The Next Generation Transit Survey (NGTS) Wheatley, Peter J; West, Richard G; Goad, Michael R ...
Monthly notices of the Royal Astronomical Society,
04/2018, Letnik:
475, Številka:
4
Journal Article
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Abstract
We describe the Next Generation Transit Survey (NGTS), which is a ground-based project searching for transiting exoplanets orbiting bright stars. NGTS builds on the legacy of previous ...surveys, most notably WASP, and is designed to achieve higher photometric precision and hence find smaller planets than have previously been detected from the ground. It also operates in red light, maximizing sensitivity to late K and early M dwarf stars. The survey specifications call for photometric precision of 0.1 per cent in red light over an instantaneous field of view of 100 deg2, enabling the detection of Neptune-sized exoplanets around Sun-like stars and super-Earths around M dwarfs. The survey is carried out with a purpose-built facility at Cerro Paranal, Chile, which is the premier site of the European Southern Observatory (ESO). An array of twelve 20 cm f/2.8 telescopes fitted with back-illuminated deep-depletion CCD cameras is used to survey fields intensively at intermediate Galactic latitudes. The instrument is also ideally suited to ground-based photometric follow-up of exoplanet candidates from space telescopes such as TESS, Gaia and PLATO. We present observations that combine precise autoguiding and the superb observing conditions at Paranal to provide routine photometric precision of 0.1 per cent in 1 h for stars with I-band magnitudes brighter than 13. We describe the instrument and data analysis methods as well as the status of the survey, which achieved first light in 2015 and began full-survey operations in 2016. NGTS data will be made publicly available through the ESO archive.
Among exoplanets, the small-size population constitutes the dominant one, with a diversity of properties and compositions ranging from rocky to gas dominated envelope. While a large fraction of them ...have masses and radii similar to or smaller than Neptune, yet none share common properties in term of orbital period and insulation with our ice giants. These exoplanets belong to multi-planet systems where planets are closely packed within the first tenth of AU and often exposed to strong irradiation from their host star. Their formation process, subsequent evolution, and fate are still debated and trigger new developments of planet formation models. This paper reviews the characteristics and properties of this extended sample of planets with radii between ∼1.6 and 4.0
R
⊕
. Even though we still lack real Neptune/Uranus analogues, these exoplanets provide us with key observational constraints that allow the formation of our ice giants to be placed in a more general framework than the sole example of our solar system.
Context. The Transiting Exoplanet Survey Satellite (TESS) has been successfully launched and has begin data acquisition. To expedite the science that may be performed with the resulting data it is ...necessary to gain a good understanding of planetary yields. Given the observing strategy employed by TESS the probability of detecting single transits in long period systems is increased. These systems require careful consideration. Aims. We aim to simulate the number of TESS transit detections during its two-year mission with a particular emphasis on single transits. We also aim to determine the feasibility of ground-based follow-up observations from a single site. Methods. A distribution of planets was simulated around the approximately four million stars in the TESS candidate target list. These planets were tested for detectable transits and characterised. Based on simulated parameters the single transit detections were further analysed to determine which are amenable to ground-based follow-up. Results. TESS will discover an approximate lower bound of 4700 planets with around 460 being single transits. A large fraction of these will be observable from a single ground-based site. This paper finds that, in a single year, approximately 1000 transit events of around 320 unique TESS single transit detections are theoretically observable. Conclusions. As we consider longer period exoplanets, the need for exploring single transit detections increases. For periods ≳45 days the number of single transit detections outnumber multitransits by a factor of three (82 ± 18 and 25 ± 7, respectively) a factor which only grows as longer period detections are considered. Therefore, based on this paper, it is worth expending the extra effort required to follow-up these more challenging, but potentially very rewarding, discoveries. Additionally, we conclude that a large fraction of these targets can be theoretically observed from a single ground-based site. However, further work is required to determine whether these follow-up efforts are feasible when accounting for target specific criteria.
ABSTRACT
Young (<1 Gyr) exoplanets represent a critically important area of exoplanet research, as they offer the opportunity to learn about the formation and early dynamic history of exoplanetary ...systems. However, finding young exoplanets is significantly complicated by the fast rotation and complex activity of their young host stars, which are often not well handled by state-of-the-art automatic pipelines. This work presents an alternative LOWESS-based pipeline focused specifically on detrending young stellar light curves from the 30-min cadence full-frame images produced by the Transiting Exoplanet Survey Satellite (TESS), and includes improvements such as automatic peak cutting of stellar variability and interpolation over masked transits to improve periodogram visibility and returned transit shapes. This work presents the details of the developed pipeline, along with initial results from its application to young stars within stellar associations in Sectors 1–5 of the TESS data. While no new exoplanet candidate signals were found in this work, interesting results included the recovery of all known 2-min TOIs around young stars in Sectors 1–5 from 30-min data alone, the recovery of the young exoplanet DS Tuc Ab, a number of young eclipsing binaries and a wide array of interesting rotation. A sensitivity analysis was also undertaken for each star, showing how the recovery of injected planets varied with both depth and period for each individual target. Challenges for future searches for young exoplanets are discussed, the largest being stellar rotation with periods less than 1 d and a lack of a large sample of confirmed young stars.
ABSTRACT
HD 179070,
aka
Kepler-21, is a
V
= 8.25 F6IV star and the brightest exoplanet host discovered by
Kepler
. An early detailed analysis by Howell et al. of the first 13 months (Q0–Q5) of
...Kepler
light curves revealed transits of a planetary companion, Kepler-21b, with a radius of about 1.60 ± 0.04
and an orbital period of about 2.7857 days. However, they could not determine the mass of the planet from the initial radial velocity (RV) observations with Keck-HIRES, and were only able to impose a 2
σ
upper limit of 10
. Here, we present results from the analysis of 82 new RV observations of this system obtained with HARPS-N, together with the existing 14 HIRES data points. We detect the Doppler signal of Kepler-21b with a RV semiamplitude
K
= 2.00 ± 0.65
, which corresponds to a planetary mass of 5.1 ± 1.7
. We also measure an improved radius for the planet of 1.639 +0.019/−0.015
, in agreement with the radius reported by Howell et al. We conclude that Kepler-21b, with a density of 6.4 ± 2.1
, belongs to the population of small, ≲6
planets with iron and magnesium silicate interiors, which have lost the majority of their envelope volatiles via stellar winds or gravitational escape. The RV analysis presented in this paper serves as an example of the type of analysis that will be necessary to confirm the masses of TESS small planet candidates.
ABSTRACT
Kepler-20 is a solar-type star (
V
= 12.5) hosting a compact system of five transiting planets, all packed within the orbital distance of Mercury in our own solar system. A transition from ...rocky to gaseous planets with a planetary transition radius of ∼1.6
has recently been proposed by several articles in the literature. Kepler-20b (
∼ 1.9
) has a size beyond this transition radius; however, previous mass measurements were not sufficiently precise to allow definite conclusions to be drawn regarding its composition. We present new mass measurements of three of the planets in the Kepler-20 system that are facilitated by 104 radial velocity measurements from the HARPS-N spectrograph and 30 archival Keck/HIRES observations, as well as an updated photometric analysis of the
Kepler
data and an asteroseismic analysis of the host star (
=
and
=
). Kepler-20b is a
planet in a 3.7 day period with a mass of
, resulting in a mean density of
, indicating a rocky composition with an iron-to-silicate ratio consistent with that of the Earth. This makes Kepler-20b the most massive planet with a rocky composition found to date. Furthermore, we report the discovery of an additional non-transiting planet with a minimum mass of
and an orbital period of ∼34 days in the gap between Kepler-20f (
P
∼ 11 days) and Kepler-20d (
P
∼ 78 days).
Kepler-10b was the first rocky planet detected by the Kepler satellite and confirmed with radial velocity follow-up observations from Keck-HIRES. The mass of the planet was measured with a precision ...of around 30%, which was insufficient to constrain models of its internal structure and composition in detail. In addition to Kepler-10b, a second planet transiting the same star with a period of 45 days was statistically validated, but the radial velocities were only good enough to set an upper limit of 20 M sub(+ in circle) for the mass of Kepler-10c. To improve the precision on the mass for planet b, the HARPS-N Collaboration decided to observe Kepler-10 intensively with the HARPS-N spectrograph on the Telescopio Nazionale Galileo on La Palma. In total, 148 high-quality radial-velocity measurements were obtained over two observing seasons. These new data allow us to improve the precision of the mass determination for Kepler-10b to 15%. With a mass of 3.33 + or - 0.49 M sub(+ in circle) and an updated radius of 1.47 super(+0.03) sub(-0.02) R sub(+ in circle), Kepler-10b has a density of 5.8 + or - 0.8 g cm super(-3), very close to the value predicted by models with the same internal structure and composition as the Earth. We were also able to determine a mass for the 45-day period planet Kepler-10c, with an even better precision of 11%. With a mass of 17.2 + or - 1.9 M sub(+ in circle) and radius of 2.35 super(+0.09) sub(-0.04) R sub(+ in circle), Kepler-10c has a density of 7.1 + or - 1.0 g cm super(-3). Kepler-10c appears to be the first strong evidence of a class of more massive solid planets with longer orbital periods.
The carbon-to-oxygen ratio (C/O) in a planet provides critical information about its primordial origins and subsequent evolution. A primordial C/O greater than 0.8 causes a carbide-dominated ...interior, as opposed to the silicate-dominated composition found on Earth; the atmosphere can also differ from those in the Solar System. The solar C/O is 0.54 (ref. 3). Here we report an analysis of dayside multi-wavelength photometry of the transiting hot-Jupiter WASP-12b (ref. 6) that reveals C/O ≥ 1 in its atmosphere. The atmosphere is abundant in CO. It is depleted in water vapour and enhanced in methane, each by more than two orders of magnitude compared to a solar-abundance chemical-equilibrium model at the expected temperatures. We also find that the extremely irradiated atmosphere (T > 2,500 K) of WASP-12b lacks a prominent thermal inversion (or stratosphere) and has very efficient day-night energy circulation. The absence of a strong thermal inversion is in stark contrast to theoretical predictions for the most highly irradiated hot-Jupiter atmospheres.
ABSTRACT
We observed a transit of WASP-166 b using nine Next Generation Transit Survey (NGTS) telescopes simultaneously with the Transiting Exoplanet Survey Satellite (TESS) observations of the same ...transit. We achieved a photometric precision of 152 ppm per 30 min 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 TC and Rp/R*. We find TC to be consistent to within 0.25σ of the result from the TESS data, and the difference between the TESS and NGTS measured Rp/R* values is 0.9σ. This experiment shows that multitelescope 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 multiplanet systems.
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