A large coronal loop in the Algol system

Peterson, William M.; Mutel, R. L.; Güdel, M.; Goss, W. M.

doi:10.1038/nature08643

Cited by 48 publications

(46 citation statements)

References 27 publications

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“…However, in the framework of the two polar lobe model (Favata et al 2000, Retter et al 2005, Peterson et al 2010 for the site of the quiescent corona, one could imagine that the absorption column density is highest in or around those lobes, where the quiescent corona is dominating. It is reduced towards the equatorial regions, at which the certainly non-polar flare of this XMM-Newton observation is located.…”

Section: Cool Absorbing Gas Surrounding the K Starmentioning

confidence: 99%

XMM-Newtonobservation of the eclipsing binary Algol

Yang

Aschenbach

et al. 2011

Res. Astron. Astrophys.

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We present an XMM-Newton observation of the eclipsing binary Algol which contains an X-ray dark B8V primary and an X-ray bright K2IV secondary. The observation covered the optical secondary eclipse and captured an X-ray flare that was eclipsed by the B star. The EPIC and RGS spectra of Algol in its quiescent state are described by a two-temperature plasma model. The cool component has a temperature around 6.4×10 6 K while that of the hot component ranges from 2 to 4.0×10 7 K. Coronal abundances of C, N, O, Ne, Mg, Si and Fe were obtained for each component for both the quiescent and the flare phases, with generally upper limits for S and Ar, and C, N, and O for the hot component. F-tests show that the abundances need not to be different between the cool and the hot component and between the quiescent and the flare phase with the exception of Fe. Whereas the Fe abundance of the cool component remains constant at ∼0.14, the hot component shows an Fe abundance of ∼0.28, which increases to ∼0.44 during the flare. This increase is expected from the chromospheric evaporation model. The absorbing column density N H of the quiescent emission is 2.5×10 20 cm −2 , while that of the flare-only emission is significantly lower and consistent with the column density of the interstellar medium. This observation substantiates earlier suggestions of the presence of X-ray absorbing material in the Algol system.

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Section: Cool Absorbing Gas Surrounding the K Starmentioning

confidence: 99%

XMM-Newtonobservation of the eclipsing binary Algol

Yang

Aschenbach

et al. 2011

Res. Astron. Astrophys.

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“…It is likely that the radio emission originates in active regions, e.g., magnetic-loop structures, approximately a stellar radius in size (see, e.g., Peterson et al 2010;Mullan et al 2006;Franciosini et al 1999;Lestrade et al 1988), which are rooted on the surface of the star. Indeed, IM Peg is of the spectral type K2, and Mullan et al (2006) show that the largest coronal loops, with sizes up to two stellar radii, occur in stars of type K2 or later.…”

Section: Rapid Evolution Of the Radio Structurementioning

confidence: 99%

“…However, the emission region is often extended by as much as the separation between the two stars (∼2 mas), which leads to the question: is there any correlation between the geometry of the emission region and the orbital phase? For example, a correlation of the amount and/or angle of elongation of the radio emission with orbital phase might be expected if the radio emission originates predominantly along the line between the two stars (as is seen in the Algol system; Peterson et al 2010; although we note that, unlike IM Peg, Algol is an interacting system for which emission predominately from within the region In each case where the total flux density did not vary discernibly within the observing interval or where the flux density was determined from VLBI rather than VLA observations, the observational uncertainty (1σ ) is shown by a dotted error bar centered on the dot; the fractional observational uncertainties for the other sessions are similar. Right panel: the same flux densities, but plotted against orbital phase (using the orbital parameters of Marsden et al 2005).…”

Section: Orientation and Elongation Of The Radio Emission Regionmentioning

confidence: 99%

VLBI FOR GRAVITY PROBE B . VII. THE EVOLUTION OF THE RADIO STRUCTURE OF IM PEGASI

Bietenholz

Bartel

Lebach

et al. 2012

ApJS

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We present measurements of the total radio flux density as well as very long baseline interferometry images of the star, IM Pegasi, which was used as the guide star for the NASA/Stanford relativity mission Gravity Probe B. We obtained flux densities and images from 35 sessions of observations at 8.4 GHz (λ = 3.6 cm) between 1997 January and 2005 July. The observations were accurately phase-referenced to several extragalactic reference sources, and we present the images in a star-centered frame, aligned by the position of the star as derived from our fits to its orbital motion, parallax, and proper motion. Both the flux density and the morphology of IM Peg are variable. For most sessions, the emission region has a single-peaked structure, but 25% of the time, we observed a two-peaked (and on one occasion perhaps a three-peaked) structure. On average, the emission region is elongated by 1.4 ± 0.4 mas (FWHM), with the average direction of elongation being close to that of the sky projection of the orbit normal. The average length of the emission region is approximately equal to the diameter of the primary star. No significant correlation with the orbital phase is found for either the flux density or the direction of elongation, and no preference for any particular longitude on the star is shown by the emission region.

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“…Recently, Peterson et al (2010) presented high-resolution radio images of the Algol binary system resolving a large coronal loop reaching from one to the other pole of the K giant secondary, being orientated towards the primary B star. The authors modeled the radio emission observed from this loop by assuming synchrotron emission from an electron population with a homogeneous density of n e = 10 −3 electrons/cm −3 and a power-law spectrum so that n(E) = n e (E/E min ) −3/2 where E min = 80 keV.…”

Section: Electron Collisional Excitationmentioning

confidence: 99%

Puzzling fluorescent emission from Orion

Czesla

Schmitt

2010

A&A

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Fluorescent X-ray emission offers a rare possibility for studying cool material surrounding active, young stars in the X-ray regime. In this work, we develop a new method to search for fluorescent emission and analyze its temporal behavior, which we apply to a sample of 106 young, active stars in Orion. Our analysis yields a sample of 23 X-ray sources with fluorescent emission, including 6 objects already reported on in an earlier study. The fluorescent sources show a wide variety of temporal behavior. While the fluorescent emission is associated with soft X-ray flares in some cases, it sometimes appears as a (quasi) persistent feature, or is seen during truly quiescent periods. We conclude that fluorescent X-ray emission can be observed in a much higher fraction of young, active stars than previously believed. Whether photoionization alone is the excitation mechanism of fluorescent X-ray emission or if electronic collisional excitation also contributes remains debatable. The temporal variability is often hard to reconcile with the photoionization model, which remains plausible if we allow for suitable geometries. Photoionization is preferred to electronic, collisional excitation mainly because the energetics of the latter challenge our current physical understanding.

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A large coronal loop in the Algol system

Cited by 48 publications

References 27 publications

XMM-Newtonobservation of the eclipsing binary Algol

XMM-Newtonobservation of the eclipsing binary Algol

VLBI FOR GRAVITY PROBE B . VII. THE EVOLUTION OF THE RADIO STRUCTURE OF IM PEGASI

Puzzling fluorescent emission from Orion

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