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D. R. Anderson

Publications and source records attributed to D. R. Anderson.

At least 55 records · Page 3Linked to original sources

TESS Hunt for Young and Maturing Exoplanets (THYME): A planet in the 45 Myr Tucana-Horologium association

Young exoplanets are snapshots of the planetary evolution process. Planets that orbit stars in young associations are particularly important because the age of the planetary system is well constrained. We present the discovery of a transiting planet larger than Neptune but smaller than Saturn in the 45 Myr Tucana-Horologium young moving group. The host star is a visual binary, and our follow-up observations demonstrate that the planet orbits the G6V primary component, DS Tuc A (HD 222259A, TIC 410214986). We first identified transits using photometry from the Transiting Exoplanet Survey Satellite (TESS; alerted as TOI 200.01). We validated the planet and improved the stellar parameters using a suite of new and archival data, including spectra from SOAR/Goodman, SALT/HRS and LCO/NRES; transit photometry from Spitzer; and deep adaptive optics imaging from Gemini/GPI. No additional stellar or planetary signals are seen in the data. We measured the planetary parameters by simultaneously modeling the photometry with a transit model and a Gaussian process to account for stellar variability. We determined that the planetary radius is $5.70\pm0.17$ Earth radii and that the orbital period is 8.1 days. The inclination angles of the host star's spin axis, the planet's orbital axis, and the visual binary's orbital axis are aligned within 15 degrees to within the uncertainties of the relevant data. DS Tuc Ab is bright enough (V=8.5) for detailed characterization using radial velocities and transmission spectroscopy.

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The EBLM Project VI. The mass and radius of five low-mass stars in F+M binaries discovered by the WASP survey

Some M-dwarfs around F-/G-type stars have been measured to be hotter and larger than predicted by stellar evolution models. Inconsistencies between observations and models need addressing with more mass, radius and luminosity measurements of low-mass stars to test and refine evolutionary models. Our aim is to measure the masses, radii and ages of the stars in five low-mass eclipsing binary systems discovered by the WASP survey. We use WASP photometry to establish eclipse-time ephemerides and to obtain initial estimates for the transit depth and width. Radial velocity measurements were simultaneously fitted with follow-up photometry to find the best-fitting orbital solution. This solution was combined with measurements of atmospheric parameters to interpolate evolutionary models and estimate the mass of the primary star, and the mass and radius of the M-dwarf companion. We assess how the best fitting orbital solution changes if an alternative limb-darkening law is used and quantify the systematic effects of unresolved companions. We also gauge how the best-fitting evolutionary model changes if different values are used for the mixing length parameter and helium enhancement. We report the mass and radius of five M-dwarfs and find little evidence of inflation with respect to evolutionary models. The primary stars in two systems are near the ``blue hook'' stage of their post sequence evolution, resulting in two possible solutions for mass and age. We find that choices in helium enhancement and mixing-length parameter can introduce an additional 3-5\,\% uncertainty in measured M-dwarf mass. Unresolved companions can introduce an additional 3-8\% uncertainty in the radius of an M-dwarf, while the choice of limb-darkening law can introduce up to an additional 2\% uncertainty.

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Three Hot-Jupiters on the upper edge of the mass-radius distribution: WASP-177, WASP-181 and WASP-183

We present the discovery of 3 transiting planets from the WASP survey, two hot-Jupiters: WASP-177b (~0.5 M_Jup, ~1.6 R_Jup) in a 3.07-d orbit of a V = 12.6 K2 star, WASP-183b (~0.5 M_Jup, ~1.5 R_Jup) in a 4.11-d orbit of a V = 12.8 G9/K0 star; and one hot-Saturn planet WASP-181b (~0.3 M_Jup, ~1.2 R_Jup) in a 4.52-d orbit of a V = 12.9 G2 star. Each planet is close to the upper bound of mass-radius space and has a scaled semi-major axis, a/R_star, between 9.6 and 12.1. These lie in the transition between systems that tend to be in orbits that are well aligned with their host-star's spin and those that show a higher dispersion.

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WASP-190b: Tomographic discovery of a transiting hot Jupiter

We report the discovery of WASP-190b, an exoplanet on a 5.37-day orbit around a mildly-evolved F6 IV-V star with V = 11.7, T_eff = 6400 $\pm$ 100 K, M$_{*}$ = 1.35 $\pm$ 0.05 M_sun and R$_{*}$ = 1.6 $\pm$ 0.1 R_sun. The planet has a radius of R_p = 1.15 $\pm$ 0.09 R_Jup and a mass of M_p = 1.0 $\pm$ 0.1 M_Jup, making it a mildly inflated hot Jupiter. It is the first hot Jupiter confirmed via Doppler tomography with an orbital period >5 days. The orbit is also marginally misaligned with respect to the stellar rotation, with $λ$ = 21 $\pm$ 6$^{\circ}$ measured using Doppler tomography.

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Three transiting planet discoveries from the Wide Angle Search for Planets: WASP-85 A b; WASP-116 b, and WASP-149 b

(abridged) We report the discovery of three new transiting planets: WASP-85 A b, WASP-116 b, and WASP-149 b. WASP-85 b orbits its host star every 2.66 days, and has a mass of 1.25 M_Jup and a radius of 1.25 R_Jup. The host star is of G5 spectral type, with magnitude V = 11.2, and lies 141 pc distant. The system has a K-dwarf binary companion, WASP-85 B, at a separation of ~1.5". The close proximity of this companion leads to contamination of our photometry, decreasing the apparent transit depth that we account for during our analysis. Analysis of the Ca II H+K lines shows strong emission that implies that both binary components are strongly active. WASP-116 b is a warm, mildly inflated super-Saturn, with a mass of 0.59 M_Jup and a radius of 1.43 R_Jup. It was discovered orbiting a metal-poor ([Fe/H] = -0.28 dex), cool (T_eff = 5950 K) G0 dwarf every 6.61 days. WASP-149 b is a typical hot Jupiter, orbiting a G6 dwarf with a period of 1.33 days. The planet has a mass and radius of 1.05 M_Jup and 1.29 R_Jup, respectively. The stellar host has an effective temperature of T_eff = 5750 K and has a metallicity of [Fe/H] = 0.16 dex. WASP photometry of the system is contaminated by a nearby star; we therefore corrected the depth of the WASP transits using the measured dilution. WASP-149 lies inside the 'Neptune desert' identified in the planetary mass-period plane by Mazeh, Holczer & Faigler (2016). We model the modulation visible in the K2 lightcurve of WASP-85 using a simple three-spot model consisting of two large spots on WASP-85 A, and one large spot on WASP-85 B, finding rotation periods of 13.1+/-0.1 days for WASP-85 A and 7.5+/-0.03 days for WASP-85 B. We estimate stellar inclinations of I_A = 66.8+/-0.7 degrees and I_B = 39.7+/-0.2 degrees, and constrain the obliquity of WASP-85 A b to be psi<27 degrees. We therefore conclude that WASP-85 A b is very likely to be aligned.

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Fundamental properties of the pre-main sequence eclipsing stars of MML 53 and the mass of the tertiary

We present the most comprehensive analysis to date of the Upper Centaurus Lupus eclipsing binary MML 53 (2.097892 d), and for the first time, confirm the bound-nature of the third star (~9yr orbit). Our analysis uses new and archival spectra and time-series photometry. We determined the temperature of the primary star to be 4880+-100 K. The study of the close binary incorporated treatment of spots and dilution by the tertiary in the light curves, allowing for the robust measurement of the masses of the eclipsing components within 1% (M1=1.0400+-0.0067 and M2=0.8907+-0.0058 Msun), their radii within 4.5% (R1=1.283+-0.043 and R2=1.107+-0.049 Rsun), and the secondary temperature (4379+-100K). From the analysis of the eclipse timings, and the change in systemic velocity of the eclipsing binary and the radial velocities of the third star, we measured the mass of the outer companion to be 0.7 Msun within 20%. The age we derived from the evolution of the temperature ratio between the eclipsing components is fully consistent with previous estimates of the age of UCL (16+-2 Myr). At this age, the tightening of the MML 53 eclipsing binary has already occurred, thus supporting close-binary formation mechanisms that act early in their evolution. The eclipsing stars roughly follow the same theoretical isochrone, but appear to be inflated in radius (by 20% for the primary and 10% for the secondary). However, our primary radius measurement of is in full agreement with the independent measurement of the secondary of NP Per which has the same mass and a similar age. The eclipsing stars of MML 53 are found to be larger but not cooler than predicted by non-magnetic models, it is not clear what is the mechanism that is causing the radius inflation given that activity, spots and/or magnetic fields slowing their contraction, require the inflated stars to be cooler to remain in thermal equilibrium.

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The discovery of WASP-134b, WASP-134c, WASP-137b, WASP-143b and WASP-146b: three hot Jupiters and a pair of warm Jupiters orbiting Solar-type stars

We report the discovery by WASP of five planets orbiting moderately bright ($V$ = 11.0-12.9) Solar-type stars. WASP-137b, WASP-143b and WASP-146b are typical hot Jupiters in orbits of 3-4 d and with masses in the range 0.68--1.11 $M_{\rm Jup}$. WASP-134 is a metal-rich ([Fe/H] = +0.40 $\pm$ 0.07]) G4 star orbited by two warm Jupiters: WASP-134b ($M_{\rm pl}$ = 1.41 $M_{\rm Jup}$; $P = 10.1$ d; $e = 0.15 \pm 0.01$; $T_{\rm eql}$ = 950 K) and WASP-134c ($M_{\rm pl} \sin i$ = 0.70 $M_{\rm Jup}$; $P = 70.0$ d; $e = 0.17 \pm 0.09$; $T_{\rm eql}$ = 500 K). From observations of the Rossiter-McLaughlin effect of WASP-134b, we find its orbit to be misaligned with the spin of its star ($λ= -44 \pm 10^\circ$). WASP-134 is a rare example of a system with a short-period giant planet and a nearby giant companion. In-situ formation or disc migration seem more likely explanations for such systems than does high-eccentricity migration.

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Discovery of three new transiting hot Jupiters: WASP-161 b, WASP-163 b and WASP-170 b

We present the discovery by the WASP-South transit survey of three new transiting hot Jupiters, WASP-161 b, WASP-163 b and WASP-170 b. Follow-up radial velocities obtained with the Euler/CORALIE spectrograph and high-precision transit light curves obtained with the TRAPPIST-North, TRAPPIST-South, SPECULOOS-South, NITES, and Euler telescopes have enabled us to determine the masses and radii for these transiting exoplanets. WASP-161\,b completes an orbit around its $V=11.1$ F6V-type host star in 5.406 days, and has a mass and radius of $2.5\pm 0.2$$M_{Jup}$ and $1.14\pm 0.06$ $R_{Jup}$ respectively. WASP-163\,b has an orbital period of 1.609 days, a mass of $1.9\pm0.2$ $M_{Jup}$, and a radius of $1.2\pm0.1$ $R_{Jup}$. Its host star is a $V=12.5$ G8-type dwarf. WASP-170\,b is on a 2.344 days orbit around a G1V-type star of magnitude $V=12.8$. It has a mass of $1.7\pm0.2$ $M_{Jup}$ and a radius of $1.14\pm0.09$ $R_{Jup}$. Given their irradiations ($\sim10^9$ erg.s$^{-1}$.cm$^{-2}$) and masses, the three new planets sizes are in good agreement with classical structure models of irradiated giant planets.

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WASP-147b, 160Bb, 164b and 165b: two hot Saturns and two Jupiters, including two planets with metal-rich hosts

We report the discovery of four transiting hot Jupiters, WASP-147, WASP-160B, WASP-164 and WASP-165 from the WASP survey. WASP-147b is a near Saturn-mass ($M_P = 0.28 M_{J}$) object with a radius of $ 1.11 \, R_{J}$ orbiting a G4 star with a period of $ 4.6 $ d. WASP-160Bb has a mass and radius ($ M_p = 0.28 \, M_J $, $ R_p = 1.09 \, R_J$) near-identical to WASP-147b, but is less irradiated, orbiting a metal-rich ([Fe/H] = 0.27) K0 star with a period of $3.8$ d. WASP-160B is part of a near equal-mass visual binary with an on-sky separation of 28.5 arcsec. WASP-164b is a more massive ($M_P = 2.13 \, M_J$, $R_p = 1.13 \, R_J$) hot Jupiter, orbiting a G2 star on a close-in ($P=1.8$ d), but tidally stable orbit. WASP-165b is a classical ($M_p = 0.66 \, M_J$, $R_P = 1.26 \, R_J$) hot Jupiter in a $3.5$~d period orbit around a metal-rich ([Fe/H] = 0.33) star. WASP-147b and WASP-160Bb are promising targets for atmospheric characterization through transmission spectroscopy, while WASP-164b presents a good target for emission spectroscopy.

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Machine-learning Approaches to Exoplanet Transit Detection and Candidate Validation in Wide-field Ground-based Surveys

Since the start of the Wide Angle Search for Planets (WASP) program, more than 160 transiting exoplanets have been discovered in the WASP data. In the past, possible transit-like events identified by the WASP pipeline have been vetted by human inspection to eliminate false alarms and obvious false positives. The goal of the present paper is to assess the effectiveness of machine learning as a fast, automated, and reliable means of performing the same functions on ground-based wide-field transit-survey data without human intervention. To this end, we have created training and test datasets made up of stellar light curves showing a variety of signal types including planetary transits, eclipsing binaries, variable stars, and non-periodic signals. We use a combination of machine learning methods including Random Forest Classifiers (RFCs) and Convolutional Neural Networks (CNNs) to distinguish between the different types of signals. The final algorithms correctly identify planets in the test data ~90% of the time, although each method on its own has a significant fraction of false positives. We find that in practice, a combination of different methods offers the best approach to identifying the most promising exoplanet transit candidates in data from WASP, and by extension similar transit surveys.

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A low-density hot Jupiter in a near-aligned, 4.5-day orbit around a $V$ = 10.8, F5V star

We report the independent discovery and characterisation of a hot Jupiter in a 4.5-d, transiting orbit around the star TYC 7282-1298-1 ($V$ = 10.8, F5V). The planet has been pursued by the NGTS team as NGTS-2b and by ourselves as WASP-179b. We characterised the system using a combination of photometry from WASP-South and TRAPPIST-South, and spectra from CORALIE (around the orbit) and HARPS (through the transit). We find the planet's orbit to be nearly aligned with its star's spin. From a detection of the Rossiter-McLaughlin effect, we measure a projected stellar obliquity of $λ= -19 \pm 6^\circ$. From line-profile tomography of the same spectra, we measure $λ= -11 \pm 5^\circ$. We find the planet to have a low density ($M_{\rm P}$ = 0.67 $\pm$ 0.09 $M_{\rm Jup}$, $R_{\rm P}$ = 1.54 $\pm$ 0.06 $R_{\rm Jup}$), which, along with its moderately bright host star, makes it a good target for transmission spectroscopy. We find a lower stellar mass ($M_*$ = $1.30 \pm 0.07$ $M_\odot$) than reported by the NGTS team ($M_*$ = $1.64 \pm 0.21$ $M_\odot$), though the difference is only $1.5$ $σ$.

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WASP-189b: an ultra-hot Jupiter transiting the bright A star HR 5599 in a polar orbit

We report the discovery of WASP-189b: an ultra-hot Jupiter in a 2.72-d transiting orbit around the $V = 6.6$ A star WASP-189 (HR 5599). We detected periodic dimmings in the star's lightcurve, first with the WASP-South survey facility then with the TRAPPIST-South telescope. We confirmed that a planet is the cause of those dimmings via line-profile tomography and radial-velocity measurements using the HARPS and CORALIE spectrographs. Those reveal WASP-189b to be an ultra-hot Jupiter ($M_{\rm P}$ = 2.13 $\pm$ 0.28 $M_{\rm Jup}$; $R_{\rm P}$ = 1.374 $\pm$ 0.082 $R_{\rm Jup}$) in a polar orbit ($λ= 89.3 \pm 1.4^\circ$; $Ψ= 90.0 \pm 5.8^\circ$) around a rapidly rotating A6IV-V star ($T_{\rm eff}$ = 8000 $\pm$ 100 K; $v_* \sin i_*$ $\approx$ 100 km\, s$^{-1}$). We calculate a predicted equilibrium temperature of $T_{\rm eql}$ = 2641 $\pm$ 34 K, assuming zero albedo and efficient redistribution, which is the third hottest for the known exoplanets. WASP-189 is the brightest known host of a transiting hot Jupiter and the third-brightest known host of any transiting exoplanet. We note that of the eight hot-Jupiter systems with $T_{\rm eff}$ $>$ 7000 K, seven have strongly misaligned orbits, and two of the three systems with $T_{\rm eff}$ $\geq$ 8000 K have polar orbits (the third is aligned).

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WASP-128b: a transiting brown dwarf in the dynamical-tide regime

Massive companions in close orbits around G dwarfs are thought to undergo rapid orbital decay due to runaway tidal dissipation. We report here the discovery of WASP-128b, a brown dwarf discovered by the WASP survey transiting a G0V host on a $2.2\,\mathrm{d}$ orbit, where the measured stellar rotation rate places the companion in a regime where tidal interaction is dominated by dynamical tides. Under the assumption of dynamical equilibrium, we derive a value of the stellar tidal quality factor $\log{Q_\star'} = 6.96 \pm 0.19$. A combined analysis of ground-based photometry and high-resolution spectroscopy reveals a mass and radius of the host, $M_\star = 1.16 \pm 0.04\,M_\odot$, $R_\star = 1.16 \pm 0.02\,R_\odot$, and for the companion, $M_\mathrm{b} =37.5 \pm 0.8\,M_\mathrm{Jup}$, $R_\mathrm{b} = 0.94 \pm 0.02\,R_\mathrm{Jup}$, placing WASP-128b in the driest parts of the brown dwarf desert, and suggesting a mild inflation for its age. We estimate a remaining lifetime for WASP-128b similar to that of some ultra-short period massive hot Jupiters, and note it may be a propitious candidate for measuring orbital decay and testing tidal theories.

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Discovery of WASP-174b: Doppler tomography of a near-grazing transit

We report the discovery and tomographic detection of WASP-174b, a planet with a near-grazing transit on a 4.23-d orbit around a $V$ = 11.9, F6V star with [Fe/H] = 0.09 $\pm$ 0.09. The planet is in a moderately misaligned orbit with a sky-projected spin-orbit angle of $λ$ = 31$^{\circ}$ $\pm$ 1$^{\circ}$. This is in agreement with the known tendency for orbits around hotter stars to be misaligned. Owing to the grazing transit the planet's radius is uncertain, with a possible range of 0.8-1.8 R$_{\rm Jup}$. The planet's mass has an upper limit of 1.3 M$_{\rm Jup}$. WASP-174 is the faintest hot-Jupiter system so far confirmed by tomographic means.

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Helium in the eroding atmosphere of an exoplanet

Helium is the second-most abundant element in the Universe after hydrogen and is one of the main constituents of gas-giant planets in our Solar System. Early theoretical models predicted helium to be among the most readily detectable species in the atmospheres of exoplanets, especially in extended and escaping atmospheres. Searches for helium, however, have hitherto been unsuccessful. Here we report observations of helium on an exoplanet, at a confidence level of 4.5 standard deviations. We measured the near- infrared transmission spectrum of the warm gas giant WASP-107b and identified the narrow absorption feature of excited metastable helium at 10,833 angstroms. The amplitude of the feature, in transit depth, is 0.049 +/- 0.011 per cent in a bandpass of 98 angstroms, which is more than five times greater than what could be caused by nominal stellar chromospheric activity. This large absorption signal suggests that WASP-107b has an extended atmosphere that is eroding at a total rate of 10^10 to 3 x 10^11 grams per second (0.1-4 per cent of its total mass per billion years), and may have a comet-like tail of gas shaped by radiation pressure.

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WASP 0639-32: a new F-type subgiant/K-type main-sequence detached eclipsing binary from the WASP project

Abridged. Our aim is to measure the masses and radii of the stars in a newly-discovered detached eclipsing binary system to a high precision ($\approx$1%), enabling the system to be used for the calibration of free parameters in stellar evolutionary models. Photometry from the Wide Angle Search for Planets (WASP) project was used to identify 1SWASP J063930.33-322404.8 (TYC 7091-888-1, WASP 0369-32 hereafter) as a detached eclipsing binary system with total eclipses and an orbital period of P=11.66 days. Lightcurve parameters for WASP 0639-32 are obtained using the ebop lightcurve model, with standard errors evaluated using a prayer-bead algorithm. Radial velocities were measured from 11 high-resolution spectra using a broadening function approach, and an orbit was fitted using sbop. Observed spectra were disentangled and an equivalent width fitting method was used to obtain effective temperatures and metallicities for both stars. A Bayesian framework is used to explore a grid of stellar evolution models, where both helium abundance and mixing length are free to vary, and use observed parameters (mass, density, temperature and metallicity) for each star to obtain the age and constrain the helium abundance of the system. The masses and radii are found to be $M_{1}=1.1544\pm0.0043\,M_{\odot}$, $R_{1}=1.833\pm0.023\,R_{\odot}$ and $M_{2}=0.7833\pm0.0028\,M_{\odot}$, $R_{2}=0.7286\pm0.0081\,R_{\odot}$ for the primary and secondary, respectively. The effective temperatures were found to be $T_{1}=6330\pm50$ K and $T_{2}=5400\pm80$ K for the primary and secondary star, respectively. The system has an age of $4.2^{+0.8}_{-0.1}$ Gyr, and a helium abundance in the range 0.251-0.271. WASP 0639-32 is a rare example of a well-characterised detached eclipsing binary system containing a star near the main-sequence turn-off point. This make it possible to measure a precise age for the stars ...

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Thermal emission of WASP-48b in the Ks-band

We report a detection of thermal emission from the hot Jupiter WASP-48b in the $K_{\rm s}$-band. We used the Wide-field Infra-red Camera on the 3.6-m Canada-France Hawaii Telescope to observe an occultation of the planet by its host star. From the resulting occultation lightcurve we find a planet-to-star contrast ratio in the Ks-band of $0.136 \pm 0.014\,\%$ , in agreement with the value of $0.109 \pm 0.027\,\%$ previously determined. We fit the two Ks-band occultation lightcurves simultaneously with occultation lightcurves in the $H$-band and the Spitzer 3.6-μm and 4.5-μm bandpasses, radial velocity data, and transit lightcurves. From this, we revise the system parameters and construct the spectral energy distribution (SED) of the dayside atmosphere. By comparing the SED with atmospheric models, we find that both models with and without a thermal inversion are consistent with the data. We find the planet's orbit to be consistent with circular ($e < 0.072$ at 3$σ$).

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New transiting hot Jupiters discovered by WASP-South, Euler/CORALIE and TRAPPIST-South

We report the discovery of eight hot-Jupiter exoplanets from the WASP-South transit survey. WASP-144b has a mass of 0.44 Mj, a radius of 0.85 Rj, and is in a 2.27-d orbit around a V = 12.9, K2 star which shows a 21-d rotational modulation. WASP-145Ab is a 0.89 Mj planet in a 1.77-d orbit with a grazing transit, which means that the planetary radius is not well constrained. The host is a V = 11.5, K2 star with a companion 5 arcsecs away and 1.4 mags fainter. WASP-158b is a relatively massive planet at 2.8 Mj with a radius of 1.1 Rj and a 3.66-d orbit. It transits a V = 12.1, F6 star. WASP-159b is a bloated hot Jupiter (1.4 Rj and 0.55 Mj) in a 3.8-d orbit around a V = 12.9, F9 star. WASP-162b is a massive planet in a relatively long and highly eccentric orbit (5.2 Mj, P = 9.6 d, e = 0.43). It transits a V = 12.2, K0 star. WASP-168b is a bloated hot Jupiter (0.42 Mj, 1.5 Rj) in a 4.15-d orbit with a grazing transit. The host is a V = 12.1, F9 star. WASP-172b is a bloated hot Jupiter (0.5 Mj; 1.6 Rj) in a 5.48-d orbit around a V = 11.0, F1 star. It is likely to be the best planet of those reported here for atmospheric characterisation. WASP-173Ab is a massive planet (3.7 Mj) with a 1.2 Rj radius in a circular orbit with a period of 1.39 d. The host is a V = 11.3, G3 star, being the brighter component of the double-star system WDS23366-3437, with a companion 6 arcsecs away and 0.8 mags fainter. One of the two stars shows a rotational modulation of 7.9 d.

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