scholarly journals Hydrodynamical models and synthetic spectra of circumstellar dust shells around AGB stars

1997 ◽  
Vol 126 (1) ◽  
pp. 39-65 ◽  
Author(s):  
M. Steffen ◽  
R. Szczerba ◽  
A. Men'shchikov ◽  
D. Schönberner
Keyword(s):  
Circumstellar Dust ◽  
Agb Stars ◽  
Hydrodynamical Models ◽  
Dust Shells ◽  
Synthetic Spectra

scholarly journals Gaia DR2 data and the evolutionary status of eight high-velocity hot post-AGB candidates

2020 ◽  
Vol 72 (6) ◽  
Author(s):  
Mudumba Parthasarathy ◽  
Tadafumi Matsuno ◽  
Wako Aoki
Keyword(s):  
Effective Temperature ◽  
High Velocity ◽  
Circumstellar Dust ◽  
Evolutionary Status ◽  
Agb Stars ◽  
Horizontal Branch ◽  
Dust Shells ◽  
The Past ◽  
Gaia Dr2 ◽  
Branch Star

Abstract From Gaia DR2 data of eight high-velocity hot post-AGB candidates, LS 3593, LSE 148, LS 5107, HD 172324, HD 214539, LS IV −12 111, LS III +52 24, and LS 3099, we found that six of them have accurate parallaxes which made it possible to derive their distances, absolute visual magnitudes (MV) and luminosity (log L/L⊙). All the stars except LS 5107 have an accurate effective temperature (Teff) in the literature. Some of these stars are metal poor, and some of them do not have circumstellar dust shells. In the past, the distances of some stars were estimated to be 6 kpc, which we find to be incorrect. The accurate Gaia DR2 parallaxes show that they are relatively nearby, post-AGB stars. When compared with post-AGB evolutionary tracks we find their initial masses to be in the range 1 M⊙ to 2 M⊙. We find the luminosity of LSE 148 to be significantly lower than that of post-AGB stars, suggesting that this is a post-horizontal-branch star or post-early-AGB star. LS 3593 and LS 5107 are new high-velocity hot post-AGB stars from Gaia DR2.

scholarly journals Ubvri Polarization Measurements of Post AGB Stars

1993 ◽  
Vol 155 ◽  
pp. 353-353
Author(s):  
M. Parthasarathy ◽  
S.K. Jain
Keyword(s):  
Position Angle ◽  
Central Star ◽  
Circumstellar Dust ◽  
Agb Stars ◽  
Polarization Data ◽  
Dust Shells ◽  
Polarization Measurements ◽  
Show Evidence

UBVRI polarization measurements of 25 post AGB stars with circumstellar dust shells (CDSs) were made. Most of them show A, F, G, K supergiant type spectra. IRAS data of these stars show evidence for the presence cool detached circumstellar dust envelopes. Some of these stars also have warm dust shells. Many show significant polarization. The observed polarization in UBVRI is most likely due to scattering of the central star radiation by CDSs. Some of these stars show variation in polarization and position angle. The polarization data suggest that several may have aspherical or bipolar CDSs.

scholarly journals Extended Dust Shells Surrounding AGB Stars Revealed with ISO

1999 ◽  
Vol 191 ◽  
pp. 401-406 ◽  
Author(s):  
H. Izumiura ◽  
O. Hashimoto
Keyword(s):  
High Resolution ◽  
Shell Structure ◽  
Far Infrared ◽  
Circumstellar Dust ◽  
Agb Stars ◽  
Infrared Images ◽  
Dust Shell ◽  
Detector Arrays ◽  
Dust Shells ◽  
Thermal Pulses

We obtained high resolution far-infrared images of the circumstellar dust shells of several AGB carbon stars using ISOPHOT on board the ISO. We used the C-100 and C-200 detector arrays in PHT32 oversampling mode at 90 μm and 160 μm except for U Ant, which was observed at 60 μm and 90 μm. AFGL 3068 is very compact in both bands. R Scl is marginally resolved at 90 μm. U Ant shows a double shell structure, a compact but well resolved shell surrounded by a very extended envelope. Y CVn exhibits a very extended, hollow dust shell. We analyse the structure of the dust shells using a simple dust shell model and discuss the mass-loss behaviors, particularly in conjunction with the thermal pulses on the AGB.

The End: Witnessing the Death of Extreme Carbon Stars

2018 ◽  
Vol 14 (S343) ◽  
pp. 305-308
Author(s):  
G. C. Sloan ◽  
K. E. Kraemer ◽  
I. McDonald ◽  
A. A. Zijlstra
Keyword(s):  
Spherical Symmetry ◽  
Magellanic Clouds ◽  
Asymptotic Giant Branch ◽  
Circumstellar Dust ◽  
Agb Stars ◽  
Carbon Stars ◽  
Dust Shells

AbstractA Last affiliation changed 3 to 4 against MS. Please check and confirm if it is fine. small number of the sample of 184 carbon stars in the Magellanic Clouds show signs that they are in the act of evolving off of the asymptotic giant branch. Most carbon stars grow progressively redder in all infrared colors and develop stronger pulsation amplitudes as their circumstellar dust shells become optically thicker. The reddest sources, however, have unexpectedly low pulsation amplitudes, and some even show blue excesses that could point to deviations from spherical symmetry as they eject the last of their envelopes. Previously, all dusty carbon-rich AGB stars have been labeled “extreme,” but that term should be reserved for the truly extreme carbon stars. These objects may well hold the clues needed to disentangle what actually happens when a star ejects the last of its envelope and evolves off of the AGB.

scholarly journals Circumstellar dust shells of hot post-AGB stars

2004 ◽  
Vol 417 (1) ◽  
pp. 201-215 ◽  
Author(s):  
G. Gauba ◽  
M. Parthasarathy
Keyword(s):  
Circumstellar Dust ◽  
Agb Stars ◽  
Dust Shells

scholarly journals Discovery of Infrared Stars in Globular Clusters in the Magellanic Clouds and Their Light Variations

1998 ◽  
Vol 11 (1) ◽  
pp. 395-395
Author(s):  
S. Nishida ◽  
T. Tanabé ◽  
S. Matsumoto ◽  
T. Onaka ◽  
Y. Nakada ◽  
...  
Keyword(s):  
Mass Loss ◽  
Globular Clusters ◽  
Main Sequence ◽  
Near Infrared ◽  
Magellanic Clouds ◽  
Infrared Light ◽  
Agb Stars ◽  
Dust Shells ◽  
Infrared Stars ◽  
Infrared Survey

A systematic near-infrared survey was made for globular clusters in the Magellanic Clouds. Two infrared stars were discovered in NGC419 (SMC) and NGC1783 (LMC). NGC419 and NGC1783 are well-studied rich globular clusters whose turn-off masses and ages are estimated MTO ~ 2.0 Mʘ and т ~1.2 Gyr for NGC419, and MT0 ~ 2.0 Mʘ and т ʘ 0.9 Gyr for NGC1783, respectively. The periods of the infrared light variations were determined to be 540 dfor NGC419IR1 and to be 480 d for NGC1783IR1, respectively. Comparison of the measurements with the period—if magnitude relation for carbon Miras in the LMC by Groenewegen and Whitelock(1996) revealed that the Kmagnitudes of the infrared stars were fainter by about 0.3 — 0.8 magnitude than those predicted by the P — K relation. This deviation can be explained if the infrared stars are surrounded by thick dust shells and are obscured even in the K band. The positions of NGC419IR1and NGC1783IR1 on the P — K diagram suggest that AGB stars with the main sequence masses of about 2 Mʘ start their heavy mass-loss when P ʘ 500 d.

scholarly journals Long Baseline Interferometric Observations of Circumstellar Dust Shells at 11 Microns

1994 ◽  
Vol 158 ◽  
pp. 383-386
Author(s):  
W.C. Danchi ◽  
L. Greenhill ◽  
M. Bester ◽  
C.G. Degiacomi ◽  
C.H. Townes ◽  
...  
Keyword(s):  
Spatial Distribution ◽  
Radiative Transfer ◽  
Circumstellar Dust ◽  
Dust Formation ◽  
Late Type ◽  
Dust Shells ◽  
Long Baseline ◽  
Higher Temperature ◽  
Single Baseline ◽  
Radiative Transfer Modeling

The spatial distribution of dust around a sample of well-known late-type stars has been studied with the Infrared Spatial Interferometer (ISI) located at Mt. Wilson. Currently operating with a single baseline as a heterodyne interferometer at 11.15 μm, the ISI has obtained visibility curves of these stars. Radiative transfer modeling of the visibility curves has yielded estimates of the inner radii of the dust shells, the optical depth at 11 μm, and the temperature of the dust at the inner radii. For stars in which the dust is resolved, estimates of the stellar diameter and temperature can also be made. Broadly speaking two classes of stars have been found. One class has inner radii of their dust shells very close to the photospheres of the stars themselves (3–5 stellar radii) and at a higher temperature (~ 1200 K) than previously measured. This class includes VY CMa, NML Tau, IRC +10216, and o Ceti. For the latter two the visibility curves change with the luminosity phase of the star and new dust appears to form at still smaller radii during minimum luminosity. The second class of stars has dust shells with substantially larger inner radii and very little dust close to the stars, and includes α Ori, α Sco, α Her, R Leo, and χ Cyg. This indicates sporadic production of dust and no dust formation within the last several decades.

scholarly journals Dust formation in oxygen-rich circumstellar shells around long–period variables

1999 ◽  
Vol 191 ◽  
pp. 233-238 ◽  
Author(s):  
Kyung Sook Jeong ◽  
Jan Martin Winters ◽  
Erwin Sedlmayr
Keyword(s):  
Variable Star ◽  
Chemical Species ◽  
Circumstellar Dust ◽  
Agb Stars ◽  
Fluid Element ◽  
Dust Grains ◽  
Promising Candidate ◽  
Long Period ◽  
Period Variable ◽  
Circumstellar Shells

We present the first steps of our work aimed at a consistent time-dependent modeling of oxygen–rich circumstellar dust shells (CDS) around pulsating AGB stars. The nature of the most likely nucleation seeds is investigated for this situation and we find that TiO2 is a most promising candidate to serve as the primary condensate, forming already at temperatures well above 1 000 K. These nuclei evolve to macroscopic dust grains by heterogeneous growth processes involving several chemical species. We investigate the varying chemical composition of the resulting dust grains as they evolve as a function of time in a fluid element moving through the CDS of an oxygen–rich long-period variable star (LPV).

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