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The Magnetic Early B-Type Stars II: Stellar Atmospheric Mon. Not. R. Astron. Soc. 000, 1–?? (2002) Printed 8 February 2019 (MN LATEX style file v2.2) The Magnetic Early B-type Stars II: stellar atmospheric parameters in the era of Gaia M. E. Shultz1⋆, G. A. Wade2, Th. Rivinius3, E. Alecian5, C. Neiner6, V. Petit7, J. P. Wisniewski8, and the MiMeS and BinaMIcS Collaborations ⋆† 1Annie Jump Cannon Fellow, Department of Physics and Astronomy, University of Delaware, 217 Sharp Lab, Newark, Delaware, 19716, USA 2Department of Physics and Space Science, Royal Military College of Canada, Kingston, Ontario K7K 7B4, Canada 3ESO - European Organisation for Astronomical Research in the Southern Hemisphere, Casilla 19001, Santiago 19, Chile 5Universit´eGrenoble Alpes, IPAG, F-38000 Grenoble, France 6LESIA, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Universit´es, UPMC Univ. Paris 06, Univ. Paris Diderot, Sorbonne Paris Cit´e, 5 place Jules Janssen, F-92195 Meudon, France 7Department of Physics and Astronomy, University of Delaware, 217 Sharp Lab, Newark, Delaware, 19716, USA 8Homer L. Dodge Department of Physics & Astronomy, The University of Oklahoma, 440 W. Brooks Street, Norman, OK 73019, USA ABSTRACT Atmospheric parameters determined via spectral modelling are unavailable for many of the known magnetic early B-type stars. We utilized high-resolution spectra together with NLTE models to measure effective temperatures Teff and surface gravities log g of stars for which these measurements are not yet available. We find good agreement be- tween our Teff measurements and previous results obtained both photometrically and spectroscopically. For log g, our results are compatible with previous spectroscopic measurements; however, surface gravities of stars previously determined photometri- cally have been substantially revised. We furthermore find that log g measurements obtained with HARPSpol are typically about 0.1 dex lower than those from compara- ble instruments. Luminosities were determined using Gaia Data Release 2 parallaxes. We find Gaia parallaxes to be unreliable for bright stars (V < 6 mag) and for bina- ries; in these cases we reverted to Hipparcos parallaxes. In general we find luminosities systematically lower than those previously reported. Comparison of log g and log L to available rotational and magnetic measurements shows no correlation between either parameter with magnetic data, but a clear slow-down in rotation with both decreas- ing log g and increasing log L, a result compatible with the expectation that magnetic braking should lead to rapid magnetic spindown that accelerates with increasing mass- loss. arXiv:1902.02713v1 [astro-ph.SR] 7 Feb 2019 Key words: stars: massive - stars: early-type - stars: magnetic fields - stars: rotation - stars: chemically peculiar - magnetic fields 1 INTRODUCTION (mostly tilted dipoles), stable over at least thousands of ro- tational cycles (e.g. Shultz et al. 2018b), and their strength About 1 in 15 early-type stars possesses a detectable mag- show no correlation with rotation (unlike what would be ex- netic field (Grunhut et al. 2012b, 2017). Their magnetic pected for magnetic fields maintained by contemporaneous fields are typically strong (102 −104 G), topologically simple dynamos). These properties lead to their characterization as fossil magnetic fields (e.g. Neiner et al. 2015). Magnetic OB stars are particularly interesting due to their magnet- ⋆ E-mail: [email protected] ically confined winds, which often lead to magnetospheres † Based on observations obtained at the Canada-France-Hawaii that can be detected via X-ray, ultraviolet, optical, and in- Telescope (CFHT) which is operated by the National Research frared emission lines (e.g. Petit et al. 2013, hereafter P13). Council of Canada, the Institut National des Sciences de l’Univers Magnetic wind confinement also leads to rapid spindown of the Centre National de la Recherche Scientifique of France, (e.g. ud-Doula et al. 2009), an effect which should intensify and the University of Hawaii; at the La Silla Observatory, ESO with increasing mass-loss rate and increasing magnetic field Chile with the MPA 2.2 m telescope; and at the Bernard Lyot strength. Telescope. c 2002 RAS 2 M. Shultz et al. Table 1. Spectropolarimetric data summary and references for magnetic detections for the 5 stars added to the sample. The first row gives the names of the stars. The second row contains remarks as to special properties. The third row gives the spectral type. The fourth through seventh rows give the number of spectropolarimetric observations available for each instrument. The eighth row gives the reference for the original magnetic detection. Rows 9 to 15 give, respectively: the projected rotational velocity v sin i; the rotational period Prot; the epoch used to determine the zero-point of the phase curve (typically the time of maximum |hBz i|); the peak observed value of hBz i; the mean value B0 of the sinusoidal fit to hBzi; the semi-amplitude B1 of the first harmonic of the sinusoidal fit to a b hBzi; and the semi-amplitude B2 of the second harmonic. Reference key: P´apics et al. (2012) ; Buysschaert et al. (2017) ; Fossati et al. (2014)c; This workd; Wisniewski et al. (2015)e; Hubrig et al. (2017a)f ; Przybilla et al. (2016)g ; Hubrig et al. (2017b)h; Castro et al. (2017)i; Hubrig et al. (2017c)j . Star HD 43317 HD 47777 HD 345439 CPD −57◦ 3509 CPD −62◦ 2124 Remarks SPB HeBe – – – Spec.Type B3IV B3V B2IV B2IV B2IV ESPaDOnS – 13 – – – Narval 34 – – – – HARPSpol – – – 1 1 FORS2 – – 18 20 17 Detection Briquet et al. (2013) Fossati et al. (2014) Hubrig et al. (2015) Przybilla et al. (2016) Castro et al. (2017) v sin i (km s−1) 115 ± 9a 60 ± 5c 270 ± 20e 35 ± 2g 35 ± 5i b c,d e,f h j Prot (d) 0.897673(4) 2.6415(6) 0.77018(2) 6.3626(3) 2.62809(5) JD0 - 2400000 (d) 56185.8380b 54461.8(2)d 56926.0425f 56984.04(6)h 57444.146(8)j b d f h j hBzimax (kG) 0.30 ± 0.01 0.68 ± 0.09 2.5 ± 0.1 1.07 ± 0.07 6.8 ± 0.5 b d f h d,j B0 (kG) 0.045 ± 0.016 −0.02 ± 0.04 0.9 ± 0.1 0.18 ± 0.05 5.5 ± 0.1 b d f h d,j B1 (kG) 0.221 ± 0.022 −0.62 ± 0.03 1.6 ± 0.1 0.89 ± 0.06 −1.2 ± 0.2 d,j B2 (kG) – – – – 1.0 ± 0.2 Magnetospheres can be divided into those in which ro- Gaia Collaboration et al. 2018) parallaxes mean that dis- tation plays a negligible role (Dynamical Magnetospheres tances and luminosities can be obtained with higher pre- or DMs), and those in which centrifugal support due to cision for many of the more distant stars in the sample. rapid rotation is decisive in sculpting the circumstellar The purpose of this paper is to combine the available high- plasma distribution (Centrifugal Magnetospheres or CMs). resolution spectroscopic data with Gaia DR2 parallaxes to P13 introduced a rotation-magnetic confinement diagram, determine high-precision atmospheric parameters. and showed that the position of a star on the diagram is An overview of the sample and observations is provided broadly predictive of its magnetospheric Hα emission status. in § 2. § 3 describes the measurements and the resulting O-type stars (with high mass-loss rates and typically very properties of the sample, together with an examination of slow rotation) are almost invariably predicted to have DMs, some of the systematics arising from different measurement and always possess detectable Hα emission. Conversely, B- methods. Results are discussed, and conclusions drawn, in type stars only possess detectable magnetospheric emission § 4. Previously unreported magnetic measurements are pro- when they are both very rapidly rotating and very strongly vided for HD 47777 in Appendix A. Surface gravity measure- magnetized, i.e. when they are predicted to have very large ments of individual single stars are detailed in Appendix B, CMs. and those of binary systems in Appendix C. For most of the stars studied by P13, rotational periods and surface magnetic field strengths were unknown, mean- ing that only limiting values of their magnetic and rota- 2 SAMPLE AND OBSERVATIONS tional properties were available, and their positions on the The sample consists of essentially all known magnetic main rotation-magnetic confinement diagram were only limiting sequence stars with spectral types between B5 and B0. values. In consequence, the conditions under which CMs be- The selection criteria and properties of the sample were come detectable were not observationally constrained. described in Paper I. One star, HD 35912, has been re- Shultz et al. (2018b, hereafter Paper I) presented mag- moved as we demonstrated in Paper I the absence of a de- netic field measurements, rotational periods, and projected tectable surface magnetic field. The study is based primarily surface rotational velocities v sin i for all known main- upon an extensive database of high-resolution ESPaDOnS, sequence early B-type stars in the P13 sample for which Narval, and HARPSpol spectropolarimetry, in some cases sufficient magnetic data had been obtained for accurate supplemented with FEROS spectroscopy; these data were characterization of their surface magnetic properties. Be- also described in Paper I. The majority of these data were fore these results can be used to obtain surface rotational acquired by the MiMeS and BinaMIcS Large Programs properties and magnetic oblique rotator models, fundamen- (LPs). The basic observational techniques and strategy of tal stellar parameters (masses and radii) must also be de- the MiMeS LPs, as well as the reduction and analysis of ES- termined, which in turn require stellar atmospheric param- PaDOnS, Narval, and HARPSpol data, were described by eters Teff , log g, and log L. For many of the stars, only Wade et al.
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