Photoionization Cross Sections of He and H<sub>2</sub>

Yan, Min; Sadeghpour, H. R.; Dalgarno, A.

doi:10.1086/305420

Cited by 247 publications

(213 citation statements)

References 83 publications

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“…For the photoelectric absorption by the interstellar medium, we used the phabs model within xspec with cross-sections from Bałucińska-Church & McCammon (1992) and Yan et al (1998). For the ionized stellar wind, we imported the stellar wind absorption model of Nazé et al (2004) into xspec as a multiplicative tabular model (hereafter called mtab{wind}).…”

Section: Spectral Fittingmentioning

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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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: Spectral Fittingmentioning

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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“…Figure 4 shows the ratios of the data to the continuum obtained for three cases: excluding none, one, and seven of the central brightest columns. The continuum model consists of a blackbody and a Comptonization component (compTT; Titarchuk 1994), modified at low energy by the photoelectric absorption (phabs; photoelectric cross-sections of Balucinska-Church & McCammon 1992 with a new He cross-section based on Yan et al 1998; and standard abundances of Anders & Grevesse 1989). This model is often used for atoll sources and gives a good fit for the continuum of this source (Barret & Olive 2002;Di Salvo et al 2005;Piraino et al 2007;Di Salvo et al 2009).…”

Section: Soft Statementioning

confidence: 99%

Testing reflection features in 4U 1705−44 withXMM-Newton,BeppoSAX, and RXTE in the hard and soft states

Egron

Salvo

Motta

et al. 2013

A&A

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We use data from the bright atoll source 4U 1705−44 taken with XMM-Newton, BeppoSAX, and RXTE both in the hard and in the soft state to perform a self-consistent study of the reflection component in this source. Although the data from these X-ray observatories are not simultaneous, the spectral decomposition is shown to be consistent among the different observations, when the source flux is similar. We have therefore selected observations performed at similar flux levels in the hard and soft states to study the spectral shape in these two states in a broad-band (0.1−200 keV) energy range, with good energy resolution, and using self-consistent reflection models. These reflection models provide a good fit for the X-ray spectrum both in the hard and in the soft state in the whole spectral range. We discuss the differences in the main spectral parameters we find in both states, providing evidence that the inner radius of the optically thick disk slightly recedes in the hard state.

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“…The local residual stellar spectrum is computed incorporating in the radiative transfer equation an accurate description of the relevant photo-electric processes: ionization of atomic hydrogen (Sobel'man 1991), helium (Yan et al 1998), ionized helium (Osterbrock 1989), molecular hydrogen (Yan et al 1998)), and Compton ionization, that, at energies > ∼ 10 keV, is more efficient than photo-ionization of H and He (Yan et al 1998). Furthermore, we adopt relativistic photoionization cross-sections of individual heavy elements and their ions given in Verner et al (1993).…”

Section: Model Descriptionmentioning

confidence: 99%

The relative role of EUV radiation and X-rays in the heating of hydrogen-rich exoplanet atmospheres

Cecchi‐Pestellini¹,

Ciaravella

Micela

et al. 2009

A&A

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Aims. We study the relative role of EUV and X-ray radiation in the heating of hydrogen-rich planet atmospheres with different composition and electron content.Methods. An accurate photo-ionization model has been used to follow the primary photo-electron energy deposition throughout the atmosphere. Results. Heating rates and efficiencies have been computed, together with column density cut-offs at which photons of given energies stop their heating production inside the atmosphere. Assuming 100 eV as the energy borderline between the extreme ultraviolet spectral range and X-rays we find that when the absorbing hydrogen column density is higher than 10 20 cm −2 only X-rays can heat the gas. Extreme ultraviolet photons heat the upper atmospheric layers. Conclusions. Using emission spectra from a sample of solar-type stars of different ages representative of the Sun's main sequence lifetime, we have derived the corresponding heating rates. We find that the existence of an energetic cross-over in atmospheric heating is present for all stars in the sample.

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Photoionization Cross Sections of He and H₂

Cited by 247 publications

References 83 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

Testing reflection features in 4U 1705−44 withXMM-Newton,BeppoSAX, and RXTE in the hard and soft states

The relative role of EUV radiation and X-rays in the heating of hydrogen-rich exoplanet atmospheres

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Photoionization Cross Sections of He and H2

Cited by 247 publications

References 83 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

Testing reflection features in 4U 1705−44 withXMM-Newton,BeppoSAX, and RXTE in the hard and soft states

The relative role of EUV radiation and X-rays in the heating of hydrogen-rich exoplanet atmospheres

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Photoionization Cross Sections of He and H₂