29 research outputs found
The Effect of Autonomy on Prosocial Worldview Defense
The present research explores an intersection between terror management theory and self-determination theory. Depending on what values are salient, terror management theory research has found that mortality salience can lead to both hostile and/or prosocial worldview defense behaviors in order to mitigate death anxiety. Self-determination theory holds that people are naturally oriented toward growth and well-being, with autonomy serving as an important component of healthy psychological functioning. Recent findings have indicated evidence of the buffering ability of autonomousorientation on death anxiety, but it has only been evidenced with eliminating hostile worldview defense behaviors. It was predicted that reminding participants of their mortality would increase their defense of a salient prosocial worldview, but priming autonomy would eliminate the effect. Participants were randomly assigned to a mortality salience vs. neutral condition and an autonomy vs. controlled-orientation condition, and then asked to indicate their support for the expanding of immigration policies. Results indicated that priming mortality (vs. neutral) led participants to uphold tolerant immigration attitudes by indicating greater support for the expansion of immigration, but priming autonomy (vs. controlled-orientation) attenuated that support, providing evidence for the general buffering effect of autonomy
Automatic vetting of planet candidates from ground based surveys : machine learning with NGTS
State of the art exoplanet transit surveys are producing ever increasing quantities of data. To make the best use of this resource, in detecting interesting planetary systems or in determining accurate planetary population statistics, requires new automated methods. Here we describe a machine learning algorithm that forms an integral part of the pipeline for the NGTS transit survey, demonstrating the efficacy of machine learning in selecting planetary candidates from multi-night ground based survey data. Our method uses a combination of random forests and self-organising-maps to rank planetary candidates, achieving an AUC score of 97.6% in ranking 12368 injected planets against 27496 false positives in the NGTS data. We build on past examples by using injected transit signals to form a training set, a necessary development for applying similar methods to upcoming surveys. We also make the autovet code used to implement the algorithm publicly accessible. autovet is designed to perform machine learned vetting of planetary candidates, and can utilise a variety of methods. The apparent robustness of machine learning techniques, whether on space-based or the qualitatively different ground-based data, highlights their importance to future surveys such as TESS and PLATO and the need to better understand their advantages and pitfalls in an exoplanetary context
NGTS-21b: An Inflated Super-Jupiter Orbiting a Metal-poor K dwarf
We report the discovery of NGTS-21b, a massive hot Jupiter orbiting a
low-mass star as part of the Next Generation Transit Survey (NGTS). The planet
has a mass and radius of M, and
R, and an orbital period of 1.543 days. The host is a K3V (, K) metal-poor (, dex) dwarf
star with a mass and radius of , M,and , R. Its age and rotation period of , Gyr
and , d respectively, are in accordance with the observed
moderately low stellar activity level. When comparing NGTS-21b with currently
known transiting hot Jupiters with similar equilibrium temperatures, it is
found to have one of the largest measured radii despite its large mass.
Inflation-free planetary structure models suggest the planet's atmosphere is
inflated by , while inflationary models predict a radius consistent
with observations, thus pointing to stellar irradiation as the probable origin
of NGTS-21b's radius inflation. Additionally, NGTS-21b's bulk density (, g/cm) is also amongst the largest within the population of
metal-poor giant hosts ([Fe/H] < 0.0), helping to reveal a falling upper
boundary in metallicity-planet density parameter space that is in concordance
with core accretion formation models. The discovery of rare planetary systems
such as NGTS-21 greatly contributes towards better constraints being placed on
the formation and evolution mechanisms of massive planets orbiting low-mass
stars.Comment: 12 pages, 13 figures, accepted for publication in MNRA
An ultrahot Neptune in the Neptune desert
About 1 out of 200 Sun-like stars has a planet with an orbital period shorter than one day: an ultrashort-period planet. All of the previously known ultrashort-period planets are either hot Jupiters, with sizes above 10 Earth radii (R⊕), or apparently rocky planets smaller than 2 R⊕. Such lack of planets of intermediate size (the ‘hot Neptune desert’) has been interpreted as the inability of low-mass planets to retain any hydrogen/helium (H/He) envelope in the face of strong stellar irradiation. Here we report the discovery of an ultrashort-period planet with a radius of 4.6 R⊕ and a mass of 29 M⊕, firmly in the hot Neptune desert. Data from the Transiting Exoplanet Survey Satellite revealed transits of the bright Sun-like star LTT 9779 every 0.79 days. The planet’s mean density is similar to that of Neptune, and according to thermal evolution models, it has a H/He-rich envelope constituting 9.0^(+2.7)_(−2.9)% of the total mass. With an equilibrium temperature around 2,000 K, it is unclear how this ‘ultrahot Neptune’ managed to retain such an envelope. Follow-up observations of the planet’s atmosphere to better understand its origin and physical nature will be facilitated by the star’s brightness (V_(mag) = 9.8)
TOI-836 : a super-Earth and mini-Neptune transiting a nearby K-dwarf
Funding: TGW, ACC, and KH acknowledge support from STFC consolidated grant numbers ST/R000824/1 and ST/V000861/1, and UKSA grant ST/R003203/1.We present the discovery of two exoplanets transiting TOI-836 (TIC 440887364) using data from TESS Sector 11 and Sector 38. TOI-836 is a bright (T = 8.5 mag), high proper motion (∼200 mas yr−1), low metallicity ([Fe/H]≈−0.28) K-dwarf with a mass of 0.68 ± 0.05 M⊙ and a radius of 0.67 ± 0.01 R⊙. We obtain photometric follow-up observations with a variety of facilities, and we use these data-sets to determine that the inner planet, TOI-836 b, is a 1.70 ± 0.07 R⊕ super-Earth in a 3.82 day orbit, placing it directly within the so-called ‘radius valley’. The outer planet, TOI-836 c, is a 2.59 ± 0.09 R⊕ mini-Neptune in an 8.60 day orbit. Radial velocity measurements reveal that TOI-836 b has a mass of 4.5 ± 0.9 M⊕, while TOI-836 c has a mass of 9.6 ± 2.6 M⊕. Photometric observations show Transit Timing Variations (TTVs) on the order of 20 minutes for TOI-836 c, although there are no detectable TTVs for TOI-836 b. The TTVs of planet TOI-836 c may be caused by an undetected exterior planet.Publisher PDFPeer reviewe
TOI-836: A super-Earth and mini-Neptune transiting a nearby K-dwarf
We present the discovery of two exoplanets transiting TOI-836 (TIC 440887364)
using data from TESS Sector 11 and Sector 38. TOI-836 is a bright (
mag), high proper motion ( mas yr), low metallicity
([Fe/H]) K-dwarf with a mass of M and a
radius of R. We obtain photometric follow-up
observations with a variety of facilities, and we use these data-sets to
determine that the inner planet, TOI-836 b, is a R
super-Earth in a 3.82 day orbit, placing it directly within the so-called
'radius valley'. The outer planet, TOI-836 c, is a R
mini-Neptune in an 8.60 day orbit. Radial velocity measurements reveal that
TOI-836 b has a mass of M , while TOI-836 c has a mass
of M. Photometric observations show Transit Timing
Variations (TTVs) on the order of 20 minutes for TOI-836 c, although there are
no detectable TTVs for TOI-836 b. The TTVs of planet TOI-836 c may be caused by
an undetected exterior planet
NGTS-4b: A sub-Neptune transiting in the desert
We report the discovery of NGTS-4b, a sub-Neptune-sized planet transiting a
13th magnitude K-dwarf in a 1.34d orbit. NGTS-4b has a mass M=M_E
and radius R=R_E, which places it well within the so-called
"Neptunian Desert". The mean density of the planet (g/cm^3) is
consistent with a composition of 100% HO or a rocky core with a volatile
envelope. NGTS-4b is likely to suffer significant mass loss due to relatively
strong EUV/X-ray irradiation. Its survival in the Neptunian desert may be due
to an unusually high core mass, or it may have avoided the most intense X-ray
irradiation by migrating after the initial activity of its host star had
subsided. With a transit depth of %, NGTS-4b represents the
shallowest transiting system ever discovered from the ground, and is the
smallest planet discovered in a wide-field ground-based photometric survey
Transit timings variations in the three-planet system : TOI-270
We present ground- and space-based photometric observations of TOI-270 (L231-32), a system of three transiting planets consisting of one super-Earth and two sub-Neptunes discovered by TESS around a bright (K-mag = 8.25) M3V dwarf. The planets orbit near low-order mean-motion resonances (5:3 and 2:1) and are thus expected to exhibit large transit timing variations (TTVs). Following an extensive observing campaign using eight different observatories between 2018 and 2020, we now report a clear detection of TTVs for planets c and d, with amplitudes of ∼10 min and a super-period of ∼3 yr, as well as significantly refined estimates of the radii and mean orbital periods of all three planets. Dynamical modelling of the TTVs alone puts strong constraints on the mass ratio of planets c and d and on their eccentricities. When incorporating recently published constraints from radial velocity observations, we obtain masses of Mb=1.48±0.18M⊕, Mc=6.20±0.31M⊕, and Md=4.20±0.16M⊕ for planets b, c, and d, respectively. We also detect small but significant eccentricities for all three planets : eb = 0.0167 ± 0.0084, ec = 0.0044 ± 0.0006, and ed = 0.0066 ± 0.0020. Our findings imply an Earth-like rocky composition for the inner planet, and Earth-like cores with an additional He/H2O atmosphere for the outer two. TOI-270 is now one of the best constrained systems of small transiting planets, and it remains an excellent target for atmospheric characterization