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Astronomy & Astrophysics manuscript no. hip65426_shine_revised_shortcorr c ESO 2017 July 6, 2017 Discovery of a warm, dusty giant planet around HIP 65426 ? G. Chauvin1; 2, S. Desidera3, A.-M. Lagrange1, A. Vigan4, R. Gratton3, M. Langlois4; 5, M. Bonnefoy1, J.-L. Beuzit1, M. Feldt6, D. Mouillet1, M. Meyer7; 8, A. Cheetham9, B. Biller6; 10, A. Boccaletti11, V. D’Orazi3, R. Galicher11, J. Hagelberg1, A.-L. Maire6, D. Mesa3, J. Olofsson6; 12, M. Samland6, T.O.B. Schmidt11, E. Sissa3, M. Bonavita3; 10, B. Charnay11, M. Cudel1, S. Daemgen7, P. Delorme1, P. Janin-Potiron13, M. Janson6; 14, M. Keppler6, H. Le Coroller4, R. Ligi4, G.D. Marleau6; 15, S. Messina3; 16, P. Mollière6, C. Mordasini6; 15, A. Müller6, S. Peretti9, C. Perrot11, L. Rodet1, D. Rouan11, A. Zurlo3; 17, C. Dominik18, T. Henning6, F. Menard1, H.-M. Schmid7, M. Turatto3, S. Udry9, F. Vakili13, L. Abe13, J. Antichi19, A. Baruffolo3, P. Baudoz11, J. Baudrand11, P. Blanchard4, A. Bazzon7, T. Buey11, M. Carbillet13, M. Carle4, J. Charton1, E. Cascone20, R. Claudi3, A. Costille4, A. Deboulbe1, V. De Caprio20, K. Dohlen4, D. Fantinel3, P. Feautrier1, T. Fusco21, P. Gigan11, E. Giro3, D. Gisler7, L. Gluck1, N. Hubin22, E. Hugot4, M. Jaquet4, M. Kasper22, F. Madec4, Y. Magnard,1, P. Martinez13, D. Maurel1, D. Le Mignant4, O. Möller-Nilsson6, M. Llored4, T. Moulin1, A. Origné4, A. Pavlov6, D. Perret11, C. Petit21, J. Pragt23, P. Puget1, P. Rabou1, J. Ramos6, R. Rigal18, S. Rochat1, R. Roelfsema23, G. Rousset11, A. Roux1, B. Salasnich3, J.-F. Sauvage21, A. Sevin11, C. Soenke22, E. Stadler1, M. Suarez19, L. Weber9, F. Wildi9, S. Antoniucci24, J.-C. Augereau1, J.-L. Baudino11; 25, W. Brandner6, N. Engler7, J. Girard1; 26, C. Gry4, Q. Kral11; 27, T. Kopytova6; 28, E. Lagadec13, J. Milli1; 26, C. Moutou4; 29, J. Schlieder6; 30, J. Szulágyi7, C. Thalmann7, Z. Wahhaj4; 26 (Affiliations can be found after the references) Received May 10th, 2017 ABSTRACT Aims. The SHINE program is a large high-contrast near-infrared survey of 600 young, nearby stars. It is aimed at searching for and characterizing new planetary systems using VLT/SPHERE’s unprecedented high-contrast and high-angular resolution imaging capabilities. It also intends at placing statistical constraints on the occurrence and orbital properties of the giant planet population at large orbits as a function of the stellar host mass and age to test planet formation theories. Methods. We use the IRDIS dual-band imager and the IFS integral field spectrograph of SPHERE to acquire high-constrast coronagraphic differ- ential near-infrared images and spectra of the young A2 star HIP 65426. It is a member of the ∼ 17 Myr old Lower Centaurus-Crux association. Results. At a separation of 830 mas (92 au projected) from the star, we detect a faint red companion. Multi-epoch observations confirm that it shares common proper motion with HIP 65426. Spectro-photometric measurements extracted with IFS and IRDIS between 0.95 and 2.2 µm indicate a warm, dusty atmosphere characteristic of young low surface-gravity L5-L7 dwarfs. Hot-start evolutionary models predict a luminosity consistent with a 6 − 12 MJup, Teff = 1300 − 1600 K and R = 1:5 ± 0:1 RJup giant planet. Finally, the comparison with Exo-REM and PHOENIX BT-Settl synthetic atmosphere models gives consistent effective temperatures but with slightly higher surface gravity solutions of log(g) = 4:0−5:0 with smaller radii (1:0 − 1:3 RJup). Conclusions. Given its physical and spectral properties, HIP 65426 b occupies a rather unique placement in terms of age, mass and spectral-type among the currently known imaged planets. It represents a particularly interesting case to study the presence of clouds as a function of particle size, composition, and location in the atmosphere, to search for signatures of non-equilibrium chemistry, and finally to test the theory of planet formation and evolution. Key words. Techniques: Imaging and spectroscopy - Star: HIP65426 - Planets and Satellites: detection, fundamental parameters, atmospheres 1. Introduction systems with coronagraphic and differential imaging techniques. They offer unprecedented detection, astrometric and spectropho- More than a decade of direct imaging surveys targeting several tometric capabilities which allow us to discover and charac- arXiv:1707.01413v1 [astro-ph.EP] 5 Jul 2017 hundreds of young, nearby stars have revealed that the occur- terize fainter and closer giant planets like the recent discovery rence of giant planets at wide orbits (≥ 20 − 40 au) is relatively of 51 Eri b (2 MJup at 14 au, T5-type, of age 20 Myr; Macin- low (e.g Bowler 2016). Despite the relatively small number of tosh et al. 2015; Samland et al. 2017). The SHINE (SpHere discoveries compared with other techniques like radial velocity INfrared survey for Exoplanets) survey aims at imaging 600 and transit, each new imaged giant planet has brought unique young, nearby stars as part of the SPHERE Guaranteed Time clues on the formation, evolution and physics of young Jupiters. Observations. In this survey, we observed the close environment The latest generation of planet imagers, SPHERE (Beuzit et al. of the young, star HIP 65426. The deep coronographic near- 2008), GPI (Macintosh et al. 2014) and SCExAO (Jovanovic infrared observations revealed the presence of a young, warm, et al. 2016), now combine innovative extreme adaptive optics and dusty L5-L7 massive jovian planet, hereafter HIP 65426 b, ? located at about 92 au (projected distance). We describe below Based on observations collected at La Silla and Paranal Observa- the observing set-up and data reduction, the physical properties tory, ESO (Chile) Program ID: 097.C-0865 and 098.C-0209 (SPHERE). Article number, page 1 of 10 A&A proofs: manuscript no. hip65426_shine_revised_shortcorr of HIP 65426 b, and finally discuss this new discovery in com- Table E.1 of App. E. To calibrate the IRDIS and IFS datasets, an parison to other imaged planetary systems and current planet for- astrometric field 47 Tuc was observed. The platescale and True mation and evolution theories. North solution at each epoch are reported in Table E.1. They are derived from the long-term analysis of the SHINE astrometric calibration described by Maire et al. (2016). 2. Host star properties All IRDIS and IFS datasets were reduced at the SPHERE 2 HIP 65426 is an A2-type (H = 6:853 ± 0:049 mag, Cutri et al. Data Center (DC) using the SPHERE Data Reduction and Han- 2003; d = 111:4 ± 3:8 pc, Gaia Collaboration et al. 2016) mem- dling (DRH) automated pipeline (Pavlov et al. 2008). Basic cor- ber of the Lower Centaurus-Crux (hereafter LCC) association rections for bad pixels, dark current, flat field were applied. For (de Zeeuw et al. 1999; Rizzuto et al. 2011). A detailed summary IFS, the SPHERE-DC complemented the DRH pipeline with ad- of the main stellar properties as found in the literature is given ditional steps that improve the wavelength calibration and the in App. A. To refine them, the star was observed with HARPS cross-talk and bad pixel correction (Mesa et al. 2015). The prod- (Mayor et al. 2003) on January 16th, 17th and 18th, 20171. ucts were then used as input of the SHINE Specal pipeline We measured the stellar absolute radial and projected rotational which applies anamorphism correction and flux normalization, velocities using a custom cross-correlation function procedure followed by applying different angular and spectral differential specifically tailored for fast-rotating early-type stars. Respective imaging algorithms (Galicher et al. 2017, in prep). For the Febru- −1 −1 values of Vrad = 5:2 ± 1:3 km.s and v sin i = 299 ± 9 km.s ary 7th 2017 and February 9th 2017 datasets, we took advan- were found (App. B). A marginally significant radial velocity tage of the waffle-spot registration to apply a frame-to-frame re- difference was found between the three epochs. This proba- centering. The TLOCI (Marois et al. 2014) and PCA (Soummer bly arose from stellar pulsations as suggested by the period- et al. 2012; Amara & Quanz 2012) algorithms were specifically icity (P ∼ 0:135 days) found from the Hipparcos photomet- used on angular differential imaging data (i.e without applying ric time series. HIP 65426 is one of the fastest rotators known any combined spectral differential processing) given the rela- with similar spectral type (Zorec & Royer 2012) and is there- tively good SNR (10 − 30 in the individual IFS channels, ≥ 50 fore likely viewed along mid- to high-inclinations with respect with IRDIS) detection of cc-0. Its position and spectra were ex- to the rotation axis. Given its spectral type, the observed colors tracted using injected fake planets and planetary signature tem- of HIP 65426 suggest a small value of reddening consistent with plates to take into account any biases related to the data pro- Chen et al. (2012). Assuming a metallicity for the LCC that is cessing. Both algorithms gave consistent results. The resulting close to solar (Viana Almeida et al. 2009), theoretical isochrones extracted TLOCI images from IFS and IRDIS for the February predict an age of 14±4 Myr for LCC members in the vicinity 7th, 2017 epoch are shown in Figure 1. of HIP 65426 (see App. A). SPHERE and HARPS observations do not show evidence of binarity (App. C). Finally, according to Chen et al. (2012), no IR excess is reported for this star. Our own SED analysis confirms this finding with only a tentative marginal excess at WISE W4 (see App. D). 3. Observations and data reduction HIP 65426 was observed on May 30th, 2016 under unstable con- ditions (strong wind) with SPHERE. The observations were then repeated on June 26th, 2016. The data were acquired in IRDIFS pupil-tracking mode with the 185 mas diameter apodized-Lyot coronograph (Carbillet et al.