共查询到20条相似文献，搜索用时 950 毫秒
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J. M. Pittard 《Monthly notices of the Royal Astronomical Society》2009,396(3):1743-1763
The dynamics of the wind–wind collision in massive stellar binaries are investigated using 3D hydrodynamical models which incorporate gravity, the driving of the winds, the orbital motion of the stars and radiative cooling of the shocked plasma. In this first paper, we restrict our study to main-sequence O+O binaries. The nature of the wind–wind collision region is highly dependent on the degree of cooling of the shocked plasma, and the ratio of the flow time-scale of the shocked plasma to the orbital time-scale. The pre-shock wind speeds are lower in close systems as the winds collide prior to their acceleration to terminal speeds. Radiative inhibition may also reduce the pre-shock wind speeds. Together, these effects can lead to rapid cooling of the post-shock gas. Radiative inhibition is less important in wider systems, where the winds are accelerated to higher speeds before they collide, and the resulting collision region can be largely adiabatic. In systems with eccentric orbits, cold gas formed during periastron passage can persist even at apastron, before being ablated and mixed into its surroundings and/or accelerated out of the system. 相似文献
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Ji&#;í Krti&#;ka Ji&#;í Kubát 《Monthly notices of the Royal Astronomical Society》2009,394(4):2065-2079
We study the influence of X-rays on the wind structure of selected O stars. For this purpose we use our non-local thermodynamic equilibrium (NLTE) wind code with inclusion of additional artificial source of X-rays, assumed to originate in the wind shocks.
We show that the influence of shock X-ray emission on wind mass-loss rate is relatively small. Wind terminal velocity may be slightly influenced by the presence of strong X-ray sources, especially for stars cooler than Teff ≲ 35 000 K .
We discuss the origin of the LX / L ∼ 10−7 relation. For stars with thick wind this relation can be explained assuming that the cooling time depends on wind density. Stars with optically thin winds exhibiting the 'weak wind problem' display enhanced X-ray emission which may be connected with large shock cooling length. We propose that this effect can explain the 'weak wind problem'.
Inclusion of X-rays leads to a better agreement of the model ionization structure with observations. However, we do not find any significant influence of X-rays on P v ionization fraction implying that the presence of X-rays cannot explain the P v problem.
We study the implications of modified ionization equilibrium due to shock emission on the line transfer in the X-ray region. We conclude that the X-ray line profiles of helium-like ions may be affected by the line absorption within the cool wind. 相似文献
We show that the influence of shock X-ray emission on wind mass-loss rate is relatively small. Wind terminal velocity may be slightly influenced by the presence of strong X-ray sources, especially for stars cooler than T
We discuss the origin of the L
Inclusion of X-rays leads to a better agreement of the model ionization structure with observations. However, we do not find any significant influence of X-rays on P v ionization fraction implying that the presence of X-rays cannot explain the P v problem.
We study the implications of modified ionization equilibrium due to shock emission on the line transfer in the X-ray region. We conclude that the X-ray line profiles of helium-like ions may be affected by the line absorption within the cool wind. 相似文献
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V. Muntean A. F. J. Moffat A. N. Chené A. de la Chevrotière 《Monthly notices of the Royal Astronomical Society》2009,399(4):1977-1987
A spectroscopic study of the binary Wolf–Rayet (WR)+O system WR 145 is performed, in order to determine the radial velocity orbits of the individual stars, the angle of orbital inclination and the stellar masses. The emission and absorption components are separated from the original spectra, allowing us to confirm the spectral classification WN 7o/CE of the hybrid WR component and to derive a spectral classification O7V((f)) for the O star. A study of the wind-collision properties is performed. Fitting the radial velocity and full width at half-maximum of the excess emission with Lührs' model results in an inclination angle of i = 63° , leading to estimates of the stellar masses: M WR = 18 M⊙ and M O = 31 M⊙ . Both of these masses are compatible with those of other stars of similar types. 相似文献
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We investigate the role of classical microturbulence in the non-LTE He i /He ii line formation problem for luminous O-type stars. We find that the shapes and strengths of certain saturated He i lines, in particular the triplets λλ4471, 4713 and the singlet λ4921, are sensitive to microturbulent velocities in excess of 5 km s−1 . Weaker lines, including most of the He i singlets, are effectively independent of this parameter, as are the Fowler series He ii lines λλ4199, 4541, 5411. We show that this behaviour is due to interaction between direct line-broadening effects in the radiative transfer, and indirect changes in the atmospheric structure and the populations of absorbing states. Using an analysis of high-resolution, high signal-to-noise ratio observations of the O9.7 supergiant HD 152003 as an illustrative example, we show how the introduction of microturbulence in non-LTE models allows consistent fits to be obtained for all blue-region He i lines — including the strong triplets λλ4026, 4713, 4471 — at an assumed solar helium abundance, thereby offering a resolution to the problem of the 'generalized dilution effect' described by Voels et al. We argue that by extension this result may also have implications for the so-called 'helium discrepancy' identified in OB-type stars by Herrero et al. 相似文献
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G. M. Hill A. F. J. Moffat † N. St-Louis P. Bartzakos 《Monthly notices of the Royal Astronomical Society》2000,318(2):402-410
We have obtained complete phase coverage of the WC7+O binaries WR 42 = HD 97152 and WR 79 = HD 152270 with high signal-to-noise ratio (S/N), moderate-resolution spectra. Remarkable orbital phase-locked profile variations of the C iii λ 5696 line are observed and interpreted as arising from colliding wind effects. Within this scenario, we have modelled the spectra using a purely geometrical model that assumes a cone-shaped wind–wind interaction region which partially wraps around the O star. Such modelling holds the exciting promise of revealing a number of interesting parameters for WR+O binaries, such as the orbital inclination, the streaming velocity of material in the interaction region and the ratio of wind momentum flux. Knowledge of these parameters in turn leads to the possibility of a better understanding of WR star masses, mass-loss rates and wind region characteristics. 相似文献
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P. G. Ostrov 《Monthly notices of the Royal Astronomical Society》2001,321(1):L25-L28
An orbital solution for the MACHO*05:34:41.3–69:31:39 eclipsing binary system is presented, based on the published light curve and spectral data obtained with the 2.15-m telescope at CASLEO. Based on these spectroscopic observations, the binary components of this system were classified as O3 If* and O6:V respectively. The radial velocity data along with the published light curve were analysed with the Wilson–Devinney code to derive the following masses and radii for the components of this system: and The solution shows that the system is in overcontact, as one would expect from the derived masses and the very short orbital period (∼1.4 d). 相似文献
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Anthony B. Kaye & Klaus G. Strassmeier 《Monthly notices of the Royal Astronomical Society》1998,294(2):L35-L39
In an investigation of the starspot hypothesis as it applies to the 'slowly variable' F-type dwarfs, we spectroscopically observed eight promising γ Doradus candidates to search for Ca ii H&K emission. We found that there are no significant emission reversals in the cores of these resonance lines. Based on the ceiling flux calculations of the Ca ii K line and on calculations of the Rossby number, we conclude that there is no support for the presence of strong magnetic activity and the starspot hypothesis in these objects. 相似文献
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We have earlier investigated the surface structures of a late‐type, single, giant FK Com for the years 1994–1998 using Doppler imaging. These surface temperature maps revealed long‐lived active regions at high latitudes. Long‐term photometric observations also show that these active regions tend to occur at two permanent active longitudes which are 180 degrees apart from each other, and that the activity switches the longitude with an average period of about 3 years (the “flip‐flop” phenomenon). In this work we present new Doppler maps of FK Com obtained 1998‐2003 and light‐curve maps obtained 2002–2003. These new maps are investigated together with the earlier temperature maps and light‐curve maps, with an aim of further studying the active longitudes, “flip‐flop” phenomenon and surface differential rotation on FK Com. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
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P. J. Amado † C. J. Butler P. B. Byrne‡ 《Monthly notices of the Royal Astronomical Society》1999,310(4):1023-1032
In the first part of this work, the empirical correlation of stellar surface brightness F V with ( I c − K ) broad-band colour is investigated by using a sample of stars cooler than the Sun. A bilinear correlation is found to represent well the brightness of G, K and M giant stars. The change in slope occurs at ( I c − K )∼2.1 or at about the transition from K to M spectral types. The same relationship is also investigated for dwarf stars and found to be distinctly different from that of the giants. The dwarf star correlation differs by an average of −0.4 in ( I c − K ) or by a maximum in F V of ∼−0.1, positioning it below that of the giants, with both trends tending towards convergence for the hotter stars in our sample. The flux distribution derived from the F V −( I c − K ) relationship for the giant stars, together with that derived from an F V −( V − K ) relationship and the blackbody flux distribution, is then utilized to compute synthetic light V and colour ( V − R )c , ( V − I )c and ( V − K ) curves of cool spotted stars. We investigate the effects on the amplitudes of the curves by using these F V –colour relations and by assuming the effective gravity of the spots to be lower than the gravity of the unspotted photosphere. We find that the amplitudes produced by using the F V −( I c − K ) relationship are larger than those produced by the other two brightness correlations, meaning smaller and/or warmer spots. 相似文献
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We investigate how the frequencies of gravity modes depend on the detailed properties of the chemical composition gradient that develops near the core of main‐sequence stars and, therefore, on the transport processes that are able to modify the μ profile in the central regions. We show that in main‐sequence models, similarly to the case of white dwarfs, the periods of high‐order gravity modes are accurately described by a uniform period spacing superposed to an oscillatory component. The periodicity and amplitude of such a component are related, respectively, to the location and sharpness of the μ gradient. We briefly discuss and interpret, by means of this simple approximation, the effect of turbulent mixing near the core on the periods of both high‐order and low‐order g modes, as well as of modes of mixed pressure‐gravity character. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献