Book Reviews

Groenewegen, Peter; Laurent, John; Hammond, J. Daniel; Freedman, Craig; Groenewegen, Peter

doi:10.1080/10370196.1992.11733105

Cited by 9 publications

(11 citation statements)

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“…The higher Z lines have characteristic widths ∼ 1000 km s −1 , whereas the N VII line is distinctly broader. The terminal velocity in the ζ Pup wind is 2260 km s −1 (Groenewegen et al 1989), so the higher Z lines are most likely emitted at only a few stellar radii, whereas N VII can come from considerably further out.…”

Section: Discussionmentioning

confidence: 99%

High resolution X-ray spectroscopy ofζPuppis with the XMM-Newton reflection grating spectrometer

Kahn

Leutenegger

Cottam

et al. 2001

A&A

177

190

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Abstract. We present the first high resolution X-ray spectrum of the bright O4Ief supergiant star ζ Puppis, obtained with the Reflection Grating Spectrometer on-board XMM-Newton. The spectrum exhibits bright emission lines of hydrogen-like and helium-like ions of nitrogen, oxygen, neon, magnesium, and silicon, as well as neon-like ions of iron. The lines are all significantly resolved, with characteristic velocity widths of order 1000-1500 km s −1 . The nitrogen lines are especially strong, and indicate that the shocked gas in the wind is mixed with CNO-burned material, as has been previously inferred for the atmosphere of this star from ultraviolet spectra. We find that the forbidden to intercombination line ratios within the helium-like triplets are anomalously low for N VI, O VII, and Ne IX. While this is sometimes indicative of high electron density, we show that in this case, it is instead caused by the intense ultraviolet radiation field of the star. We use this interpretation to derive constraints on the location of the X-ray emitting shocks within the wind that are consistent with current theoretical models for this system.

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Section: Discussionmentioning

confidence: 99%

High resolution X-ray spectroscopy ofζPuppis with the XMM-Newton reflection grating spectrometer

Kahn

Leutenegger

Cottam

et al. 2001

A&A

177

190

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“…where Ṁ is the mass loss rate (see Table 1). The velocity of the wind v w (r) is calculated using a β velocity law with β w = 0.8 (Groenewegen & Lamers 1989):…”

Section: Drag Forcementioning

confidence: 99%

Stagnation and Infall of Dense Clumps in the Stellar Wind of τ Scorpii

Howk

Cassinelli

Bjorkman

et al. 2000

ApJ

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Observations of the B0.2 V star τ Scorpii have revealed unusual stellar wind characteristics: red-shifted absorption in the far-ultraviolet O VI resonance doublet up to ∼ +250 km s −1 , and extremely hard X-ray emission implying gas at temperatures in excess of 10 7 K. We describe a phenomenological model to explain these properties. We assume the wind of τ Sco consists of two components: ambient gas in which denser clumps are embedded. The clumps are optically thick in the UV resonance lines primarily responsible for accelerating the ambient wind. The reduced acceleration causes the clumps to slow and even infall, all the while being confined by the ram pressure of the outflowing ambient wind. We calculate detailed trajectories of the clumps in the ambient stellar wind, accounting for a line radiation driving force and the momentum deposited by the ambient wind in the form of drag. We show these clumps will fall back towards the star with velocities of several hundred km s −1 for a broad range of initial conditions. The velocities of the clumps relative to the ambient stellar wind can approach 2000 km s −1 , producing X-ray emitting plasmas with temperatures in excess of (1 − 6) × 10 7 K in bow shocks at their leading edge. The infalling material explains the peculiar red-shifted absorption wings seen in the O VI doublet. Of order 10 3 clumps with individual masses m c ∼ 10 19 − 10 20 g are needed to explain the observed X-ray luminosity and also to explain the strength of the O VI absorption lines. These values correspond to a mass loss rate in clumps ofṀ c ∼ 10 −9 to 10 −8 M ⊙ yr −1 , a small fraction of the total mass loss rate (Ṁ ∼ 3 × 10 −8 M ⊙ yr −1 ). We discuss the position of τ Sco in the HR diagram, concluding that τ Sco is in a crucial position on the main sequence. Hotter stars near the spectral type of τ Sco have too powerful winds for clumps to fall back to the stars, and cooler stars have too low mass loss rates to produce observable effects. The model developed here can be generally applied to line-driven outflows with clumps or density irregularities.

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“…From lowresolution optical spectra, we determined the reddening to be E(B − V ) = 0.79 ± 0.1, which was estimated using the method described in Luna and Costa (2005). This reddening corresponds to a column density of N H = 3.0 × 10 21 cm −2 (Groenewegen and Lamers, 1989), which was used as the starting value for the X-ray spectral fitting. The best-fit model (χ 2 ∞ν = 1.22) has kT = 0.268 0.291 0.249 keV (3.11 3.37 2.88 × 10 6 K), N H = 5.5 6.3 5.2 × 10 21 cm 2 and line energy 0.55 0.57 0.53 keV.…”

Section: Resultsmentioning

confidence: 99%

X-rays from the Symbiotic Star RX Pup

Luna

Sokoloski

Costa

2006

Astrophys Space Sci

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We describe X-ray and optical observations of the symbiotic star RX Pup. From low resolution optical spectra, we obtain a reddening for RX Pup of E(B − V ) = 0.79. We use the neutral column density corresponding to this reddening as a lower limit for the X-ray spectra fits. The X-ray spectra can be fitted with either a two-temperature thermal plasma model or a single-temperature plasma plus a narrow line at ≈0.55 keV, each modified by interstellar absorption. The RX Pup X-ray flux is not variable within the observation exposure time, suggesting that unlike in most CVs, an accretion disk boundary layer does not contribute significantly to the X-ray flux. Instead, the X-ray emission may come from shock-heated gas further away from the compact object.

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Book Reviews

Cited by 9 publications

References 0 publications

High resolution X-ray spectroscopy ofζPuppis with the XMM-Newton reflection grating spectrometer

High resolution X-ray spectroscopy ofζPuppis with the XMM-Newton reflection grating spectrometer

Stagnation and Infall of Dense Clumps in the Stellar Wind of τ Scorpii

X-rays from the Symbiotic Star RX Pup

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