On the Periodic X-Ray Emission from θ[TSUP]1[/TSUP] Orionis C

Babel, J.; Montmerle, T.

doi:10.1086/310806

Cited by 346 publications

(496 citation statements)

References 12 publications

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“…In the pioneering work of Babel & Montmerle (1997b), the X-ray luminosity originating from magnetically confined wind shocks fundamentally scales linearly with wind massloss rate, because the thermal energy content of the radiating post-shock plasma depends on the wind kinetic energy flux across the magnetically channeled shock front. This model was recently refined by ud- Doula et al (2014), who combined MHD simulations and analytical scalings taking into account the effects of instrument-specific bandpass and "shock retreat".…”

Section: Discussionmentioning

confidence: 99%

“…Indeed, strong and rotationally modulated X-ray emission due to a combination of occultation and local absorption was predicted to be the hallmark of the wind-fed dynamical magnetospheres of magnetic O stars with dipole fields misaligned with their rotational axis (e.g. Babel & Montmerle 1997b;Gagné et al 2005;ud-Doula et al 2014). The X-rays are due to the radiative cooling of plasma that is shock-heated X-rays The bulk of the X-rays are produced in the region indicated in purple; see §6.…”

Section: Introductionmentioning

confidence: 99%

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X-ray emission from the giant magnetosphere of the magnetic O-type star NGC 1624-2

Petit

Cohen

Wade

et al. 2015

Mon. Not. R. Astron. Soc.

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We observed NGC 1624-2, the O-type star with the largest known magnetic field (B p ∼ 20 kG), in X-rays with the ACIS-S camera onboard the Chandra X-ray Observatory. Our two observations were obtained at the minimum and maximum of the periodic Hα emission cycle, corresponding to the rotational phases where the magnetic field is the closest to equator-on and pole-on, respectively. With these observations, we aim to characterise the star's magnetosphere via the X-ray emission produced by magnetically confined wind shocks. Our main findings are: (i) The observed spectrum of NGC 1624-2 is hard, similar to the magnetic O-type star θ 1 Ori C, with only a few photons detected below 0.8 keV. The emergent X-ray flux is 30% lower at the Hα minimum phase. (ii) Our modelling indicated that this seemingly hard spectrum is in fact a consequence of relatively soft intrinsic emission, similar to other magnetic Of?p stars, combined with a large amount of local absorption (∼1-3×10 22 cm −2 ). This combination is necessary to reproduce both the prominent Mg and Si spectral features, and the lack of flux at low energies. NGC 1624-2 is intrinsically luminous in X-rays (log L em X ∼33.4) but 70-95% of the X-ray emission produced by magnetically confined wind shocks is absorbed before it escapes the magnetosphere (log L ISMcor X ∼32.5). (iii) The high X-ray luminosity, its variation with stellar rotation, and its large attenuation are all consistent with a large dynamical magnetosphere with magnetically confined wind shocks.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

X-ray emission from the giant magnetosphere of the magnetic O-type star NGC 1624-2

Petit

Cohen

Wade

et al. 2015

Mon. Not. R. Astron. Soc.

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“…The field A0p star IQ Aur (HD 34452, HR 1732) belongs to the class of α 2 CVn spectrum variable stars and is thought to be a single star with V = 5.4 and small E B−V 0.01. 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 • .…”

Section: The Targets α 2 Cvn and Iq Aurmentioning

confidence: 99%

“…However, especially peculiar Ap/Bp stars and young Herbig AeBe stars are prime candidates for being intrinsic X-ray emitters (e.g. Babel & Montmerle 1997;Stelzer et al 2009). In the Ap/Bp stars discussed here an interplay between stellar winds and large scale magnetic fields is thought to play the major role in the X-ray generation.…”

Section: Introductionmentioning

confidence: 99%

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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“…Finally, for stars hosting magnetic fields at their surface, X-rays can be produced through the Magnetically Confined Wind Shock model (MCWS; Babel & Montmerle 1997, ud-Doula & Owocki 2002. In this paradigm, the star's radiation-driven wind is channeled by a large-scale dipole magnetic field such that material is forced to flow along the field lines and collide near the tops of closed loops, producing a shock-heated volume of plasma.…”

Section: X-ray Emission Processes For Ob Starsmentioning

confidence: 99%

X-rays from magnetic massive OB stars

Petit¹,

Cohen

Nazé

et al. 2013

Proc. IAU

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Abstract. The magnetic activity of solar-type and low-mass stars is a well known source of coronal X-ray emission. At the other end of the main sequence, X-rays emission is instead associated with the powerful, radiatively driven winds of massive stars. Indeed, the intrinsically unstable line-driving mechanism of OB star winds gives rise to shock-heated, soft emission (∼0.5 keV) distributed throughout the wind. Recently, the latest generation of spectropolarimetric instrumentation has uncovered a population of massive OB-stars hosting strong, organized magnetic fields. The magnetic characteristics of these stars are similar to the apparently fossil magnetic fields of the chemically peculiar ApBp stars. Magnetic channeling of these OB stars' strong winds leads to the formation of large-scale shock-heated magnetospheres, which can modify UV resonance lines, create complex distributions of cooled Halpha emitting material, and radiate hard (∼2-5 keV) X-rays. This presentation summarizes our coordinated observational and modelling efforts to characterize the manifestation of these magnetospheres in the X-ray domain, providing an important contrast between the emission originating in shocks associated with the large-scale fossil fields of massive stars, and the X-rays associated with the activity of complex, dynamo-generated fields in lower-mass stars.

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On the Periodic X-Ray Emission from θ[TSUP]1[/TSUP] Orionis C

Cited by 346 publications

References 12 publications

X-ray emission from the giant magnetosphere of the magnetic O-type star NGC 1624-2

X-ray emission from the giant magnetosphere of the magnetic O-type star NGC 1624-2

New X-ray observations of IQ Aurigae andα² Canum Venaticorum

X-rays from magnetic massive OB stars

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On the Periodic X-Ray Emission from θ[TSUP]1[/TSUP] Orionis C

Cited by 346 publications

References 12 publications

X-ray emission from the giant magnetosphere of the magnetic O-type star NGC 1624-2

X-ray emission from the giant magnetosphere of the magnetic O-type star NGC 1624-2

New X-ray observations of IQ Aurigae andα2 Canum Venaticorum

X-rays from magnetic massive OB stars

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Product

Resources

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New X-ray observations of IQ Aurigae andα² Canum Venaticorum