NGC 6611 601: a hot pre-main-sequence spectroscopic binary containing a centrifugal magnetosphere host star. Issue 3 (27th April 2021)

• Record Type: Journal Article
• Authors: Shultz, M E; Alecian, E; Petit, V; Bagnulo, S; Böhm, T; Folsom, C P; Wade, G A
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 504:Issue 3(2021)
• Page Start: 3203
• Page End: 3220
• Publication Date: 2021-04-27
• Subjects: stars: early-type -- stars: individual: NGC 6611 601 -- stars: magnetic field -- stars: massive -- stars: rotation; Astronomy -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnras/stab822
• Languages: English
• ISSNs: 0035-8711

Abstract

ABSTRACT: W 601 (NGC 6611 601) is one of the handful of known magnetic Herbig Ae/Be stars. We report the analysis of a large data set of high-resolution spectropolarimetry. The star is a previously unreported spectroscopic binary, consisting of two B2 stars with a mass ratio of 1.8, masses of 12 and 6.2 M⊙, in an eccentric 110-d orbit. The magnetic field belongs to the secondary, W 601 B. The H α emission is consistent with an origin in W 601 B's centrifugal magnetosphere; the star is therefore not a classical Herbig Be star in the sense that its emission is not formed in an accretion disc. However, the low value of log g = 3.8 determined via spectroscopic analysis and the star's membership in the young NGC 6611 cluster are most consistent with it being on the pre-main sequence. The rotational period inferred from the variability of the H α line and the longitudinal magnetic field 〈 Bz 〉 is 1.13 d. Modelling of Stokes V and 〈 Bz 〉 indicates a surface dipolar magnetic field B d between 6 and 11 kG. With its strong emission, rapid rotation, and strong surface magnetic field, W 601 B is likely a precursor to H α-bright magnetic B-type stars such as σ Ori E. By contrast, the primary is an apparently non-magnetic ( B d < 300 G) pre-main-sequence early B-type star. In accordance with expectations from magnetic braking, the non-magnetic primary is apparently more rapidly rotating than the magnetic star.