Stars with hot Jupiters (HJs) tend to rotate faster than other stars of the same age and mass. This trend has been attributed to tidal interactions between the star and planet. A constraint on the ...dissipation parameter follows from the assumption that tides have managed to spin up the star to the observed rate within the age of the system. This technique was applied previously to HATS-18 and WASP-19. Here, we analyze the sample of all 188 known HJs with an orbital period <3.5 days and a "cool" host star (Teff < 6100 K). We find evidence that the tidal dissipation parameter ( ) increases sharply with forcing frequency, from 105 at 0.5 day−1 to 107 at 2 day−1. This helps to resolve a number of apparent discrepancies between studies of tidal dissipation in binary stars, HJs, and warm Jupiters. It may also allow for a HJ to damp the obliquity of its host star prior to being destroyed by tidal decay.
Abstract
Recent analyses of the Gaia data have identified diffuse stellar populations surrounding nearby open clusters. It is important to verify that these “halos,” “tails,” and “strings” are of ...similar ages and compositions as stars in the denser part of the cluster. We present an analysis of NGC 2516 (≈150 Myr), which has a classical tidal radius of 10 pc and an apparent halo of stars spanning 500 pc (20° on-sky). Combining photometry from Gaia, rotation periods from TESS, and lithium measurements from Gaia-ESO and GALAH, we find that the halo of NGC 2516 is the same age as the cluster’s core. Two-thirds of kinematically selected halo members out to 250 pc from the cluster center have rotation periods consistent with a gyrochronological age of 150 Myr. A comparison sample of field stars shows no such trend. The lithium abundances of stars in the halo are higher than in the field and correlated with the stellar rotation rate and binarity fraction, as has been noted in other young open clusters. Broadly speaking, this work supports a new paradigm wherein the halos of open clusters are often more populous than their cores. We highlight implications for spectroscopic survey targeting, open cluster dispersal, and planet searches around young stars.
Abstract
Kepler 1627A is a G8V star previously known to host a 3.8
R
⊕
planet on a 7.2 day orbit. The star was observed by the Kepler space telescope because it is nearby (
d
= 329 pc) and it ...resembles the Sun. Here, we show using Gaia kinematics, TESS stellar rotation periods, and spectroscopic lithium abundances that Kepler 1627 is a member of the
38
−
5
+
6
Myr old
δ
Lyr cluster. To our knowledge, this makes Kepler 1627Ab the youngest planet with a precise age yet found by the prime Kepler mission. The Kepler photometry shows two peculiarities: the average transit profile is asymmetric, and the individual transit times might be correlated with the local light-curve slope. We discuss possible explanations for each anomaly. More importantly, the
δ
Lyr cluster is one of ∼10
3
coeval groups whose properties have been clarified by Gaia. Many other exoplanet hosts are candidate members of these clusters; their ages can be verified with the trifecta of Gaia, TESS, and ground-based spectroscopy.
The Transiting Exoplanet Survey Satellite (TESS) recently observed 18 transits of the hot Jupiter WASP-4b. The sequence of transits occurred 81.6 11.7 s earlier than had been predicted, based on data ...stretching back to 2007. This is unlikely to be the result of a clock error, because TESS observations of other hot Jupiters (WASP-6b, 18b, and 46b) are compatible with a constant period, ruling out an 81.6 s offset at the 6.4 level. The 1.3 day orbital period of WASP-4b appears to be decreasing at a rate of ms per year. The apparent period change might be caused by tidal orbital decay or apsidal precession, although both interpretations have shortcomings. The gravitational influence of a third body is another possibility, though at present there is minimal evidence for such a body. Further observations are needed to confirm and understand the timing variation.
Wide-field surveys for transiting planets, such as the NASA Kepler and TESS missions, are usually conducted without knowing which stars have binary companions. Unresolved and unrecognized binaries ...give rise to systematic errors in planet occurrence rates, including misclassified planets and mistakes in completeness corrections. The individual errors can have different signs, making it difficult to anticipate the net effect on inferred occurrence rates. Here, we use simplified models of signal-to-noise limited transit surveys to try and clarify the situation. We derive a formula for the apparent occurrence rate density measured by an observer who falsely assumes all stars are single. The formula depends on the binary fraction, the mass function of the secondary stars, and the true occurrence of planets around primaries, secondaries, and single stars. It also takes into account the Malmquist bias by which binaries are over-represented in flux-limited samples. Application of the formula to an idealized Kepler-like survey shows that for planets larger than 2 R⊕, the net systematic error is of order 5%. In particular, unrecognized binaries are unlikely to be the reason for the apparent discrepancies between hot-Jupiter occurrence rates measured in different surveys. For smaller planets the errors are potentially larger: the occurrence of Earth-sized planets could be overestimated by as much as 50%. We also show that whenever high-resolution imaging reveals a transit host star to be a binary, the planet is usually more likely to orbit the primary star than the secondary star.
Many of the known hot Jupiters are formally unstable to tidal orbital decay. The only hot Jupiter for which orbital decay has been directly detected is WASP-12, for which transit-timing measurements ...spanning more than a decade have revealed that the orbital period is decreasing at a rate of , corresponding to a reduced tidal quality factor of about 2 × 105. Here, we present a compilation of transit-timing data for WASP-12 and 11 other systems that are especially favorable for detecting orbital decay: KELT-16; WASP-18, 19, 43, 72, 103, 114, and 122; HAT-P-23; HATS-18; and OGLE-TR-56. For most of these systems we present new data that extend the time baseline over which observations have been performed. None of the systems besides WASP-12 display convincing evidence for period changes, with typical upper limits on dP/dt on the order of 10−9 or 10−10, and lower limits on the reduced tidal quality factor on the order of 105. One possible exception is WASP-19, which shows a statistically significant trend, although it may be a spurious effect of starspot activity. Further observations are encouraged.
The Transiting Exoplanet Survey Satellite (TESS) is providing precise time-series photometry for most star clusters in the solar neighborhood. Using the TESS images, we have begun a Cluster ...Difference Imaging Photometric Survey, in which we are focusing both on stars that are candidate cluster members and on stars that show indications of youth. Our aims are to discover giant transiting planets with known ages, and to provide light curves suitable for studies in stellar astrophysics. For this work, we made 159,343 light curves of candidate young stars, across 596 distinct clusters. Each light curve represents between 20 and 25 days of observations of a star brighter than GRp = 16, with 30-minute sampling. We describe the image-subtraction and time-series analysis techniques we used to create the light curves, which have noise properties that agree with theoretical expectations. We also comment on the possible utility of the light-curve sample for studies of stellar rotation evolution and binary eccentricity damping. The light curves, which cover about one-sixth of the galactic plane, are available at archive.stsci.edu/hlsp/cdips.
We present simulations of multi-year radial velocity (RV) follow-up campaigns of the TESS exoplanet yield on the Automated Planet Finder telescope, using four different schemes to sample the ...transiting planets' RV phase curves. For planets below roughly 10 M⊕, we see a systematic bias of measured masses that are higher than the true planet mass, regardless of the observing scheme used. This produces a statistically significant difference in the mass-radius relation we recover, where planet masses are predicted to be too high and too similar across the entire super-Earth to Neptune radius range. This bias is due in part to only reporting masses that are measured with high statistical significance. Incorporating all mass measurements, even those that are essentially only upper limits, significantly mitigates this bias. We also find statistically significant differences between the mean number of planets measured at the 1-, 3-, and 5 K level by the different prioritization schemes. Our results show that prioritization schemes which more evenly sample the RV phase curves produce a larger number of significant mass detections. The scheme that aims to most uniformly sample the phase curve performs best, followed closely by the scheme that randomly samples, and then an in-quadrature sampling approach. The fourth scheme, out of quadrature, performs noticeably worse. These results have important implications for determining accurate planet compositions and for designing effective RV follow-up campaigns in the era of large planet detection surveys such as K2, TESS, and PLATO.
Abstract
Stellar positions and velocities from Gaia are yielding a new view of open cluster dispersal. Here we present an analysis of a group of stars spanning Cepheus (
l
= 100°) to Hercules (
l
= ...40°), hereafter the Cep-Her complex. The group includes four Kepler objects of interest: Kepler-1643 b (
R
p
= 2.32 ± 0.13
R
⊕
,
P
= 5.3 days), KOI-7368 b (
R
p
= 2.22 ± 0.12
R
⊕
,
P
= 6.8 days), KOI-7913 Ab (
R
p
= 2.34 ± 0.18
R
⊕
,
P
= 24.2 days), and Kepler-1627 Ab (
R
p
= 3.85 ± 0.11
R
⊕
,
P
= 7.2 days). The latter Neptune-sized planet is in part of the Cep-Her complex called the
δ
Lyr cluster. Here we focus on the former three systems, which are in other regions of the association. Based on kinematic evidence from Gaia, stellar rotation periods from TESS, and spectroscopy, these three objects are also ≈40 million years (Myr) old. More specifically, we find that Kepler-1643 is
46
−
7
+
9
Myr old, based on its membership in a dense subcluster of the complex called RSG-5. KOI-7368 and KOI-7913 are
36
−
8
+
10
Myr old, and are in a diffuse region that we call CH-2. Based on the transit shapes and high-resolution imaging, all three objects are most likely planets, with false-positive probabilities of 6 × 10
−9
, 4 × 10
−3
, and 1 × 10
−4
for Kepler-1643, KOI-7368, and KOI-7913, respectively. These planets demonstrate that mini-Neptunes with sizes of ≈2 Earth radii exist at ages of 40 Myr.
The Transiting Exoplanet Survey Satellite (TESS) will embark in 2018 on a 2 year wide-field survey mission, discovering over a thousand terrestrial, super-Earth and sub-Neptune-sized exoplanets ( R ...pl ≤ 4 R ⊕ ) potentially suitable for follow-up observations using the James Webb Space Telescope (JWST). This work aims to understand the suitability of anticipated TESS planet discoveries for atmospheric characterization by JWST's Near InfraRed Imager and Slitless Spectrograph (NIRISS) by employing a simulation tool to estimate the signal-to-noise (S/N) achievable in transmission spectroscopy. We applied this tool to Monte Carlo predictions of the TESS expected planet yield and then compared the S/N for anticipated TESS discoveries to our estimates of S/N for 18 known exoplanets. We analyzed the sensitivity of our results to planetary composition, cloud cover, and presence of an observational noise floor. We find that several hundred anticipated TESS discoveries with radii 1.5 R ⊕ < R pl ≤ 2.5 R ⊕ will produce S/N higher than currently known exoplanets in this radius regime, such as K2-3b or K2-3c. In the terrestrial planet regime, we find that only a few anticipated TESS discoveries will result in higher S/N than currently known exoplanets, such as the TRAPPIST-1 planets, GJ1132b, and LHS1140b. However, we emphasize that this outcome is based upon Kepler-derived occurrence rates, and that co-planar compact multi-planet systems (e.g., TRAPPIST-1) may be under-represented in the predicted TESS planet yield. Finally, we apply our calculations to estimate the required magnitude of a JWST follow-up program devoted to mapping the transition region between hydrogen-dominated and high molecular weight atmospheres. We find that a modest observing program of between 60 and 100 hr of charged JWST time can define the nature of that transition (e.g., step function versus a power law).
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