Tom M. Louden

SPATIALLY RESOLVED EASTWARD WINDS AND ROTATION OF HD 189733b

We measure wind velocities on opposite sides of the hot Jupiter HD 189733b by modeling sodium absorption in high-resolution transmission spectra from the High Accuracy Radial Velocity Planet Searcher. Our model implicitly accounts for the Rossiter–McLaughlin effect, which we show can explain the high wind velocities suggested by previous studies. Our results reveal a strong eastward motion of the atmosphere of HD 189733b, with a redshift of

The Next Generation Transit Survey (NGTS)

{2.3}_{-1.5}^{+1.3}

Strong XUV irradiation of the Earth-sized exoplanets orbiting the ultracool dwarf TRAPPIST-1

km s−1 on the leading limb of the planet and a blueshift of

Transmission spectroscopy of the inflated exoplanet WASP-52b, and evidence for a bright region on the stellar surface

{5.3}_{-1.4}^{+1.0}

Reconstructing the high-energy irradiation of the evaporating hot Jupiter HD 209458b

km s−1 on the trailing limb. These velocities can be understood as a combination of tidally locked planetary rotation and an eastward equatorial jet, closely matching the predictions of atmospheric circulation models. Our results show that the sodium absorption of HD 189733b is intrinsically velocity broadened, so previous studies of the average transmission spectrum are likely to have overestimated the role of pressure and thermal broadening.

Single transit candidates from K2: detection and period estimation

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 20 cm 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.

Centroid vetting of transiting planet candidates from the Next Generation Transit Survey

We present an XMM-Newton X-ray observation of TRAPPIST-1, which is an ultracool dwarf star recently discovered to host three transiting and temperate Earth-sized planets. We find the star is a relatively strong and variable coronal X-ray source with an X-ray luminosity similar to that of the quiet Sun, despite its much lower bolometric luminosity. We find L_X/L_bol=2-4x10^-4, with the total XUV emission in the range L_XUV/L_bol=6-9x10^-4, and XUV irradiation of the planets that is many times stronger than experienced by the present-day Earth. Using a simple energy-limited model we show that the relatively close-in Earth-sized planets, which span the classical habitable zone of the star, are subject to sufficient X-ray and EUV irradiation to significantly alter their primary and any secondary atmospheres. Understanding whether this high-energy irradiation makes the planets more or less habitable is a complex question, but our measured fluxes will be an important input to the necessary models of atmospheric evolution.

NGTS-1b: A hot Jupiter transiting an M-dwarf

We have measured the transmission spectrum of the extremely inflated hot Jupiter WASP-52b using simultaneous photometric observations in Sloan Digital Sky Survey u΄, g΄ and a filter centred on the sodium doublet (Na i) with the ULTRACAM instrument mounted on the 4.2-m William Herschel Telescope. We find that Rayleigh scattering is not the dominant source of opacity within the planetary atmosphere and find a transmission spectrum more consistent with wavelength-independent opacity such as from clouds. We detect an in-transit anomaly that we attribute to the presence of stellar activity and find that this feature can be more simply modelled as a bright region on the stellar surface akin to solar faculae rather than spots. A spot model requires a significantly larger planet/star radius ratio than that found in previous studies. Our results highlight the precision that can be achieved by ground-based photometry with errors in the scaled planetary radii of less than one atmospheric scale height, comparable to Hubble Space Telescope observations.

Rayleigh scattering in the transmission spectrum of HAT-P-18b

The atmosphere of the exoplanet HD 209458b is undergoing sustained mass loss, believed to be caused by X-ray and extreme-ultraviolet (XUV) irradiation from its star. The majority of this flux is not directly observable due to interstellar absorption, but is required in order to correctly model the photo-evaporation of the planet and photo-ionisation of the outflow. We present a recovered high energy spectrum for HD 209458 using a Differential Emission Measure (DEM) retrieval technique. We construct a model of the stellar corona and transition region for temperatures between 10^4.1 and 10^8 K which is constrained jointly by ultraviolet line strengths measured with the Cosmic Origins Spectrograph (COS) on the Hubble Space Telescope (HST) and X-ray flux measurements from XMM-Newton. The total hydrogen ionising luminosity (λ 40%. However, our luminosity is compatible with early estimates of the mass loss rate of HD 209458b based on results from the HST Space Telescope Imaging Spectrograph (STIS). Precisely reconstructed XUV irradiation is a key input to determining mass loss rates and efficiencies for exoplanet atmospheres.

From Dense Hot Jupiter to Low Density Neptune: The Discovery of WASP-127b, WASP-136b and WASP-138b

Photometric surveys such as Kepler have the precision to identify exoplanet and eclipsing binary candidates from only a single transit. K2, with its 75 d campaign duration, is ideally suited to detect significant numbers of single-eclipsing objects. Here we develop a Bayesian transit-fitting tool (‘Namaste: An Mcmc Analysis of Single Transit Exoplanets’) to extract orbital information from single transit events. We achieve favourable results testing this technique on known Kepler planets, and apply the technique to seven candidates identified from a targeted search of K2 campaigns 1, 2 and 3. We find EPIC203311200 to host an excellent exoplanet candidate with a period, assuming zero eccentricity, of 540+410 −230 d and a radius of 0.51 ± 0.05RJup. We also find six further transit candidates for which more follow-up is required to determine a planetary origin. Such a technique could be used in the future with TESS, PLATO and ground-based photometric surveys such as NGTS, potentially allowing the detection of planets in reach of confirmation by Gaia.