21 research outputs found
Revisiting the Kepler field with TESS: Improved ephemerides using TESS 2min data
Up to date planet ephemerides are becoming increasingly important as
exoplanet science moves from detecting exoplanets to characterising their
architectures and atmospheres in depth. In this work ephemerides are updated
for 22 Kepler planets and 4 Kepler planet candidates, constituting all Kepler
planets and candidates with sufficient signal to noise in the TESS 2min
dataset. A purely photometric method is utilised here to allow ephemeris
updates for planets even when they do not posses significant radial velocity
data. The obtained ephemerides are of very high precision and at least seven
years 'fresher' than archival ephemerides. In particular, significantly reduced
period uncertainties for Kepler-411d, Kepler-538b and the candidates
K00075.01/K00076.01 are reported. O-C diagrams were generated for all objects,
with the most interesting ones discussed here. Updated TTV fits of five known
multiplanet systems with significant TTVs were also attempted (Kepler-18,
Kepler-25, Kepler-51, Kepler-89, and Kepler-396), however these suffered from
the comparative scarcity and dimness of these systems in TESS. Despite these
difficulties, TESS has once again shown itself to be an incredibly powerful
follow-up instrument as well as a planet-finder in its own right. Extension of
the methods used in this paper to the 30min-cadence TESS data and TESS extended
mission has the potential to yield updated ephemerides of hundreds more systems
in the future.Comment: 13 pages, 11 figures, 4 tables, accepted for publication in MNRA
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
Two mini-Neptunes Transiting the Adolescent K-star HIP 113103 Confirmed with TESS and CHEOPS
We report the discovery of two mini-Neptunes in near 2:1 resonance orbits
( d for HIP 113103 b and d for HIP 113103 c) around
the adolescent K-star HIP 113103 (TIC 121490076). The planet system was first
identified from the TESS mission, and was confirmed via additional photometric
and spectroscopic observations, including a 17.5 hour observation for the
transits of both planets using ESA CHEOPS. We place min and
min limits on the absence of transit timing variations over the three year
photometric baseline, allowing further constraints on the orbital
eccentricities of the system beyond that available from the photometric transit
duration alone. With a planetary radius of
, HIP 113103 b resides within the
radius gap, and this might provide invaluable information on the formation
disparities between super-Earths and mini-Neptunes. Given the larger radius
for HIP 113103 c, and close proximity
of both planets to HIP 113103, it is likely that HIP 113103 b might have lost
(or is still losing) its primordial atmosphere. We therefore present simulated
atmospheric transmission spectra of both planets using JWST, HST, and Twinkle.
It demonstrates a potential metallicity difference (due to differences in their
evolution) would be a challenge to detect if the atmospheres are in chemical
equilibrium. As one of the brightest multi sub-Neptune planet systems suitable
for atmosphere follow up, HIP 113103 b and HIP 113103 c could provide insight
on planetary evolution for the sub-Neptune K-star population.Comment: 18 pages, 12 figures, accepted for publication in the Monthly Notices
of the Royal Astronomical Societ
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
NGTS clusters survey – V. Rotation in the Orion star-forming complex
We present a study of rotation across 30 square degrees of the Orion Star-forming Complex, following a ∼200 d photometric monitoring campaign by the Next Generation Transit Survey (NGTS). From 5749 light curves of Orion members, we report periodic signatures for 2268 objects and analyse rotation period distributions as a function of colour for 1789 stars with spectral types F0–M5. We select candidate members of Orion using Gaia data and assign our targets to kinematic sub-groups. We correct for interstellar extinction on a star-by-star basis and determine stellar and cluster ages using magnetic and non-magnetic stellar evolutionary models. Rotation periods generally lie in the range 1–10 d, with only 1.5 per cent of classical T Tauri stars or Class I/II young stellar objects rotating with periods shorter than 1.8 d, compared with 14 per cent of weak-line T Tauri stars or Class III objects. In period–colour space, the rotation period distribution moves towards shorter periods among low-mass (&gt;M2) stars of age 3–6 Myr, compared with those at 1–3 Myr, with no periods longer than 10 d for stars later than M3.5. This could reflect a mass-dependence for the dispersal of circumstellar discs. Finally, we suggest that the turnover (from increasing to decreasing periods) in the period–colour distributions may occur at lower mass for the older-aged population: ∼K5 spectral type at 1–3 Myr shifting to ∼M1 at 3–6 Myr
Early Release Science of the exoplanet WASP-39b with JWST NIRCam
Measuring the metallicity and carbon-to-oxygen (C/O) ratio in exoplanet
atmospheres is a fundamental step towards constraining the dominant chemical
processes at work and, if in equilibrium, revealing planet formation histories.
Transmission spectroscopy provides the necessary means by constraining the
abundances of oxygen- and carbon-bearing species; however, this requires broad
wavelength coverage, moderate spectral resolution, and high precision that,
together, are not achievable with previous observatories. Now that JWST has
commenced science operations, we are able to observe exoplanets at previously
uncharted wavelengths and spectral resolutions. Here we report time-series
observations of the transiting exoplanet WASP-39b using JWST's Near InfraRed
Camera (NIRCam). The long-wavelength spectroscopic and short-wavelength
photometric light curves span 2.0 - 4.0 m, exhibit minimal systematics,
and reveal well-defined molecular absorption features in the planet's spectrum.
Specifically, we detect gaseous HO in the atmosphere and place an upper
limit on the abundance of CH. The otherwise prominent CO feature at 2.8
m is largely masked by HO. The best-fit chemical equilibrium models
favour an atmospheric metallicity of 1-100 solar (i.e., an enrichment
of elements heavier than helium relative to the Sun) and a sub-stellar
carbon-to-oxygen (C/O) ratio. The inferred high metallicity and low C/O ratio
may indicate significant accretion of solid materials during planet formation
or disequilibrium processes in the upper atmosphere.Comment: 35 pages, 13 figures, 3 tables, Nature, accepte
A mini-Neptune from TESS and CHEOPS around the 120 Myr Old AB Dor Member HIP 94235
The Transiting Exoplanet Survey Satellite (TESS) mission has enabled discoveries of the brightest transiting planet systems around young stars. These systems are the benchmarks for testing theories of planetary evolution. We report the discovery of a mini-Neptune transiting a bright star in the AB Doradus moving group. HIP 94235 (TOI-4399, TIC 464646604) is a Vmag = 8.31 G-dwarf hosting a mini-Neptune in a 7.7 day period orbit. HIP 94235 is part of the AB Doradus moving group, one of the youngest and closest associations. Due to its youth, the host star exhibits significant photometric spot modulation, lithium absorption, and X-ray emission. Three 0.06% transits were observed during Sector 27 of the TESS Extended Mission, though these transit signals are dwarfed by the 2% peak-to-peak photometric variability exhibited by the host star. Follow-up observations with the Characterising Exoplanet Satellite confirmed the transit signal and prevented the erosion of the transit ephemeris. HIP 94235 is part of a 50 au G-M binary system. We make use of diffraction limited observations spanning 11 yr, and astrometric accelerations from Hipparcos and Gaia, to constrain the orbit of HIP 94235 B. HIP 94235 is one of the tightest stellar binaries to host an inner planet. As part of a growing sample of bright, young planet systems, HIP 94235 b is ideal for follow-up transit observations, such as those that investigate the evaporative processes driven by high-energy radiation that may sculpt the valleys and deserts in the Neptune population
TOI-1259Ab – a gas giant planet with 2.7 per cent deep transits and a bound white dwarf companion
We present TOI-1259Ab, a 1.0RJup gas giant planet transiting a 0.71R⊙ K-dwarf on a 3.48 d orbit. The system also contains a bound white dwarf companion TOI-1259B with a projected distance of ∼1600 au from the planet host. Transits are observed in nine TESS sectors and are 2.7 per cent deep – among the deepest known – making TOI-1259Ab a promising target for atmospheric characterization. Our follow-up radial velocity measurements indicate a variability of semiamplitude , implying a planet mass of 0.44MJup. By fitting the spectral energy distribution of the white dwarf, we derive a total age of Gyr for the system. The K dwarf’s light curve reveals rotational variability with a period of 28 d, which implies a gyrochronology age broadly consistent with the white dwarf’s total age
NGTS clusters survey – IV. Search for Dipper stars in the Orion Nebular Cluster
The dipper is a novel class of young stellar object associated with large drops in flux on the order of 10–50 per cent lasting for hours to days. Too significant to arise from intrinsic stellar variability, these flux drops are currently attributed to disc warps, accretion streams, and/or transiting circumstellar dust. Dippers have been previously studied in young star-forming regions, including the Orion Complex. Using Next Generation Transit Survey (NGTS) data, we identified variable stars from their light curves. We then applied a machine learning random forest classifier for the identification of new dipper stars in Orion using previous variable classifications as a training set. We discover 120 new dippers, of which 83 are known members of the Complex. We also investigated the occurrence rate of discs in our targets, again using a machine learning approach. We find that all dippers have discs, and most of these are full discs. We use dipper periodicity and model-derived stellar masses to identify the orbital distance to the inner disc edge for dipper objects, confirming that dipper stars exhibit strongly extended sublimation radii, adding weight to arguments that the inner disc edge is further out than predicted by simple models. Finally, we determine a dipper fraction (the fraction of stars with discs which are dippers) for known members of 27.8 ± 2.9 per cent. Our findings represent the largest population of dippers identified in a single cluster to date.</p