Gas Outflow Velocity Research Articles

Age of Geminids derived from the statistics of meteoroid orbits

ABSTRACT Statistical analysis of samples of the orbits of celestial bodies is complicated by the fact that the Keplerian orbit is a multidimensional object, the coordinate representation of which non-linearly depends on the choice of orbital elements. In this work, using the construction of the Fréchet mean, concepts of mean orbit and dispersion of the orbit family are introduced, consistent with the distance function on the orbit set. The introduced statistical characteristics serve as analogues of sample mean and variance of a one-dimensional random variable. Exact formulas for calculating the elements of mean orbits and dispersion quantities with respect to two metrics on the orbit space are derived. For a large sample of meteoroid orbits from the Geminid stream, numerical simulations of orbit evolution over 20 000 yr in the past were conducted. By analysing the dependency of statistical characteristics on time, estimates for the age of the stream and the gas outflow velocity are obtained under the assumption of the birth of the Geminids due to the rapid destruction of the cometary nucleus. The estimate of the age of the stream lies in the interval from 1200 to 2400 yr, and the speed of gas outflow at perihelion should have been more than 1.2 km s−1.

Coma composition of comet 67P/Churyumov-Gerasimenko from radio-wave spectroscopy

We present the results of a molecular survey of comet 67P/Churyumov-Gerasimenko undertaken with the Institut de RadioAstronomie Millimétrique (IRAM) 30-m radio telescope in November–December 2021, when it had its most favourable apparition in decades. Observations at IRAM 30-m during the 12–16 November period covered 8 GHz bandwidth at 3 mm, 16 GHz at 2 mm, and 60 GHz in the 1 mm window domain. These were completed by snapshots at 1 mm on 12–13 December and a short observation of the H2O line at 557 GHz with the Odin sub-millimetre observatory on 17.0 November 2021, and with 18-cm observations of OH with the Nançay radio telescope. Less sensitive observations obtained at a previous perihelion passage on 18–22 September 2015 with IRAM and 9–12 November 2015 with Odin are also presented. The gas outflow velocity, outgassing pattern, and temperature have been accurately constrained by the observations. They are perfectly consistent with those measured in situ with the Rosetta/MIRO sub-millimetre instrument in 2015. In particular, the asymmetry of the line is well represented by a jet concentrating three-quarters of the outgassing in about π steradians. We derived abundances relative to water for seven molecules and significant upper limits for approximately five others. The retrieved abundances were compared to those measured in situ at the previous perihelion with Rosetta. While those of HCN, CH3OH, and HNCO are comparable, 67P is found to be depleted in H2S and relatively normal in CS (H2S/CS ≈ 3) in strong contradiction with the Rosetta/ROSINA mass spectrometer measurement of the H2S/CS2 (≈100) abundance ratio. While the formaldehyde total abundance found with IRAM 30-m when assuming it to be mostly produced by a distributed source (Haser parent scale length ≈8000 km) is similar to the one derived by Rosetta/ROSINA, we find that the formaldehyde coming from the nucleus is one order of magnitude less abundant than measured in situ by Rosetta/ROSINA.

EXPERIMENTAL RESEARCH OF MIXING NATURAL GAS IMPINGING JETS AND AIR DURING COMBUSTION AT A VERTICAL REFRACTORY SURFACE

In the work determined the conditions for the start of chemical reactions of natural gas and air mixture at combustion on a refractory surface, when a single submerged turbulent impinging jet is fed from a natural gas collector at the angle α to the vertical refractory surface, at the relative distance L/d0 along the geometric axis of the jet. It is determined that combustion starts under the condition when the excess air coefficient in the mixture reaches about λ = 0.93, at which the laminar flame propagation velocity S°L, m/s, for a premixed mixture of methane and air is maximum. The dependence of the height of the flame Lf, m, on the relative dimensionless step of the location of the nozzles s/d0 in the row was obtained during studying the groups of gas nozzles with the supply of natural gas for combustion through them range diameters 1–3.5 mm (which are used at precent time in the construction of slot bottom burners). It was determined that the flame height of slot bottom burner during its operation on natural gas (tested for the pressure of natural gas in the collector from 2 kPa to 18 kPa, respectively, natural gas outflow velocity, WNG from about 60 m/s to 185 m/s) depends slightly on gas pressure, the relative distance L/d0 that the aerated jet of natural gas travels to the refractory surface in the range of 15 ≤ L/d0 ≤ 30 and the Reynolds number, and strongly depends from on the dimensionless step of the nozzles in the row — s/d0. It has been experimentally proven that by adjusting the dimensionless step of the nozzles (holes) s/d0 in the row of the slot bottom burner, it is possible to adjust the height of the flame and thus obtain the flame of the appropriate height for different heights of fireboxes and boilers powers. Bibl. 29, Fig. 3, Tab. 3.

Analysis of CN Coma Morphology Features of Comet 21P/Giacobini–Zinner

We analyze jet features found in the coma of comet 21P/Giacobini–Zinner (21P/GZ) during its 2018 perihelion passage using narrowband CN photometric imaging in order to determine the comet’s rotational period, and we constrain the CN gas outflow velocity and rotational state through the analysis of azimuthally enhanced morphological features. We find that 21P/GZ has a period of either 7.39 ± 0.01 hr or 10.66 ± 0.01 hr. We measure a lower limit to the outflow velocity for the northern jet of 730 ± 30 m s−1 and for the southern jet of 740 ± 30 m s−1. We analyze the morphologies of the jet features and determine that the northern jet possesses a corkscrew pattern, and we utilize that knowledge to determine a rotational pole position at an R.A. of deg and a decl. of deg, with an undetermined sense of rotation.

Molecular composition of comet 46P/Wirtanen from millimetre-wave spectroscopy

We present the results of a molecular survey of comet 46P/Wirtanen undertaken with the IRAM 30-m and NOEMA radio telescopes in December 2018. Observations at IRAM 30-m during the 12–18 December period comprise a 2 mm spectral survey covering 25 GHz and a 1 mm survey covering 62 GHz. The gas outflow velocity and kinetic temperature have been accurately constrained by the observations. We derive abundances of 11 molecules, some being identified remotely for the first time in a Jupiter-family comet, including complex organic molecules such as formamide, ethylene glycol, acetaldehyde, or ethanol. Sensitive upper limits on the abundances of 24 other molecules are obtained. The comet is found to be relatively rich in methanol (3.4% relative to water), but relatively depleted in CO, CS, HNC, HNCO, and HCOOH.

Study on the Bubble Growth and Departure with A Lattice Boltzmann Method

For the growth and departure of bubbles from an orifice, a free energy lattice Boltzmann model is adopted to deal with this complex multiphase flow phenomenon. A virtual layer is set at the boundary of the flow domain to deal with the no-slip boundary condition. Effects of the viscosity, surface tension, gas inertial force and buoyancy on the characteristics of bubbles when they grow and departure from an orifice in quiescent liquid are studied. The releasing period and departure diameter of the bubble are influenced by the residual gas at the orifice, and the interaction between bubbles is taken into consideration. The relations between the releasing period or departure diameter and the gravity acceleration show fair agreements with previous numerical and theoretical results. And the influence of the gas outflow velocity on bubble formation is discussed as well. For the bubbles growing in cross-flow field, effects of the cross-flow speed and the gas outflow velocity on the bubble formation are discussed, which is related to the application in ship resistance reduction. And optimal choice of the ship speed and gas outflow velocity is studied. Cases in this paper also prove that this high density ratio LBM model has its flexibility and effectiveness on multiphase flow simulations.

AERODYNAMICS OF JETS INTERACTING WITH A FLAT SURFACE

In this paper, the development features of a single free jet of hightemperature nitrogen interacting with a flat surface were studied. Calculation of the heat exchange process during heating by the attacking jets is very difficult to implement analytically due to complexity of the gas-dynamic processes occurring both in a single jet and in a system of jets interacting with the metal. The computational difficulties are aggravated by the fact that when interacting with the surface the jet as such disappears. The flat (fan) flow interacts with the surface: form, aerodynamic properties and thermal state of the flow strongly differ from those of the original jet. The studies were conducted on the basis of numerical simulation in the FloEFD software and computing complex for multiphysical simulation based on solution of the equations of gas dynamics and heat transfer. The solved system of equations consisted of Navier-Stokes equations, equations of energy and continuity and was supplemented by k – ε turbulence model. A three-dimensional model was developed for simulation, the necessary properties, initial and boundary conditions were specified. In the study of aerodynamics of a single high-temperature jet interacting with the surface, the main defining values were: nitrogen flow rate from the nozzle U0 , nitrogen temperature T, internal diameter of the nozzle d0 , distance from the nozzle section to the surface h, distance from the critical point (point of intersection of the jet axis with the surface) along the flow radius r. Data on the gas velocity decrease as the jet develops due to the loss of initial energy to engage the motionless surrounding gas in motion, is presented. The studies have shown that increase in the initial velocity of gas outflow brings the area of higher velocities closer to the surface both in the jet itself and in the fan jet. This factor contributes to heat transfer intensification. In addition, high speeds increase the total thickness of the fan flow and reduce the thickness of hydrodynamic boundary layer, which increases with distance from the critical point.

Simulation of three-dimensional bubble formation and interaction using the high-density-ratio lattice Boltzmann method

The growth and departure of bubbles from an orifice and their interactions is a common phenomenon. In this paper, a multiphase flow model based on the lattice Boltzmann method is constructed to study this process, with an improved interface capture method being adopted to deal with the high density ratio between liquid and gas. A virtual layer is added outside the computational domain to handle the boundary condition at the orifice. The processes of bubble formation and interaction are well simulated by the model, and the results agree well with those of theoretical calculations for single-bubble formation and departure diameter and period. Bubble formation is controlled by the inertial force of the gas, buoyancy, surface tension, and the viscous force of the liquid. The inertial force of the gas and buoyancy promote bubble growth and departure, respectively, while the surface tension controls bubble deformation and the viscous force affects the necking process. Increases in both the orifice size and the gas outflow velocity can enlarge the departure diameter of the bubble, but the orifice size plays a more important role here. Both of these two parameters have obvious effects on the departure period. For the interaction of bubbles growing from orifices with the same or different sizes, different coalescence categories are distinguished according to the stage of coalescence, and the characteristics of the coalescence process are considered in terms of their dependence on surface tension, viscous force, and buoyancy. Finally, the departure diameter and departure period of coalesced bubbles are studied under the different coalescence conditions.

Determination of the physical parameters of gas in the neutral atmospheres of comets: The circular aperture method

A new method—the circular aperture method—is proposed for determining the physical parameters of gas in the neutral atmospheres of comets. A check has shown that this method is applicable to calculate the hydrodynamic velocity of gas outflow and the lifetime of molecules in the neutral atmosphere of comet 2009/P1 (Garradd).

Evidence for a Companion to BM Gem, a Silicate Carbon Star

Balmer and Paschen continuum emission, as well as Balmer series lines of P Cygni-type profile from Hγ through H23, are revealed in the violet spectra of BM Gem, a carbon star associated with an oxygen-rich circumstellar shell (silicate carbon star). The blueshifted absorption in the Balmer lines indicates the presence of an outflow, the line-of-sight velocity of which is at least 400 km s−1. The Balmer lines show a significant change in profile over a period of 75 days. We argue that the observed unusual features in BM Gem are strong evidence for the presence of a companion, which should form an accretion disk that gives rise to both an ionized gas region and a high-velocity variable outflow. The estimated luminosity of ~0.2 (0.03-0.6) L☉ for the ionized gas can be maintained by a mass accretion rate for a dwarf companion of ~10−8 M☉ yr−1, while ~10−10 M☉ yr−1 is sufficient for accretion to a white dwarf companion. These accretion rates are feasible for some detached binary configurations on the basis of the Bondi-Hoyle-type accretion process. Therefore, we conclude that the carbon star BM Gem is in a detached binary system with a companion of low mass and low luminosity. However, we are unable to determine whether this companion object is a dwarf or a white dwarf, although the gas outflow velocity of 400 km s−1, as well as the nondetection in the X-ray survey, favor its identity as a dwarf star. The upper limits for binary separation are 210 and 930 AU for a dwarf and a white dwarf, respectively, in the case of circular orbit. We also note that the observed features of BM Gem mimic those of Mira (o Cet), which may suggest actual similarities in their binary configurations and circumstellar structures.

행성상 성운 NGC 6881의 운동학적 특성과 기하학적 구조

행성상성운 NGC 6881은 4극자형태를 이루고 있고 JET이 영상에 나타난다. Lick 천문대에 있는 Hamilton Echelle Spectrograph(HES)을 사용하여 관측한 가시광 영역의 방출선 스펙트럼의 선윤곽을 연구하였다. 우리가 연구하는 HES 분광 자료는 직경이 4초각인 영역의 안쪽에서 관측된 것이다. IRAF와 StarLink/Dipso분석프로그램을 사용하여 HI, HeI, HeII, [OIII], [NII], [ArIII], [SII], [SIII] 등의 강한 선들의 선윤곽을 통해 팽창속도를 얻었다. HI선의 경우 단일 정상을 보이는 반면, He과 다른 금지선들은 두 개의 정상 분포가 겹치는 특성을 보였다. 가스 유출 속도는 중심별의 복사압에 의해 바깥쪽으로 갈수록 가속되는 것으로 분석되었다. 우리는 팽창속도자료를 통해, HST 영상에서 보여진 중심부분의 세 개의 고리는 양극콘(HI 선등에 나타남)과 고리(He, [SIII]선에 특성이 보임)의 복합 구조가 투영된 것으로 결론지었다. The Planetary nebula NGC 6881 displays quadrupole morphology and it also has a jet feature in its image. We investigated the line profiles of the optical region spectral emission lines, using the Hamilton Echelle Spectrograph (HES) at the Lick observatory. The HES data obtained in this study was the radiation coming from the inner region within the diameter of 4 second of arc. Expansion velocity was obtained, based on the strong emission line profiles of e.g. H, Hel, Hell, [OIII], [NII], [ArIII], [SII], and [SIII}, using the IRAF and StarLink/Dipso reduction packages. The HI recombination lines showed one single peak profile, while the He and forbidden strong lines displayed double peaks. The results of this study show that the outflow velocity of gas increases radially outwards due to the central stellar radiation pressure. It was concluded that three central rings appeared in the HST image are the result of a combined structure of bipolar cones (seen in e.g. HI lines) and a ring (seen in He, [SIII] lines) in projection.

Radio OH observations of 9P/Tempel 1 before and after Deep Impact

We observed 18-cm OH emission in Comet 9P/Tempel 1 before and after Deep Impact. Observations using the Arecibo Observatory 305 m telescope took place between 8 April and 9 June, 2005, followed by post-impact observations using the National Radio Astronomy Observatory 100 m Green Bank Telescope 4–12 July, 2005. The resulting spectra were analyzed with a kinematic Monte Carlo model which allows estimation of the OH production rate, neutral gas outflow velocity, and distribution of the out-gassing from the nucleus. We detected typically 24% variability from the overall OH production rate trend in the two months leading up to the impact, and no dramatic increase in OH production in the days post-impact. Generally, the coma is well-described, within uncertainties, by a symmetric model with OH production rates from 1.6 to 7.4 × 10 27 mol s −1 , and mean water outflow velocity of 0.75 ± 0.03 km s −1 . At these low production rates, collisional quenching is expected to occur only within 20,000 km of the nucleus. However, our best-fit average quenching radius is 64,200 ± 22,000 km in April and May.

Radio OH observations of 9P/Tempel 1 before and after Deep Impact

We observed 18-cm OH emission in Comet 9P/Tempel 1 before and after Deep Impact. Observations using the Arecibo Observatory 305 m telescope took place between 8 April and 9 June, 2005, followed by post-impact observations using the National Radio Astronomy Observatory 100 m Green Bank Telescope 4–12 July, 2005. The resulting spectra were analyzed with a kinematic Monte Carlo model which allows estimation of the OH production rate, neutral gas outflow velocity, and distribution of the out-gassing from the nucleus. We detected typically 24% variability from the overall OH production rate trend in the two months leading up to the impact, and no dramatic increase in OH production in the days post-impact. Generally, the coma is well-described, within uncertainties, by a symmetric model with OH production rates from 1.6 to 7.4 × 10 27 mol s −1 , and mean water outflow velocity of 0.75 ± 0.03 km s −1 . At these low production rates, collisional quenching is expected to occur only within 20,000 km of the nucleus. However, our best-fit average quenching radius is 64,200 ± 22,000 km in April and May.

Heterogeneous condensation of presolar titanium carbide core‐graphite mantle spherules

Abstract— We investigate heterogeneous nucleation and growth of graphite on precondensed TiC grains in the gas outflows from carbon‐rich asymptotic giant branch (AGB) stars employing a newly‐derived heterogeneous nucleation rate taking into account of the chemical reactions at condensation. Competition between heterogeneous and homogeneous nucleations and growths of graphite is investigated to reveal the formation conditions of the TiC core‐graphite mantle spherules found in the Murchison meteorite. It is shown that no homogeneous graphite grain condenses whenever TiC condenses prior to graphite in the plausible ranges of the stellar parameters. Heterogeneous condensation of graphite occurs on the surfaces of growing TiC grains, and prevents the TiC cores from reaching the sizes realized if all available Ti atoms were incorporated into TiC grains. The physical conditions at the formation sites of the TiC core‐graphite mantle spherules observed in the Murchison meteorite are expressed by the relation 0.2 < n̈0.1 (M5/ζ)−1/2L41/4 < 0.7, where v0.1 is the gas outflow velocity at the formation site in units of 0.1 km s−1, M5 the mass loss rate in 10−5 M⊙ year−1, L4 the stellar luminosity in 104 L⊙, and M/ζ is the effective mass loss rate taking account of non‐spherical symmetry of the gas outflows. The total gas pressures Pc at the formation sites for the effective mass loss rates M/ζ = 10−5‐10−3 M⊙ year−1 correspond to 0.01 < Pc < 0.9 dyn cm−2, implying that the observed TiC core‐graphite mantle spherules are formed not only at the superwind stage but also at the earlier stage of low mass loss rates. The constraint on the C/O abundance ratio, 1 < ∍ ≲ 1.03, is imposed to reproduce the observed sizes of the TiC cores. The derived upper limit of the C/O ratio is lower than the values estimated from the calculations without taking into account of heterogeneous condensation of graphite, and is close to the lower end of the C/O ratios inferred from the astronomical observations of carbon‐rich AGB stars. Brief discussion is given on other types of graphite spherules.

Hydrodynamics of two-chamber vortex dryers with counter-colliding twisted flows of a gaseous suspension

Results of experimental studies of the hydrodynamics of two-chamber vortex dryers are presented. Empirical relations are obtained for determining the critical velocity of gas outflow and the retentivity of an apparatus as a function of the operating and design parameters and the properties of the disperse material. It is found that the hydraulic resistance of the developed dryers does not depend on the properties of the treated material and is proportional to the square of the gas flow rate. Relations for calculation of the coefficients of hydraulic resistance for apparatuses not loaded and loaded with material are obtained.

Formation Conditions of Presolar TiC Core–Graphite Mantle Spherules in the Murchison Meteorite

Formation of TiC and graphite grains in the gas outflows from carbon-rich asymptotic giant branch (AGB) stars is investigated to reveal the formation conditions of presolar TiC core-graphite mantle spherules extracted from the Murchison meteorite. We employ the nonequilibrium condensation theory involving chemical reactions in nucleation and grain growth to derive the formation conditions not only from the condensation sequence for realizing the core-mantle structure but also from the sizes of observed TiC cores and graphite mantles. The results of calculations show that the sizes of TiC cores constrain the mass-loss rate and the gas outflow velocity v at the formation sites to satisfy the relation 2.5×10−3<v2L½4/5<0.185, where L4 is the stellar luminosity in units of 104 L☉, v is in km s-1, and 5 is in 10−5 M☉ yr−1. The constraint on the condensation sequence limits the C/O abundance ratio to less than 1.26-1.48 for =10−6 to 10−4 M☉ yr−1. The more stringent constraint on and v at the formation sites expressed by 2.5×10−3<v2L½4/5<1.35×10−2 with <1.26-1.48 is imposed by the conditions necessary for reproducing the range of the observed sizes of TiC cores and graphite mantles simultaneously. The derived total gas pressure in the range of 2×10−3<P<0.1 dyn cm−2 and gas outflow velocity in the range 0.015<v<0.4 km s−1 at the formation sites of TiC cores seem to be consistent with the picture of steady state dust-driven winds around carbon-rich AGB stars. The discrepancy between the observed and the predicted size ratios of graphite mantles to TiC cores would be closely related to the detailed formation process of graphite mantles on TiC cores.

Evolution of the outgassing of comet Hale-Bopp (C/1995 O1) from radio observations.

Spectra obtained from ground-based radio telescopes show the progressive release of CO, CH3OH, HCN, H2O (from OH), H2S, CS, H2CO, CH3CN, and HNC as comet Hale-Bopp (C/1995 01) approached the sun from 6.9 to 1.4 astronomical units (AU). The more volatile species were relatively more abundant in the coma far from the sun, but there was no direct correlation between overabundance and volatility. Evidence for H2O sublimation from icy grains was seen beyond 3.5 AU from the sun. The change from a CO-driven coma to an H2O-driven coma occurred at about 3 AU. The gas outflow velocity and temperature increased as Hale-Bopp approached the sun.

The spectral energy distribution and mass-loss history of IRC + 10420

We present a study of the spectral energy distribution of the peculiar hypergiant IRC + 10420. To this end we have collected published photometry of IRC + 10420 and obtained some new data, in order to construct the spectral energy distribution and fit it with a radiative transfer model. In addition high-quality (CO)-C-12 spectra of the rotational J=1-0, 2-1, 3-2 and 4-3 transitions have been obtained to determine the gas outflow velocity and independently estimate the gas mass-loss rate. The main conclusions from this work are that the photometric changes over the last 20 years indicate that the object has increased in temperature by more than 1000 K and that the spectral energy distribution cannot be fitted with a single-shell model without first including a hot component. This hot component is likely to be a circumstellar disc. Finally, we present evidence that IRC + 10420 is nota post-AGE star.

Water clusters in the coma of comet halley and their effect on the gas density, temperature, and velocity

The formation of water clusters of all sizes by water recondensation in an expanding cometary atmosphere is investigated. Several competing algorithms are used, and the present uncertainties concerning the physical properties of the clusters are carefully taken into account. Numerical estimates appropriate to Comet P/Halley at the time of the flyby observations are given. The results strongly suggest that about 15% of the water recondenses into clusters of 100 to 1000 water molecules which disappear beyond a cometocentric distance of about 500 nucleus radii. Surprisingly, these predictions are found to be weakly sensitive to the existing uncertainties concerning the mathematical model of the nucleation process and the physical properties of the water clusters. The most probable observable effect of these large clusters is a strong perturbation of the water radial temperature profile at all altitudes including beyond that of cluster disparition. Recondensation also increases the gas outflow velocity in the inner coma: the present results suggest that the gas velocities derived in situ by the Giotto mass spectrometer could be about 30% below the coma-averaged outflow velocities. This study does not support previously published speculations concerning the detectability of chemical or optical effects associated with the formation of small water clusters, particularly of the dimer (H 2O) 2. It also excludes the detectability of the continuum emissions from the clusters, at any wavelength because of the masking effect of the coma dust. Finally, it indicates that recondensation cannot form a dense halo of macroscopic ice grains: such a halo, if discovered in the future, can only result from surface fragmentation.