B fields in OB stars (BOB): FORS 2 spectropolarimetric follow-up of the two rare rigidly rotating magnetosphere stars HD 23478 and HD 345439

Hubrig, S.; Schöller, M.; Fossati, L.; Morel, Thierry; Castro, N.; Oskinova, L. M.; Przybilla, N.; Eikenberry, S. S.; Nieva, M. F.; Langer, N.

doi:10.1051/0004-6361/201526262

Cited by 25 publications

(38 citation statements)

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“…The line presents a central absorption component and line-wing emissions on both sides of the Hα line extending up to approximately ±300 km s −1 . The presence of similar Hα emission wings has been reported for other strongly magnetic He-strong stars, such as HD 23478 ( B z = 1.5 kG; Hubrig et al 2015) and HD 37479 (σ Ori E, B z = 2.4 kG; Oksala et al 2012), for example. Despite the similarities between the He-strong stars CPD −62 • 2124 and CPD −57 • 3509, the latter does not show any spectral feature indicative of circumstellar material (see Fig.…”

Section: Discussionsupporting

confidence: 82%

“…Landstreet & Borra 1978;Borra & Landstreet 1979;Bohlender 1988;Bagnulo et al 2006;Hubrig et al 2015), pointing out Hestrong stars as a sub-class of strong magnetic early B-type stars. Within the context of the "B fields in OB stars" (BOB) collaboration (Morel et al 2014(Morel et al , 2015Hubrig et al 2014aHubrig et al , 2015Fossati et al 2015b;Schöller et al 2017), here we report the detection of an exceptionally strong magnetic field in the He-strong B2IV star CPD −62 • 2124 (V = 11.04 mag ;Drilling 1981;Walborn 1983;Zboril et al 1997;Renson & Manfroid 2009). The star was observed using two different instruments (Sect.…”

Section: Introductionmentioning

confidence: 99%

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B field in OB stars (BOB): The outstandingly strong magnetic field in the evolved He-strong star CPD −62° 2124

Castro

Fossati

Hubrig

et al. 2017

A&A

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The origin and evolution of magnetism in OB stars is far from being well understood. With approximately 70 magnetic OB stars known, any new object with unusual characteristics may turn out to be a key piece of the puzzle. We report the detection of an exceptionally strong magnetic field in the He-strong B2IV star CPD −62 • 2124. Spectropolarimetric FORS2 and HARPSpol observations were analysed by two independent teams and procedures, concluding on a strong longitudinal magnetic field of approximately 5.2 kG. The quantitative characterisation of the stellar atmosphere yields an effective temperature of 23 650 ± 250 K, a surface gravity of 3.95 ± 0.10 dex and a surface helium fraction of 0.35 ± 0.02 by number. The metal composition is in agreement with the cosmic abundance standard, except for Mg, Si and S, which are slightly non-solar. The strong and broad (∼300 km s −1 ) disc-like emission displayed by the Hα line suggests a centrifugal magnetosphere supported by the strong magnetic field. Our results imply that CPD −62 • 2124 is an early B-type star hosting one of the strongest magnetic fields discovered to date, and one of the most evolved He-strong stars known, with a fractional main-sequence lifetime of approximately 0.6.

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Section: Discussionsupporting

confidence: 82%

Section: Introductionmentioning

confidence: 99%

B field in OB stars (BOB): The outstandingly strong magnetic field in the evolved He-strong star CPD −62° 2124

Castro

Fossati

Hubrig

et al. 2017

A&A

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“…Evolutionary tracks of Brott et al (2011) for initial rotational velocity of ∼300 km s −1 are shown (full lines), labelled by initial stellar mass. The magnetic star in the Trifid nebula and HD 345439 (Hubrig et al 2014(Hubrig et al , 2015b are not included here because of difficulties in establishing their properties. (Lotkin & Matkin 1994).…”

Section: Discussionmentioning

confidence: 99%

“…Some material may also be trapped in a centrifugal magnetosphere (see e.g. Petit et al 2013;Hubrig et al 2015b), giving rise to "doublehorned" line profiles in Hα and some near-IR hydrogen lines that are characteristic of the σ Ori E analogues. The He-strong nature of CPD −57 • 3509 was first noticed by Evans et al (2005, designated as NGC 3293-034) in a systematic spectroscopic survey of the massive star content of the open cluster NGC 3293.…”

Section: Introductionmentioning

confidence: 99%

B fields in OB stars (BOB): Detection of a magnetic field in the He-strong star CPD −57° 3509

Przybilla

Fossati

Hubrig

et al. 2016

A&A

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Aims. We report the detection of a magnetic field in the helium-strong star CPD −57 • 3509 (B2 IV), a member of the Galactic open cluster NGC 3293, and characterise the star's atmospheric and fundamental parameters. Methods. Spectropolarimetric observations with FORS2 and HARPSpol are analysed using two independent approaches to quantify the magnetic field strength. A high-S/N FLAMES/GIRAFFE spectrum is analysed using a hybrid non-LTE model atmosphere technique. Comparison with stellar evolution models constrains the fundamental parameters of the star. Results. We obtain a firm detection of a surface averaged longitudinal magnetic field with a maximum amplitude of about 1 kG. Assuming a dipolar configuration of the magnetic field, this implies a dipolar field strength larger than 3.3 kG. Moreover, the large amplitude and fast variation (within about 1 day) of the longitudinal magnetic field implies that CPD −57 • 3509 is spinning very fast despite its apparently slow projected rotational velocity. The star should be able to support a centrifugal magnetosphere, yet the spectrum shows no sign of magnetically confined material; in particular, emission in Hα is not observed. Apparently, the wind is either not strong enough for enough material to accumulate in the magnetosphere to become observable or, alternatively, some leakage process leads to loss of material from the magnetosphere. The quantitative spectroscopic analysis of the star yields an effective temperature and a logarithmic surface gravity of 23 750 ± 250 K and 4.05 ± 0.10, respectively, and a surface helium fraction of 0.28 ± 0.02 by number. The surface abundances of C, N, O, Ne, S, and Ar are compatible with the cosmic abundance standard, whereas Mg, Al, Si, and Fe are depleted by about a factor of 2. This abundance pattern can be understood as the consequence of a fractionated stellar wind. CPD −57 • 3509 is one of the most evolved He-strong stars known with an independent age constraint due to its cluster membership.

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“…The prototype of a rigidly rotating magnetosphere (RRM) is σ Ori E (Groote & Hunger 1997;Townsend, Owocki & Groote 2005). Evidence of circumstellar matter bound to the strong stellar magnetic field has been reported in a few other cases (Leone et al 2010;Bohlender & Monin 2011;Grunhut et al 2012a;Rivinius et al 2013;Hubrig et al 2015;Sikora et al 2015).…”

Section: Introductionmentioning

confidence: 99%

The detection of variable radio emission from the fast rotating magnetic hot B-star HR 7355 and evidence for its X-ray aurorae

Leto

Trigilio

Oskinova

et al. 2017

Monthly Notices of the Royal Astronomical Society

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In this paper we investigate the multiwavelengths properties of the magnetic early B-type star HR 7355. We present its radio light curves at several frequencies, taken with the Jansky Very Large Array, and X-ray spectra, taken with the XMM-Newton X-ray telescope. Modeling of the radio light curves for the Stokes I and V provides a quantitative analysis of the HR 7355 magnetosphere. A comparison between HR 7355 and a similar analysis for the Ap star CU Vir, allows us to study how the different physical parameters of the two stars affect the structure of the respective magnetospheres where the non-thermal electrons originate. Our model includes a cold thermal plasma component that accumulates at high magnetic latitudes that influences the radio regime, but does not give rise to X-ray emission. Instead, the thermal X-ray emission arises from shocks generated by wind stream collisions close to the magnetic equatorial plane. The analysis of the X-ray spectrum of HR 7355 also suggests the presence of a non-thermal radiation. Comparison between the spectral index of the power-law X-ray energy distribution with the non-thermal electron energy distribution indicates that the non-thermal X-ray component could be the auroral signature of the non-thermal electrons that impact the stellar surface, the same non-thermal electrons that are responsible for the observed radio emission. On the basis of our analysis, we suggest a novel model that simultaneously explains the X-ray and the radio features of HR 7355 and is likely relevant for magnetospheres of other magnetic early type stars.

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B fields in OB stars (BOB): FORS 2 spectropolarimetric follow-up of the two rare rigidly rotating magnetosphere stars HD 23478 and HD 345439

Cited by 25 publications

References 20 publications

B field in OB stars (BOB): The outstandingly strong magnetic field in the evolved He-strong star CPD −62° 2124

B field in OB stars (BOB): The outstandingly strong magnetic field in the evolved He-strong star CPD −62° 2124

B fields in OB stars (BOB): Detection of a magnetic field in the He-strong star CPD −57° 3509

The detection of variable radio emission from the fast rotating magnetic hot B-star HR 7355 and evidence for its X-ray aurorae

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