: Accepted to MNRAS. 11 page
TESS duotransit candidates from the Southern Ecliptic Hemisphere
Discovering transiting exoplanets with long orbital periods allows us to study warm and cool planetary systems with temperatures similar to the planets in our own Solar system. The Transiting Exoplanet Survey Satellite (TESS) mission has photometrically surveyed the entire Southern Ecliptic Hemisphere in Cycle 1 (2018 August–2019 July), Cycle 3 (2020 July–2021 June), and Cycle 5 (2022 September–2023 September). We use the observations from Cycle 1 and Cycle 3 to search for exoplanet systems that show a single transit event in each year, which we call duotransits. The periods of these planet candidates are typically in excess of 20 d, with the lower limit determined by the duration of individual TESS observations. We find 85 duotransit candidates, which span a range of host star brightnesses: 8 < Tmag < 14, transit depths between 0.1 per cent and 1.8 per cent, and transit durations between 2 and 10 h with the upper limit determined by our normalization function. Of these candidates, 25 are already known, and 60 are new. We present these candidates along with the status of photometric and spectroscopic follow-up
Separated twins or just siblings? A multi-planet system around an M dwarf including a cool sub-Neptune
We report the discovery of two TESS sub-Neptunes orbiting the early M dwarf
TOI-904 (TIC 261257684). Both exoplanets, TOI-904 b and c, were initially
observed in TESS sector 12 with twin sizes of 2.49R and
2.31R, respectively. Through observations in five additional sectors
in the TESS primary mission and the first and second extended missions, the
orbital periods of both planets were measured to be 10.8870.001 and
83.9990.001 days, respectively. Reconnaissance radial velocity
measurements (taken with EULER/CORALIE) and high resolution speckle imaging
with adaptive optics (obtained from SOAR/HRCAM and Gemini South/ZORRO) show no
evidence of an eclipsing binary or a nearby companion, which together with the
low false positive probabilities calculated with the statistical validation
software TRICERATOPS establish the planetary nature of these candidates. The
outer planet, TOI-904 c, is the longest-period M dwarf exoplanet found by TESS,
with an estimated equilibrium temperature of 217K. As the three other validated
planets with comparable host stars and orbital periods were observed by Kepler
around much dimmer stars (J 12), TOI-904 c, orbiting a brighter
star (J 9.6), is the coldest M dwarf planet easily accessible for
atmospheric follow-up. Future mass measurements and transmission spectroscopy
of the similar sized planets in this system could determine whether they are
also similar in density and composition, suggesting a common formation pathway,
or whether they have distinct origins.Comment: 18 pages, 6 figures, Accepted by the Astrophysical Journal Letter
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