10 research outputs found
NGTS clusters survey -- II. White-light flares from the youngest stars in Orion
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 Ă 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 Ă 1035 ergs for early M stars in nearby young associations
NGTS clusters survey - I. Rotation in the young benchmark open cluster Blanco 1
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 0.3 M) 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
Simultaneous TESS and NGTS Transit Observations of WASP-166b
We observed a transit of WASP-166 b using nine NGTS telescopes simultaneously
with TESS observations of the same transit. We achieved a photometric precision
of 152 ppm per 30 minutes with the nine NGTS telescopes combined, matching the
precision reached by TESS for the transit event around this bright (T=8.87)
star. The individual NGTS light curve noise is found to be dominated by
scintillation noise and appears free from any time-correlated noise or any
correlation between telescope systems. We fit the NGTS data for and
. We find to be consistent to within 0.25 of the result
from the TESS data, and the difference between the TESS and NGTS measured
values is 0.9. This experiment shows that multi-telescope
NGTS photometry can match the precision of TESS for bright stars, and will be a
valuable tool in refining the radii and ephemerides for bright TESS candidates
and planets. The transit timing achieved will also enable NGTS to measure
significant transit timing variations in multi-planet systems
NGTS and WASP photometric recovery of a single-transit candidate from TESS
The Transiting Exoplanet Survey Satellite (TESS) produces a large number of single-transit event candidates, since the mission monitors most stars for only âŒ27d. 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 h around the moderately evolved F-dwarf star TIC-238855958 (Tmag = 10.23, Teff = 6280 ± 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 M2 = 0.148 ± 0.003Mâ, indicating this system is an F-M eclipsing binary. The radius of the M-dwarf companion is R2 = 0.171 ± 0.003 Râ, making this one of the most well characterized stars in this mass regime. We find that its radius is 2.3Ï lower than expected from stellar evolution models
NGTS-19b: a high-mass transiting brown dwarf in a 17-d eccentric orbit
We present the discovery of NGTS-19b, a high mass transiting brown dwarf
discovered by the Next Generation Transit Survey (NGTS). We investigate the
system using follow up photometry from the South African Astronomical
Observatory, as well as sector 11 TESS data, in combination with radial
velocity measurements from the CORALIE spectrograph to precisely characterise
the system. We find that NGTS-19b is a brown dwarf companion to a K-star, with
a mass of M and radius of R. The system has a reasonably long period of 17.84
days, and a high degree of eccentricity of . The
mass and radius of the brown dwarf imply an age of Gyr,
however this is inconsistent with the age determined from the host star SED,
suggesting that the brown dwarf may be inflated. This is unusual given that its
large mass and relatively low levels of irradiation would make it much harder
to inflate. NGTS-19b adds to the small, but growing number of brown dwarfs
transiting main sequence stars, and is a valuable addition as we begin to
populate the so called brown dwarf desert
NGTS-11 b / TIC-54002556 b: A transiting warm Saturn recovered from a TESS single-transit event
We report the discovery of NGTS-11 b (=TIC-54002556 b), a transiting Saturn
in a 35.46-day orbit around a mid K-type star (Teff=5050+-80 K). The system was
initially identified from a single-transit event in our TESS full-frame image
light-curves. Following seventy-nine nights of photometric monitoring with an
NGTS telescope, we observed a second full transit of NGTS-11 b approximately
one year after the TESS single-transit event. The NGTS transit confirmed the
parameters of the transit signal and restricted the orbital period to a set of
13 discrete periods. We combined our transit detections with precise radial
velocity measurements to determine the true orbital period and measure the mass
of the planet. We find NGTS-11 b has a radius of 0.823+-0.035 RJup, a mass of
0.37+-0.14 MJup, and an equilibrium temperature of just 440+-40 K, making it
one of the coolest known transiting gas giants. NGTS-11 b is the first
exoplanet to be discovered after being initially identified as a TESS single
transit event, and its discovery highlights the power of intense photometric
monitoring in recovering longer-period transiting exoplanets from
single-transit events
NGTS 15b, 16b, 17b and 18b: four hot Jupiters from the Next Generation Transit Survey
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 (d) planets orbiting G-type main sequence stars, with radii
and masses between and . By considering the
host star luminosities and the planets' small orbital separations
( 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 reveals 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 which 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 which give rise to
inflated planets
NGTS 15b, 16b, 17b and 18b: four hot Jupiters from the Next Generation Transit Survey
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 (d) planets orbiting G-type main sequence stars, with radii
and masses between and . By considering the
host star luminosities and the planets' small orbital separations
( 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 reveals 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 which 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 which give rise to
inflated planets
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 planet1,2. All of the previously known ultrashort-period planets are either hot Jupiters, with sizes above 10 Earth radii (Râ), or apparently rocky planets smaller than 2âRâ. Such lack of planets of intermediate size (the âhot Neptune desertâ) 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 4.6âRâ and a mass of 29âMâ, firmly in the hot Neptune desert. Data from the Transiting Exoplanet Survey Satellite3 revealed transits of the bright Sun-like star LTT 9779 every 0.79âdays. The planetâs mean density is similar to that of Neptune, and according to thermal evolution models, it has a H/He-rich envelope constituting 9.0+2.7â2.9% of the total mass. With an equilibrium temperature around 2,000âK, it is unclear how this âultrahot Neptuneâ managed to retain such an envelope. Follow-up observations of the planetâs atmosphere to better understand its origin and physical nature will be facilitated by the starâs brightness (Vmagâ=â9.8).<br
TOI-431/HIP 26013: a super-Earth and a sub-Neptune transiting a bright, early K dwarf, with a third RV planet
We present the bright (Vmag = 9.12), multiplanet system TOI-431, characterized with photometry and radial velocities (RVs). We estimate the stellar rotation period to be 30.5 ± 0.7 d using archival photometry and RVs. Transiting Exoplanet Survey Satellite (TESS) objects of Interest (TOI)-431 b is a super-Earth with a period of 0.49 d, a radius of 1.28 ± 0.04 R, a mass of 3.07 ± 0.35 M, and a density of 8.0 ± 1.0 g cm-3; TOI-431 d is a sub-Neptune with a period of 12.46 d, a radius of 3.29 ± 0.09 R, a mass of 9.90+1.53-1.49 M, and a density of 1.36 ± 0.25 g cm-3. We find a third planet, TOI-431 c, in the High Accuracy Radial velocity Planet Searcher RV data, but it is not seen to transit in the TESS light curves. It has an Msin i of 2.83+0.41-0.34 M, and a period of 4.85 d. TOI-431 d likely has an extended atmosphere and is one of the most well-suited TESS discoveries for atmospheric characterization, while the super-Earth TOI-431 b may be a stripped core. These planets straddle the radius gap, presenting an interesting case-study for atmospheric evolution, and TOI-431 b is a prime TESS discovery for the study of rocky planet phase curves