The Next Generation Transit Survey (NGTS) Wheatley, Peter J; West, Richard G; Goad, Michael R ...
Monthly Notices of the Royal Astronomical Society,
04/2018, Volume:
475, Issue:
4
Journal Article
Peer reviewed
Open access
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.
NGTS-1b: a hot Jupiter transiting an M-dwarf Bayliss, Daniel; Gillen, Edward; Eigmüller, Philipp ...
Monthly Notices of the Royal Astronomical Society,
04/2018, Volume:
475, Issue:
4
Journal Article
Peer reviewed
Open access
Abstract
We present the discovery of NGTS-1b, a hot Jupiter transiting an early M-dwarf host (Teff,* = $3916\, ^{+71}_{-63}$ K) in a P = 2.647 d orbit discovered as part of the Next Generation ...Transit Survey (NGTS). The planet has a mass of $0.812\, ^{+0.066}_{-0.075}$ MJ, making it the most massive planet ever discovered transiting an M-dwarf. The radius of the planet is $1.33\, ^{+0.61}_{-0.33}$ RJ. Since the transit is grazing, we determine this radius by modelling the data and placing a prior on the density from the population of known gas giant planets. NGTS-1b is the third transiting giant planet found around an M-dwarf, reinforcing the notion that close-in gas giants can form and migrate similar to the known population of hot Jupiters around solar-type stars. The host star shows no signs of activity, and the kinematics hint at the star being from the thick disc population. With a deep (2.5 per cent) transit around a K = 11.9 host, NGTS-1b will be a strong candidate to probe giant planet composition around M-dwarfs via James Webb Space Telescope transmission spectroscopy.
ABSTRACT
We determine rotation periods for 127 stars in the ∼115-Myr-old Blanco 1 open cluster using ∼200 d of photometric monitoring with the Next Generation Transit Survey. These stars span F5–M3 ...spectral types (1.2 M⊙ ≳ M ≳ 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, generalized autocorrelation function (G-ACF), and Lomb–Scargle (LS) periodogram, and find that the GP and G-ACF methods 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 d, 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.
ABSTRACT
Using high-resolution ground-based transmission spectroscopy to probe exoplanetary atmospheres is difficult due to the inherent telluric contamination from absorption in Earth’s atmosphere. ...A variety of methods have previously been used to remove telluric features in the optical regime and calculate the planetary transmission spectrum. In this paper we present and compare two such methods, specifically focusing on Na detections using high-resolution optical transmission spectra: (1) calculating the telluric absorption empirically based on the airmass and (2) using a model of the Earth’s transmission spectrum. We test these methods on the transmission spectrum of the hot Jupiter HD 189733 b using archival data obtained with the HARPS spectrograph during three transits. Using models for Centre-to-Limb Variation and the Rossiter–McLaughlin effect, spurious signals which are imprinted within the transmission spectrum are reduced. We find that correcting tellurics with an atmospheric model of the Earth is more robust and produces consistent results when applied to data from different nights with changing atmospheric conditions. We confirm the detection of sodium in the atmosphere of HD 189733 b, with doublet line contrasts of $-0.64 \pm 0.07~{{\ \rm per\ cent}}$ (D2) and $-0.53 \pm 0.07~{{\ \rm per\ cent}}$ (D1). The average line contrast corresponds to an effective photosphere in the Na line located around 1.13 Rp. We also confirm an overall blueshift of the line centroids corresponding to net atmospheric eastward winds with a speed of 1.8 ± 1.2 km s−1. Our study highlights the importance of accurate telluric removal for consistent and reliable characterization of exoplanetary atmospheres using high-resolution transmission spectroscopy.
NGTS-4b: A sub-Neptune transiting in the desert West, Richard G; Gillen, Edward; Bayliss, Daniel ...
Monthly Notices of the Royal Astronomical Society,
07/2019, Volume:
486, Issue:
4
Journal Article, Web Resource
Peer reviewed
Open access
Abstract
We report the discovery of NGTS-4b, a sub-Neptune-sized planet transiting a 13th magnitude K-dwarf in a 1.34 d orbit. NGTS-4b has a mass M = 20.6 ± 3.0 M⊕ and radius R = 3.18 ± 0.26 R⊕, ...which places it well within the so-called ‘Neptunian Desert’. The mean density of the planet (3.45 ± 0.95 g cm−3) is consistent with a composition of 100 per cent H2O or a rocky core with a volatile envelope. NGTS-4b is likely to suffer significant mass loss due to relatively strong EUV/X-ray irradiation. Its survival in the Neptunian desert may be due to an unusually high-core mass, or it may have avoided the most intense X-ray irradiation by migrating after the initial activity of its host star had subsided. With a transit depth of 0.13 ± 0.02 per cent, NGTS-4b represents the shallowest transiting system ever discovered from the ground, and is the smallest planet discovered in a wide-field ground-based photometric survey.
An automated search for transiting exocomets Kennedy, Grant M; Hope, Greg; Hodgkin, Simon T ...
Monthly Notices of the Royal Astronomical Society,
02/2019, Volume:
482, Issue:
4
Journal Article
Transient astronomy with the Gaia satellite Hodgkin, Simon T.; Wyrzykowski, ukasz; Blagorodnova, Nadejda ...
Philosophical transactions - Royal Society. Mathematical, Physical and engineering sciences/Philosophical transactions - Royal Society. Mathematical, physical and engineering sciences,
06/2013, Volume:
371, Issue:
1992
Journal Article
Peer reviewed
Open access
Gaia is a cornerstone European Space Agency astrometry space mission and a successor to the Hipparcos mission. Gaia will observe the whole sky for 5 years, providing a serendipitous opportunity for ...the discovery of large numbers of transient and anomalous events, e.g. supernovae, novae and microlensing events, gamma-ray burst afterglows, fallback supernovae, as well as theoretical or unexpected phenomena. In this paper, we discuss our preparations to use Gaia to search for transients at optical wavelengths, and briefly describe the early detection, classification and prompt publication of anomalous sources.
Spectroscopic studies have demonstrated that nearly all Galactic globular clusters (GCs) harbour multiple stellar populations with different chemical compositions. Moreover, colour-magnitude diagrams ...based exclusively on Strömgrem photometry have allowed us to identify and characterise multiple populations along the RGB of a large number of clusters. In this paper we show for the first time that Strömgren photometry is also very efficient at identifying multiple populations along the AGB, and demonstrate that the AGB of M 3, M 92, NGC 362, NGC 1851, and NGC 6752 are not consistent with a single stellar population. We also provide a catalogue of RGB and AGB stars photometrically identified in these clusters for further spectroscopic follow-up studies. We combined photometry and elemental abundances from the literature for RGB and AGB stars in NGC 6752 where the presence of multiple populations along the AGB has been widely debated. We find that, while the MS, SGB, and RGB host three stellar populations with different helium and light element abundances, only two populations of AGB stars are present in the cluster. These results are consistent with standard evolutionary theory.
ABSTRACT
We present the results of a search for stellar flares in the first data release from the Next Generation Transit Survey (NGTS). We have found 610 flares from 339 stars, with spectral types ...between F8 and M6, the majority of which belong to the Galactic thin disc. We have used the 13-s cadence NGTS light curves to measure flare properties such as the flare amplitude, duration, and bolometric energy. We have measured the average flare occurrence rates of K and early to mid-M stars and present a generalized method to measure these rates while accounting for changing detection sensitivities. We find that field age K and early M stars show similar flare behaviour, while fully convective M stars exhibit increased white-light flaring activity, which we attribute to their increased spin-down time. We have also studied the average flare rates of pre-main-sequence K and M stars, showing they exhibit increased flare activity relative to their main-sequence counterparts.
Gaia 17bpi: An FU Ori-type Outburst Hillenbrand, Lynne A.; Peña, Carlos Contreras; Morrell, Sam ...
Astrophysical journal/The Astrophysical journal,
12/2018, Volume:
869, Issue:
2
Journal Article
Peer reviewed
Open access
We report on the source Gaia 17bpi and identify it as a new, ongoing FU Ori-type outburst, associated with a young stellar object. The optical light curve from Gaia exhibited a 3.5 mag rise with the ...source appearing to plateau in mid-/late 2018. Mid-infrared observations from NEOWISE also show a >3 mag rise that occurred in two stages, with the second one coincident with the optical brightening, and the first one preceding the optical brightening by ∼1.5 yr. We model the outburst as having started between October and December of 2014. This wavelength-dependent aspect of young star accretion-driven outbursts has never been documented before. Both the mid-infrared and the optical colors of the object become bluer as the outburst proceeds. Optical spectroscopic characteristics in the outburst phase include: a GK-type absorption spectrum, strong wind/outflow in, e.g., Mgb, NaD, H , K i, O i, and Ca ii profiles, and detection of Li i 6707 . The infrared spectrum in the outburst phase is similar to that of an M-type spectrum, notably exhibiting prominent H2O and 12CO (2-0) bandhead absorption in the K band, and likely He i wind in the Y band. The new FU Ori source Gaia 17bpi is associated with a little-studied dark cloud in the galactic plane, located at a distance of 1.27 kpc.
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