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A. T. Bajkova - One of the best experts on this subject based on the ideXlab platform.
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Vertical distribution and kinematics of protoplanetary nebulae in the galaxy
Astronomy Letters, 2017Co-Authors: V. V. Bobylev, A. T. BajkovaAbstract:The catalogue of protoplanetary nebulae by Vickers et al. has been supplemented with the line-of-sight velocities and proper motions of their central stars from the literature. Based on an exponential density distribution, we have estimated the vertical scale height from objects with an age less than 3 Gyr belonging to the Galactic thin disk (luminosities higher than 5000 L _⊙) to be h = 146 ± 15 pc, while from a sample of older objects (luminosities lower than 5000 L _⊙) it is h = 568 ± 42 pc. We have produced a list of 147 nebulae in which there are only the line-of-sight velocities for 55 nebulae, only the proper motions for 25 nebulae, and both line-of-sight velocities and proper motions for 67 nebulae. Based on this kinematic sample, we have estimated the Galactic rotation parameters and the residual velocity dispersions of protoplanetary nebulae as a function of their age. We have established that there is a good correlation between the kinematic properties of nebulae and their separation in luminosity proposed by Vickers. Most of the nebulae are shown to be involved in the Galactic rotation, with the circular rotation velocity at the Solar Distance being V _0 = 227 ± 23 km s^−1. The following principal semiaxes of the residual velocity dispersion ellipsoid have been found: (σ_1, σ_2, σ_3) = (47, 41, 29) km s^−1 from a sample of young protoplanetary nebulae (with luminosities higher than 5000 L _⊙), (σ_1, σ_2, σ_3) = (50, 38, 28) km s^−1 from a sample of older protoplanetary nebulae (with luminosities of 4000 L _⊙ or 3500 L _⊙), and (σ_1, σ_2, σ_3) = (91, 49, 36) km s^−1 from a sample of halo nebulae (with luminosities of 1700 L _⊙).
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Determination of the galactic rotation curve from OB stars
Astronomy Letters, 2015Co-Authors: V. V. Bobylev, A. T. BajkovaAbstract:We consider three samples of O- and B-type stars from the Solar neighborhood 0.6–4 kpc for which we have taken the Distances, line-of-sight velocities, and proper motions from published sources. The first sample contains 120 massive spectroscopic binaries. O stars with spectroscopic Distances from Patriarchi et al. constitute the second sample. The third sample consists of 168 OB3 stars whose Distances have been determined from interstellar calcium lines. The angular velocity of Galactic rotation at the Solar Distance Ω_0, its two derivatives Ω_0 ^′ and Ω_0 ^″, and the peculiar velocity components of the Sun ( U , V , W )_⊙ are shown to be well determined from all three samples of stars. They are determined with the smallest errors from the sample of spectroscopic binary stars and the sample of stars with the calcium Distance scale. The fine structure of the velocity field associated with the influence of the Galactic spiral density wave clearly manifests itself in the radial velocities of spectroscopic binary stars and in the sample of stars with the calcium Distance scale.
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Determination of the Solar Galactocentric Distance from the Kinematics of Masers
Open Astronomy, 2015Co-Authors: A. T. Bajkova, V. V. BobylevAbstract:We have determined the Galactic rotation parameters and the Solar Galactocentric Distance $R_0$ by simultaneously solving Bottlinger's kinematic equations using data on masers with known line-of-sight velocities and highly accurate trigonometric parallaxes and proper motions measured by VLBI. Our sample includes 93 masers spanning the range of Galactocentric Distances R from 3 to 15 kpc. The solutions found are \Omega_0 = 29.7+/-0.5 km s^{-1} kpc^{-1}, \Omega'_0 = -4.20+/-0.11 km s^{-1} kpc^{-2}, \Omega"_0 =0.730+/-0.029 km s^{-1} kpc^{-3}, and R_0=8.03+/-0.12 kpc. In this case, the linear rotation velocity at the Solar Distance R_0 is V_0=238+/-6 km s^{-1}.
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Determination of galactic rotation parameters and the Solar galactocentric Distance R _0 from 73 masers
Astronomy Letters, 2014Co-Authors: V. V. Bobylev, A. T. BajkovaAbstract:We have determined the Galactic rotation parameters and the Solar Galactocentric Distance R _0 by simultaneously solving Bottlinger’s kinematic equations using data on masers with known line-of-sight velocities and highly accurate trigonometric parallaxes and proper motions measured by VLBI. Our sample includes 73 masers spanning the range of Galactocentric Distances from 3 to 14 kpc. The solutions found are Ω_0 = 28.86 ± 0.45 km s^−1 kpc^−1, Ω′_0 = −3.96 ± 0.09 km s^−1 kpc^−2, Ω″_0 = 0.790 ± 0.027 km s^−1 kpc^−3, and R _0 = 8.3 ± 0.2 kpc. In this case, the linear rotation velocity at the Solar Distance R _0 is V = 241 ± 7 km s^−1. Note that we have obtained the R _0 estimate, which is of greatest interest, from masers for the first time; it is in good agreement with the most recent estimates and even surpasses them in accuracy.
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Galactic kinematics from OB3 stars with Distances determined from interstellar Ca II lines
Astronomy Letters, 2011Co-Authors: V. V. Bobylev, A. T. BajkovaAbstract:Based on data for 102 OB3 stars with known proper motions and radial velocities, we have tested the Distances derived by Megier et al. from interstellar Ca II spectral lines. The internal reconciliation of the Distance scales using the first derivative of the angular velocity of Galactic rotation Ω′_0 and the external reconciliation with Humphreys’s Distance scale for OB associations refined by Mel’nik and Dambis show that the initial Distances should be reduced by ≈20%. Given this correction, the heliocentric Distances of these stars lie within the range 0.6–2.6 kpc. A kinematic analysis of these stars at a fixed Galactocentric Distance of the Sun, R _0 = 8 kpc, has allowed the following parameters to be determined: (1) the Solar peculiar velocity components ( u _⊙, v _⊙, ω _⊙) = (8.9, 10.3, 6.8) ± (0.6, 1.0, 0.4) km s^−1; (2) the Galactic rotation parameters Ω_0 = −31.5 ± 0.9 km s^−1 kpc^−1, Ω′_0 = +4.49 ± 0.12 km s^−1 kpc^−2, Ω″_0 = −1.05 ± 0.38 km s^−1 kpc^−3 (the corresponding Oort constants are A = 17.9 ± 0.5 km s^−1 kpc^−1, B = −13.6 ± 1.0 km s^−1 kpc^−1 and the circular rotation velocity of the Solar neighborhood is | V _0| = 252 ± 14 km s^−1); (3) the spiral density wave parameters, namely: the perturbation amplitudes for the radial and azimuthal velocity components, respectively, f _ R = −12.5±1.1 km s^−1 and f _ ϑ = 2.0 ± 1.6 km s^−1; the pitch angle for the two-armed spiral pattern i = −5.3° ± 0.3°, with the wavelength of the spiral density wave at the Solar Distance being λ = 2.3 ± 0.2 kpc; the Sun’s phase in the spiral wave x _⊙ = −91° ± 4°.
V. V. Bobylev - One of the best experts on this subject based on the ideXlab platform.
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Vertical distribution and kinematics of protoplanetary nebulae in the galaxy
Astronomy Letters, 2017Co-Authors: V. V. Bobylev, A. T. BajkovaAbstract:The catalogue of protoplanetary nebulae by Vickers et al. has been supplemented with the line-of-sight velocities and proper motions of their central stars from the literature. Based on an exponential density distribution, we have estimated the vertical scale height from objects with an age less than 3 Gyr belonging to the Galactic thin disk (luminosities higher than 5000 L _⊙) to be h = 146 ± 15 pc, while from a sample of older objects (luminosities lower than 5000 L _⊙) it is h = 568 ± 42 pc. We have produced a list of 147 nebulae in which there are only the line-of-sight velocities for 55 nebulae, only the proper motions for 25 nebulae, and both line-of-sight velocities and proper motions for 67 nebulae. Based on this kinematic sample, we have estimated the Galactic rotation parameters and the residual velocity dispersions of protoplanetary nebulae as a function of their age. We have established that there is a good correlation between the kinematic properties of nebulae and their separation in luminosity proposed by Vickers. Most of the nebulae are shown to be involved in the Galactic rotation, with the circular rotation velocity at the Solar Distance being V _0 = 227 ± 23 km s^−1. The following principal semiaxes of the residual velocity dispersion ellipsoid have been found: (σ_1, σ_2, σ_3) = (47, 41, 29) km s^−1 from a sample of young protoplanetary nebulae (with luminosities higher than 5000 L _⊙), (σ_1, σ_2, σ_3) = (50, 38, 28) km s^−1 from a sample of older protoplanetary nebulae (with luminosities of 4000 L _⊙ or 3500 L _⊙), and (σ_1, σ_2, σ_3) = (91, 49, 36) km s^−1 from a sample of halo nebulae (with luminosities of 1700 L _⊙).
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The Galaxy Kinematics from the Cepheids with the Proper Motions from the GAIA DR1 Catalog
arXiv: Astrophysics of Galaxies, 2016Co-Authors: V. V. BobylevAbstract:The sample of classic Cepheids with known Distances and line-of-sight velocities is supplemented by the proper motions from the Gaia DR1 catalog. From spatial velocities of 260 stars the components of the peculiar Solar velocity: (U,V,W)_\odot=(7.90,11.73,7.39)+/-(0.65,0.77,0.62) km/s, parameters of the Galactic rotation curve: \Omega_0 =28.840+/-.33 km/s/kpc, \Omega'_0=-4.05+/-0.10 km/s/kpc^2, \Omega''_0=0.805+/-0.067 km/s/kpc^3 are obtained. For the adopted Galactocentric Solar Distance R_0=8 kpc the linear circular velocity of the Local Standard of Rest is found as V_0=231+/-6 km/s.
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Determination of the galactic rotation curve from OB stars
Astronomy Letters, 2015Co-Authors: V. V. Bobylev, A. T. BajkovaAbstract:We consider three samples of O- and B-type stars from the Solar neighborhood 0.6–4 kpc for which we have taken the Distances, line-of-sight velocities, and proper motions from published sources. The first sample contains 120 massive spectroscopic binaries. O stars with spectroscopic Distances from Patriarchi et al. constitute the second sample. The third sample consists of 168 OB3 stars whose Distances have been determined from interstellar calcium lines. The angular velocity of Galactic rotation at the Solar Distance Ω_0, its two derivatives Ω_0 ^′ and Ω_0 ^″, and the peculiar velocity components of the Sun ( U , V , W )_⊙ are shown to be well determined from all three samples of stars. They are determined with the smallest errors from the sample of spectroscopic binary stars and the sample of stars with the calcium Distance scale. The fine structure of the velocity field associated with the influence of the Galactic spiral density wave clearly manifests itself in the radial velocities of spectroscopic binary stars and in the sample of stars with the calcium Distance scale.
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Determination of the Solar Galactocentric Distance from the Kinematics of Masers
Open Astronomy, 2015Co-Authors: A. T. Bajkova, V. V. BobylevAbstract:We have determined the Galactic rotation parameters and the Solar Galactocentric Distance $R_0$ by simultaneously solving Bottlinger's kinematic equations using data on masers with known line-of-sight velocities and highly accurate trigonometric parallaxes and proper motions measured by VLBI. Our sample includes 93 masers spanning the range of Galactocentric Distances R from 3 to 15 kpc. The solutions found are \Omega_0 = 29.7+/-0.5 km s^{-1} kpc^{-1}, \Omega'_0 = -4.20+/-0.11 km s^{-1} kpc^{-2}, \Omega"_0 =0.730+/-0.029 km s^{-1} kpc^{-3}, and R_0=8.03+/-0.12 kpc. In this case, the linear rotation velocity at the Solar Distance R_0 is V_0=238+/-6 km s^{-1}.
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Determination of galactic rotation parameters and the Solar galactocentric Distance R _0 from 73 masers
Astronomy Letters, 2014Co-Authors: V. V. Bobylev, A. T. BajkovaAbstract:We have determined the Galactic rotation parameters and the Solar Galactocentric Distance R _0 by simultaneously solving Bottlinger’s kinematic equations using data on masers with known line-of-sight velocities and highly accurate trigonometric parallaxes and proper motions measured by VLBI. Our sample includes 73 masers spanning the range of Galactocentric Distances from 3 to 14 kpc. The solutions found are Ω_0 = 28.86 ± 0.45 km s^−1 kpc^−1, Ω′_0 = −3.96 ± 0.09 km s^−1 kpc^−2, Ω″_0 = 0.790 ± 0.027 km s^−1 kpc^−3, and R _0 = 8.3 ± 0.2 kpc. In this case, the linear rotation velocity at the Solar Distance R _0 is V = 241 ± 7 km s^−1. Note that we have obtained the R _0 estimate, which is of greatest interest, from masers for the first time; it is in good agreement with the most recent estimates and even surpasses them in accuracy.
E. Marsch - One of the best experts on this subject based on the ideXlab platform.
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Global and local expansion of magnetic clouds in the inner heliosphere
Astronomy and Astrophysics, 2009Co-Authors: A. M. Gulisano, Sergio Dasso, Pascal Démoulin, Maria Emilia Ruiz, E. MarschAbstract:Context. Observations of magnetic clouds (MCs) are consistent with the presence of flux ropes detected in the Solar wind (SW) a few days after their expulsion from the Sun as coronal mass ejections (CMEs). Aims. Both the in situ observations of plasma velocity profiles and the increase of their size with Solar Distance show that MCs are typically expanding structures. The aim of this work is to derive the expansion properties of MCs in the inner heliosphere from 0.3 to 1A U. Methods. We analyze MCs observed by the two Helios spacecraft using in situ magnetic field and velocity measurements. We split the sample in two subsets: those MCs with a velocity profile that is significantly perturbed from the expected linear profile and those that are not. From the slope of the in situ measured bulk velocity along the Sun-Earth direction, we compute an expansion speed with respect to the cloud center for each of the analyzed MCs. Results. We analyze how the expansion speed depends on the MC size, the translation velocity, and the heliocentric Distance, finding that all MCs in the subset of non-perturbed MCs expand with almost the same non-dimensional expansion rate (ζ). We find departures from this general rule for ζ only for perturbed MCs, and we interpret the departures as the consequence of a local and strong SW perturbation by SW fast streams, affecting the MC even inside its interior, in addition to the direct interaction region between the SW and the MC. We also compute the dependence of the mean total SW pressure on the Solar Distance and we confirm that the decrease of the total SW pressure with Distance is the main origin of the observed MC expansion rate. We found that ζ was 0.91 ± 0.23 for non-perturbed MCs while ζ was 0.48 ± 0.79 for perturbed MCs, the larger spread in the last ones being due to the influence of the Solar wind local environment conditions on the expansion.
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TWO-FLUID MODEL FOR HEATING OF THE Solar CORONA AND ACCELERATION OF THE Solar WIND BY HIGH-FREQUENCY ALFVÉN WAVES
Solar Physics, 1997Co-Authors: C.-y. Tu, E. MarschAbstract:A model of the Solar corona and wind is developed which includes for the first time the heating and acceleration effects of high-frequency Alfvén waves in the frequency range between 1 Hz and 1 kHz. The waves are assumed to be generated by the small-scale magnetic activity in the chromospheric network. The wave dissipation near the gyro-frequency, which decreases with increasing Solar Distance, leads to strong coronal heating. The resulting heating function is different from other artificial heating functions used in previous model calculations. The associated thermal pressure-gradient force and wave pressure-gradient force together can accelerate the wind to high velocities, such as those observed by Helios and Ulysses. Classical Coulomb heat conduction is also considered and turns out to play a role in shaping the temperature profiles of the heated protons. The time-dependent two-fluid (electrons and protons) model equations and the time-dependent wave-spectrum equation are numerically integrated versus Solar Distance out to about 0.3 AU. The solutions finally converge and settle on time-stationary profiles which are discussed in detail. The model computations can be made to fit the observed density profiles of a polar coronal hole and polar plume with the sonic point occurring at 2.4 R _⊙ and 3.2 R _⊙, respectively. The Solar wind speeds obtained at 63 R _⊙ are 740 km s^-1 and 540 km s^-1; the mass flux is 2.1 and 2.2 × 10^8 cm^-2 s^-1 (normalized to 1 AU), respectively. The proton temperature increases from a value of 4 × 10^5 K at the lower boundary to 2 × 10^6 K in the corona near 2 R _⊙.
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TWO-FLUID MODEL FOR HEATING OF THE Solar CORONA AND ACCELERATION OF THE Solar WIND BY HIGH-FREQUENCY ALFVÉN WAVES
Solar Physics, 1997Co-Authors: Chuanyi Tu, E. MarschAbstract:A model of the Solar corona and wind is developed which includes for the first time the heating and acceleration effects of high-frequency Alfven waves in the frequency range between 1 Hz and 1 kHz. The waves are assumed to be generated by the small-scale magnetic activity in the chromospheric network. The wave dissipation near the gyro-frequency, which decreases with increasing Solar Distance, leads to strong coronal heating. The resulting heating function is different from other artificial heating functions used in previous model calculations. The associated thermal pressure-gradient force and wave pressure-gradient force together can accelerate the wind to high velocities, such as those observed by Helios and Ulysses. Classical Coulomb heat conduction is also considered and turns out to play a role in shaping the temperature profiles of the heated protons. The time-dependent two-fluid (electrons and protons) model equations and the time-dependent wave-spectrum equation are numerically integrated versus Solar Distance out to about 0.3 AU. The solutions finally converge and settle on time-stationary profiles which are discussed in detail. The model computations can be made to fit the observed density profiles of a polar coronal hole and polar plume with the sonic point occurring at 2.4 R⊙ and 3.2 R⊙, respectively. The Solar wind speeds obtained at 63 R⊙ are 740 km s-1 and 540 km s-1; the mass flux is 2.1 and 2.2 × 108 cm-2 s-1 (normalized to 1 AU), respectively. The proton temperature increases from a value of 4 × 105 K at the lower boundary to 2 × 106 K in the corona near 2 R⊙.
Hans-jörg Fahr - One of the best experts on this subject based on the ideXlab platform.
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On the thermodynamics of MHD wave-heated Solar wind protons
Astronomy and Astrophysics, 2002Co-Authors: Hans-jörg Fahr, I. V. ChasheiAbstract:It has been clearly observed by the NASA deep-space probes that the Solar wind protons do not adiabatically cool as expected towards larger Solar Distances, but appear to be heated by non-collisional energy sources. In some papers these heating sources were directly or indirectly ascribed to pick-up ions incorporated as suprathermal ions into the background Solar wind. Neutral interstellar H-atoms penetrate into the inner heliosphere and at ionization they are converted into pick-up ions. Here we do not consider how the magnetized Solar wind flow incorporates these ions into the plasma bulk when enforcing their co-motion. We simply take the first step of their incorporation for guaranteed, namely the fast redistribution of pick- ups from an initially unstable toroidal to a quasistable bi-spherical distribution. The free energy lost by pick-ups during this redistribution goes into the turbulent MHD waves, and as such cascades down to the proton dissipation scale and finally is absorbed by Solar wind protons. Here we investigate the thermodynamics of Solar wind protons being heated by absorption of this free energy of pick-ups. In addition we also consider as a relevant and competing proton heat source the heating due to absorption of wave energy of convected MHD turbulences, showing that the latter source always dominates inside some critical Solar Distance, whereas the first one dominates in the outer heliospheric regions. We then solve the resulting dierential equation for the Solar wind proton temperature and show in the solutions obtained that a quasipolytropic behaviour of the Solar wind protons with a Distance-dependent polytropic index is found. The expression for the pressure clearly shows the change from an adiabatic to a quasipolytropic behaviour with a decreasing polytropic index at increasing Distances as observed by the VOYAGERs. The quantitative run of the temperature and the polytropic index with Solar Distance thereby is strongly influenced by the interstellar H-atom density. The (pick-up ion)-induced heating also evidently leads to a wind-asymmetric Solar wind temperature distribution with higher temperatures occuring in upwind direction compared to downwind direction.
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Physical reasons and consequences of a three-dimensionally structured heliosphere
Space Science Reviews, 1991Co-Authors: Hans-jörg Fahr, Horst FichtnerAbstract:In this article we have discussed reasons both of Solar and of interstellar origin giving rise to a pronounced three-dimensional structure of the expanding Solar wind and thus of the global configuration of the heliosphere. Our present observational knowledge on these structurings is reviewed, and all attempts to theoretically model these Solar wind structures are critically analysed with respect to their virtues and flaws. It is especially studied here by what mechanisms interstellar imprints on the actual type of Solar wind expansion can be envisaged. With concern to this aspect it hereby appears to be of eminent importance that the Solar system maintains a relative motion with a submagnetosonic velocity of about 23 km/sec with respect to the ambient magnetized interstellar medium corresponding to a magnetosonic Mach number of about 0.5. A heliopause closing the distant heliospheric cavity within a Solar Distance of about 100 AU on the upwind side and opening it into an largely extended tail on the downwind side results as a first consequence from this relative motion. As a second consequence an asymmetric heliospheric shockfront with upwind Distances smaller than downwind Distances by ratios between 1/3 and 2/3 is most likely provoked which gives rise to at least two important upwind-downwind asymmetric processes influencing the supersonic Solar wind expansion downstream from the shock: the anomalous cosmic ray diffusion into the Solar wind, and high energetic jet electrons originating at the shock and moving inwards up to an inner critical point at around 20 AU . As we shall demonstrate both processes are influencing the Solar wind expansion beyond 20 AU , however, more efficiently in the upwind hemisphere as compared to the downwind hemisphere. In the region inside 20 AU other mechanisms are operating to propagate the interstellar imprint on the Solar wind expansion further downstream into the inner heliosphere because here even the original Solar wind electrons, in view of the Solar wind bulk velocities, behave as a subsonic plasma constituent which can modify the Solar wind solutions by means of an appropriate detuning of the circumSolar electric polarisation field. We give quantitative estimates for these effects. What concerns the theory of a Solar wind expansion into a counterflowing ambient interstellar medium, some flaws of the present theoretical attempts are identified impeding that the interstellar influence on the actual Solar wind solutions can become visible. We thus conclude that there is a clear need for three-dimensional and time-dependent Solar wind models with a free outflow geometry taking into account the multisonicity of the Solar wind plasma with different eigenmodes for a perturbation propagation.
C.-y. Tu - One of the best experts on this subject based on the ideXlab platform.
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TWO-FLUID MODEL FOR HEATING OF THE Solar CORONA AND ACCELERATION OF THE Solar WIND BY HIGH-FREQUENCY ALFVÉN WAVES
Solar Physics, 1997Co-Authors: C.-y. Tu, E. MarschAbstract:A model of the Solar corona and wind is developed which includes for the first time the heating and acceleration effects of high-frequency Alfvén waves in the frequency range between 1 Hz and 1 kHz. The waves are assumed to be generated by the small-scale magnetic activity in the chromospheric network. The wave dissipation near the gyro-frequency, which decreases with increasing Solar Distance, leads to strong coronal heating. The resulting heating function is different from other artificial heating functions used in previous model calculations. The associated thermal pressure-gradient force and wave pressure-gradient force together can accelerate the wind to high velocities, such as those observed by Helios and Ulysses. Classical Coulomb heat conduction is also considered and turns out to play a role in shaping the temperature profiles of the heated protons. The time-dependent two-fluid (electrons and protons) model equations and the time-dependent wave-spectrum equation are numerically integrated versus Solar Distance out to about 0.3 AU. The solutions finally converge and settle on time-stationary profiles which are discussed in detail. The model computations can be made to fit the observed density profiles of a polar coronal hole and polar plume with the sonic point occurring at 2.4 R _⊙ and 3.2 R _⊙, respectively. The Solar wind speeds obtained at 63 R _⊙ are 740 km s^-1 and 540 km s^-1; the mass flux is 2.1 and 2.2 × 10^8 cm^-2 s^-1 (normalized to 1 AU), respectively. The proton temperature increases from a value of 4 × 10^5 K at the lower boundary to 2 × 10^6 K in the corona near 2 R _⊙.