[ITAL]Chandra[/ITAL] Discovers a Very High Density X-Ray Plasma on the O Star ζ Orionis

Waldron, W. L.; Cassinelli, J. P.

doi:10.1086/318926

Cited by 122 publications

(120 citation statements)

References 22 publications

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“…Although the origin of the emission was initially a matter of debate, it is now generally believed that instabilities and clumping in the strong line-driven stellar wind is the mechanism that heats small parts of the wind (e.g., Lucy & Solomon 1970;Lucy & White 1980;Lucy 1982;Owocki et al 1988;Dessart & Owocki 2005). The launches of Chandra and XMM-Newton in 1999 with high-resolution instruments aboard have offered the possibility to study the X-ray spectra in more detail, resulting in, e.g., estimates of line ratios, line profiles, temperatures, emission measures, and abundances (Waldron & Cassinelli 2001Cohen et al 2006;Kahn et al 2001;Raassen et al 2008). Generally, the overall spectra have been described by means of collisional ionization equilibrium (CIE) models with several temperature components, often complemented by analysis of individual line profiles, line fluxes, and line flux ratios of He-like ions.…”

Section: Introductionmentioning

confidence: 99%

The X-ray spectrum ofδOrionis observed by LETGS aboardChandra

Raassen

Pollock

2013

A&A

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Aims. We analyze the high-resolution X-ray spectrum of the supergiant O-star δ Orionis (O9.5II) with line ratios of He-like ions and a thermal plasma model, and we examine its variability. Methods. The O-supergiant δ Ori was observed in the wavelength range 5-175 Å by the X-ray detector HRC-S in combination with the grating LETG aboard Chandra. We studied the He-like ions in combination with the UV-radiation field to determine local plasma temperatures and to establish the distance of the X-ray emitting ions to the stellar surface. We measured individual lines by means of Gaussian profiles, folded through the response matrix, to obtain wavelengths, line fluxes, half widths at half maximum (HWHM) and line shifts to characterize the plasma. We consider multitemperature models in collisional ionization equilibrium (CIE) to determine temperatures, emission measures, and abundances.Results. Analysis of the He-like triplets extended to N vi and C v implies ionization stratification with the hottest plasma to be found within a few stellar radii 3 R * (Mg xi) and the coolest farther out, far beyond the acceleration zone, up to 49 R * (N vi) and 75 R * (C v).The observed temperatures cover a range from about 0.1 to 0.7 keV, i.e., 1-8 MK. The X-ray luminosity (L x ) is ∼1.5 × 10 32 erg/s in the range from 0.07 to 3 keV covered by LETGS. Velocity widths of about 1040 km s −1 have been determined.

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Section: Introductionmentioning

confidence: 99%

The X-ray spectrum ofδOrionis observed by LETGS aboardChandra

Raassen

Pollock

2013

A&A

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“…However, we note that (1) because of the noise in our data, only large asymmetries would have been detected, if present; and (2) even for bright sources with much better RGS spectra, conflicting results are sometimes found (see, e.g. the case of ζ Ori in Waldron & Cassinelli 2001;Raassen et al 2008;vs. Cohen et al 2006;Pollock 2007).…”

Section: The Observed X-ray Emission Of Hd 155806mentioning

confidence: 77%

Hot and cool: two emission-line stars with constrasting behaviours in the same XMM-Newtonfield

Nazé

Rauw

ud‐Doula

2010

A&A

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High-energy emissions are good indicators of peculiar behaviours in stars. We have therefore obtained an XMM-Newton observation of HD 155806 and 1RXS J171502.4−333344, and derived their spectral properties for the first time. The X-ray spectrum of HD 155806 appears soft, even slightly softer than usual for O-type stars (as shown by a comparison with the O9 star HD 155889 in the same XMM-Newton field). It is well-fitted with a two-component thermal model with low temperatures (0.2 and 0.6 keV), and it shows no overluminosity (log[L X /L BOL ] = −6.75). The high-resolution spectrum, though noisy, reveals a few broad, symmetric X-ray lines (FWHM ∼ 2500 km s −1 ). The X-ray emission is compatible with the wind-shock model and therefore appears unaffected by the putative dense equatorial regions at the origin of the Oe classification. 1RXS J171502.4−333344 is a nearby flaring source of moderate X-ray luminosity (log[L X /L BOL ] = −3), with a soft thermal spectrum composed of narrow lines and presenting a larger abundance of elements (e.g. Ne) with a high first ionization potential (FIP) compared to lower-FIP elements. All the evidence indicates a coronal origin for the X-ray emission, in agreement with the dMe classification of this source.

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“…Schulz et al (2003) show that these hottest lines are the likely result of magnetic confinement. Some magnetic Waldron & Cassinelli (2000); (c) Kahn et al (2001).…”

Section: X-raymentioning

confidence: 99%

“…Hot stars of spectral O and B have been observed with X-ray emission. Most of the X-ray emission with temperatures of several million degrees from early-type stars appears to originate in their winds (Waldron & Cassinelli 2000, 2007. Solartype coronal emission was first assumed to explain X-ray emission (Cassinelli & Olson 1979), but the observations did not show the expected large attenuation by the cold winds in the soft X-ray band.…”

Section: Introductionmentioning

confidence: 99%

“…Much research has shown that the hot, X-ray emitting plasma is distributed throughout winds (Kramer et al 2003;Leutenegger et al 2006a;Cohen et al 2006). The locations and temperatures of the X-ray sources have been measured in terms of the high-resolution X-ray emission lines (Waldron & Cassinelli 2000, 2007Cohen et al 2003). Waldron (2005) shows that the X-ray temperature distributions decline outward through the winds for OB supergiants.…”

Section: Introductionmentioning

confidence: 99%

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X-ray temperatures and their radial distributions from winds of O-type supergiants: the effects of clumps

Guo

2010

A&A

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Context. Based on the multiphase hydrodynamical flows and the clump model, a two-fluid model of the O stars ζ Ori A and ζ Pup is investigated, in which the flow is described by a set of two components. Aims. I investigate the influence of clumps on the production of X-ray and derive wind parameters from a comparison with the X-ray temperature distributions in the wind of O-type supergiants. Methods. The velocity structure of the clump is assumed to be beta law, thus the transonic velocity structure of the ambient wind can be attained via the shooting method. Results. The mass, filling factor, and velocity structure of the clump are very sensitive to the post-shock temperatures. I find that the filling factor must be about 0.01 for fitting the observed X-ray temperatures. The mass of the clump cannot be smaller than 10 18 g. A clump carries about 10 −4Ṁ and 10 −5Ṁ for ζ Ori A and ζ Pup, respectively. The model with the exponent of clump velocity β = 0.5−0.6 for O-type supergiants fits the observations better than one with the exponent β = 0.8. Conclusions. These results indicate that the forward shock scenario can explain the X-ray emission, except for the hottest X-ray lines for O-type supergiants. Theoretical and observable evidence shows that a low velocity law should be applied to O-type supergiants.

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[ITAL]Chandra[/ITAL] Discovers a Very High Density X-Ray Plasma on the O Star ζ Orionis

Cited by 122 publications

References 22 publications

The X-ray spectrum ofδOrionis observed by LETGS aboardChandra

The X-ray spectrum ofδOrionis observed by LETGS aboardChandra

Hot and cool: two emission-line stars with constrasting behaviours in the same XMM-Newtonfield

X-ray temperatures and their radial distributions from winds of O-type supergiants: the effects of clumps

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