scholarly journals Improving the parallaxes of OH bearing Miras

2007 ◽  
Vol 3 (S242) ◽  
pp. 342-343
Author(s):  
W. H. T. Vlemmings ◽  
H. J. van Langevelde
Keyword(s):  
Physical Properties ◽  
Mass Loss ◽  
Solar Minimum ◽  
Asymptotic Giant Branch ◽  
High Mass ◽  
Agb Stars ◽  
Long Baseline ◽  
Mira Variables ◽  
High Mass Loss ◽  
Very Long Baseline Array

AbstractWe have carried out observations with the Very Long Baseline Array (VLBA) to measure the parallaxes of Mira variables and are able to improve the distance estimates significantly for a fraction of our sample (U Her, S CrB and RR Aql). This is predominantly because we have enhanced our technique by making use of nearby, in-beam calibrators. Additionally, the observing conditions have improved during the current solar minimum. The distances of these stars are of fundamental importance for studying the physical properties of Asymptotic Giant Branch (AGB) stars with high mass loss.

Millimetre Observations of Evolved Stars

1996 ◽  
Vol 13 (2) ◽  
pp. 185-186
Author(s):  
Jessica M. Chapman
Keyword(s):  
Mass Loss ◽  
Stellar Atmosphere ◽  
Asymptotic Giant Branch ◽  
High Mass ◽  
Circumstellar Envelope ◽  
Agb Stars ◽  
Circumstellar Envelopes ◽  
Evolved Stars ◽  
High Mass Loss ◽  
Transfer Momentum

Radio emission at centimetre and millimetre wavelengths provides a powerful tool for studying the circumstellar envelopes of evolved stars. These include stars on the asymptotic giant branch (AGB), post-AGB stars and a small number of massive M-type supergiant stars. The AGB stars and M-type supergiants are characterised by extremely high mass-loss rates. The mass loss in such an evolved star is driven by radiation pressure acting on grains which form in the outer stellar atmosphere. The grains are accelerated outwards and transfer momentum to the gas through grain–gas collisions. The outflowing dust and gas thus form an expanding circumstellar envelope through which matter flows from the star to the interstellar medium, at a typical velocity of 15 km s−1. For a recent review of circumstellar mass loss see Chapman, Habing & Killeen (1995).

scholarly journals Binary post-AGB stars

1997 ◽  
Vol 180 ◽  
pp. 313-318 ◽  
Author(s):  
L.B.F.M. Waters ◽  
C. Waelkens ◽  
H. Van Winckel
Keyword(s):  
Mass Loss ◽  
Central Star ◽  
Asymptotic Giant Branch ◽  
High Mass ◽  
Agb Stars ◽  
Chemical Abundances ◽  
Intermediate Mass Stars ◽  
High Mass Loss ◽  
Complicating Factors ◽  
Circumstellar Environment

Low and intermediate mass stars leave the Asymptotic Giant Branch (AGB) when the mass in their H-rich envelope is less than about 0.01 M⊙, and the high mass loss drops several orders of magnitude. The central star rapidly evolves to the left part of the HR diagram along a track of constant luminosity (e.g. Schönberner 1983). In principle the evolution of the central star to higher Teff and the expansion and cooling of the AGB remnant are easy to calculate. In practice several complicating factors arise which make it much more difficult to predict the morphology and properties of post-AGB stars, such as binarity, post-AGB mass loss and aspherical AGB mass loss. Binarity of post-AGB stars affects the morphology of the circumstellar environment, and it affects evolutionary timescales and surface chemical abundances of the components in the system. This review discusses some properties of binary post-AGB stars.

scholarly journals ISOCAM and DENIS Survey of 0.5 square degrees in the Bar of the LMC. Detection of the whole TP-AGB Star Population

1999 ◽  
Vol 191 ◽  
pp. 561-566
Author(s):  
C. Loup ◽  
E. Josselin ◽  
M.-R. Cioni ◽  
H.J. Habing ◽  
J.A.D.L. Blommaert ◽  
...  
Keyword(s):  
Mass Loss ◽  
High Mass ◽  
Evolutionary Models ◽  
Agb Stars ◽  
Complete Sample ◽  
High Mass Loss ◽  
Low Mass ◽  
The One ◽  
Good Agreement ◽  
Loss Rates

We surveyed 0.5 square degrees in the Bar of the LMC with ISOCAM at 4.5 and 12 μm, and with DENIS in the I, J, and Ks bands. Our goal was to build a complete sample of Thermally-Pulsing AGB stars. Here we present the first analysis of 0.14 square degrees. In total we find about 300 TP-AGB stars. Among these TP-AGB stars, 9% are obscured AGB stars (high mass-loss rates); 9 of them were detected by IRAS, and only 1 was previously identified. Their luminosities range from 2 500 to 14 000 L⊙, with a distribution very similar to the one of optical TP-AGB stars (i.e. those with low mass-loss rates). Such a luminosity distribution, as well as the percentage of obscured stars among TP-AGB stars, is in very good agreement with the evolutionary models of Vassiliadis & Wood (1993) if most of the TP-AGB stars that we find have initial masses smaller than 1.5 to 2 M⊙.

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 First detection of X-ray line emission from Type IIn supernova 1978K with XMM-Newton’s RGS

2020 ◽  
Vol 72 (2) ◽  
Author(s):  
Yuki Chiba ◽  
Satoru Katsuda ◽  
Takashi Yoshida ◽  
Koh Takahashi ◽  
Hideyuki Umeda
Keyword(s):  
Mass Loss ◽  
Surface Composition ◽  
Massive Stars ◽  
Line Emission ◽  
Asymptotic Giant Branch ◽  
High Mass ◽  
Expansion Velocity ◽  
X Ray ◽  
Elemental Abundances ◽  
High Mass Loss

Abstract We report on robust measurements of elemental abundances of the Type IIn supernova SN 1978K, based on the high-resolution X-ray spectrum obtained with the Reflection Grating Spectrometer (RGS) onboard XMM-Newton. The RGS clearly resolves a number of emission lines, including N Ly$\alpha$, O Ly$\alpha$, O Ly$\beta$, Fe xvii, Fe xviii, Ne He$\alpha$, and Ne Ly$\alpha$ for the first time from SN 1978K. The X-ray spectrum can be represented by an absorbed, two-temperature thermal emission model, with temperatures of $kT \sim 0.6$ keV and 2.7 keV. The elemental abundances are obtained to be N $=$$2.36_{{-0.80}}^{{+0.88}}$, O $=$$0.20 \pm {0.05}$, Ne $=$$0.47 \pm {0.12}$, Fe $=$$0.15_{{-0.02}}^{{+0.01}}$ times the solar values. The low metal abundances except for N show that the X-ray emitting plasma originates from the circumstellar medium blown by the progenitor star. The abundances of N and O are far from the CNO-equilibrium abundances expected for the surface composition of a luminous blue variable, and resemble the H-rich envelope of less massive stars with masses of 10–25$\, M_{\odot }$. Together with other peculiar properties of SN 1978K, i.e., a low expansion velocity of 500–1000 km s$^{-1}$ and SN IIn-like optical spectra, we propose that SN 1978K is a result of either an electron-capture SN from a super asymptotic giant branch star, or a weak Fe core-collapse explosion of a relatively low-mass ($\sim \! \! 10\, M_{\odot }$) or high-mass ($\sim$20–25$\, M_{\odot }$) red supergiant star. However, these scenarios cannot naturally explain the high mass-loss rate of the order of $\dot{M} \sim 10^{-3}\, M_{\odot }\:{\rm yr^{-1}}$ over $\gtrsim$1000 yr before the explosion, which is inferred by this work as well as many other earlier studies. Further theoretical studies are required to explain the high mass-loss rates at the final evolutionary stages of massive stars.

scholarly journals High-mass-loss AGB Stars in the South Galactic Cap

1994 ◽  
Vol 267 (3) ◽  
pp. 711-742 ◽  
Author(s):  
P. Whitelock ◽  
J. Menzies ◽  
M. Feast ◽  
F. Marang ◽  
B. Carter ◽  
...  
Keyword(s):  
Mass Loss ◽  
High Mass ◽  
Agb Stars ◽  
The South ◽  
High Mass Loss

Discovery of a complex spiral-shell structure around the oxygen-rich AGB star GX Monocerotis

2020 ◽  
Vol 636 ◽  
pp. A123 ◽  
Author(s):  
S. K. Randall ◽  
A. Trejo ◽  
E. M. L. Humphreys ◽  
H. Kim ◽  
M. Wittkowski ◽  
...  
Keyword(s):  
Mass Loss ◽  
Mass Loss Rate ◽  
Close Binary System ◽  
Asymptotic Giant Branch ◽  
High Mass ◽  
Close Binary ◽  
Chemical Compositions ◽  
Circumstellar Envelopes ◽  
Wide Range ◽  
High Mass Loss

The circumstellar envelopes of asymptotic giant branch (AGB) stars exhibit a wide range of morphologies and chemical compositions that can be exploited to unravel their mass-loss history as well as binary status. Here, we present ALMA Band 6 observations centred upon the oxygen-rich, high mass-loss rate AGB star GX Mon. The resulting CO (2–1) map reveals an intricate, complex circumstellar spiral-arc structure consistent with hydrodynamical models for an AGB experiencing mass loss in a highly eccentric, close binary system with an orbital period of around 140 years. Several other transitions (including SiO, SiS, SO2, and CS) are detected in the data, however only the SO (5–4) map shows a similar – although much weaker – distribution as imaged for the CO.

scholarly journals Formation of crystalline silicate around oxygen–rich AGB stars

1999 ◽  
Vol 191 ◽  
pp. 239-244 ◽  
Author(s):  
Takashi Kozasa ◽  
Hisato Sogawa
Keyword(s):  
Mass Loss ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
Emission Feature ◽  
High Mass ◽  
Agb Stars ◽  
Dust Grains ◽  
High Mass Loss ◽  
Calculation Results ◽  
History Of

Crystallization of silicate has been investigated within the framework of dust formation in steady state gas outflows around oxygen–rich AGB stars, where silicates are locked not only into homogeneous silicate grains but also into the mantles of heterogeneous grains. Based on the thermal history of dust grains after their formation, the crystallization calculation results in no crystalline silicate for the mass loss rate Ṁ ≤ 2 × 10−5M⊙ yr−1. Only silicate in the mantles of heterogeneous grains can be crystallized for Ṁ ≥ 3 × 10−5M⊙ yr−1, while homogeneous silicate grains remain amorphous. The mass fraction of crystalline silicate increases with increasing Ṁ. The radiation transfer calculations confirm the appearance of an emission feature around 33.5 μm, taking olivine as a representative of crystalline silicates. On the other hand, the 10μm feature appears in absorption, being dominated by homogeneous silicate grains. These trends are consistent with the observations. Thus the crystalline silicate is a diagnostics of high mass loss rate at the late stage of AGB stellar evolution, reflecting the formation process of dust grains.

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