MNRAS 000, 1–10 (2018) Preprint 14 September 2018 Compiled using MNRAS LATEX style file v3.0 WASP-189b: an ultra-hot Jupiter transiting the bright A star HR5599 in a polar orbit⋆ D. R. Anderson,1 L. Y. Temple,1 L. D. Nielsen,2 A. Burdanov,3 C. Hellier,1 † F. Bouchy,2 D. J. A. Brown,4,5 A. Collier Cameron,6 M. Gillon,3 E. Jehin,3 P. F. L. Maxted,1 F. Pepe,2 D. Pollacco,4,5 F. J. Pozuelos,3 D. Queloz,2,7 D. S´egransan,2 B. Smalley,1 A. H. M. J. Triaud,8 O. D. Turner,2 S. Udry2 and R. G. West4,5 1Astrophysics Group, Keele University, Staffordshire ST5 5BG, UK 2Observatoire de Gen`eve, Universit´ede Gen`eve, 51 Chemin des Maillettes, 1290 Sauverny, Switzerland 3Space sciences, Technologies and Astrophysics Research (STAR) Institute, Universit´ede Li`ege, Li`ege 1, Belgium 4Department of Physics, University of Warwick, Coventry CV4 7AL, UK 5Centre for Exoplanets and Habitability, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, UK 6SUPA, School of Physics and Astronomy, University of St. Andrews, North Haugh, Fife KY16 9SS, UK 7Cavendish Laboratory, J J Thomson Avenue, Cambridge CB3 0HE, UK 8School of Physics & Astronomy, University of Birmingham, Edgbaston, Birmingham, B15 2TT, UK Accepted XXX. Received YYY; in original form 2018 September 13 ABSTRACT 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 dim- mings 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 dim- mings via line-profile tomography and radial-velocity measurements using the HARPS and CORALIE spectrographs. Those reveal WASP-189b to be an ultra-hot Jupiter (MP = 2.13 0.28 MJup; RP = 1.374 0.082 RJup) in a polar orbit (λ = 89.3 1.4 ; ± ± ± ◦ Ψ = 90.0 5.8◦) around a rapidly rotating A6IV–V star (Teff = 8000 100 K; v sin i ±1 ± ∗ ∗ ≈ 100km s− ). We calculate a predicted equilibrium temperature of Teql = 2641 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 Teff > 7000 K, seven have strongly misaligned orbits, and two of the three systems with Teff 8000 K have polar orbits (the third is aligned). ≥ Key words: planets and satellites: detection – planets and satellites: individual: arXiv:1809.04897v1 [astro-ph.EP] 13 Sep 2018 WASP-189b – stars: individual: WASP-189 – stars: individual: HR 5599 1 INTRODUCTION tive temperature Teff > 7000 K. This is because the spectral lines of very hot, rapidly rotating stars are sparse and broad, With 750 transiting planets well studied the emphasis is ∼ which complicates the radial-velocity verification of planets. on pushing planet discovery into regimes where there are Hence we know little about the formation and evolution of few known planets. Of the 580 host stars listed in the TEP- planets around hot stars. Cat database (Southworth 2011), only 9 have stellar effec- Under the core accretion model of planet formation, giant planets are expected to be more common around ⋆ Based on observations collected at the European Organisation more massive stars (Pollack et al. 1996), with an occurrence for Astronomical Research in the Southern Hemisphere under rate predicted by Kennedy & Kenyon (2008) to increase lin- ESO programme 0100.C-0847. early with stellar mass over the range 0.4–3 M . Indeed, ⊙ E-mail: [email protected] Cumming et al. (2008) found that the occurrence rate of gi- † © 2018 The Authors 2 D. R. Anderson et al. M M P ant planets (planet mass P = 0.3–10 Jup; orbital period 1.01 = 2–2000 d) is ten times lower for M dwarfs (1 per cent) than for FGK stars (10.5 per cent). Whether this trend contin- ues to A stars is unknown. Borgniet et al. (2017) reported +10 M an occurrence rate of 4 4 per cent for A-type stars ( P = 1 0.1–10 MJup; P = 1–1000− d), which is too imprecise to tell. An additional motivation to discover planets around hot Relative flux stars is their potential for characterisation. As hot stars are intrinsically luminous, many bright stars (which are eas- 0.99 ier to study) are hot stars: of the Bright Star Catalogue 0.4 0.6 0.8 1 1.2 1.4 1.6 (Hoffleit & Jaschek 1991), 41 per cent are listed as OBA Orbital phase stars and 21 per cent are listed as A stars. Also, plan- ets in close orbits around hot stars are intensely irradi- Figure 1. ated, which facilitates the probing of their atmospheres. For WASP-South survey lightcurve folded on the adopted ephemeris from Table 3 and binned (bin width equivalent to example, a great deal of work has been done to charac- 2 min). terise the atmosphere of WASP-33b (Collier Cameron et al. 2010b; Teff = 7430 K; V = 8.2; P = 1.22 d) from detections of its thermal emission (Smith et al. 2011; Deming et al. 2012; Using HARPS on the ESO 3.6-m telescope (Pepe et al. de Mooij et al. 2013; Haynes et al. 2015; von Essen et al. 2000), we obtained a series of spectra during the tran- 2015; Nugroho et al. 2017; Zhang et al. 2018). sit night of 2018 Mar 26. Using the HARPS Data Re- In their initial configuration the WASP survey facil- duction Software (DRS), we computed average stellar line ities operated with 200-mm f/1.8 lenses, as described by profiles, or cross-correlation functions (CCFs), by cross- Pollacco et al. (2006), targetting stars in the range V = 9– correlating the HARPS spectra with a weighted A0 binary 13. WASP-South ran in this mode from 2006 to 2012, re- mask from which we had removed various tellurics and ISM sulting in the discovery of 125 planets (some jointly with lines (Baranne et al. 1996; Pepe et al. 2002). The time-series SuperWASP-North). But WASP-South saturated at V = 9, of these CCFs constitute the HARPS Doppler tomography and the brightest planet-host found in the South was WASP- data set, DTHAR. We discarded the last two spectra of the se- 18 at V = 9.3 (Hellier et al. 2009). Since several brighter ries as they were visibly affected by twilight. In the resulting hosts were known in the North we decided to switch to tomogram (top-left panel of Fig. 2), there is a trace indica- Canon 85-mm f/1.2 lenses, with an SDSS r-band filter and tive of a planet in a polar orbit crossing the red-shifted hemi- shorter exposures (three 20-s exposures per pointing instead sphere of the star. However, due to ephemeris uncertainty of two 30-s exposures), so covering the range V = 6.5–11. (our initial attempts to refine the ephemeris with additional WASP-South ran in this configuration from 2012 to 2015. transit photometry were unsuccessful) we had missed the This survey mode is similar to that of the KELT ingress of the event and we were concerned about possible project (Pepper et al. 2007), which uses a Mamiya 80- lunar contamination. The Moon, which was 77 per cent illu- mm f/1.9 lens, and which has been vindicated by spec- minated and at a distance of 95 from the target, had set ∼ ◦ tacular discoveries such as KELT-9 (Gaudi et al. 2017) at 06:46 UT. The barycentric Earth velocity was 18.5 km 1 and KELT-20/MASCARA-2 (Lund et al. 2017; Talens et al. s− . The trace in the tomogram occurs at a similar veloc- 2018), which are both V = 7.6 systems. KELT-9b, which ity and is apparent in the CCFs taken up to 06:04 UT. We transits the hottest known hot-Jupiter host (T 10 200 K), eff≈ cross-correlated with the A0 mask the sky spectra taken si- is already proving invaluable for atmospheric characterisa- multaneously using the secondary HARPS fibre and found tion (Hoeijmakers et al. 2018). no signal (Fig. 3), which indicates that the signal in the In this paper we present the discovery of WASP-189b, target tomogram is not due to the Moon. an ultra-hot Jupiter transiting an even brighter star, being Using CORALIE, we obtained a series of spectra dur- in a polar orbit around the mid-A star WASP-189 (HR 5599; ing the transit night of 2018 Jul 13. The Moon posed no V = T 6.6; eff = 8000 K). issue as it was only 2 per cent illuminated and it set at 23:01 UT (26 min before the CORALIE sequence began). We again computed CCFs using the A0 mask to produce 2 PHOTOMETRIC AND SPECTROSCOPIC the CORALIE Doppler tomography data set, DTCOR. In OBSERVATIONS the resulting tomogram (top-right panel of Fig. 2), there is a trace indicative of a planet in a polar orbit crossing the We present in Table 1 a summary of our photometric red-shifted hemisphere of the star. This is similar to the and spectroscopic observations of WASP-189. We observed trace in the DTHARPS tomogram, which occurs at a similar WASP-189 during 2012 Jul to 2013 Aug with the modified barcyentric RV.