HD 156324: a tidally locked magnetic triple spectroscopic binary with a disrupted magnetosphere

Author:

Shultz M1,Rivinius Th2,Wade G A3,Alecian E456,Petit V7,

Affiliation:

1. Department of Physics and Astronomy, Uppsala University, Box 516, SE-75120 Uppsala, Sweden

2. ESO -- European Organisation for Astronomical Research in the Southern Hemisphere, Casilla 19001, Santiago 19, Chile

3. Department of Physics, Royal Military College of Canada, Kingston, Ontario K7K 7B4, Canada

4. Université Grenoble Alpes, IPAG, F-38000 Grenoble, France

5. CNRS, IPAG, F-38000 Grenoble, France

6. LESIA, Observatoire de Paris, CNRS UMR 8109, UPMC, Université Paris Diderot, 5 place Jules Janssen, F-92190 Meudon, France

7. Department of Physics and Astronomy, University of Delaware, 217 Sharp Lab, Newark, DE 19716, USA

Abstract

Abstract HD 156324 is an SB3 (B2V/B5V/B5V) system in the Sco OB4 association. The He-strong primary possesses both a strong magnetic field and Hα emission believed to originate in its centrifugal magnetosphere. We analyse a large spectroscopic and high-resolution spectropolarimetric data set. The radial velocities (RVs) indicate that the system is composed of two subsystems, which we designate A and B. Period analysis of the RVs of the three components yields orbital periods Porb = 1.5806(1) d for the Aa and Ab components, and Porb = 6.67(2) d for the B component, a PGa star. Period analysis of the longitudinal magnetic field 〈Bz〉 and Hα equivalent widths, which should both be sensitive to the rotational period Prot of the magnetic Aa component, both yield ∼1.58 d. Since Porb = Prot Aa and Ab must be tidally locked. Consistent with this, the orbit is circularized, and the rotational and orbital inclinations are identical within uncertainty, as are the semimajor axis and the Kepler corotation radius. The star's Hα emission morphology differs markedly from both theoretical and observational expectations in that there is only one, rather than two, emission peaks. We propose that this unusual morphology may be a consequence of modification of the gravitocentrifugal potential by the presence of the close stellar companion. We also obtain upper limits on the magnetic dipole strength Bd for the Ab and B components, respectively, finding Bd < 2.6 and <0.7 kG.

Publisher

Oxford University Press (OUP)

Subject

Space and Planetary Science,Astronomy and Astrophysics

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