scholarly journals Twodimensional Axialsymmetrical Hydrodynamical Simulations of PN-Evolution

1993 ◽  
Vol 155 ◽  
pp. 373-373
Author(s):  
J. Zweigle ◽  
M. Bremer ◽  
M. Grewing
Keyword(s):  
Numerical Method ◽  
Central Star ◽  
Density Contrast ◽  
Initial Model ◽  
Cylindrical Coordinates ◽  
Model Parameter ◽  
Thick Disks ◽  
Red Giant ◽  
Hydrodynamical Simulations ◽  
Key Parameter

In order to investigate the early evolution of planetary nebulae (PNe) we solved numerically the hydrodynamical equations in cylindrical coordinates (r, z) assuming azimutal symmetry. The numerical method used is described in detail by Mair et al. (1988). Our simulations model the interaction of a fast, tenuous, spherical symmetrical central star wind with a slow, dense, aspherical Red Giant Envelope (RGE) expelled from the progenitor star. For the aspherical RGE with a polar/equatorial density contrast we used the initial model given by Mellema et al. (1991) in cylindrical coordinates. We have investigated the influence of each initial model parameter upon the evolution of PNe. Thereby we confirm that the polar/equatorial density contrast in the RGE and the thickness of the RGE-disk play an important role for the morphology of PNe. In agreement with the results from Mellema et al. (1991). The polar/equatorial density contrast in the RGE influences the ratio of the distances of the bright inner rim to the central star in z- and r-direction. This ratio increases with decreasing polar/equatorial density contrast. We find the thickness of the RGE-disk to be a key parameter for getting an elliptical or a butterfly PN: thin RGE-disks produce the first type of nebulae, thick disks the latter. We thank G. Mair, E. Müller and W. Hillebrandt for making available to us a copy of the SADIE code.

scholarly journals V471 Tauri and SuWt 2: The Exotic Descendants of Triple Systems?

2002 ◽  
Vol 187 ◽  
pp. 239-243 ◽  
Author(s):  
Howard E. Bond ◽  
M. Sean O’Brien ◽  
Edward M. Sion ◽  
Dermott J. Mullan ◽  
Katrina Exter ◽  
...  
Keyword(s):  
Main Sequence ◽  
Central Star ◽  
High Mass ◽  
Eclipsing Binary ◽  
Triple Systems ◽  
Common Envelope ◽  
Short Period ◽  
Efficiency Parameter ◽  
Hydrodynamical Simulations ◽  
Good Agreement

AbstractV471 Tauri is a short-period eclipsing binary, and a member of the Hyades. It is composed of a hot DA white dwarf (WD) and a cool main-sequence dK2 companion. HST radial velocities of the WD, in combination with the ground-based spectroscopic orbit of the K star, yield dynamical masses of MWD = 0.84 and MdK = 0.93 M⊙. During the UV observations we serendipitously detected coronal mass ejections from the K star, passing in front of the WD and appearing as sudden, transient metallic absorption. Eclipse timings show that the active dK star is 18% larger than a main-sequence star of the same mass, an apparent consequence of its extensive starspot coverage. The high Teff and high mass of the WD are paradoxical: the WD is the most massive in the Hyades, but also the youngest. A plausible scenario is that the progenitor system was a triple, with a close inner pair that merged after several × 108 yr to produce a single blue straggler. When this star evolved to the AGB phase, it underwent a common-envelope interaction with a distant dK companion, which spiraled down to its present separation and ejected the envelope. The common-envelope efficiency parameter, αCE, was of order 0.3–1.0, in good agreement with recent hydrodynamical simulations.SuWt 2 is a southern-hemisphere planetary nebula (PN) with an unusual ring-shaped morphology. The central star is an eclipsing binary with a period of 4.9 days. Surprisingly, the binary is composed of two main-sequence A-type stars with similar masses of ~ 2.5 M⊙. We discuss scenarios involving a third companion which ejected and ionizes the PN.WeBo 1 is a northern PN with a ring morphology remarkably similar to that of SuWt 2. Although we hoped that its central star would shed light on the nature of SuWt 2, it has proven instead to be a late-type barium star!

scholarly journals High Resolution CO Observations of the Bipolar Nebula CRL2688

1987 ◽  
Vol 115 ◽  
pp. 400-402
Author(s):  
R. Kawabe ◽  
T. Kasuga ◽  
M. Ishiguro ◽  
K-I. Morita ◽  
N. Ukita ◽  
...  
Keyword(s):  
High Resolution ◽  
Mass Loss ◽  
Planetary Nebulae ◽  
Optical Emission ◽  
Central Star ◽  
Reflection Nebula ◽  
Red Giant ◽  
Molecular Envelope ◽  
Rapid Mass ◽  
Co Observations

CRL2688 is suggested to be one of the proto-planetary nebulae which are probably at a stage in which the central star is evolving from the red giant phase with rapid mass loss (Zuckerman 1978). The bipolar shape in both the optical and H2emission indicates that a dense toroid of dust and gas obscures the star and surrounds the optical emission. The toroid is probably responsible for channelling the mass loss to the polar directions (Neyet al.1975, Morris 1981, Beckwithet al.1984). We present the results of mapping observations of CO (J = 1-0) emission from the expanding molecular envelope (Zuckermanet al.1976, Loet al.1976, Knappet al.1982, Thronsonet al.1983) of the bipolar reflection nebula CRL2688 using the Nobeyama 45-m telescope with a 1.5″ resolution at a 7″.5 observing spacing.

scholarly journals Molecular Abundances in the Envelopes Around Evolved Stars

1994 ◽  
Vol 146 ◽  
pp. 113-133
Author(s):  
Hans Olofsson
Keyword(s):  
Mass Loss ◽  
Carbon Star ◽  
Central Star ◽  
Asymptotic Giant Branch ◽  
Circumstellar Envelope ◽  
Intense Mass ◽  
Red Giant ◽  
Ultimate Fate ◽  
Molecular Abundances ◽  
Loss Rates

Red giant stars on the asymptotic giant branch (AGB), AGB-stars, lose copious amounts of matter in a slow stellar wind (Olofsson 1993). Mass loss rates in excess of 10-4M⊙yr-1have been measured. The primary observational consequence of this mass loss is the formation of an expanding envelope of gas and dust, a circumstellar envelope (CSE), that surrounds the star. This is a truly extended atmosphere that continues thousands of stellar radii away from the star. At the highest mass loss rates (which probably occur at the end of the AGB evolution) the CSE becomes so opaque that the photosphere is hidden and essentially all information about the object stems from the circumstellar emission. At some point on the AGB a star may change from being O-rich (i.e., the abundance of O is higher than that of C) to becoming C-rich (i.e., a carbon star where the abundance of C is higher than that of O) as a result of nuclear-processed material being dredged up to the surface. The chemical composition of the CSE will follow that of the central star, although with some time delay so that there may be some rare cases of O-rich CSEs around carbon stars. The mass loss decreases and changes its nature as the star leaves the AGB and starts its post-AGB evolution. Eventually the star becomes hot enough to ionize the inner part of the AGB-CSE and a planetary nebula (PN) is formed. The ultimate fate of the star is a long life as a slowly cooling white dwarf. The CSE will gradually disperse and its metal-enriched matter will mix with the interstellar medium, and thereby it contributes to the chemical evolution of a galaxy. The intense mass loss makes it possible for stars as massive as 8 M⊙, i.e., the bulk of all stars in a galaxy, to follow this evolutionary sequence. Similar CSEs are also found around supergiants.

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 Model Planetaries with rapidly evolving central stars: A case for FG Sge

1997 ◽  
Vol 180 ◽  
pp. 391-391
Author(s):  
K. Kifonidis ◽  
D. Schönberner
Keyword(s):  
White Dwarfs ◽  
Central Star ◽  
Frequency Of Occurrence ◽  
Helium Burning ◽  
Temporary Growth ◽  
Red Giant ◽  
Born Again ◽  
Thermal Pulses ◽  
Central Stars

Ever since the pioneering work of Schönberner (1979, A&A, 79, 108) and Iben (1984, ApJ, 277, 333) who showed that the evolution of post-AGB remnants might be affected by late thermal pulses of the helium-burning shell, resulting in a temporary growth of these objects to red giant dimensions, many attempts were made to explain a number of puzzling objects, among them the well-known variable central star FG Sge as well as the R CrB and PG 1159 stars, by this so-called “born-again AGB” scenario (Iben et al. 1983, ApJ, 264, 605; Iben & MacDonald 1995, in: White Dwarfs, Springer, p. 48). However, it is still not clear if the frequency of occurrence of such events is high enough as to be consistent with the number of born-again candidates. This is due to the very short evolutionary timescales during the pulse and the character of the post-pulse evolution which resembles the first post-AGB phase and makes it difficult for an observer to distinguish such objects from “normal” central stars.

scholarly journals The Multiple Shell PN NGC 2438: Shell Modeling and the Influence of Different Central Star Models

2003 ◽  
Vol 209 ◽  
pp. 511-512
Author(s):  
Birgit Armsdorfer ◽  
Stefan Kimeswenger ◽  
Thomas Rauch
Keyword(s):  
Density Profile ◽  
Planetary Nebulae ◽  
Central Star ◽  
Blackbody Model ◽  
Star Models ◽  
Excitation Profile ◽  
Hydrodynamical Simulations ◽  
Central Stars

Modeling the shells of multiple shell planetary nebulae using different model spectra for hot central stars, we found that a blackbody model leads to wrong nebular parameters. We model the density profile of the outer shells, varying the results of hydrodynamical simulations. This leads to a spatial excitation profile which reproduces well the observations.

scholarly journals A Speculation into the Origin of Neutral Globules in Planetary Nebulae: Could the Helix’s Comets Really be Comets?

1995 ◽  
Vol 12 (2) ◽  
pp. 170-173
Author(s):  
Grant Gussie
Keyword(s):  
Solar System ◽  
Planetary Nebula ◽  
Planetary Nebulae ◽  
Central Star ◽  
Oort Cloud ◽  
Asymptotic Giant Branch ◽  
Neutral Gas ◽  
Red Giant ◽  
The Masses

AbstractA novel explanation for the origin of the cometary globules within NGC 7293 (the ‘Helix’ planetary nebula) is examined, namely that these globules originate as massive cometary bodies at large astrocentric radii. The masses of such hypothetical cometary bodies would have to be several orders of magnitude larger than those of any such bodies observed in our solar system in order to supply the observed mass of neutral gas. It is, however, shown that comets at ‘outer Oort cloud’ distances are likely to survive past the red giant and asymptotic giant branch evolutionary phases of the central star, allowing them to survive until the formation of the planetary nebula. Some observational tests of this hypothesis are proposed.

scholarly journals Infrared interferometric imaging of the compact dust disk around the AGB star HR3126 with the bipolar Toby Jug Nebula

2020 ◽  
Vol 643 ◽  
pp. A175
Author(s):  
K. Ohnaka ◽  
D. Schertl ◽  
K.-H. Hofmann ◽  
G. Weigelt
Keyword(s):  
Gravity Data ◽  
Spectral Energy Distribution ◽  
Central Star ◽  
Asymptotic Giant Branch ◽  
Binary Interaction ◽  
Spectral Energy ◽  
Interferometric Imaging ◽  
Long Baseline ◽  
Dust Disk ◽  
Red Giant

Aims. The asymptotic giant branch (AGB) star HR3126, associated with the arcminute-scale bipolar Toby Jug Nebula, provides a rare opportunity to study the emergence of bipolar structures at the end of the AGB phase. Our goal is to image the central region of HR3126 with high spatial resolution. Methods. We carried out long-baseline interferometric observations with AMBER and GRAVITY (2–2.45 μm) at the Very Large Telescope Interferometer with spectral resolutions of 1500 and 4500, speckle interferometric observations with VLT/NACO (2.24 μm), and imaging with SPHERE-ZIMPOL (0.55 μm) and VISIR (7.9–19.5 μm). Results. The images reconstructed in the continuum at 2.1–2.29 μm from the AMBER+GRAVITY data reveal the central star surrounded by an elliptical ring-like structure with a semimajor and semiminor axis of 5.3 and 3.5 mas, respectively. The ring is interpreted as the inner rim of an equatorial dust disk viewed from an inclination angle of ~50°, and its axis is approximately aligned with the arcminute-scale bipolar nebula. The disk is surprisingly compact, with an inner radius of a mere 3.5 R⋆ (2 au). Our 2-D radiative transfer modeling shows that an optically thick flared disk with silicate grains as large as ~4 μm can simultaneously reproduce the observed continuum images and the spectral energy distribution. The images reconstructed in the CO first overtone bands reveal elongated extended emission around the central star, suggesting the oblateness of the star’s atmosphere or the presence of a CO gas disk inside the dust cavity. The object is unresolved with SPHERE-ZIMPOL, NACO, and VISIR. Conclusions. If the disk formed together with the bipolar nebula, the grain growth from sub-micron to a few microns should have taken place over the nebula’s dynamical age of ~3900 yrs. The non-detection of a companion in the reconstructed images implies that either its 2.2 μm brightness is more than ~30 times lower than that of the red giant or it might have been shredded due to binary interaction.

scholarly journals Solar p-mode damping rates: Insight from a 3D hydrodynamical simulation

2019 ◽  
Vol 625 ◽  
pp. A20 ◽  
Author(s):  
K. Belkacem ◽  
F. Kupka ◽  
R. Samadi ◽  
H. Grimm-Strele
Keyword(s):  
Normal Modes ◽  
Turbulent Convection ◽  
Time Duration ◽  
Definitive Answer ◽  
Physical Mechanisms ◽  
Relative Contribution ◽  
Hydrodynamical Simulation ◽  
Red Giant ◽  
Hydrodynamical Simulations ◽  
Mixing Length Theory

Space-borne missions such as CoRoT and Kepler have provided a rich harvest of high-quality photometric data for solar-like pulsators. It is now possible to measure damping rates for hundreds of main-sequence and thousands of red-giant stars with an unprecedented precision. However, among the seismic parameters, mode damping rates remain poorly understood and thus barely used for inferring the physical properties of stars. Previous approaches to model mode damping rates were based on mixing-length theory or a Reynolds-stress approach to model turbulent convection. While they can be used to grasp the main physics of the problem, such approaches are of little help to provide quantitative estimates as well as a definitive answer on the relative contribution of each physical mechanism. Indeed, due to the high complexity of the turbulent flow and its interplay with the oscillations, those theories rely on many free parameters which inhibits an in-depth understanding of the problem. Our aim is thus to assess the ability of 3D hydrodynamical simulations to infer the physical mechanisms responsible for damping of solar-like oscillations. To this end, a solar high-spatial resolution and long-duration hydrodynamical 3D simulation computed with the ANTARES code allows probing the coupling between turbulent convection and the normal modes of the simulated box. Indeed, normal modes of the simulation experience realistic driving and damping in the super-adiabatic layers of the simulation. Therefore, investigating the properties of the normal modes in the simulation provides a unique insight into the mode physics. We demonstrate that such an approach provides constraints on the solar damping rates and is able to disentangle the relative contribution related to the perturbation (by the oscillation) of the turbulent pressure, the gas pressure, the radiative flux, and the convective flux contributions. Finally, we conclude that using the normal modes of a 3D numerical simulation is possible and is potentially able to unveil the respective role of the different physical mechanisms responsible for mode damping provided the time-duration of the simulation is long enough.

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