Discovery of X-ray flaring on the magnetic Bp-star $\mathsf{\sigma}$ Ori E

Groote, D.; Schmitt, J. H. M. M.

doi:10.1051/0004-6361:20034300

Cited by 47 publications

(45 citation statements)

References 30 publications

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“…We visually inspected the X-ray light curve of σ Ori E and detected a modulation with a sinusoidal-like variation in the HRC-I count rate between 20 and 50 ks −1 and an estimated period slightly longer than the duration of the observations (>97.6 ks), which is also consistent with the rotational period. In contrast to Groote & Schmitt (2004), Sanz-Forcada et al (2004), and Caballero et al (2009), who reported strong X-ray flares in the light curves of σ Ori E, we did not find any. The flares originate in its low-mass companion ).…”

Section: X-ray Light Curvescontrasting

confidence: 99%

HRC-I/ChandraX-ray observations towardsσ Orionis

Caballero

Colombo

López‐Santiago

2010

A&A

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Aims. We investigated the X-ray emission from young stars and brown dwarfs in the σ Orionis cluster (τ ∼ 3 Ma, d ∼ 385 pc) and its relation to mass, the presence of circumstellar discs, and separation to the cluster centre by taking advantage of the superb spatial resolution of the Chandra X-ray Observatory. Methods. We used public HRC-I/Chandra data from a 97.6 ks pointing towards the cluster centre and complemented them with X-ray data from IPC/Einstein, HRI/ROSAT, EPIC/XMM-Newton, and ACIS-S/Chandra together with optical and infrared photometry and spectroscopy from the literature and public catalogues. On our HRC-I/Chandra data, we measured count rates, estimated X-ray fluxes, and searched for short-term variability. We also looked for long-term variability by comparing with previous X-ray observations. Results. Among the 107 detected X-ray sources, there were 70 cluster stars with known signposts of youth, two young brown dwarfs, 12 cluster member candidates, four field dwarfs, and two galaxies with optical-infrared counterpart. The remaining sources were extragalactic. Based on a robust Poisson-χ 2 analysis, nine cluster stars displayed flares or rotational modulation during the HRC-I observations, while eight other stars and one brown dwarf showed X-ray flux variations between the HRC-I and IPC, HRI, and EPIC epochs. We constructed a cluster X-ray luminosity function from O9.5 (about 18 M ) to M6.5 (about 0.06 M ). We found: (i) that early-type stars in multiple systems or with spectroscopic peculiarities tend to display X-ray emission; (ii) that the two detected brown dwarfs and the least-massive star are among the σ Orionis objects with the highest L X /L J ratios; and (iii) that a large fraction of known classical T Tauri stars in the cluster are absent in this and other X-ray surveys. Finally, from a spatial distribution analysis, we quantified the impact of sensitivity degradation towards the HRC-I borders on the detection of faint X-ray sources and concluded that dozens X-ray σ Orionis stars and brown dwarfs still need to be detected.

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Section: X-ray Light Curvescontrasting

confidence: 99%

HRC-I/ChandraX-ray observations towardsσ Orionis

Caballero

Colombo

López‐Santiago

2010

A&A

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“…Skinner et al (2008), using data obtained with the High Energy Transmission Grating Spectrometer onboard Chandra, considered possible alternatives to the radiative wind shock, including magneticallyconfined and colliding wind shocks. Sanz-Forcada et al (2004) reported a strong X-ray flare on the magnetic B2Vp star σ Ori E, the second brightest star in the cluster, confirming the previous discovery of a flare on the star by Groote & Schmitt (2004) with ROSAT data. Caballero et al (in prep.…”

Section: Introductionsupporting

confidence: 76%

New deepXMM-Newtonobservations to the west of the σ Orionis cluster

López‐Santiago

Caballero

2008

A&A

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Aims. The objective of this study is to determine the general X-ray properties of the young stars in the external regions of the σ Orionis cluster (τ ∼ 3 Ma, d ∼ 385 pc) and determine constraints on the X-ray emission of brown dwarfs. Methods. We carried out a careful analysis of public data obtained from an unexplored region to the west of the centre of the cluster with the three EPIC cameras onboard the XMM-Newton mission. We looked for new X-ray young stars among the 41 identified X-ray sources in the area with maximum likelihood parameters L > 15 by cross-correlation with the USNO-B1, DENIS, and 2MASS databases.Results. Based on colour-colour, colour-magnitude, and hardness ratio diagrams, and previous spectroscopic, astrometric, and infrared-flux excess information, we classified the optical/near-infrared counterparts of the X-ray sources into: young stars (15), field stars (4), galaxies (19), and sources of unknown nature (3). Most of the X-ray detections, including those of nine young stars, are new. We derived the X-ray properties (e.g. temperatures, metallicities, column densities) of the twelve young stars with the largest signal-to-noise ratios. The X-ray parameters determined here are in good agreement with those found in the cluster centre, where the stellar density is higher. There is no relation between infrared excess and column density in the X-ray measurements in our data. We detected flaring events in two young stars of the sample. One of them showed a very large (∼30) relative increase in flux. Both stars showed high coronal temperatures during the observation. Finally, we determined upper limits to the flux of the young stars and brown dwarfs not detected by our search algorithm.

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“…θ 1 Ori C shows relatively hard X-ray emission from very hot plasma at temperatures of up to 30 MK, but no strong flaring. Noteworthy, there have also been reports of X-ray flares on early type magnetic stars, a prominent example is the B2p star σ Ori E. While Groote & Schmitt (2004) attribute a flare seen with ROSAT to σ Ori E itself, Sanz-Forcada et al (2004) report a long duration (>10 h) flare with a count-rate increase by a factor of ten in an XMM-Newton observation and concluded that this more likely originates in a companion. They derived a QQ X-ray luminosity of L X = 9 × 10 30 erg s −1 and plasma temperatures up to 10-15 MK for σ Ori E. Also non CP, magnetic early-B stars are X-ray sources, e.g.…”

Section: What About Hotter Magnetic Stars?mentioning

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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Discovery of X-ray flaring on the magnetic Bp-star $\mathsf{\sigma}$ Ori E

Cited by 47 publications

References 30 publications

HRC-I/ChandraX-ray observations towardsσ Orionis

HRC-I/ChandraX-ray observations towardsσ Orionis

New deepXMM-Newtonobservations to the west of the σ Orionis cluster

New X-ray observations of IQ Aurigae andα² Canum Venaticorum

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Discovery of X-ray flaring on the magnetic Bp-star $\mathsf{\sigma}$ Ori E

Cited by 47 publications

References 30 publications

HRC-I/ChandraX-ray observations towardsσ Orionis

HRC-I/ChandraX-ray observations towardsσ Orionis

New deepXMM-Newtonobservations to the west of the σ Orionis cluster

New X-ray observations of IQ Aurigae andα2 Canum Venaticorum

Contact Info

Product

Resources

About

New X-ray observations of IQ Aurigae andα² Canum Venaticorum