scholarly journals Modelling the delivery of dust from discs to ionized winds

2021 ◽  
Vol 502 (2) ◽  
pp. 1569-1578
Author(s):  
Richard A Booth ◽  
Cathie J Clarke
Keyword(s):  
Mass Loss ◽  
Gas Flow ◽  
Extreme Ultraviolet ◽  
Mass Loss Rate ◽  
Maximum Size ◽  
Simple Relation ◽  
Ionization Front ◽  
Order Of Magnitude ◽  
Novel Method ◽  
Flow Through

ABSTRACT A necessary first step for dust removal in protoplanetary disc winds is the delivery of dust from the disc to the wind. In the case of ionized winds, the disc and wind are sharply delineated by a narrow ionization front where the gas density and temperature vary by more than an order of magnitude. Using a novel method that is able to model the transport of dust across the ionization front in the presence of disc turbulence, we revisit the problem of dust delivery. Our results show that the delivery of dust to the wind is determined by the vertical gas flow through the disc induced by the mass-loss, rather than turbulent diffusion (unless the turbulence is strong, i.e. α ≳ 0.01). Using these results, we provide a simple relation between the maximum size of particle that can be delivered to the wind and the local mass-loss rate per unit area from the wind. This relation is independent of the physical origin of the wind and predicts typical sizes in the 0.01–$1\, \rm{\mu m}$ range for extreme-ultraviolet- or X-ray-driven winds. These values are a factor of ∼10 smaller than those obtained when considering only whether the wind is able to carry away the grains.

scholarly journals Dust delivery and entrainment in photoevaporative winds

2020 ◽  
Vol 501 (1) ◽  
pp. 1127-1142
Author(s):  
Mark A Hutchison ◽  
Cathie J Clarke
Keyword(s):  
Large Scale ◽  
Gas Flow ◽  
Maximum Size ◽  
Ionization Front ◽  
Be Stars ◽  
Dust Transport ◽  
T Tauri ◽  
Order Of Magnitude ◽  
Extreme Uv ◽  
Good Agreement

ABSTRACT We model the gas and dust dynamics in a turbulent protoplanetary disc undergoing extreme-UV photoevaporation in order to better characterize the dust properties in thermal winds (e.g. size distribution, flux rate, trajectories). Our semi-analytic approach allows us to rapidly calculate these dust properties without resorting to expensive hydrodynamic simulations. We find that photoevaporation creates a vertical gas flow within the disc that assists turbulence in supplying dust to the ionization front. We examine both the delivery of dust to the ionization front and its subsequent entrainment in the overlying wind. We derive a simple analytic criterion for the maximum grain size that can be entrained and show that this is in good agreement with the results of previous simulations where photoevaporation is driven by a range of radiation types. We show that, in contrast to the case for magnetically driven winds, we do not expect large-scale dust transport within the disc to be effected by photoevaporation. We also show that the maximum size of grains that can be entrained in the wind (smax) is around an order of magnitude larger than the maximum size of grains that can be delivered to the front by advection alone ($s_{\mathrm{crit}}\lesssim 1 \,\, \mu {\mathrm{m}}$ for Herbig Ae/Be stars and $\lesssim 0.01 \,\, \mu {\mathrm{m}}$ for T Tauri stars). We further investigate how larger grains, up to a limiting size slimit, can be delivered to the front by turbulent diffusion alone. In all cases, we find smax ≳ slimit so that we expect that any dust that is delivered to the front can be entrained in the wind and that most entrained dust follows trajectories close to that of the gas.

Evaluation of the Effect of Gas Leakage on Operation of an Optical Engine

2010 ◽  
Author(s):  
E. Kapusuz ◽  
B. Ekici
Keyword(s):  
Gas Flow ◽  
Combustion Engine ◽  
Numerical Study ◽  
Mass Loss Rate ◽  
Ic Engine ◽  
Gas Leakage ◽  
Engine Model ◽  
Optical Engine ◽  
Laser Diagnostic ◽  
Flow Through

An experimental and numerical study is carried out to evaluate the significance of gas leakage for a non-lube optically accessible internal combustion engine and to obtain estimation for the gas flow out of the combustion chamber at each engine cycle and its effect on the in-cylinder component states during optical engine’s operation. Attention is paid to blow-by and circumferential flow through the gaps between the piston rings and the liner. Optical engines are typically operated without lubrication to avoid window fouling and generation of fluorescence by oil particles that interfere with laser diagnostic signals, in view of this circumstance significant blow-by is expected in optical engines due to lack of “wet-seal” on the cylinder walls which permits circumferential flow of gases through the piston ring pack region resulting in increased blow-by. Semi analytical model estimating the mass loss rate is incorporated into zero dimensional thermodynamic IC engine model which simulates in-cylinder processes. Predicted results are compared for leaking and non-leaking engine simulations.

scholarly journals Surface brightness fluctuations, tracers of stellar mass-loss?

2009 ◽  
Vol 5 (S262) ◽  
pp. 48-51
Author(s):  
Rosa A. González-Lópezlira ◽  
Gustavo Bruzual-A. ◽  
Stéphane Charlot ◽  
Javier Ballesteros-Paredes ◽  
Laurent Loinard
Keyword(s):  
Mass Loss ◽  
Stellar Population ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
Broad Band ◽  
Global Changes ◽  
Agb Stars ◽  
Near Ir ◽  
Surface Brightness Fluctuations ◽  
Order Of Magnitude

AbstractWe present optical and IR integrated colors and SBF magnitudes, computed from stellar population synthesis models that include emission from the dusty envelopes surrounding mass-loosing TP-AGB stars. We explore the effects of varying the mass-loss rate by one order of magnitude around the fiducial value, modifying accordingly both the stellar parameters and the output spectra of the TP-AGB stars plus their dusty envelopes. We compare these models to optical and near-IR data of single AGB stars and Magellanic star clusters. Neither broad-band colors nor SBF measurements in the optical or the near-IR can discern global changes in the mass-loss rate of a stellar population. However, we predict that mid-IR SBF measurements can pick out such changes, and actually resolve whether a relation between metallicity and mass-loss exists.

scholarly journals On the evolutionary status and instability mechanism of the Luminous Blue Variables (LBV)

1989 ◽  
Vol 113 ◽  
pp. 15-26
Author(s):  
André Maeder
Keyword(s):  
Mass Loss ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
Light Curves ◽  
Evolutionary Status ◽  
Average Mass ◽  
Luminous Blue Variables ◽  
Ir Sources ◽  
Order Of Magnitude ◽  
Lower Luminosity

AbstractVarious evolutionary sequences leading to LBV are examined. The sequence O-Of-LBV-WR-SN is well supported by the models; some LBV with relatively lower luminosity may turn into OH/IR sources. The overall duration of the LBV phase depends mainly on the average mass loss rate; for <Ṁ> = 10−3M⊙y−1, it lasts about 104y.Very massive stars undergo, when they reach logTeff= 3.9, strong departure from hydrostatic equilibrium due to supra-Eddington luminosities at some depth in the outer layers. This results in heavy mass loss, as the growth rate of the instability is very fast. We suggest that the amount of mass ejected in a shell episode is mainly determined by the mass of such a layer that its thermal adjustment timescale is within an order of magnitude of the stellar dynamical timescale. Simulations of B-light curves due to shell ejections by LBV are performed and some sensitive properties are identified.

scholarly journals The Influence of the Ratio of Total to Selective Extinction on the Determination of the Mass Loss Rate of Wolf Rayet Stars from Infrared Excess Measurements

1982 ◽  
Vol 99 ◽  
pp. 197-201
Author(s):  
P.S. The ◽  
K.A. van der Hucht ◽  
M. Arens
Keyword(s):  
Mass Loss ◽  
Loss Rate ◽  
Near Infrared ◽  
Mass Loss Rate ◽  
Infrared Excess ◽  
Photometric Observations ◽  
Order Of Magnitude ◽  
Selective Extinction ◽  
Loss Rates

It is shown that the mass loss rate of the WN7 star HD 93162 decreases with larger values of the ratio of total to selective extinction R. for HD 93162 the mass loss rate will change one order of magnitude, only if ΔR ∼ 2. Mass loss rates are derived for nine other WR stars of which visual, red and near-infrared photometric observations were obtained.

scholarly journals Mass loss and fate of the most massive stars

2011 ◽  
Vol 7 (S279) ◽  
pp. 29-33
Author(s):  
Jorick S. Vink
Keyword(s):  
Mass Loss ◽  
Effective Temperature ◽  
Loss Rate ◽  
Massive Stars ◽  
Mass Loss Rate ◽  
Normal Type ◽  
Novel Method ◽  
Loss Rates

AbstractThe fate of massive stars up to 300M⊙ is highly uncertain. Do these objects produce pair-instability explosions, or normal Type Ic supernovae? In order to address these questions, we need to know their mass-loss rates during their lives. Here we present mass-loss predictions for very massive stars (VMS) in the range of 60-300M⊙. We use a novel method that simultaneously predicts the wind terminal velocities v∞ and mass-loss rate Ṁ as a function of the stellar parameters: (i) luminosity/mass Γ, (ii) metallicity Z, and (iii) effective temperature Teff. Using our results, we evaluate the likely outcomes for the most massive stars.

Buffeting Excitation of Boiler Tube Vibration

1965 ◽  
Vol 7 (4) ◽  
pp. 431-439 ◽  
Author(s):  
P. R. Owen
Keyword(s):  
Nuclear Power ◽  
Gas Flow ◽  
Reynolds Numbers ◽  
Dominant Frequency ◽  
Simple Argument ◽  
Regular Feature ◽  
Power Stations ◽  
Order Of Magnitude ◽  
Flow Through ◽  
Stiffness And Damping

The origin of the vibration generated within an extensive bank of tubes that run transverse to the direction of gas flow through a boiler shell and whose movement is small enough in amplitude to have no perceptible effect on the motion of the gas, is examined on the supposition that, sufficiently deep inside the bank, the flow is essentially turbulent and, except for a general drift through the bank, exhibits no regular feature. Conditions of this kind are thought to be appropriate to certain types of heat exchanger used in nuclear power stations and operating at large Reynolds numbers. The source of vibration, either structural or gaseous, is associated with the randomly fluctuating forces imposed on the tubes by the turbulent eddies, and a simple argument is put forward to account approximately for the length scale of the most energetic of these eddies and consequently the frequency with which they encounter the tubes. It is further argued that the tubes are aerodynamically discriminating in their force response which is thereby narrowed spectrally and confined to the neighbourhood of the frequency corresponding to the energetic eddies. The subsequent structural or acoustic response is even more sharpened spectrally, owing to the small damping inherent in the system. A relation between the dominant frequency of the force fluctuations, the gas velocity and the geometrical arrangement of the tubes, that emerges from the argument, agrees in form with published observations of the sound emission from boilers under resonant conditions. A disposable constant appearing in the relation is also satisfactorily predicted in order of magnitude. The analysis applies to only one possible form of the vibration phenomenon; other forms, aero-elastic and vortex-excited, may appear under suitable conditions dependent upon Reynolds number, structural stiffness and damping.

scholarly journals The dichotomy of atmospheric escape in AU Mic b

2020 ◽  
Vol 498 (1) ◽  
pp. L53-L57
Author(s):  
S Carolan ◽  
A A Vidotto ◽  
P Plavchan ◽  
C Villarreal D’Angelo ◽  
G Hazra
Keyword(s):  
Mass Loss ◽  
Stellar Wind ◽  
Evaporation Rate ◽  
Loss Rate ◽  
Extreme Ultraviolet ◽  
Mass Loss Rate ◽  
Young Star ◽  
Planetary Atmosphere ◽  
The Other ◽  
Atmospheric Escape

ABSTRACT Here, we study the dichotomy of the escaping atmosphere of the newly discovered close-in exoplanet AU Microscopii (AU Mic) b. On one hand, the high extreme-ultraviolet stellar flux is expected to cause a strong atmospheric escape in AU Mic b. On the other hand, the wind of this young star is believed to be very strong, which could reduce or even inhibit the planet’s atmospheric escape. AU Mic is thought to have a wind mass-loss rate that is up to 1000 times larger than the solar wind mass-loss rate ($\dot{\mathrm{ M}}_\odot$). To investigate this dichotomy, we perform 3D hydrodynamics simulations of the stellar wind–planetary atmosphere interactions in the AU Mic system and predict the synthetic Ly α transits of AU Mic b. We systematically vary the stellar wind mass-loss rate from a ‘no wind’ scenario to up to a stellar wind with a mass-loss rate of $1000~\dot{\mathrm{ M}}_\odot$. We find that, as the stellar wind becomes stronger, the planetary evaporation rate decreases from 6.5 × 1010  g s−1 to half this value. With a stronger stellar wind, the atmosphere is forced to occupy a smaller volume, affecting transit signatures. Our predicted Ly α absorption drops from $\sim 20{{\ \rm per\ cent}}$ in the case of ‘no wind’ to barely any Ly α absorption in the extreme stellar wind scenario. Future Ly α transits could therefore place constraints not only on the evaporation rate of AU Mic b, but also on the mass-loss rate of its host star.

Dynamics of windowless vapour containment systems for absorption spectroscopy

1975 ◽  
Vol 344 (1639) ◽  
pp. 563-577 ◽  
Keyword(s):  
Optical Absorption ◽  
Mass Loss ◽  
Cross Sections ◽  
Mass Loss Rate ◽  
Density Measurement ◽  
Simple Relation ◽  
Number Density ◽  
Containment System ◽  
Wide Range ◽  
And Performance

The relations between mass loss-rates and path number-density integrals for certain windowless dynamic vapour containment system geometries are developed for non-turbulent vapour flow. The results are applicable not only to the design and performance prediction of such devices, but to integrated number density measurement. A simple relation is found between the flow regime required to observe optical absorption and the ratio of absorption to gas collisional cross sections. A furnace employing tubular flow impedance elements extending nearly from the vapour source to the ends of the system appears to optimize optical absorption depth with respect to mass loss rate over a wide range of pressures, giving order-ofmagnitude improvements over simple orifice impedances. Containment system designs based on this geometry have been tested at the Bonn synchrotron radiation facility and shown to be practical

scholarly journals The abundance of S- and Si-bearing molecules in O-rich circumstellar envelopes of AGB stars

2020 ◽  
Vol 641 ◽  
pp. A57
Author(s):  
S. Massalkhi ◽  
M. Agúndez ◽  
J. Cernicharo ◽  
L. Velilla-Prieto
Keyword(s):  
Mass Loss ◽  
Mass Loss Rate ◽  
Asymptotic Giant Branch ◽  
Agb Stars ◽  
Circumstellar Envelopes ◽  
Fractional Abundance ◽  
Wide Range ◽  
Order Of Magnitude ◽  
Large Velocity Gradient ◽  
Loss Rates

Aims. We aim to determine the abundances of SiO, CS, SiS, SO, and SO2 in a large sample of oxygen-rich asymptotic giant branch (AGB) envelopes covering a wide range of mass loss rates to investigate the potential role that these molecules could play in the formation of dust in these environments. Methods. We surveyed a sample of 30 oxygen-rich AGB stars in the λ 2 mm band using the IRAM 30m telescope. We performed excitation and radiative transfer calculations based on the large velocity gradient method to model the observed lines of the molecules and to derive their fractional abundances in the observed envelopes. Results. We detected SiO in all 30 targeted envelopes, as well as CS, SiS, SO, and SO2 in 18, 13, 26, and 19 sources, respectively. Remarkably, SiS is not detected in any envelope with a mass loss rate below 10−6 M⊙ yr−1, whereas it is detected in all envelopes with mass loss rates above that threshold. From a comparison with a previous, similar study on C-rich sources, it becomes evident that the fractional abundances of CS and SiS show a marked differentiation between C-rich and O-rich sources, being two orders of magnitude and one order of magnitude more abundant in C-rich sources, respectively, while the fractional abundance of SiO turns out to be insensitive to the C/O ratio. The abundance of SiO in O-rich envelopes behaves similarly to C-rich sources, that is, the denser the envelope the lower its abundance. A similar trend, albeit less clear than for SiO, is observed for SO in O-rich sources. Conclusions. The marked dependence of CS and SiS abundances on the C/O ratio indicates that these two molecules form more efficiently in C- than O-rich envelopes. The decline in the abundance of SiO with increasing envelope density and the tentative one for SO indicate that SiO and possibly SO act as gas-phase precursors of dust in circumstellar envelopes around O-rich AGB stars.

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