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 An ALMA view of SO and SO2 around oxygen-rich AGB stars

2020 ◽  
Vol 494 (1) ◽  
pp. 1323-1347 ◽  
Author(s):  
T Danilovich ◽  
A M S Richards ◽  
L Decin ◽  
M Van de Sande ◽  
C A Gottlieb
Keyword(s):  
Mass Loss ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
Energy Levels ◽  
High Mass ◽  
High Angular Resolution ◽  
Circumstellar Envelope ◽  
Agb Stars ◽  
Abundance Distribution ◽  
High Mass Loss

ABSTRACT We present and analyse SO and SO2, recently observed with high angular resolution and sensitivity in a spectral line survey with ALMA, for two oxygen-rich AGB stars: the low mass-loss rate R Dor and high mass-loss rate IK Tau. We analyse 8 lines of SO detected towards both stars, 78 lines of SO2 detected towards R Dor, and 52 lines of SO2 detected towards IK Tau. We detect several lines of 34SO, 33SO, and 34SO2 towards both stars, and tentatively S18O towards R Dor, and hence derive isotopic ratios for these species. The spatially resolved observations show us that the two sulphur oxides are co-located towards R Dor and trace out the same wind structures in the circumstellar envelope. Much of the emission is well reproduced with a Gaussian abundance distribution spatially centred on the star. Emission from the higher energy levels of SO and SO2 towards R Dor provides evidence in support of a rotating inner region of gas identified in earlier work. The new observations allow us to refine the abundance distribution of SO in IK Tau derived from prior observations with single antennas, and confirm that the distribution is shell like with the peak in the fractional abundance not centred on the star. The confirmation of different types of SO abundance distributions will help fine-tune chemical models and allows for an additional method to discriminate between low and high mass-loss rates for oxygen-rich AGB stars.

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 Stellar Pulsation: (I) Analysis of Stability of Envelope

1993 ◽  
Vol 134 ◽  
pp. 167-168
Author(s):  
Yu Zhi-Yao
Keyword(s):  
Mass Loss ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
Life Time ◽  
Circumstellar Envelope ◽  
Constant Mass ◽  
Mira Variable ◽  
Stellar Pulsation ◽  
Analysis Of Stability

AbstractThe life-time of the star on AGB is approximately 6 × 104 yr. We divide it into front half and back half of AGB (including to optical Mira variable and OH/IR star) according to their evolution character. The observations show that the star has non-pulsation, but constant mass loss rate (~ 5 × 10−7M⊙ yr−1) on front half of AGB. Its circumstellar envelope is formed. When the star has pulsation on back half of AGB, its mass loss rate is relative with time, and increases gradually. In this time the star is on the stage of optical Mira variable. When the mass loss rate reaches the value of ~ 3 × 10−6M⊙ yr−1, the star evoluted from the stage of optical variable into the stage of radio bright OH/IR star. On the end of AGB the mass loss rate reaches ~10−4M⊙ yr−1. (Band and Habing 1983, Hermen and Habing 1985).

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 ALMA spectral line and imaging survey of a low and a high mass-loss rate AGB star between 335 and 362 GHz

2019 ◽  
Vol 621 ◽  
pp. C2
Author(s):  
L. Decin ◽  
A. M. S. Richards ◽  
T. Danilovich ◽  
W. Homan ◽  
J. A. Nuth
Keyword(s):  
Spectral Line ◽  
Mass Loss ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
High Mass ◽  
High Mass Loss

scholarly journals Wolf-Rayet stars in starbursts: Effects of a change of mass loss rate

1995 ◽  
Vol 163 ◽  
pp. 318-319
Author(s):  
G. Meynet
Keyword(s):  
Mass Loss ◽  
Loss Rate ◽  
Main Sequence ◽  
Mass Loss Rate ◽  
High Mass ◽  
New Models ◽  
Theoretical Predictions ◽  
High Mass Loss ◽  
Low Metallicity ◽  
Loss Rates

We present here starburst models based on the most recent grids of stellar evolutionary tracks obtained by the Geneva group. These new models, computed with enhanced mass loss rates during the main sequence and the Wolf-Rayet WNL phases, very well reproduce the luminosities, surface abundances and statistics of WR stars (Maeder & Meynet 1994). This change of the mass loss rates considerably affects the way the WR stars, born in a starburst's episode, are distributed among the different WR subtypes. We compare the theoretical predictions with recent observations and conclude that: (1) to reproduce the high observed ratios of WNL to O-type stars, a flat IMF seems to be required; and (2) the models which reproduce the best the observed characteristics of WR stars, i.e., those computed with an enhanced mass loss rate, can also account for the observed properties of the WR populations observed in starbursts. Moreover, the possible presence of numerous WC stars found in the low metallicity He2-10 A starburst by Vacca and Conti (1992), can only be accounted for when the high mass loss rate stellar models are used.

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 The nature of stellar winds in the star-disk interaction

2007 ◽  
Vol 3 (S243) ◽  
pp. 299-306 ◽  
Author(s):  
Sean Matt ◽  
Ralph E. Pudritz
Keyword(s):  
Angular Momentum ◽  
Mass Loss ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
T Tauri Stars ◽  
High Mass ◽  
Stellar Winds ◽  
Accretion Process ◽  
T Tauri ◽  
High Mass Loss

AbstractStellar winds may be important for angular momentum transport from accreting T Tauri stars, but the nature of these winds is still not well-constrained. We present some simulation results for hypothetical, hot (∼ 106 K) coronal winds from T Tauri stars, and we calculate the expected emission properties. For the high mass loss rates required to solve the angular momentum problem, we find that the radiative losses will be much greater than can be powered by the accretion process. We place an upper limit to the mass loss rate from accretion-powered coronal winds of ∼ 10−11M yr−1. We conclude that accretion powered stellar winds are still a promising scenario for solving the stellar angular momentum problem, but the winds must be cool (e.g., 104 K) and thus are not driven by thermal pressure.

scholarly journals The 14 μm Band of Carbon Stars

1999 ◽  
Vol 191 ◽  
pp. 267-272 ◽  
Author(s):  
I. Yamamura ◽  
T. de Jong ◽  
L.B.F.M. Waters ◽  
J. Cami ◽  
K. Justtanont
Keyword(s):  
Mass Loss ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
Wavelength Region ◽  
Circumstellar Envelope ◽  
Carbon Stars ◽  
Space Observatory ◽  
Infrared Space Observatory ◽  
Absorption Bands ◽  
Different Temperatures

We have studied the absorption bands around 14 μm in the spectra of 11 carbon stars with mass-loss rates ranging from 10−8 to 10−4 M⊙ yr−1, based on data obtained with the Short Wavelength Spectrometer (SWS) on board the Infrared Space Observatory (ISO). All stars clearly show a C2H2 absorption band peaking at 13.7 μm, while the contribution from HCN molecules is small in this wavelength region. A simple plane-parallel LTE model with two layers at different temperatures is used to derive the C2H2 abundances in the outer photosphere and in the circumstellar envelope. We find that (1) the column density of the hot-layer, placed at about 3R* with a temperature of 1400 K is roughly the same for all stars regardless of the mass-loss rate, and (2) the contribution of cool molecules in the circumstellar envelope increases with the dust mass-loss rate, (3) the abundance of C2H2 in the two layers is about the same, i.e. no obvious depletion of C2H2 molecules seems to occur in the circumstellar envelope.

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.

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