scholarly journals Radiation driven winds from CV accretion disks

1997 ◽  
Vol 163 ◽  
pp. 782-782 ◽  
Author(s):  
Daniel Proga ◽  
Janet E. Drew ◽  
James M. Stone
Keyword(s):  
Mass Loss ◽  
Radiation Field ◽  
Surface Brightness ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
Cataclysmic Variables ◽  
Central Star ◽  
Disk Structure ◽  
Two Parameters ◽  
Initial Results

AbstractWe present some initial results of our numerical, 2D hydrodynamical models of line driven flows from the accretion disk in cataclysmic variables. We assume the disk radiation pressure pushes out the isothermal material from a flat, geometrically thin, Keplerian disk.We calculate the disk radiation field using the surface brightness of a standard “α disk” (Shakura & Sunyaev 1973). We do not include a bright boundary layer in the calculations. We approximate the total radiative line acceleration, adopting the formalism due to Castor, Abbott, & Klein (1975). We use our generalized 2D version of their force multiplier. The multiplier is still described by two parameters representing the number of lines and the ratio of optically thin to optically thick lines. The main modification of the original CAK force multiplier is in the depth parameter, which is now a function of the gradients of two velocity components instead of the single velocity gradient as in the ID case.We investigate how the disk structure and mass loss rate depend on the disk and central star luminosity, and boundary conditions such as the disk density.We find that transonic flows from disks do not relax toward steady states. However, their time averaged properties become constant after some time. Our models show that most of mass loss originates from close to the central star – a few stellar radii. Models without a central star radiation field produce flows more vertical than models in which one is present. However, other global, time averaged properties of flows such as the total wind mass, the wind mass loss rate, and velocity are similar. The ratio between the wind mass loss and disk accretion rate increases rapidly with the accrection rate.

scholarly journals Chemical content of the circumstellar envelope of the oxygen-rich AGB star R Doradus

2018 ◽  
Vol 609 ◽  
pp. A63 ◽  
Author(s):  
M. Van de Sande ◽  
L. Decin ◽  
R. Lombaert ◽  
T. Khouri ◽  
A. de Koter ◽  
...  
Keyword(s):  
Mass Loss ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
Central Star ◽  
High Mass ◽  
Circumstellar Envelope ◽  
Gaussian Profile ◽  
Macro Scale ◽  
Abundance Profile ◽  
Envelope Model

Context. The stellar outflows of low- to intermediate-mass stars are characterised by a rich chemistry. Condensation of molecular gas species into dust grains is a key component in a chain of physical processes that leads to the onset of a stellar wind. In order to improve our understanding of the coupling between the micro-scale chemistry and macro-scale dynamics, we need to retrieve the abundance of molecules throughout the outflow. Aims. Our aim is to determine the radial abundance profile of SiO and HCN throughout the stellar outflow of R Dor, an oxygen-rich AGB star with a low mass-loss rate. SiO is thought to play an essential role in the dust-formation process of oxygen-rich AGB stars. The presence of HCN in an oxygen-rich environment is thought to be due to non-equilibrium chemistry in the inner wind. Methods. We analysed molecular transitions of CO, SiO, and HCN measured with the APEX telescope and all three instruments on the Herschel Space Observatory, together with data available in the literature. Photometric data and the infrared spectrum measured by ISO-SWS were used to constrain the dust component of the outflow. Using both continuum and line radiative transfer methods, a physical envelope model of both gas and dust was established. We performed an analysis of the SiO and HCN molecular transitions in order to calculate their abundances. Results. We have obtained an envelope model that describes the dust and the gas in the outflow, and determined the abundance of SiO and HCN throughout the region of the stellar outflow probed by our molecular data. For SiO, we find that the initial abundance lies between 5.5 × 10-5 and 6.0 × 10-5 with respect to H2. The abundance profile is constant up to 60 ± 10 R∗, after which it declines following a Gaussian profile with an e-folding radius of 3.5 ± 0.5 × 1013 cm or 1.4 ± 0.2 R∗. For HCN, we find an initial abundance of 5.0 × 10-7 with respect to H2. The Gaussian profile that describes the decline starts at the stellar surface and has an e-folding radius re of 1.85 ± 0.05 × 1015 cm or 74 ± 2 R∗. Conclusions. We cannot unambiguously identify the mechanism by which SiO is destroyed at 60 ± 10 R∗. The initial abundances found are higher than previously determined (except for one previous study on SiO), which might be due to the inclusion of higher-J transitions. The difference in abundance for SiO and HCN compared to high mass-loss rate Mira star IK Tau might be due to different pulsation characteristics of the central star and/or a difference in dust condensation physics.

scholarly journals Formation of a planetary nebula by continuous mass loss

1981 ◽  
Vol 59 ◽  
pp. 345-346
Author(s):  
A. Harpaz ◽  
A. Kovetz
Keyword(s):  
Mass Loss ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
Central Star ◽  
Red Giants ◽  
Giant Star ◽  
Continuous Mass ◽  
Red Giant ◽  
Significant Mass Loss ◽  
Significant Mass

The evolution of a 1.2Mʘ star along the asymptotic branch with continuous mass loss is presented, showing that this mass loss leads to the formation of a PN with a typical central star in its center.A former investigation (Harpaz and Kovetz, 1980) has shown that mechanisms for PN creation based on sudden violent processes are not likely to work in the envelope of a red giant star. On the other hand, significant mass loss from red giants was observed as a general phenomenon.We have followed the evolution of a 1.2Mʘ star along the asymptotic branch, including in the evolutionary calculations a mass loss according to Reimers’ empirical formula. It was found that towards the end of this stage, the mass loss rate was about 2.7xl0-6Mʘ/y, which is consistent with the formation of a typical PN within 30,000 years. When the mass content of the hydrogen rich envelope dropped to 1.5x10-3Mʘ, the star began to contract rapidly, forming a typical central star of 0.6Mʘ

scholarly journals Molecule formation in dust-poor irradiated jets

2020 ◽  
Vol 636 ◽  
pp. A60 ◽  
Author(s):  
B. Tabone ◽  
B. Godard ◽  
G. Pineau des Forêts ◽  
S. Cabrit ◽  
E. F. van Dishoeck
Keyword(s):  
Mass Loss ◽  
Gas Phase ◽  
Radiation Field ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
Single Point ◽  
Abundance Ratio ◽  
High Mass ◽  
Visible Radiation ◽  
Molecular Abundances

Context. Recent ALMA observations suggest that the highest velocity part of molecular protostellar jets (≳80 km s−1) are launched from the dust-sublimation regions of the accretion disks (≲0.3 au). However, the formation and survival of molecules in inner protostellar disk winds, in the presence of a harsh far-ultraviolet radiation field and the absence of dust, remains unexplored. Aims. We aim to determine if simple molecules, such as H2, CO, SiO, and H2O, can be synthesized and spared in fast and collimated dust-free disk winds or if a fraction of dust is necessary to explain the observed molecular abundances. Methods. This work is based on a recent version of the Paris-Durham shock code designed to model irradiated environments. Fundamental properties of the dust-free chemistry are investigated from single point models. A laminar 1D disk wind model was then built using a parametric flow geometry. This model includes time-dependent chemistry and the attenuation of the radiation field by gas-phase photoprocesses. The influence of the mass-loss rate of the wind and of the fraction of dust on the synthesis of the molecules and on the attenuation of the radiation field is studied in detail. Results. We show that a small fraction of H2 (≤10−2), which primarily formed through the H− route, can efficiently initiate molecule synthesis, such as CO and SiO above TK ~ 800 K. We also propose new gas-phase formation routes of H2 that can operate in strong visible radiation fields, involving CH+ for instance. The attenuation of the radiation field by atomic species (e.g., C, Si, and S) proceeds through continuum self-shielding. This process ensures the efficient formation of CO, OH, SiO, and H2O through neutral–neutral reactions and the survival of these molecules. Class 0 dust-free winds with high mass-loss rates (Ṁw ≥ 2 × 10−6 M⊙ yr−1) are predicted to be rich in molecules if warm (TK ≥ 800 K). Interestingly, we also predict a steep decrease in the SiO-to-CO abundance ratio with the decline of mass-loss rate, from Class 0 to Class I protostars. The molecular content of disk winds is very sensitive to the presence of dust, and a mass-fraction of surviving dust as small as 10−5 significantly increases the H2O and SiO abundances. Conclusions. Chemistry of high velocity jets is a powerful tool to probe their content in dust and uncover their launching point. Models of internal shocks are required to fully exploit the current (sub)millimeter observations and prepare future JWST observations.

scholarly journals Mass loss from central stars of planetary nebulae

1981 ◽  
Vol 59 ◽  
pp. 45-50
Author(s):  
Mario Perinotto ◽  
Piero Benvenuti ◽  
Carla Cacciari
Keyword(s):  
Mass Loss ◽  
Planetary Nebula ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
Planetary Nebulae ◽  
Central Star ◽  
High Resolution Spectrum ◽  
Preliminary Evaluation ◽  
Associated Mass ◽  
Central Stars

AbstractFrom a high resolution spectrum taken with IUE, the central star of the planetary nebula IC 2149 is found to exibit a wind with edge velocity of 1440 ± 100 km s-1. Our preliminary evaluation of the associated mass loss rate gives 10-8 M0 yr-1. Other planetary nebulae nuclei are studied with low resolution IUE spectra and indications are found of mass loss rates consistent with the above value.

scholarly journals Evolution of Planetary Nebulae: A comparison with Observed Central Stars

1989 ◽  
Vol 131 ◽  
pp. 543-544
Author(s):  
M. Schmidt-Voigt
Keyword(s):  
Mass Loss ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
Planetary Nebulae ◽  
Central Star ◽  
Evolutionary Time ◽  
Line Model ◽  
Highly Nonlinear ◽  
Visual Magnitude ◽  
Central Stars

The relation between nebular excitation E(He II λ4686/Hβ-ratio) and absolute visual magnitude of the central star (CS) is compared with hydrodynamical models of planetary nebulae (PNe) from Schmidt-Voigt and Köppen (Astron. Astrophys., 174, 211 and 223) (see figure below, data from D. Schönberner, Astron. Astrophys., 169, 189). Models marked by drawn lines have a 0.644 M⊙ CS following a Schönberner track, an initially expelled PN of 0.1 M⊙, and different mass loss rates of the precursor star on the AGB, described by the Reimers parameter η;η = 1 corresponds to a mass loss rate of 1.55 × 10−6M⊙ α−1 the dashed line model has a higher initially expelled mass (0.3 M⊙), the dash-dotted line model a CS of 0.6 M⊙ which evolves more slowly. Model numbers refer to the above cited studies. Since MV increases with evolutionary time, the MV axis represents a (highly) nonlinear time axis: for MV < 4 the CS heats up towards its temperature maximum and the PN is optically thin. Differences for high excitation nebulae are most probably due to different helium abundances. When the rate of ionizing photons decreases as the nuclear energy sources extinguish (MV > 4), the excitation may decline, depending on the density in the nebula. For the so called “accreting models” (M > 10−6M⊙ α−1) the mass accretion from the AGB wind determines the density hence nebular excitation. For an AGB mass loss rate M < 10−5M⊙α−1 the numerical results approximately fit an exponential law E= E0exp (-M⊙) with E0 ≊ 1.1 and M⊙ ≊ 6.1 × 10−6M⊙ α−1. From the spread of the observed E(MV = 4) we conclude a mean AGB mass loss rate of 6.+3.3−2.3 10−6M⊙ α−1 within 1σ error bars. Obviously the model 11 reproduces the data best since most of the observed objects are found in the dark shadowed regions of the histogram. This is totally consistent with our previous results (cited above). The colliding-wind models, having no initially PN, behave quite similar as model 11.

scholarly journals AGB mass loss

2011 ◽  
Vol 7 (S283) ◽  
pp. 71-78
Author(s):  
Lee A. Willson ◽  
Qian Wang
Keyword(s):  
Mass Loss ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
Central Star ◽  
Constant Mass ◽  
Single Star ◽  
The Core ◽  
Maximum Mass Loss ◽  
Loss Formula ◽  
Remnant Mass

AbstractMass loss on the AGB removes most of the envelope and leaves a compact remnant to become a white dwarf and perhaps first the central star of a planetary nebula. The envelope mass provides an upper limit on the material available to form the PN, and the terminal mass loss rate plus the small remnant mass left on the core determines how much of that would still be available to form the PN after the star has evolved far enough to the blue. Given a mass loss formula based on observations or models, we can find the deathline where −dMstar/dt = (M/L) dL/dt and can find the contours of constant mass loss rate on a plot of M vs. L. From such plots we can derive the mass available for a PN and the lowest mass single star that can produce a PN of a given mass. However, some details important for PN formation remain uncertain, including the maximum mass loss rate achieved and the envelope mass left when AGB mass loss ceases.

scholarly journals Molecular Radio Line Observations of Mass Loss From Red Giants

1989 ◽  
Vol 106 ◽  
pp. 321-338
Author(s):  
H. Olofsson
Keyword(s):  
Mass Loss ◽  
Planetary Nebula ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
Central Star ◽  
Circumstellar Envelope ◽  
Red Giants ◽  
Radio Line ◽  
Red Giant ◽  
Evolution With Time

AbstractThe number of molecules detected at radio wavelengths in envelopes around red giants stands presently at 36. Among these OH and CO have proven to be the most useful for the study of the physical characteristics of a circumstellar envelope. The mass loss rate of the central star can be relatively accurately estimated and it appears possible to trace its evolution with time. Also fascinating objects in transition from the red giant phase to the planetary nebula phase are becoming observationally accessible.

scholarly journals Winds from Cataclysmic Variables

1997 ◽  
Vol 163 ◽  
pp. 465-474
Author(s):  
J. E. Drew
Keyword(s):  
Boundary Layer ◽  
Mass Loss ◽  
Radiation Pressure ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
Cataclysmic Variables ◽  
Recent Developments ◽  
Orbital Phase ◽  
The Impact

AbstractThe winds associated with high states of non-magnetic (diskaccreting) cataclysmic variables are described and discussed. A quick summary of the basic phenomenology is given, and followed by a presentation of some of the more important recent developments in our understanding. The near-ubiquity of orbital-phase linked variability of the UV resonance lines (generally thought of as mainly wind-produced) is noted and its implications are considered. The impact of the much lower-thanexpected boundary layer luminosity upon mass loss rate determinations is also discussed. Current work on the role of radiation pressure (mediated by line opacity) is placed in context.

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