10 research outputs found
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-21b: an inflated Super-Jupiter orbiting a metal-poor K dwarf
We report the discovery of NGTS-21bâ, 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 2.36 ± 0.21âMJâand 1.33 ± 0.03âRJ, and an orbital period of 1.543âd. The host is a K3V (Teff = 4660 ± 41âK) metal-poor ([Fe/H] = â0.26 ± 0.07âdex) dwarf star with a mass and radius of 0.72 ± 0.04âMââand 0.86 ± 0.04Râ. Its age and rotation period of 10.02+3.29â7.30âGyr and 17.88 ± 0.08âd, 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 planetâs atmosphere is inflated by âŒ21 per centâ , while inflationary models predict a radius consistent with observations, thus pointing to stellar irradiation as the probable origin of NGTS-21bâs radius inflation. Additionally, NGTS-21bâs bulk density (1.25 ± 0.15âg cmâ3) 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 metallicityâplanet 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.</p
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
NGTS-28Ab: a short period transiting brown dwarf
We report the discovery of a brown dwarf orbiting a M1 host star. We first identified the brown dwarf within the Next Generation Transit Survey data, with supporting observations found in TESS sectors 11 and 38. We confirmed the discovery with follow-up photometry from the South African Astronomical Observatory, SPECULOOS-S, and TRAPPIST-S, and radial velocity measurements from HARPS, which allowed us to characterize the system. We find an orbital period of âŒ1.25 d, a mass of âMJ, close to the hydrogen burning limit, and a radius of 0.95 ± 0.05âRJ. We determine the age to be >0.5 Gyr, using model isochrones, which is found to be in agreement with spectral energy distribution fitting within errors. NGTS-28Ab is one of the shortest period systems found within the brown dwarf desert, as well as one of the highest mass brown dwarfs that transits an M dwarf. This makes NGTS-28Ab another important discovery within this scarcely populated region.</p
Populating the brown dwarf and stellar boundary: Five stars with transiting companions near the hydrogen-burning mass limit
We report the discovery of five transiting companions near the hydrogen-burning mass limit in close orbits around main sequence stars originally identified by the Transiting Exoplanet Survey Satellite (TESS) as TESS objects of interest (TOIs): TOI-148, TOI-587, TOI-681, TOI-746, and TOI-1213. Using TESS and ground-based photometry as well as radial velocities from the CORALIE, CHIRON, TRES, and FEROS spectrographs, we found the companions have orbital periods between 4.8 and 27.2 days, masses between 77 and 98 MJup, and radii between 0.81 and 1.66 RJup. These targets have masses near the uncertain lower limit of hydrogen core fusion (~73-96 MJup), which separates brown dwarfs and low-mass stars. We constrained young ages for TOI-587 (0.2 ± 0.1 Gyr) and TOI-681 (0.17 ± 0.03 Gyr) and found them to have relatively larger radii compared to other transiting companions of a similar mass. Conversely we estimated older ages for TOI-148 and TOI-746 and found them to have relatively smaller companion radii. With an effective temperature of 9800 ± 200 K, TOI-587 is the hottest known main-sequence star to host a transiting brown dwarf or very low-mass star. We found evidence of spin-orbit synchronization for TOI-148 and TOI-746 as well as tidal circularization for TOI-148. These companions add to the population of brown dwarfs and very low-mass stars with well measured parameters ideal to test formation models of these rare objects, the origin of the brown dwarf desert, and the distinction between brown dwarfs and hydrogen-burning main sequence stars
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