We report the characterization and independent detection of K2-60b, as well as the detection and characterization of K2-107b, two transiting hot gaseous planets from the K2 space mission. We confirm ...the planetary nature of the two systems and determine their fundamental parameters combining the K2 time-series data with FIES@NOT and HARPS-N@TNG spectroscopic observations. K2-60b has a radius of 0.683 0.037 RJup and a mass of 0.426 0.037 MJup and orbits a G4 V star with an orbital period of 3.00267 0.00006 days. K2-107b has a radius of 1.44 0.15 RJup and a mass of 0.84 0.08 MJup and orbits an F9 IV star every 3.31392 0.00002 days. K2-60b is among the few planets at the edge of the so-called "desert" of short-period sub-Jovian planets. K2-107b is a highly inflated Jovian planet orbiting an evolved star about to leave the main sequence.
ABSTRACT
We present the detection of high-energy white-light flares from pre-main-sequence stars associated with the Orion Complex, observed as part of the Next Generation Transit Survey (NGTS). With ...energies up to 5.2 × 1035 erg these flares are some of the most energetic white-light flare events seen to date. We have used the NGTS observations of flaring and non-flaring stars to measure the average flare occurrence rate for 4 Myr M0–M3 stars. We have also combined our results with those from previous studies to predict average rates for flares above 1 × 1035 erg for early M stars in nearby young associations.
ABSTRACT
We analyse 829 481 stars from the Next Generation Transit Survey (NGTS) to extract variability periods. We utilize a generalization of the autocorrelation function (the G-ACF), which applies ...to irregularly sampled time series data. We extract variability periods for 16 880 stars from late-A through to mid-M spectral types and periods between ∼0.1 and 130 d with no assumed variability model. We find variable signals associated with a number of astrophysical phenomena, including stellar rotation, pulsations, and multiple-star systems. The extracted variability periods are compared with stellar parameters taken from Gaia DR2, which allows us to identify distinct regions of variability in the Hertzsprung–Russell Diagram. We explore a sample of rotational main-sequence objects in period-colour space, in which we observe a dearth of rotation periods between 15 and 25 d. This ‘bi-modality’ was previously only seen in space-based data. We demonstrate that stars in sub-samples above and below the period gap appear to arise from a stellar population not significantly contaminated by excess multiple systems. We also observe a small population of long-period variable M-dwarfs, which highlight a departure from the predictions made by rotational evolution models fitted to solar-type main-sequence objects. The NGTS data spans a period and spectral type range that links previous rotation studies such as those using data from Kepler, K2, and MEarth.
ABSTRACT
We report the discovery of four new hot Jupiters with the Next-Generation Transit Survey (NGTS). NGTS-15b, NGTS-16b, NGTS-17b, and NGTS-18b are short-period (P < 5 d) planets orbiting G-type ...main-sequence stars, with radii and masses between 1.10 and 1.30RJ and 0.41 and 0.76MJ, respectively. By considering the host star luminosities and the planets’ small orbital separations (0.039–0.052 au), we find that all four hot Jupiters are highly irradiated and therefore occupy a region of parameter space in which planetary inflation mechanisms become effective. Comparison with statistical studies and a consideration of the planets’ high incident fluxes reveal that NGTS-16b, NGTS-17b, and NGTS-18b are indeed likely inflated, although some disparities arise upon analysis with current Bayesian inflationary models. However, the underlying relationships that govern radius inflation remain poorly understood. We postulate that the inclusion of additional hyperparameters to describe latent factors such as heavy element fraction, as well as the addition of an updated catalogue of hot Jupiters, would refine inflationary models, thus furthering our understanding of the physical processes that give rise to inflated planets.
ABSTRACT
We present the discovery of NGTS J214358.5–380102, an eccentric M-dwarf binary discovered by the Next-Generation Transit Survey (NGTS). The system period of 7.618 d is greater than many ...known eclipsing M-dwarf binary systems. Its orbital eccentricity of $0.323^{+0.0014}_{-0.0037}$ is large relative to the period and semimajor axis of the binary. Global modelling of photometry and radial velocities indicates stellar masses of MA = $0.426 ^{+0.0056}_{-0.0049}$ M⊙, MB = $0.455 ^{+0.0058}_{-0.0052}$ M⊙ and stellar radii RA = $0.461 ^{+0.038}_{-0.025}$ R⊙, RB = $0.411 ^{+0.027}_{-0.039}$ R⊙, respectively. Comparisons with stellar models for low-mass stars show that one star is consistent with model predictions whereas the other is substantially oversized. Spectral analysis of the system suggests a primary of spectral type M3V, consistent with both modelled masses and radii, and with spectral energy distribution fitting of NGTS photometry. As the most eccentric eclipsing M-dwarf binary known, NGTS J214358.5–380102 provides an interesting insight into the strength of tidal effects in the circularization of stellar orbits.
We present the discovery of three small planets transiting K2-136 (LP 358 348, EPIC 247589423), a late K dwarf in the Hyades. The planets have orbital periods of 7.9757 0.0011, , and , and radii of ...1.05 0.16, 3.14 0.36, and , respectively. With an age of 600-800 Myr, these planets are some of the smallest and youngest transiting planets known. Due to the relatively bright (J = 9.1) host star, the planets are compelling targets for future characterization via radial velocity mass measurements and transmission spectroscopy. As the first known star with multiple transiting planets in a cluster, the system should be helpful for testing theories of planet formation and migration.
ABSTRACT We report the discovery of K2-31b, the first confirmed transiting hot Jupiter detected by the K2 space mission. We combined K2 photometry with FastCam lucky imaging and FIES and HARPS ...high-resolution spectroscopy to confirm the planetary nature of the transiting object and derived the system parameters. K2-31b is a 1.8-Jupiter-mass planet on a 1.26-day orbit around a G7 V star ( M , R ). The planetary radius is poorly constrained (0.7 < Rp < 1.4 RJup),15 owing to the grazing transit and the low sampling rate of the K2 photometry.16
Abstract
The Next Generation Transit Survey (NGTS), operating in Paranal since 2016, is a wide-field survey to detect Neptunes and super-Earths transiting bright stars, which are suitable for precise ...radial velocity follow-up and characterization. Thereby, its sub-mmag photometric precision and ability to identify false positives are crucial. Particularly, variable background objects blended in the photometric aperture frequently mimic Neptune-sized transits and are costly in follow-up time. These objects can best be identified with the centroiding technique: if the photometric flux is lost off-centre during an eclipse, the flux centroid shifts towards the centre of the target star. Although this method has successfully been employed by the Kepler mission, it has previously not been implemented from the ground. We present a fully automated centroid vetting algorithm developed for NGTS, enabled by our high-precision autoguiding. Our method allows detecting centroid shifts with an average precision of 0.75 milli-pixel (mpix), and down to 0.25 mpix for specific targets, for a pixel size of 4.97 arcsec. The algorithm is now part of the NGTS candidate vetting pipeline and automatically employed for all detected signals. Further, we develop a joint Bayesian fitting model for all photometric and centroid data, allowing to disentangle which object (target or background) is causing the signal, and what its astrophysical parameters are. We demonstrate our method on two NGTS objects of interest. These achievements make NGTS the first ground-based wide-field transit survey ever to successfully apply the centroiding technique for automated candidate vetting, enabling the production of a robust candidate list before follow-up.
ABSTRACT
We present the discovery of NGTS J0930−18, an extreme mass ratio eclipsing M-dwarf binary system with an early M-dwarf primary and a late M-dwarf secondary close to the hydrogen burning ...limit. Global modelling of photometry and radial velocities reveals that the secondary component (NGTS J0930−18 B) has a mass of M* = $0.0818 ^{+0.0040}_{-0.0015}$ M⊙ and radius of R* = $0.1059 ^{+0.0023}_{-0.0021}$ R⊙, making it one of the lowest mass stars with direct mass and radius measurements. With a mass ratio of q = $0.1407 ^{+0.0065}_{-0.017}$, NGTS J0930−18 has the lowest mass ratio of any known eclipsing M-dwarf binary system, posing interesting questions for binary star formation and evolution models. The mass and radius of NGTS J0930−18 B is broadly consistent with stellar evolutionary models. NGTS J0930−18 B lies in the sparsely populated mass radius parameter space close to the substellar boundary. Precise measurements of masses and radii from single lined eclipsing binary systems of this type are vital for constraining the uncertainty in the mass–radius relationship – of importance due to the growing number of terrestrial planets being discovered around low-mass stars.
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