Line ratios for helium-like ions: Applications to collision-dominated plasmas

Porquet, D.; Mewe, R.; Dubau, J.; Raassen, A. J. J.; Kaastra, J. S.

doi:10.1051/0004-6361:20010959

Cited by 237 publications

(350 citation statements)

References 47 publications

(55 reference statements)

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“…This value is better constrained than in Paper I because of the higher S/N of the RGS spectrum analysed here. Comparing this ratio with the tables of Porquet et al (2001) and with the radial dependence of the f /i ratio shown in Fig. 4 of Paper I indicates that the Ne ix lines must form in a harsh UV radiation field.…”

Section: High-resolution X-ray Spectroscopysupporting

confidence: 60%

“…The He-like triplets, which consist of a resonance line (r), an intercombination doublet (i), and a forbidden line ( f ), can be used as a diagnostic of the UV radiation field in the region of the X-ray plasma (for details see Gabriel & Jordan 1969;Blumenthal et al 1972;Porquet et al 2001). The RGS spectrum of 9 Sgr indicates that the empirical f /i intensity ratios are strongly reduced compared to the ratios of the transition probabilities.…”

Section: High-resolution X-ray Spectroscopymentioning

confidence: 99%

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Testing the theory of colliding winds: the periastron passage of 9 Sagittarii

Rauw

Blomme

Nazé

et al. 2016

A&A

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Context. The long-period, highly eccentric O-star binary 9 Sgr, known for its non-thermal radio emission and its relatively bright X-ray emission, went through its periastron in 2013. Aims. Such an event can be used to observationally test the predictions of the theory of colliding stellar winds over a broad range of wavelengths. Methods. We conducted a multi-wavelength monitoring campaign of 9 Sgr around the 2013 periastron. In this paper, we focus on X-ray observations and optical spectroscopy. Results. The optical spectra allow us to revisit the orbital solution of 9 Sgr and to refine its orbital period to 9.1 years. The X-ray flux is maximum at periastron over all energy bands, but with clear differences as a function of energy. The largest variations are observed at energies above 2 keV, whilst the spectrum in the soft band (0.5−1.0 keV) remains mostly unchanged, indicating that it arises far from the collision region, in the inner winds of the individual components. The level of the hard emission at periastron clearly deviates from the 1/r relation expected for an adiabatic wind-interaction zone, whilst this relation seems to hold at the other phases that are covered by our observations. The spectra taken at phase 0.946 reveal a clear Fe xxv line at 6.7 keV, but no such line is detected at periastron (φ = 0.000), although a simple model predicts a strong line that should be easily visible in the data. Conclusions. The peculiarities of the X-ray spectrum of 9 Sgr could reflect the effect of radiative inhibition as well as a phasedependent efficiency of particle acceleration on the shock properties.

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Section: High-resolution X-ray Spectroscopysupporting

confidence: 60%

Section: High-resolution X-ray Spectroscopymentioning

confidence: 99%

Testing the theory of colliding winds: the periastron passage of 9 Sagittarii

Rauw

Blomme

Nazé

et al. 2016

A&A

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“…For example, if collisions are dominant, the ratio G = (i + f )/r ∼ 1 obtains, whereas if photoionizations dominate the exitation G ∼ 4 (e.g. Porquet & Dubau 2000;Porquet et al 2001). From the O VII f ir complex in our XMM-Newton spectrum, we estimate G ∼ 0.9 ± 0.1 for γ Cas.…”

Section: Helium-like Diagnostics Of Electron Densitiesmentioning

confidence: 76%

γCassiopeiae: an X-ray Be star with personality

Oliveira

Smith

Motch

2010

A&A

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An exciting unsolved problem in the study of high energy processes of early type stars concerns the physical mechanism for producing X-rays near the Be star γ Cassiopeiae. By now we know that this source and several "γ Cas analogs" exhibit an unusual hard thermal Xray spectrum, compared both to normal massive stars and the non-thermal emission of known Be/X-ray binaries. Also, its light curve is variable on almost all conceivable timescales. In this study we reanalyze a high dispersion spectrum obtained by Chandra in 2001 and combine it with the analysis of a new (2004) spectrum and light curve obtained by XMM-Newton. We find that both spectra can be fit well with 3-4 optically thin, thermal components consisting of a hot component having a temperature kT Q ∼ 12-14 keV, perhaps one with a value of ∼2.4 keV, and two with well defined values near 0.6 keV and 0.11 keV. We argue that these components arise in discrete (almost monothermal) plasmas. Moreover, they cannot be produced within an integral gas structure or by the cooling of a dominant hot process. Consistent with earlier findings, we also find that the Fe abundance arising from K-shell ions is significantly subsolar and less than the Fe abundance from L-shell ions. We also find novel properties not present in the earlier Chandra spectrum, including a dramatic decrease in the local photoelectric absorption of soft X-rays, a decrease in the strength of the Fe and possibly of the Si K fluorescence features, underpredicted lines in two ions each of Ne and N (suggesting abundances that are ∼1.5-3× and ∼4× solar, respectively), and broadening of the strong Ne X Lyα and O VIII Lyα lines. In addition, we note certain traits in the γ Cas spectrum that are different from those of the fairly well studied analog HD 110432 -in this sense the stars have different "personalities." In particular, for γ Cas the hot X-ray component remains nearly constant in temperature, and the photoelectric absorption of the X-ray plasmas can change dramatically. As found by previous investigators of γ Cas, changes in flux, whether occurring slowly or in rapidly evolving flares, are only seldomly accompanied by variations in hardness. Moreover, the light curve can show a "periodicity" that is due to the presence of flux minima that recur semiregularly over a few hours, and which can appear again at different epochs.

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“…O vii traces the location of plasma at temperatures around 2 MK, and its forbidden ( f ) to intercombination (i) line ratio is sensitive to density and UV radiation, specifically one finds f /i = R 0 /(1 + φ/φ c + n e /n c ), see, e.g. Mewe & Schrijver (1978); Porquet et al (2001). In the low-density case (n e < ∼ 10 10 cm −3 ) additional photons in the i-line are only due to the radiation term φ/φ c .…”

Section: The High Resolution X-ray Spectrummentioning

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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Line ratios for helium-like ions: Applications to collision-dominated plasmas

Cited by 237 publications

References 47 publications

Testing the theory of colliding winds: the periastron passage of 9 Sagittarii

Testing the theory of colliding winds: the periastron passage of 9 Sagittarii

γCassiopeiae: an X-ray Be star with personality

New X-ray observations of IQ Aurigae andα² Canum Venaticorum

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Line ratios for helium-like ions: Applications to collision-dominated plasmas

Cited by 237 publications

References 47 publications

Testing the theory of colliding winds: the periastron passage of 9 Sagittarii

Testing the theory of colliding winds: the periastron passage of 9 Sagittarii

γCassiopeiae: an X-ray Be star with personality

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