<i>MOST</i>OBSERVATIONS OF σ Ori E: CHALLENGING THE CENTRIFUGAL BREAKOUT NARRATIVE

Townsend, R. H. D.; Rivinius, Thomas; Rowe, Jason F.; Moffat, A. F. J.; Matthews, J. M.; Bohlender, D.; Neiner, C.; Telting, J. H.; Guenther, D. B.; Kallinger, T.; Kuschnig, R.; Ruciński, S. M.; Sasselov, Dimitar; Weiß, W. W.

doi:10.1088/0004-637x/769/1/33

Cited by 55 publications

(61 citation statements)

References 37 publications

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“…Although these magnetospheres are dynamic in nature, there are many indications that their volumeintegrated properties are quite stable, namely based on numerical simulations (ud-Doula et al 2013), on observational diagnostics (Howarth et al 2007;Townsend et al 2013), and on the lack of short term variability observed here. With this picture in mind, we therefore do not expect the intrinsic X-ray emissivity of the magnetosphere itself to change significantly in time, but rather its sky-projected structure to modulate with the rotational phase.…”

Section: Spectral Analysismentioning

confidence: 67%

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: Spectral Analysismentioning

confidence: 67%

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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“…In particular, the magnetic Be star σ Ori E shows clear∼5% eclipses twice per rotation period; these eclipses have been attributed to clouds of plasma thatare trapped in the magnetosphere and most dense at the corotation radius (Townsend et al 2013). The phenomenon of a narrow flux dip in phase with, and superposed on, semisinusoidal modulation has also been observed in the X-ray light curve of the accreting white dwarf PQ Gem (Mason 1997;Evans et al 2006).…”

Section: Transits Of Magnetospheric Clouds?mentioning

confidence: 88%

A Transient Transit Signature Associated with the Young Star RIK-210

David

Petigura

Hillenbrand

et al. 2017

ApJ

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We find transienttransit-like dimming events within the K2 time series photometry of the young star RIK-210 in the Upper Scorpius OB association. These dimming events are variable in depth, duration, and morphology. High spatial resolution imaging revealed thatthe star is singleand radial velocity monitoring indicated that the dimming events cannot be due to an eclipsing stellar or brown dwarf companion. Archival and follow-up photometry suggest the dimming events are transient in nature. The variable morphology of the dimming events suggests they are not due to a singlespherical body. The ingress of each dimming event is always shallower than egress, as one would expect for an orbiting body with a leading tail. The dimming events are periodic and synchronous with the stellar rotation. However, we argue it is unlikely the dimming events could be attributed to anything on the stellar surface based on the observed depths and durations. Variable obscuration by a protoplanetary disk is unlikely on the basis that the star is not actively accreting and lacks the infrared excess associated with an inner disk. Rather, we explore the possibilities that the dimming events are due to magnetospheric clouds, a transiting protoplanet surrounded by circumplanetary dust and debris, eccentric orbiting bodies undergoing periodic tidal disruption, or an extended field of dust or debris near the corotation radius.

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“…σ Ori E is a rapidly rotating Be star. Ground-based and MOST light curves for σ Ori E show it to have two short-duration flux dips (widths about 0.2 in phase) superposed on a wave-shaped undulation with a period of 1.19 days (Townsend et al 2013). The light-curve shape is apparently stable over many years.…”

Section: Could Scattered/emitted Light From Circumstellar Gasmentioning

confidence: 94%

Orbiting Clouds of Material at the Keplerian Co-rotation Radius of Rapidly Rotating Low-mass WTTs in Upper Sco

et al. 2017

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Using K2 data, we identified 23 very-low-mass members of the ρ Oph and Upper Scorpius star-forming region as having periodic photometric variability not easily explained by well-established physical mechanisms such as star spots, eclipsing binaries, or pulsation. All of these unusual stars are mid-to-late M dwarfs without evidence of active accretion, and with photometric periods generally <1 day. Often the unusual light-curve signature takes the form of narrow flux dips; when we also have rotation periods from star spots, the two periods agree, suggesting that the flux dips are due to material orbiting the star at the Keplerian co-rotation radius. We sometimes see "statechanges" in the phased light-curve morphologies where ∼25% of the waveform changes shape on timescales less than a day; often, the "state-change" takes place immediately after a strong flare. For the group of stars with these sudden light-curve morphology shifts, we attribute their flux dips as most probably arising from eclipses of warm coronal gas clouds, analagous to the slingshot prominences postulated to explain transient Hα absorption features in AB Doradus and other rapidly rotating late-type stars. For another group of stars with somewhat longer periods, we find the short-duration flux dips to be highly variable on both short and long timescales, with generally asymmetric flux-dip profiles. We believe that these flux dips are due to particulate clouds possibly associated with a close-in planet or resulting from a recent collisional event.

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MOSTOBSERVATIONS OF σ Ori E: CHALLENGING THE CENTRIFUGAL BREAKOUT NARRATIVE

Cited by 55 publications

References 37 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

A Transient Transit Signature Associated with the Young Star RIK-210

Orbiting Clouds of Material at the Keplerian Co-rotation Radius of Rapidly Rotating Low-mass WTTs in Upper Sco

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