scholarly journals Radiation-Pressure Ejection of Planetary Nebulae in Asymptotic-Giant-Branch Stars

1999 ◽  
Vol 190 ◽  
pp. 370-371
Author(s):  
A. V. Sweigart
Keyword(s):  
Radiation Pressure ◽  
Critical Value ◽  
Magellanic Clouds ◽  
Asymptotic Giant Branch ◽  
Asymptotic Giant Branch Stars ◽  
Agb Stars ◽  
Core Mass ◽  
The Core ◽  
Giant Branch Stars ◽  
Eddington Limit

We have investigated the possibility that radiation pressure might trigger planetary nebula (PN) ejection during helium-shell flashes in asymptotic-giant-branch (AGB) stars. We find that the outward flux at the base of the hydrogen envelope during a flash will reach the Eddington limit when the envelope mass Menv falls below a critical value that depends on the core mass MH and composition. These results may help to explain the helium-burning PN nuclei found in the Magellanic Clouds.

Dust Structure Around Asymptotic Giant Branch Stars

2018 ◽  
Vol 14 (S343) ◽  
pp. 525-526 ◽  
Author(s):  
Devendra Raj Upadhyay ◽  
Lochan Khanal ◽  
Priyanka Hamal ◽  
Binil Aryal
Keyword(s):  
Inclination Angle ◽  
Asymptotic Giant Branch ◽  
Color Temperature ◽  
Asymptotic Giant Branch Stars ◽  
Agb Stars ◽  
Physical Conditions ◽  
The Core ◽  
Cavity Structure ◽  
Temperature Ranges ◽  
Giant Branch Stars

AbstractThis paper presents mass, temperature profile, and the variation of Planck’s function in different regions around asymptotic giant branch (AGB) stars. The physics of the interstellar medium (ISM) is extremely complex because the medium is very inhomogeneous and is made of regions with fairly diverse physical conditions. We studied the dust environment such as flux, temperature, mass, and inclination angle of the cavity structure around C-rich asymptotic giant branch stars in 60 μm and 100 μm wavelengths band using Infrared Astronomical Survey. We observed the data of AGB stars named IRAS 01142+6306 and IRAS 04369+4501. Flexible image transport system image was downloaded from Sky View Observatory; we obtained the surrounding flux density using software Aladin v2.5. The average dust color temperature and mass are found to be 25.08 K, 23.20 K and 4.73 × ;1026 kg (0.00024 M⊙), 2.58 × 1028 kg (0.013 M⊙), respectively. The dust color temperature ranges from 18.76 K ± 3.16 K to 33.21K ± K and 22.84 K ± 0.18 K to 24.48 K ± 0.63 K. The isolated cavity like structure around the AGB stars has an extension of 45.67 pc × 17.02 pc and 42.25 pc × 17.76 pc, respectively. The core region is found to be edge-on having an inclination angle of 79.46° and 73.99°, respectively.

scholarly journals Asymptotic Giant Branch Stars: Thermal Pulses, Carbon Production, and Dredge Up; Neutron Sources and s-Process Nucleosynthesis

1991 ◽  
Vol 145 ◽  
pp. 257-274
Author(s):  
Icko Iben
Keyword(s):  
Neutron Source ◽  
Lower Boundary ◽  
Source Model ◽  
Asymptotic Giant Branch ◽  
Asymptotic Giant Branch Stars ◽  
Agb Stars ◽  
Core Mass ◽  
Convective Envelope ◽  
Thermal Pulses ◽  
Giant Branch Stars

A brief review is given of the structure of asymptotic giant branch (AGB) stars and of the characteristics of the thermal pulses which these stars experience. Following a pulse, model AGB stars with a large core mass easily dredge up fresh carbon, which is the main product of incomplete helium burning, and s-process isotopes, which are made as a consequence of the activation of the 22Ne neutron source. Model AGB stars of small core mass activate the 13C neutron source and produce s-process isotopes in nearly the solar system distribution. They also dredge up fresh carbon and s-process isotopes, but only if overshoot or some other form of “extra” mixing beyond the lower boundary of the convective envelope is invoked.

scholarly journals Obscured Asymptotic Giant Branch stars in the Magellanic Clouds

1999 ◽  
Vol 191 ◽  
pp. 567-572 ◽  
Author(s):  
Jacco Th. van Loon
Keyword(s):  
Magellanic Clouds ◽  
Asymptotic Giant Branch ◽  
Asymptotic Giant Branch Stars ◽  
Agb Stars ◽  
Recent Advances ◽  
Giant Branch Stars

We report on some recent advances in the study and understanding of heavily obscured AGB stars in the Magellanic Clouds.

scholarly journals Mass-Losing AGB Stars in the Magellanic Clouds

1993 ◽  
Vol 155 ◽  
pp. 319-319
Author(s):  
Neill Reid
Keyword(s):  
Mass Loss ◽  
Stellar Evolution ◽  
Planetary Nebula ◽  
Luminosity Function ◽  
Magellanic Clouds ◽  
Asymptotic Giant Branch ◽  
Asymptotic Giant Branch Stars ◽  
Agb Stars ◽  
The Future ◽  
Giant Branch Stars

Asymptotic giant branch stars are the immediate precursors to the planetary nebula stage of stellar evolution. It is clear that the latter stages of a stars life on the AGB are accompanied by either continuous or episodic mass-loss, with the final convulsion being the ejection of the envelope (the future planetary shell), the gradual exposure of the bare CO core and the rapid horizontal evolution to the blue in the H-R diagram. Thus, the structure of the planetary nebula luminosity function, particularly at the higher luminosities (although this phase is extremely rapid), is intimately tied to the luminosity function of the AGB.

scholarly journals Parameterising the Third Dredge-up in Asymptotic Giant Branch Stars

2002 ◽  
Vol 19 (4) ◽  
pp. 515-526 ◽  
Author(s):  
A. I. Karakas ◽  
J. C. Lattanzio ◽  
O. R. Pols
Keyword(s):  
Mass Loss ◽  
Asymptotic Giant Branch ◽  
Asymptotic Giant Branch Stars ◽  
Core Mass ◽  
The Third ◽  
The Core ◽  
Intermediate Mass Stars ◽  
Homogeneous Set ◽  
Efficiency Parameter ◽  
Giant Branch Stars

AbstractWe present new evolutionary sequences for low and intermediate mass stars (1−6M⊙) for three different metallicities, Z = 0.02, 0.008, and 0.004. We evolve the models from the pre-main sequence to the thermally-pulsing asymptotic giant branch phase. We have two sequences of models for each mass, one which includes mass loss and one without mass loss. Typically 20 or more pulses have been followed for each model, allowing us to calculate the third dredge-up parameter for each case. Using the results from this large and homogeneous set of models, we present an approximate fit for the core mass at the first thermal pulse, Mc1, as well as for the third dredge-up efficiency parameter, λ, and the core mass at the first dredge-up episode, Mcmin, as a function of metallicity and total mass. We also examine the effect of a reduced envelope mass on the value of λ.

scholarly journals Thermally-pulsing asymptotic giant branch stars in the Magellanic Clouds

2008 ◽  
Vol 4 (S256) ◽  
pp. 385-390
Author(s):  
Paola Marigo ◽  
Léo Girardi ◽  
Alessandro Bressan ◽  
Martin A. T. Groenewegen ◽  
Bernhard Aringer ◽  
...  
Keyword(s):  
Magellanic Clouds ◽  
Asymptotic Giant Branch ◽  
Circumstellar Dust ◽  
Stellar Winds ◽  
Asymptotic Giant Branch Stars ◽  
Stellar Clusters ◽  
Agb Stars ◽  
Wide Range ◽  
Giant Branch Stars ◽  
Theoretical Project

AbstractWe present the latest results of a theoretical project aimed at investigating the properties of thermally-pulsing asymptotic giant branch (TP-AGB) stars in different host systems. For this purpose, we have recently calculated calibrated synthetic TP-AGB tracks — covering a wide range of metallicities (0.0001 ≤ Z ≤ 0.03) up to the complete ejection of the envelope by stellar winds (Marigo & Girardi 2007) — and used them to generate new sets of stellar isochrones (Marigo et al. 2008). The latter are converted to about 25 different photometric systems, including the mid-infrared filters of Spitzer and AKARI as the effect of circumstellar dust from AGB stars is taken into account. First comparisons with AGB data in the MC field and stellar clusters are discussed.

Infrared Studies of the Variability and Mass Loss of Some of the Dustiest Asymptotic Giant Branch Stars in the Magellanic Clouds

2018 ◽  
Vol 14 (S343) ◽  
pp. 498-499
Author(s):  
B. Sargent ◽  
S. Srinivasan ◽  
M. Boyer ◽  
M. Feast ◽  
P. Whitelock ◽  
...  
Keyword(s):  
Large Magellanic Cloud ◽  
Magellanic Cloud ◽  
Magellanic Clouds ◽  
Asymptotic Giant Branch ◽  
Asymptotic Giant Branch Stars ◽  
Agb Stars ◽  
Infrared Studies ◽  
Infrared Wavelengths ◽  
Optical Wavelengths ◽  
Giant Branch Stars

AbstractThe asymptotic giant branch (AGB) stars with the reddest colors have the largest amounts of circumstellar dust. AGB stars vary in their brightness, and studies show that the reddest AGB stars tend to have longer periods than other AGB stars and are more likely to be fundamental mode pulsators than other AGB stars. Such stars are difficult to study, as they are often not detected at optical wavelengths. Therefore, they must be observed at infrared wavelengths. Using the Spitzer Space Telescope, we have observed a sample of very dusty AGB stars in the Large Magellanic Cloud (LMC) and Small Magellanic Cloud (SMC) over Cycles 9 through 12 during the Warm Spitzer mission. For each cycle’s program, we typically observed a set of AGB stars at both 3.6 and 4.5 μm wavelength approximately monthly for most of a year. We present results from our analysis of the data from these programs.

scholarly journals Obscured Asymptotic Giant Branch Stars in the Magellanic Clouds

1999 ◽  
Vol 190 ◽  
pp. 387-388
Author(s):  
Jacco Th. van Loon
Keyword(s):  
Mass Loss ◽  
Magellanic Clouds ◽  
Asymptotic Giant Branch ◽  
Ongoing Study ◽  
Asymptotic Giant Branch Stars ◽  
Agb Stars ◽  
Circumstellar Envelopes ◽  
Giant Branch Stars

I present results from an ongoing study of the evolution and mass loss of AGB stars with optically thick circumstellar envelopes in the Magellanic Clouds.

scholarly journals Luminosity functions for asymptotic giant branch stars

1984 ◽  
Vol 105 ◽  
pp. 175-178 ◽  
Author(s):  
Jay A. Frogel ◽  
V.M. Blanco
Keyword(s):  
Main Sequence ◽  
Magellanic Clouds ◽  
Asymptotic Giant Branch ◽  
Asymptotic Giant Branch Stars ◽  
Agb Stars ◽  
Ideal Situation ◽  
Luminosity Functions ◽  
Ranking Scheme ◽  
Giant Branch Stars

To understand the evolution of carbon and oxygen rich asymptotic giant branch (AGB) stars it is important to observationally establish the relations between parameters such as luminosity, age, and metallicity. The existence of luminous (brighter than the top of the first giant branch) AGB stars in clusters in the Magellanic Clouds (Mould and Aaronson 1979; Frogel, et al. 1980) provides a nearly ideal situation in which these relations can be determined. Although metallicities and main sequence turn-off ages are known for only a fraction of the clusters, the ranking scheme devised by Searle, et al. (1980; SWB) indicates that age and metallicity are closely related to one another.

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