We report the discovery of the transiting exoplanet NGTS-12b by the Next Generation Transit Survey (NGTS). The host star, NGTS-12, is a V=12.38 mag star with an effective temperature of T\(_{\rm ...eff}\)=\(5690\pm130\) K. NGTS-12b orbits with a period of \(P=7.53\)d, making it the longest period planet discovered to date by the main NGTS survey. We verify the NGTS transit signal with data extracted from the TESS full-frame images, and combining the photometry with radial velocity measurements from HARPS and FEROS we determine NGTS-12b to have a mass of \(0.208\pm0.022\) M\(_{J}\) and a radius of \(1.048\pm0.032\) R\(_{J}\). NGTS-12b sits on the edge of the Neptunian desert when we take the stellar properties into account, highlighting the importance of considering both the planet and star when studying the desert. The long period of NGTS-12b combined with its low density of just \(0.223\pm0.029\) g cm\(^{-3}\) make it an attractive target for atmospheric characterization through transmission spectroscopy with a Transmission Spectroscopy Metric of 89.4.
Vetting of exoplanet candidates in transit surveys is a manual process, which suffers from a large number of false positives and a lack of consistency. Previous work has shown that Convolutional ...Neural Networks (CNN) provide an efficient solution to these problems. Here, we apply a CNN to classify planet candidates from the Next Generation Transit Survey (NGTS). For training datasets we compare both real data with injected planetary transits and fully-simulated data, as well as how their different compositions affect network performance. We show that fewer hand labelled lightcurves can be utilised, while still achieving competitive results. With our best model, we achieve an AUC (area under the curve) score of \((95.6\pm{0.2})\%\) and an accuracy of \((88.5\pm{0.3})\%\) on our unseen test data, as well as \((76.5\pm{0.4})\%\) and \((74.6\pm{1.1})\%\) in comparison to our existing manual classifications. The neural network recovers 13 out of 14 confirmed planets observed by NGTS, with high probability. We use simulated data to show that the overall network performance is resilient to mislabelling of the training dataset, a problem that might arise due to unidentified, low signal-to-noise transits. Using a CNN, the time required for vetting can be reduced by half, while still recovering the vast majority of manually flagged candidates. In addition, we identify many new candidates with high probabilities which were not flagged by human vetters.
We determine rotation periods for 127 stars in the ~115 Myr old Blanco 1 open cluster using ~200 days of photometric monitoring with the Next Generation Transit Survey (NGTS). These stars span F5-M3 ...spectral types (1.2 \(\gtrsim M \gtrsim\) 0.3 M\(_{\odot}\)) and increase the number of known rotation periods in Blanco 1 by a factor of four. We determine rotation periods using three methods: Gaussian process (GP) regression, generalised autocorrelation (G-ACF) and Lomb-Scargle (LS) periodograms, and find that GPs and G-ACF are more applicable to evolving spot modulation patterns. Between mid-F and mid-K spectral types, single stars follow a well-defined rotation sequence from ~2 to 10 days, whereas stars in photometric multiple systems typically rotate faster. This may suggest that the presence of a moderate-to-high mass ratio companion inhibits angular momentum loss mechanisms during the early pre-main sequence, and this signature has not been erased at ~100 Myr. The majority of mid-F to mid-K stars display evolving modulation patterns, whereas most M stars show stable modulation signals. This morphological change coincides with the shift from a well-defined rotation sequence (mid-F to mid-K stars) to a broad rotation period distribution (late-K and M stars). Finally, we compare our rotation results for Blanco 1 to the similarly-aged Pleiades: the single star populations in both clusters possess consistent rotation period distributions, which suggests that the angular momentum evolution of stars follows a well-defined pathway that is, at least for mid-F to mid-K stars, strongly imprinted by ~100 Myr.
The Transiting Exoplanet Survey Satellite (TESS) has produced a large number of single transit event candidates which are being monitored by the Next Generation Transit Survey (NGTS). We observed a ...second epoch for the TIC-231005575 system (Tmag = 12.06, Teff = 5500 +- 85 K) with NGTS and a third epoch with Las Cumbres Observatory's (LCO) telescope in South Africa to constrain the orbital period (P = 61.777 d). Subsequent radial velocity measurements with CORALIE revealed the transiting object has a mass of M2 = 0.128 +- 0.003 M\(_\odot\), indicating the system is a G-M binary. The radius of the secondary is R2 = 0.154 +- 0.008 R\(_\odot\) and is consistent with models of stellar evolution to better than 1-\(\sigma\).
The Transiting Exoplanet Survey Satellite (\tess) produces a large number of single-transit event candidates, since the mission monitors most stars for only \(\sim\)27\,days. Such candidates ...correspond to long-period planets or eclipsing binaries. Using the \tess\ Sector 1 full-frame images, we identified a 7750\,ppm single-transit event with a duration of 7\,hours around the moderately evolved F-dwarf star \tic\ (Tmag=10.23, \teff=6280\(\pm{85}\)\,K). Using archival WASP photometry we constrained the true orbital period to one of three possible values. We detected a subsequent transit-event with NGTS, which revealed the orbital period to be 38.20\,d. Radial velocity measurements from the CORALIE Spectrograph show the secondary object has a mass of \(M_2\)= \(0.148\pm{0.003}\)\,M\(_{\odot}\), indicating this system is an F-M eclipsing binary. The radius of the M-dwarf companion is \(R_2\) = \(0.171\pm{0.003}\)\,R\(_{\odot}\), making this one of the most well characterised stars in this mass regime. We find that its radius is 2.3-\(\sigma\) lower than expected from stellar evolution models.
We report the discovery, by the Next Generation Transit Survey (NGTS), of two hot-Jupiters NGTS-8b and NGTS-9b. These orbit a V = 13.68 K0V star (Teff = 5241 +/- 50 K) with a period of 2.49970 days, ...and a V = 12.80 F8V star (Teff = 6330 +/- 130 K) in 4.43527 days, respectively. The transits were independently verified by follow-up photometric observations with the SAAO 1.0-m and Euler telescopes, and we report on the planetary parameters using HARPS, FEROS and CORALIE radial velocities. NGTS-8b has a mass, 0.93 +0.04 -0.03 MJ and a radius, 1.09 +/- 0.03 RJ similar to Jupiter, resulting in a density of 0.89 +0.08 -0.07 g cm-3. This is in contrast to NGTS-9b, which has a mass of 2.90 +/- 0.17 MJ and a radius of 1.07 +/- 0.06 RJ , resulting in a much greater density of 2.93 +0.53 -0.49 g cm-3. Statistically, the planetary parameters put both objects in the regime where they would be expected to exhibit larger than predicted radii. However, we find that their radii are in agreement with predictions by theoretical non-inflated models.
We present the detection of an energetic flare on the pre-main sequence M3 star NGTS J121939.5-355557, which we estimate as only 2 Myr old. The flare had an energy of \(3.2\pm^{0.4}_{0.3}\times ...10^{36}\)erg and a fractional amplitude of \(7.2\pm0.8\), making it one of the most energetic flares seen on an M star. The star is also X-ray active, in the saturated regime with \(log L_{X}/L_{Bol} = -3.1\). In the flare peak we have identified multi-mode quasi-periodic pulsations formed of two statistically significant periods of approximately 320 and 660 seconds. This flare is one of the largest amplitude events to exhibit such pulsations. The shorter period mode is observed to start after a short-lived spike in flux lasting around 30 seconds, which would not have been resolved in Kepler or TESS short cadence modes. Our data shows how the high cadence of NGTS can be used to apply solar techniques to stellar flares and identify potential causes of the observed oscillations. We also discuss the implications of this flare for the habitability of planets around M star hosts and how NGTS can aid in our understanding of this.
We report the discovery of a new ultra-short period hot Jupiter from the Next Generation Transit Survey. NGTS-6b orbits its star with a period of 21.17~h, and has a mass and radius of ...\(1.330^{+0.024}_{-0.028}\)\mjup\, and \(1.271^{+0.197}_{-0.188}\)\rjup\, respectively, returning a planetary bulk density of 0.711\(^{+0.214}_{-0.136}\)~g~cm\(^{-3}\). Conforming to the currently known small population of ultra-short period hot Jupiters, the planet appears to orbit a metal-rich star (Fe/H\(=+0.11\pm0.09\)~dex). Photoevaporation models suggest the planet should have lost 5\% of its gaseous atmosphere over the course of the 9.6~Gyrs of evolution of the system. NGTS-6b adds to the small, but growing list of ultra-short period gas giant planets, and will help us to understand the dominant formation and evolutionary mechanisms that govern this population.
We present the discovery of NGTS-7Ab, a high mass brown dwarf transiting an M dwarf with a period of 16.2 hours, discovered as part of the Next Generation Transit Survey (NGTS). This is the shortest ...period transiting brown dwarf around a main or pre-main sequence star to date. The M star host (NGTS-7A) has an age of roughly 55 Myr and is in a state of spin-orbit synchronisation, which we attribute to tidal interaction with the brown dwarf acting to spin up the star. The host star is magnetically active and shows multiple flares across the NGTS and follow up lightcurves, which we use to probe the flare-starspot phase relation. The host star also has an M star companion at a separation of 1.13 arcseconds with very similar proper motion and systemic velocity, suggesting the NGTS-7 system is a hierarchical triple. The combination of tidal synchronisation and magnetic braking is expected to drive ongoing decay of the brown dwarf orbit, with a remaining lifetime of only 5-10 Myr.
We report the discovery of a new ultra-short period transiting hot Jupiter from the Next Generation Transit Survey (NGTS). NGTS-10b has a mass and radius of \(2.162\,^{+0.092}_{-0.107}\) M\(_{\rm ...J}\) and \(1.205\,^{+0.117}_{-0.083}\) R\(_{\rm J}\) and orbits its host star with a period of \(0.7668944\pm0.0000003\) days, making it the shortest period hot Jupiter yet discovered. The host is a \(10.4\pm2.5\) Gyr old K5V star (\(T_\mathrm{eff}\)=\(4400\pm100\)\,K) of Solar metallicity (Fe/H = \(-0.02\pm0.12\)\,dex) showing moderate signs of stellar activity. NGTS-10b joins a short list of ultra-short period Jupiters that are prime candidates for the study of star-planet tidal interactions. NGTS-10b orbits its host at just \(1.46\pm0.18\) Roche radii, and we calculate a median remaining inspiral time of \(38\)\,Myr and a potentially measurable transit time shift of \(7\)\,seconds over the coming decade, assuming a stellar tidal quality factor \(Q'_{\rm s}=2\times10^{7}\).
