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The Triple System HD 150136: from Periastron Passage to Actual Masses ?,?? L

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The Triple System HD 150136: from Periastron Passage to Actual Masses ?,?? L A&A 616, A75 (2018) Astronomy https://doi.org/10.1051/0004-6361/201832810 & © ESO 2018 Astrophysics The triple system HD 150136: From periastron passage to actual masses ?,?? L. Mahy1,2,???, E. Gosset2,????, J. Manfroid2, C. Nitschelm3, A. Hervé4,5, T. Semaan2,6, H. Sana1, J.-B. Le Bouquin7, and S. Toonen8 1 Instituut voor Sterrenkunde, KU Leuven, Celestijnlaan 200D, Bus 2401, 3001 Leuven, Belgium e-mail: [email protected] 2 Space Sciences, Technologies, and Astrophysics Research (STAR) Institute, Université de Liège, Quartier Agora, Bât B5c, Allée du 6 août, 19c, 4000 Liège, Belgium 3 Unidad de Astronomía, Facultad de Ciencias Básicas, Universidad de Antofagasta, Antofagasta, Chile 4 Astronomical Institute ASCR, Fricova˘ 298, 251 65 Ondrejov,˘ Czech Republic 5 Visitor Scientist at Gemini Observatory, Northern Operations Center, 670 North A’ohoku Place, Hilo, HI 96720, USA 6 Institute of Astronomy, University of Geneva, 51 chemin des Maillettes, 1290 Versoix, Switzerland 7 UJF-Grenoble 1/CNRS-INSU, Institut de Planétologie et d’Astrophysique de Grenoble (IPAG), UMR 5274, Grenoble, France 8 Anton Pannekoek Institute for Astronomy, University of Amsterdam, 1090 GE Amsterdam, The Netherlands Received 12 February 2018 / Accepted 30 April 2018 ABSTRACT + Context. The triple system HD 150136 is composed of an O3 V((f∗))–O3.5 V((f )) primary, of an O5.5–6 V((f)) secondary, and of a more distant O6.5–7 V((f)) tertiary. The latter component went through periastron in 2015–2016, an event that will not occur again within the next eight years. Aims. We aim to analyse the tertiary periastron passage to determine the orbital properties of the outer system, to constrain its incli- nation and its eccentricity, and to determine the actual masses of the three components of the system. Methods. We conducted an intensive spectroscopic monitoring of the periastron passage of the tertiary component and combined the outcoming data with new interferometric measurements. This allows us to derive the orbital solution of the outer orbit in three- dimensional space. We also obtained the light curve of the system to further constrain the inclination of the inner binary. Results. We determine an orbital period of 8:61 0:02 years, an eccentricity of 0:682 0:002, and an inclination of 106:18 0:14◦ ± ± +8:45 +4:96 ± for the outer orbit. The actual masses of the inner system and of the tertiary object are 72:32 8:49 M and 15:54 4:97 M , respectively. From the mass of the inner system and accounting for the known mass ratio between the primary− and the secondary,− we determine actual masses of 42.81 M and 29.51 M for the primary and the secondary components, respectively. We infer, from the different mass ratios and the inclination of the outer orbit, an inclination of 62:4◦ for the inner system. This value is confirmed by photometry. Grazing eclipses and ellipsoidal variations are detected in the light curve of HD 150136. We also compute the distance of the system to 1:096 0:274 kpc. Conclusions.± By combining spectroscopy, interferometry, and photometry, HD 150136 offers us a unique chance to compare theory and observations. The masses estimated through our analysis are smaller than those constrained by evolutionary models. The formation of this triple system suggests similar ages for the three components within the errorbars. Finally, we show that Lidov–Kozai cycles have no effect on the evolution of the inner binary, which suggests that the latter will experience mass transfer leading to a merger of the two stars. Key words. stars: early-type – binaries: spectroscopic – stars: fundamental parameters – stars: individual: HD150136 1. Introduction massive star formation and evolution are still to be understood. Most of their fundamental parameters are poorly constrained, Massive stars are key objects in the galaxies. They influence both especially their masses. In this context, investigating the binary the chemical and the mechanical evolution of their surround- system population is the best way to derive these masses. The rel- ings through the creation of bubbles and of induced or inhibited atively small number of extremely massive galactic stars implies star formation. They are also the main sources of ultraviolet and that any system whose orbital parameters are accurately deter- ionizing radiations. Despite their importance, actual details of mined provides important new constraints to stellar evolution. Binarity, however, affects the way that stars evolve, making their ? Based on observations collected at the European Southern Observa- evolution more complex than that of single stars. This is espe- tory (Paranal and La Silla, Chile). cially relevant for massive stars, given their high fraction of ?? The journal of observations and the radial velocity data are only available at the CDS via anonymous ftp to multiple systems (Duchêne & Kraus 2013; Sana et al. 2012, cdsarc.u-strasbg.fr (130.79.128.5) or via 2014). The situation is even more complex with gravitationally- http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/616/A75 bound hierarchical systems since the evolution of the stars in ??? F.R.S.-FNRS Postdoctoral Researcher. those systems can be ruled by the Lidov–Kozai cycles (Kozai ???? F.R.S.-FNRS Research Director. 1962; Lidov 1962). The latter can modulate the eccentricity Article published by EDP Sciences A75, page 1 of7 A&A 616, A75 (2018) of the inner binary triggering modulations in their interactions spectroscopic monitoring covering both sides of the periastron (Toonen et al. 2016). In this context, HD 150136 is perfectly passage of the tertiary component. suited to better constrain this phenomenon. The present paper provides the analysis of the new spectro- This system is one of the two brightest stars hosted scopic data coupled with new interferometric and with unprece- in the center of the young open cluster NGC 6193 in the dented photometric observations of HD 150136. The paper Ara OB1 association, for which the distance was first esti- is organized as follows. In Sect.2, we present the observa- mated by Herbst & Havlen(1977) to be 1.32 kpc. This object tional campaign and the different instruments used. Section3 is a triple hierarchical system formed of an inner binary with is devoted to the determination of the radial velocities of the + an O3 V((f∗))–O3.5 V((f )) primary and an O5.5–6 V((f)) sec- three components. Section4 presents the global orbital solution ondary1, orbiting around each other with a period of 2.67455 for the inner and the outer systems by combining spectroscopy days, and of an O6.5–7 V((f)) physically bound tertiary com- and interferometry. The light curve of the system is studied ponent located on a much longer orbit (Mahy et al. 2012). in Sect.5. Section6 discusses the evolutionary statuses of the This object is the nearest system harbouring an O3 star. It thus different components and, finally, we give our conclusions in constitutes a target of choice for investigating the fundamental Sect.7. parameters of such a star. HD 150136 is one of the X-ray-brightest massive stars known (log L = 33:39 (cgs), log(L =L ) = 6:4; Skinner et al. 2005), 2. Observations and data reduction X X bol − most likely as the result of a radiative colliding-wind interac- 2.1. Spectroscopic observations tion. Its X-ray light curve, however, presents variations whose origin remains unclear. The star was also reported as a non- We collected and retrieved 177 optical spectra of HD 150136 thermal radio emitter (Benaglia et al. 2006; De Becker 2007). obtained with the Fibre-fed Extended Range Optical Spec- This suggests that the system harbours a relativistic population trograph (FEROS) mounted successively on the ESO 1.52 m of electrons, probably accelerated through shocks in colliding- (for observations before 2002) and on the MPG/ESO 2.2 m wind regions. Mahy et al.(2012) showed that a non-thermal radio (for observations after 2002) telescopes at La Silla observa- emission originating in the inner system would hardly escape. tory (Chile). These data were partially presented and analysed The presence of the third object is thus required in order to in Mahy et al.(2012) and in Sana et al.(2013) but spectra that displace the emitting region in the outer system. were newly acquired around the periastron passage of the third Following the study of Mahy et al.(2012), the third com- component are introduced in the present paper. The monitoring ponent is expected to be sufficiently far from the inner system of HD 150136 on FEROS started in 1999, and went on every year to be observable with long baseline interferometric facilities. until 2016, with breaks in 2007 and in 2010. FEROS provides The first detections of the outer pair were reported by Sana a resolving power of R = 48 000 and covers the entire optical et al.(2013) from the Precision Integrated-Optics Near-infrared range from 3800 to 9200 Å. The data were reduced following the Imaging ExpeRiment (PIONIER) and by Sanchez-Bermudez procedure described in Mahy et al.(2012). et al.(2013) from the Astrometrical Multi BEam combineR We also obtained Director’s Discretionary Time (DDT) (AMBER). Sana et al.(2013) combined the preliminary inter- with the UV-Visual Echelle Spectrograph (UVES; PI: Mahy ferometric observations with high-resolution spectroscopic data 297.D-5007, PI: Gosset 295.D-5025, and PI: Gosset 294.D-5041) to derive a first orbital solution of the outer companion in the mounted on the ESO-VLT to acquire eight additional spectra, three-dimensional space. These authors reported a period of which we have completed with two additional spectra pro- 3008 days, and an eccentricity of 0.73 for the outer orbit.
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