Magnetic field measurements of helium-strong stars

Bohlender, D.; Brown, Douglas; Landstreet, J. D.; Thompson, I. B.

doi:10.1086/165830

Cited by 158 publications

(206 citation statements)

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“…Babel & Montmerle (1997), who report the ROSAT X-ray detection at log L X = 29.6 erg s −1 , assume a 4 kG dipolar field for IQ Aur and determine an inclination of i ≈ 32 • and an obliquity of β ≈ 50 • , whereas Hubrig et al (2007) find i = 87 • and of β = 7 • . Bohlender et al (1993) state: 'a large range of values for i is possible: if i is large β is fairly small and if i is as small as allowed by our assumptions, β may be more than 80 • . The stellar parameter differ somewhat as well, e.g.…”

Section: The Targets α 2 Cvn and Iq Aurmentioning

confidence: 93%

“…Indeed, IQ Aur is extreme for an A0p star; as a main-sequence star it would be of spectral type mid-B with its B − V = −0.16. The adopted basic stellar data for IQ Aur and α 2 CVn as compiled from Bohlender et al (1993), Bychkov et al (2003), Kochukhov & Bagnulo (2006) and Kochukhov & Wade (2010) are summarized in Table 1.…”

Section: The Targets α 2 Cvn and Iq Aurmentioning

confidence: 99%

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New X-ray observations of IQ Aurigae andα² Canum Venaticorum

Robrade

Schmitt

2011

A&A

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Aims. We re-examine the scenario of X-ray emission from magnetically confined/channeled wind shocks (MCWS) for Ap/Bp stars, a model originally developed to explain the ROSAT detection of the A0p star IQ Aur. Methods. We present new X-ray observations of the A0p stars α 2 CVn (Chandra) and IQ Aur (XMM-Newton) and discuss our findings in the context of X-ray generating mechanisms of magnetic, chemically peculiar intermediate mass stars. Results. The X-ray luminosities of IQ Aur with log L X = 29.6 erg s −1 and α 2 CVn with log L X 26.0 erg s −1 differ by at least three orders of magnitude, although both are A0p stars. By studying a sample of comparison stars, we find that X-ray emission is preferably generated by more massive objects such as IQ Aur. Besides a strong, cool plasma component, significant amounts of hot (>10 MK) plasma are present during the quasi-quiescent phase of IQ Aur; moreover, diagnostics of the UV sensitive f /i line ratio in He-like O vii triplet point to X-ray emitting regions well above the stellar surface of IQ Aur. In addition we detect a large flare from IQ Aur with temperatures up to ∼100 MK and a peak X-ray luminosity of log L X ≈ 31.5 erg s −1 . The flare, showing a fast rise and e-folding decay time of less than half an hour, originates in a fairly compact structure and is accompanied by a significant metallicity increase. The X-ray properties of IQ Aur cannot be described by wind shocks only and require the presence of magnetic reconnection. This is most evident in the, to our knowledge, first X-ray flare reported from an A0p star. Conclusions. Our study indicates that the occurrence the of X-ray emission in A0p stars generated by magnetically channeled wind shocks depends on stellar properties such as luminosity, which promote a high mass loss rate, whereas magnetic field configuration and transient phenomena refine their appearance. While we cannot rule out unknown close companions, the X-ray emission from IQ Aur can be described consistently in the MCWS scenario, in which the very strong magnetic confinement of the stellar wind has led to the build-up of a rigidly rotating disk around the star, where magnetic reconnection and centrifugal breakout events occur.

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Section: The Targets α 2 Cvn and Iq Aurmentioning

confidence: 93%

Section: The Targets α 2 Cvn and Iq Aurmentioning

confidence: 99%

New X-ray observations of IQ Aurigae andα² Canum Venaticorum

Robrade

Schmitt

2011

A&A

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“…For HD 81009 we used r = 0.64, determined by Landstreet & Mathys (2000). The v sin i values have been measured on our spectra or taken from published spectroscopic studies (Abt 2001;Abt, Levato & Grosso 2002;Bagnulo et al 2002;Balona & Laney 2003;Bohlender, Landstreet & Thompson 1993;Hensberge et al 1979;Landstreet 1970;Landstreet & Mathys 2000;Levato et al 1996;Nielsen & Wahlgren 2002;Royer et al 2002;Wade et al 2000). We could not find in the literature values of v sin i for three stars: HD 54118, HD 73340 and HD 133880.…”

Section: The Magnetic Field Geometrymentioning

confidence: 99%

Evolution of magnetic fields in stars across the upper main sequence: II. Observed distribution of the magnetic field geometry

Hubrig¹,

North

Schöller

2007

Astron Nachr

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We re-discuss the evolutionary state of upper main sequence magnetic stars using a sample of Ap and Bp stars with accurate Hipparcos parallaxes and definitely determined longitudinal magnetic fields. We confirm our previous results obtained from the study of Ap and Bp stars with accurate measurements of the mean magnetic field modulus and mean quadratic magnetic fields that magnetic stars of mass M < 3 M are concentrated towards the centre of the main-sequence band. In contrast, stars with masses M > 3 M seem to be concentrated closer to the ZAMS. The study of a few known members of nearby open clusters with accurate Hipparcos parallaxes confirms these conclusions. Stronger magnetic fields tend to be found in hotter, younger and more massive stars, as well as in stars with shorter rotation periods. The longest rotation periods are found only in stars which spent already more than 40% of their main sequence life, in the mass domain between 1.8 and 3 M and with log g values ranging from 3.80 to 4.13. No evidence is found for any loss of angular momentum during the main-sequence life. The magnetic flux remains constant over the stellar life time on the main sequence. An excess of stars with large obliquities β is detected in both higher and lower mass stars. It is quite possible that the angle β becomes close to 0 • in slower rotating stars of mass M > 3 M too, analog to the behaviour of angles β in slowly rotating stars of M < 3 M . The obliquity angle distribution as inferred from the distribution of r-values appears random at the time magnetic stars become observable on the H-R diagram. After quite a short time spent on the main sequence, the obliquity angle β tends to reach values close to either 90 • or 0 • for M < 3 M . The evolution of the obliquity angle β seems to be somewhat different for low and high mass stars. While we find a strong hint for an increase of β with the elapsed time on the main sequence for stars with M > 3 M , no similar trend is found for stars with M < 3 M . However, the predominance of high values of β at advanced ages in these stars is notable. As the physics governing the processes taking place in magnetised atmospheres remains poorly understood, magnetic field properties have to be considered in the framework of dynamo or fossil field theories.

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“…5 3 ± 0.37 This paper v sin i (km s sharp-lined star with clearly resolved Zeeman splitting in several spectra lines (Mathys 1990). Bohlender et al (1993) report a projected rotational velocity of v sin i < 6 km s −1 and a roughly constant line-of-sight magnetic field strength of B z = −2520 G, based on measurements using Hβ. A period of rotation of order 2700 d was first proposed by Hensberge (1993) and later discussed by with respect to B data.…”

Section: Introductionmentioning

confidence: 99%

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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Magnetic field measurements of helium-strong stars

Cited by 158 publications

References 0 publications

New X-ray observations of IQ Aurigae andα² Canum Venaticorum

New X-ray observations of IQ Aurigae andα² Canum Venaticorum

Evolution of magnetic fields in stars across the upper main sequence: II. Observed distribution of the magnetic field geometry

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

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Magnetic field measurements of helium-strong stars

Cited by 158 publications

References 0 publications

New X-ray observations of IQ Aurigae andα2 Canum Venaticorum

New X-ray observations of IQ Aurigae andα2 Canum Venaticorum

Evolution of magnetic fields in stars across the upper main sequence: II. Observed distribution of the magnetic field geometry

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

Contact Info

Product

Resources

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New X-ray observations of IQ Aurigae andα² Canum Venaticorum

New X-ray observations of IQ Aurigae andα² Canum Venaticorum