HD 96446: a puzzle for current models of magnetospheres?

Neiner, C.; Landstreet, J. D.; Alécian, E.; Owocki, Stan; Kochukhov, Oleg; Bohlender, D.; collaboration, MiMeS

doi:10.1051/0004-6361/201218988

Cited by 39 publications

(71 citation statements)

References 36 publications

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“…Neiner et al 2012), and pulsations are known to have an impact on the analysis of the presence of a magnetic field and its strength (e.g. Schnerr et al 2006;Hubrig et al 2011a), we verified that no change in the line profile shape or radial velocity shifts are present in the obtained sub-exposures.…”

Section: Potsdam Reduction and Analysissupporting

confidence: 65%

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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Section: Potsdam Reduction and Analysissupporting

confidence: 65%

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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“…These features are often detected in short-period binaries or pulsating stars. Neiner et al (2012) report the analysis of similar spurious signatures observed in the null profiles of the magnetic star HD 96446. They showed that the radial velocities of the spectral lines have changed between the four sub-exposures of one polarised observation, and that such rapid changes (relative to the exposure time) in the radial velocities of the spectral lines, with an amplitude of about 7 km s −1 , create spurious signatures in the null profiles.…”

Section: Origin Of the Lsd V Signaturesmentioning

confidence: 84%

“…Neiner et al 2012, and references hereinafter). Our findings are (4) and (6): surface gravity of the stars obtained from Strömgren and Geneva photometry.…”

Section: Spectrum Description and Peculiaritiesmentioning

confidence: 99%

Discovery of new magnetic early-B stars within the MiMeS HARPSpol survey

Alécian

Kochukhov

Petit

et al. 2014

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Context. The Magnetism in Massive Stars (MiMeS) project aims at understanding the origin of the magnetic fields in massive stars as well as their impact on stellar internal structure, evolution, and circumstellar environment. Aims. One of the objectives of the MiMeS project is to provide stringent observational constraints on the magnetic fields of massive stars; however, identification of magnetic massive stars is challenging, as only a few percent of high-mass stars host strong fields detectable with the current instrumentation. Hence, one of the first objectives of the MiMeS project was to search for magnetic objects among a large sample of massive stars, and to build a sub-sample for in-depth follow-up studies required to test the models and theories of fossil field origins, magnetic wind confinement and magnetospheric properties, and magnetic star evolution. Methods. We obtained high-resolution spectropolarimetric observations of a large number of OB stars thanks to three large programs (LP) of observations that have been allocated on the high-resolution spectropolarimeters ESPaDOnS, Narval, and the polarimetric module HARPSpol of the HARPS spectrograph. We report here on the methods and first analysis of the HARPSpol magnetic detections. We identified the magnetic stars using a multi-line analysis technique. Then, when possible, we monitored the new discoveries to derive their rotation periods, which are critical for follow-up and magnetic mapping studies. We also performed a first-look analysis of their spectra and identified obvious spectral anomalies (e.g., surface abundance peculiarities, Hα emission), which are also of interest for future studies. Results. In this paper, we focus on eight of the 11 stars in which we discovered or confirmed a magnetic field from the HARPSpol LP sample (the remaining three were published in a previous paper). Seven of the fields were detected in early-type Bp stars, while the last field was detected in the Ap companion of a normal early B-type star. We report obvious spectral and multiplicity properties, as well as our measurements of their longitudinal field strengths, and their rotation periods when we are able to derive them. We also discuss the presence or absence of Hα emission with respect to the theory of centrifugally-supported magnetospheres.

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“…Therefore, it is not possible to verify the plausibility of the ∼0.5 d period solution. However, as shown by Neiner et al (2012), rapid RV variations that occur over the timescale of a single polarimetric sequence can induce detectable signatures in the diagnostic null profiles. These signatures result from residual polarisation signals that were not properly cancelled during processing because of the RV shifts.…”

Section: Radial Velocity Variationsmentioning

confidence: 98%

A comprehensive analysis of the magnetic standard star HD 94660: Host of a massive compact companion?

Bailey

Grunhut²,

Landstreet

2015

A&A

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Aims. Detailed information about the magnetic geometry, atmospheric abundances and radial velocity variations has been obtained for the magnetic standard star HD 94660 based on high-dispersion spectroscopic and spectropolarimetric observations from the UVES, HARPSpol and ESPaDOnS instruments. Methods. We perform a detailed chemical abundance analysis using the spectrum synthesis code ZEEMAN for a total of 17 elements. Using both line-of-sight and surface magnetic field measurements, we derive a simple magnetic field model that consists of dipole, quadrupole and octupole components. Results. The observed magnetic field variations of HD 94660 are complex and suggest an inhomogeneous distribution of chemical elements over the stellar surface. This inhomogeneity is not reflected in the abundance analysis, from which all available spectra are modelled, but only a mean abundance is reported for each element. The derived abundances are mostly non-solar, with striking overabundances of Fe-peak and rare-earth elements. Of note are the clear signatures of vertical chemical stratification throughout the stellar atmosphere, most notably for the Fe-peak elements. We also report on the detection of radial velocity variations with a total range of 35 km s −1 in the spectra of HD 94660. A preliminary analysis shows the most likely period of these variations to be of order 840 d and, based on the derived orbital parameters of this star, suggests the first detection of a massive compact companion for a main sequence magnetic star. Conclusions. HD 94660 exhibits interestingly complex magnetic field variations and remarkable radial velocity variations. Long term monitoring is necessary to provide further constraints on the nature of these radial velocity variations. Detection of a companion will help establish the role of binarity in the origin of magnetism in stars with radiative envelopes.

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HD 96446: a puzzle for current models of magnetospheres?

Cited by 39 publications

References 36 publications

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

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

Discovery of new magnetic early-B stars within the MiMeS HARPSpol survey

A comprehensive analysis of the magnetic standard star HD 94660: Host of a massive compact companion?

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