Richard G. West

The Next Generation Transit Survey (NGTS)

The Next Generation Transit Survey (NGTS) is a new ground-based sky survey designed to find transiting Neptunes and super-Earths. By covering at least sixteen times the sky area of Kepler , we will find small planets around stars that are sufficiently bright for radial velocity confirmation, mass determination and atmospheric characterisation. The NGTS instrument will consist of an array of twelve independently pointed 20u2009cm telescopes fitted with red-sensitive CCD cameras. It will be constructed at the ESO Paranal Observatory, thereby benefiting from the very best photometric conditions as well as follow up synergy with the VLT and E-ELT. Our design has been verified through the operation of two prototype instruments, demonstrating white noise characteristics to sub-mmag photometric precision. Detailed simulations show that about thirty bright super-Earths and up to two hundred Neptunes could be discovered. Our science operations are due to begin in 2014.

EL CVn-type binaries - Discovery of 17 helium white dwarf precursors in bright eclipsing binary star systems

The star 1SWASP J024743.37−251549.2 was recently discovered to be a binary star in which an A-type dwarf star eclipses the remnant of a disrupted red giant star (WASP 0247−25 B). The remnant is in a rarely observed state evolving to higher effective temperatures at nearly constant luminosity prior to becoming a very low mass white dwarf composed almost entirely of helium, i.e. it is a pre-helium white dwarf (pre-He-WD). We have used the photometric database from the Wide Angle Search for Planets (WASP) to find 17 eclipsing binary stars with orbital periods P = 0.7–2.2 d with similar light curves to 1SWASP J024743.37−251549.2. The only star in this group previously identified as a variable star is the brightest one, EL CVn, which we adopt as the prototype for this class of eclipsing binary star. The characteristic light curves of EL CVn-type stars show a total eclipse by an A-type dwarf star of a smaller, hotter star and a secondary eclipse of comparable depth to the primary eclipse. We have used new spectroscopic observations for six of these systems to confirm that the companions to the A-type stars in these binaries have very low masses (≈0. 2M � ). This includes the companion to EL CVn which was not previously known to be a pre-He-WD. EL CVn-type binary star systems will enable us to study the formation of very low mass white dwarfs in great detail, particularly in those cases where the pre-He-WD star shows non-radial pulsations similar to those recently discovered in WASP0247−25 B.

WASP-103 b: a new planet at the edge of tidal disruption

We report the discovery of WASP-103 b, a new ultra-short-period planet (P = 22:2 hr) transiting a 12.1 V-magnitude F8-type mainsequence star (1:22 0:04 M , 1:44 +0:05

High-frequency A-type pulsators discovered using SuperWASP

We present the results of a survey using the WASP archive to search for high-frequency pulsations in F-, A- and B-type stars. Over 1.5 million targets have been searched for pulsations with amplitudes greater than 0.5 millimagnitude. We identify over 350 stars which pulsate with periods less than 30 min. Spectroscopic follow-up of selected targets has enabled us to confirm 10 new rapidly oscillating Ap stars, 13 pulsating Am stars and the fastest known delta Scuti star. We also observe stars which show pulsations in both the high-frequency domain and the low-frequency delta Scuti range. This work shows the power of the WASP photometric survey to find variable stars with amplitudes well below the nominal photometric precision per observation.

K2 variable catalogue – II. Machine learning classification of variable stars and eclipsing binaries in K2 fields 0–4

We are entering an era of unprecedented quantities of data from current and planned survey telescopes. To maximize the potential of such surveys, automated data analysis techniques are required. Here we implement a new methodology for variable star classification, through the combination of Kohonen Self-Organizing Maps (SOMs, an unsupervised machine learning algorithm) and the more common Random Forest (RF) supervised machine learning technique. We apply this method to data from the K2 mission fields 0–4, finding 154 ab-type RR Lyraes (10 newly discovered), 377 δ Scuti pulsators, 133 γ Doradus pulsators, 183 detached eclipsing binaries, 290 semidetached or contact eclipsing binaries and 9399 other periodic (mostly spot-modulated) sources, once class significance cuts are taken into account. We present light-curve features for all K2 stellar targets, including their three strongest detected frequencies, which can be used to study stellar rotation periods where the observed variability arises from spot modulation. The resulting catalogue of variable stars, classes, and associated data features are made available online. We publish our SOM code in PYTHON as part of the open source PYMVPA package, which in combination with already available RF modules can be easily used to recreate the method.

Three newly discovered sub-Jupiter-mass planets : WASP-69b and WASP-84b transit active K dwarfs and WASP-70Ab transits the evolved primary of a G4+K3 binary

We report the discovery of the transiting exoplanets WASP-69b, WASP-70Ab and WASP84b, each of which orbits a bright star (V ∼ 10). WASP-69b is a bloated Saturn-mass planet (0.26 MJup ,1 .06RJup) in a 3.868-d period around an active, ∼1-Gyr, mid-K dwarf. ROSAT detected X-rays 60±27 arcsec from WASP-69. If the star is the source then the planet could be undergoing mass-loss at a rate of ∼10 12 gs −1 . This is one to two orders of magnitude higher than the evaporation rate estimated for HD 209458b and HD 189733b, both of which have exhibited anomalously large Lyman α absorption during transit. WASP-70Ab is a subJupiter-mass planet (0.59 MJup ,1 .16RJup) in a 3.713-d orbit around the primary of a spatially resolved, 9–10-Gyr, G4+K3 binary, with a separation of 3.3 arcsec (≥800 au). WASP-84b is a sub-Jupiter-mass planet (0.69 MJup ,0 .94RJup) in an 8.523-d orbit around an active, ∼1-Gyr, early-Kdwarf.Ofthetransitingplanets discovered fromtheground todate,WASP-84b has the third-longest period. For the active stars WASP-69 and WASP-84, we pre-whitened the radial velocities using a low-order harmonic series. We found that this reduced the residual scatter more than did the oft-used method of pre-whitening with a fit between residual radial velocity and bisector span. The system parameters were essentially unaffected by pre-whitening.

Transiting hot Jupiters from WASP-South, Euler and TRAPPIST : WASP-95b to WASP-101b

We report the discovery of the transiting exoplanets WASP-95b, WASP-96b, WASP-97b, nWASP-98b, WASP-99b, WASP-100b and WASP-101b. All are hot Jupiters with orbital periods nin the range 2.1–5.7 d, masses of 0.5–2.8 MJup and radii of 1.1–1.4 RJup. The orbits of all the nplanets are compatible with zero eccentricity. WASP-99b produces the shallowest transit yet nfound by WASP-South, at 0.4 per cent. nThe host stars are of spectral type F2–G8. Five have metallicities of [Fe/H] from −0.03 nto +0.23, while WASP-98 has a metallicity of −0.60, exceptionally low for a star with a ntransiting exoplanet. Five of the host stars are brighter than V = 10.8, which significantly nextends the number of bright transiting systems available for follow-up studies. WASP-95 nshows a possible rotational modulation at a period of 20.7 d. We discuss the completeness of nWASP survey techniques by comparing to the HATnet project

WASP-40b: Independent discovery of the 0:6 M transiting exoplanet HAT-P-27b

ABSTRACT.From WASP photometry and SOPHIE radial velocities we report the discovery of WASP-40b (HAT-P-27b), a 0.6xa0MJup0.6u2009u2009MJup planet that transits its 12th magnitude host star every 3.04 days. The host star is of late G-type or early K-type and likely has a metallicity greater than solar ([Fe/H]xa0=xa00.14xa0±xa00.11[Fe/H]=0.14±0.11). The planet’s mass and radius are typical of the known hot Jupiters, thus adding another system to the apparent pileup of transiting planets with periods near 3–4 days. Our parameters match those of the recent HATnet announcement of the same planet, thus giving confidence in the techniques used. We report a possible indication of stellar activity in the host star.

WASP-20b and WASP-28b: a hot Saturn and a hot Jupiter in near-aligned orbits around solar-type stars ,

We report the discovery of the planets WASP-20b and WASP-28b along with measurements of their sky-projected orbital obliquities. WASP-20b is an inflated, Saturn-mass planet (0.31 MJup ;1 .46RJup) in a 4.9-day, near-aligned (λ = 12.7±4.2 ◦ ) orbit around CD-24 102 (V = 10.7; F9). Due to the low density of the planet and the apparent brightness of the host star, WASP-20 is a good target for atmospheric characterisation via transmission spectroscopy. WASP-28b is an inflated, Jupiter-mass planet (0.91 MJup ;1 .21RJup )i n a 3.4-day, near-aligned (λ = 8 ± 18 ◦ ) orbit around a V = 12, F8 star. As intermediate-mass planets in short orbits around aged, cool stars (7 +2 −1 Gyr and 6000 ± 100 K for WASP-20; 5 +3 −2 Gyr and 6100 ± 150 K for WASP-28), their orbital alignment is consistent with the hypothesis that close-in giant planets are scattered into eccentric orbits with random alignments, which are then circularised and aligned with their stars’ spins via tidal dissipation.

WASP-94 A and B planets: hot-Jupiter cousins in a twin-star system ?

We report the discovery of two hot-Jupiter planets, each orbiting one of the stars of a wide binary system. WASP-94A (2MASS 20550794‐3408079) is an F8 type star hosting a transiting planet with a radius of 1:72 0:06 RJup, a mass of 0:452 0:034 MJup, and an orbital period of 3.95 days. The Rossiter-McLaughlin e ect is clearly detected, and the measured projected spin-orbit angle indicates that the planet occupies a retrograde orbit. WASP-94B (2MASS 20550915‐3408078) is an F9 stellar companion at an angular separation of 15 00 (projected separation 2700 au), hosting a gas giant with a minimum mass of 0:618 0:028 MJup with a period of 2.008 days, detected by Doppler measurements. The orbital planes of the two planets are inclined relative to each other, indicating that at least one of them is inclined relative to the plane of the stellar binary. These hot Jupiters in a binary system bring new insights into the formation of close-in giant planets and the role of stellar multiplicity.