The local velocity distribution from a stellar system with two Gaussian components

The superposition of two stellar velocity distribution functions of Gaussian type is applied in order to study the velocity distribution of a stellar sample in the galactic plane. Assuming that the Galaxy is symmetric respect to this plane, the relationships to be fulfilled by the central velocity moments of the total stellar sample are obtained. If the total velocity distribution is consistent with this type of superposition, the partial moments of the subsamples, which are associated with the Gaussian components, can be calculated and, also, the population percentage. Our results show that first component corresponds to young disk population and the second one to intermediate disk population.Paper presented at the 12th European Astronomical Meeting of theIAU on European Astronomers Look to the Future, held 8–11 October, 1990, Davos, Switzerland.     

The asymmetry of the velocity distribution in the rotating ring in U Gem stars

It is shown that the non-keplerian character of the rotation of the ring of gas particles in a close binary system gives too large an amplitude of the radial velocity curve if this amplitude is determined from the positions of the emission lines of the ring.     

Local standard of rest based on Gaia DR2 catalog

The local standard of rest(LSR) provides a reference framework for studies of Galactic kinematics. Determination of the LSR corresponds to the measurement of solar peculiar motion, which is under debate due to the fact that different methods and samples have been used. Adopting the astrometric data and line-of-sight velocities of main sequence stars from Gaia DR2, we present a detailed analytical study of stellar kinematics in the solar neighborhood. Based on an improved version of the Stromberg relation, we obtain a robust estimation of the solar peculiar motion, which is given by(U☉,V☉,W☉)=(8.63 ± 0.64, 4.76 ± 0.49, 7.26 ± 0.36) km s^-1. The corresponding radial scalelength is yielded as Rd ～ 2.5 kpc. The radial and vertical components of solar peculiar motion are basically consistent with the classical values, while the tangential component is a few km s^-1 smaller than most estimates in literature.     

Masses of the local group and of the M81 group estimated from distortions in the local velocity field

Based on high precision measurements of the distances to nearby galaxies with the Hubble telescope, we have determined the radii of the zero velocity spheres for the local group, R₀ = 0.96±0.03Mpc, and for the group of galaxies around M 81/M 82, 0.89±0.05Mpc. These yield estimates of M_T = (1.29±0.14)· 10¹² M_⊙ and (1.03±0.17)· 10¹² M_⊙, respectively, for the total masses of these groups. The R₀ method allows us to determine the mass ratios for the two brightest members in both groups, as well. By varying the position of the center of mass between the two principal members of a group to obtain minimal scatter in the galaxies on a Hubble diagram, we find mass ratios of 0.8:1.0 for our galaxy and Andromeda and 0.54:1.00 for the M82 and M81 galaxies, in good agreement with the observed ratios of the luminosities of these galaxies. __________ Translated from Astrofizika, Vol. 49, No. 1, pp. 5–22 (February 2006).     

On the velocity distribution of the minor planets and stars

The velocity distribution of the minor planets is studied in comparison with that of the stars in the neighbourhood of the Sun. The phase configuration at a given instant has been obtained and the distribution has been studied for different ecliptic sectors. The velocity distribution of the minor planets is similar to that of the stars and differs little form the trivariate normal distribution. The vertex presents a deviation from the direction of the Sun which is positive or negative for different sectors. This vertex deviation is a consequence of the orbit orientations. The relaxation time, deduced from the encounters between the minor planets, is of the order of 10¹⁴ to 10¹⁶ yr.     

The quasar-frame velocity distribution of narrow C iv absorbers

We report on a survey for narrow (full widths at half-minimum <600 km s⁻¹) C  iv absorption lines in a sample of bright quasars at redshifts  1.8 ≤ z < 2.25  in the Sloan Digital Sky Survey. Our main goal is to understand the relationship of narrow C  iv absorbers to quasar outflows and, more generally, to quasar environments. We determine velocity zero-points using the broad Mg  ii emission line, and then measure the absorbers' quasar-frame velocity distribution. We examine the distribution of lines arising in quasar outflows by subtracting model fits to the contributions from cosmologically intervening absorbers and absorption due to the quasar host galaxy or cluster environment. We find that a substantial number (  ≥43 ± 6  per cent) of absorbers with   W ^λ1548₀ > 0.3  Å in the velocity range  +750 ≲ v ≲+ 12 000  km s⁻¹ are intrinsic to the active galactic nucleus outflow. This 'outflow fraction' peaks near   v =+2000  km s⁻¹ with a value of   f _outflow≃ 0.81 ± 0.13  . At velocities below   v ≈+ 2000  km s⁻¹, the incidence of outflowing systems drops, possibly due to geometric effects or to the over-ionization of gas that is nearer the accretion disc. Furthermore, we find that outflow absorbers are on average broader and stronger than cosmologically intervening systems. Finally, we find that ∼14 per cent of the quasars in our sample exhibit narrow, outflowing C  iv absorption with   W ^λ1548₀ > 0.3  Å, slightly larger than that for broad absorption line systems.     

The influence of the angular velocity distribution on the energy transport in the Sun's convection zone

This contribution is a purely exploratory search to investigate the way the distribution of angular velocity inside the Sun's convection zone affects the energy transport. This is related with problems concerning the magnetic activity, whose appearance at the Sun's surface depends on the shape of the isorotation surfaces, and the latitudinal variations in flux. The proposed model is non-linear and axisymmetric.Proceedings of the 14th ESLAB Symposium on Physics of Solar Variations, 16–19 September 1980, Scheveningen, The Netherlands.     

The effect of a non-maxwellian electron velocity distribution on Be-like ion diagnostics in the Sun

Non-Maxwellian collision rates of the Be-sequence ions Ciii and Ov in the solar transition region are derived for quiet Sun and flare conditions using the electron velocity distribution functions of Shoub. The rates are found to be enhanced relative to the Maxwellian values but only at low temperatures where the fractional abundances of these species is very small. This implies that the electron density and temperature diagnostics used by previous authors for the transition region will be unchanged by non-Maxwellian effects. It is noted that such effects will only be important for species that are formed at low temperatures and have large transition energies such as Hei.     

Auroral ion velocity distribution function: The Boltzmann model revisited

The velocity distribution of ion populations is calculated for auroral conditions where strong convection electric fields exist. The Boltzmann equation has been solved for the E and F regions of the ionosphere where plasma is weakly dense, weakly ionized and where the ion-neutral collision frequency is small in regard to the ion cyclotron frequency. The ion distribution function has been expanded in a generalized orthogonal polynomial series about a bi-Maxwellian “temperature” varying weight function. This generalized Grad solution expansion enables us to obtain good approximations for electric field strengths as large as 75 mV m^?1 and 115 mV m^?1 respectively, for both the resonant charge exchange and the polarization collision models. The instability threshold of these distribution functions appears to be higher than the two respective electric field strengths considered above.     

On the angular velocity distribution in a nonhomogeneously rotating star

Some results of the calculations of the angular velocity distribution in the equatorial plane of a nonhomogeneously rotating star, in particular of the Sun, are presented. Hence the hypothesis is advanced of the turbulent viscosity as one of the main factors of the angular momentum transport from a rapidly rotating core through the radiative equilibrium region.     

Dark matter distribution in the Draco dwarf from velocity moments

If the observed relativistic plasma outflows in astrophysical jets are magnetically collimated and a single-component model is adopted, consisting of a wind-type outflow from a central object, then a problem arises with the inefficiency of magnetic self-collimation to collimate a sizeable portion of the mass and magnetic fluxes in the relativistic outflow from the central object. To solve this dilemma, we have applied the mechanism of magnetic collimation to a two-component model consisting of a relativistic wind-type outflow from a central source and a non-relativistic wind from a surrounding disc. By employing a numerical code for a direct numerical solution of the steady-state problem in the zone of super-fast magnetized flow, which allows us to perform a determination of the flow with shocks, it is shown that in this two-component model it is possible to collimate into cylindrical jets all the mass and magnetic fluxes that are available from the central source. In addition, it is shown that the collimation of the plasma in this system is usually accompanied by the formation of oblique shock fronts. The non-relativistic disc-wind not only plays the role of the jet collimator, but it also induces the formation of shocks as it collides with the initially radial inner relativistic wind and also as the outflow is reflected by the system axis. Another interesting feature of this process of magnetic collimation is a sequence of damped oscillations in the width of the jet.     

Angular velocity distribution in convective regions and the origin of solar differential rotation

The observed differential rotation of the Sun is explained as a result of interaction between global rotation and convective eddies.     

The non-linear probability distribution function in models with local primordial non-Gaussianity

We use the spherical evolution approximation to investigate non-linear evolution from the non-Gaussian initial conditions characteristic of the local f _nl model. We provide an analytic formula for the non-linearly evolved probability distribution function (PDF) of the dark matter which shows that the underdense tail of the non-linear PDF in the f _nl model should differ significantly from that for Gaussian initial conditions. Measurements of the underdense tail in numerical simulations may be affected by discreteness effects, and we use a Poisson counting model to describe this effect. Once this has been accounted, our model is in good quantitative agreement with the simulations. In principle, our calculation is an important first step in programs which seek to reconstruct the shape of the initial PDF from observations of large-scale structures in the Lyα forest and the galaxy distribution at later times.