scholarly journals Effects of Convective Overshooting, Mass Loss (and Chemical Composition) across the HR Diagram

1986 ◽  
Vol 116 ◽  
pp. 317-338
Author(s):  
C. Chiosi
Keyword(s):  
Mass Loss ◽  
Reaction Rate ◽  
Mass Range ◽  
Asymptotic Giant Branch ◽  
Stellar Structure ◽  
Asymptotic Giant Branch Stars ◽  
The Novel ◽  
Pressure Scale ◽  
Red Giant ◽  
Giant Branch Stars

The far reaching consequences of convective overshooting during the core H and He-burning phases of stars in the mass range 1.3 M⊙ to 100 M⊙ are discussed. In addition to this, the effects of mass loss in luminous stars of all spectral types, and in the red giant and asymptotic giant branch stars are briefly outlined. Furthermore, the effects of the novel 12C(α γ)16O reaction rate are also illustrated. The main purpose of this review resides however in lending convincing support to the idea that convective cores of real stars are greater than commonly supposed in classic models. To this aim, several observational embarrassments that could not be explained by classic models are reanalyzed in the light of the new ones. Since a much better agreement between theory and observations is now possible, we are inclined to conclude that convective overshooting may be of paramount importance in stellar structure theories and that convective cores in real stars ought to be larger by approximately one pressure scale height than predicted by classic models.

scholarly journals Asteroseismology of luminous red giants with Kepler. II. Dependence of mass loss on pulsations and radiation

2020 ◽  
Author(s):  
Jie Yu ◽  
Saskia Hekker ◽  
Timothy R Bedding ◽  
Dennis Stello ◽  
Daniel Huber ◽  
...  
Keyword(s):  
Mass Loss ◽  
Mass Loss Rate ◽  
Asymptotic Giant Branch ◽  
Red Giants ◽  
Asymptotic Giant Branch Stars ◽  
Chemical Enrichment ◽  
Dust Mass ◽  
Red Giant ◽  
The Masses ◽  
Loss Rates

Abstract Mass loss by red giants is an important process to understand the final stages of stellar evolution and the chemical enrichment of the interstellar medium. Mass-loss rates are thought to be controlled by pulsation-enhanced dust-driven outflows. Here we investigate the relationships between mass loss, pulsations, and radiation, using 3213 luminous Kepler red giants and 135000 ASAS–SN semiregulars and Miras. Mass-loss rates are traced by infrared colours using 2MASS and WISE and by observed-to-model WISE fluxes, and are also estimated using dust mass-loss rates from literature assuming a typical gas-to-dust mass ratio of 400. To specify the pulsations, we extract the period and height of the highest peak in the power spectrum of oscillation. Absolute magnitudes are obtained from the 2MASS Ks band and the Gaia DR2 parallaxes. Our results follow. (i) Substantial mass loss sets in at pulsation periods above ∼60 and ∼100 days, corresponding to Asymptotic-Giant-Branch stars at the base of the period-luminosity sequences C′ and C. (ii) The mass-loss rate starts to rapidly increase in semiregulars for which the luminosity is just above the red-giant-branch tip and gradually plateaus to a level similar to that of Miras. (iii) The mass-loss rates in Miras do not depend on luminosity, consistent with pulsation-enhanced dust-driven winds. (iv) The accumulated mass loss on the Red Giant Branch consistent with asteroseismic predictions reduces the masses of red-clump stars by 6.3%, less than the typical uncertainty on their asteroseismic masses. Thus mass loss is currently not a limitation of stellar age estimates for galactic archaeology studies.

scholarly journals EVOLUTION OF THERMALLY PULSING ASYMPTOTIC GIANT BRANCH STARS. V. CONSTRAINING THE MASS LOSS AND LIFETIMES OF INTERMEDIATE-MASS, LOW-METALLICITY AGB STARS

2016 ◽  
Vol 822 (2) ◽  
pp. 73 ◽  
Author(s):  
Philip Rosenfield ◽  
Paola Marigo ◽  
Léo Girardi ◽  
Julianne J. Dalcanton ◽  
Alessandro Bressan ◽  
...  
Keyword(s):  
Mass Loss ◽  
Asymptotic Giant Branch ◽  
Asymptotic Giant Branch Stars ◽  
Agb Stars ◽  
Intermediate Mass ◽  
Low Metallicity ◽  
Giant Branch Stars

scholarly journals EVOLUTION OF THERMALLY PULSING ASYMPTOTIC GIANT BRANCH STARS. IV. CONSTRAINING MASS LOSS AND LIFETIMES OF LOW MASS, LOW METALLICITY AGB STARS

2014 ◽  
Vol 790 (1) ◽  
pp. 22 ◽  
Author(s):  
Philip Rosenfield ◽  
Paola Marigo ◽  
Léo Girardi ◽  
Julianne J. Dalcanton ◽  
Alessandro Bressan ◽  
...  
Keyword(s):  
Mass Loss ◽  
Asymptotic Giant Branch ◽  
Asymptotic Giant Branch Stars ◽  
Agb Stars ◽  
Low Metallicity ◽  
Low Mass ◽  
Giant Branch Stars

scholarly journals Observations of Lithium in red giant stars

2009 ◽  
Vol 5 (S268) ◽  
pp. 301-309
Author(s):  
Verne V. Smith
Keyword(s):  
Stellar Evolution ◽  
Asymptotic Giant Branch ◽  
Red Giants ◽  
Asymptotic Giant Branch Stars ◽  
Multiple Sources ◽  
Lithium Abundance ◽  
Giant Stars ◽  
Red Giant ◽  
First Time ◽  
Giant Branch Stars

AbstractConnections between observations of the lithium abundance in various types of red giants and stellar evolution are discussed here. The emphasis is on three main topics; 1) the depletion of Li as stars ascend the red giant branch for the first time, 2) the synthesis of 7Li in luminous and massive asymptotic giant branch stars via the mechanism of hot-bottom burning, and 3) the possible multiple sources of excess Li abundances found in a tiny fraction of various types of G and K giants.

scholarly journals Evolved massive stars at low metallicity

2020 ◽  
Vol 639 ◽  
pp. A116
Author(s):  
Ming Yang ◽  
Alceste Z. Bonanos ◽  
Bi-Wei Jiang ◽  
Jian Gao ◽  
Panagiotis Gavras ◽  
...  
Keyword(s):  
Mass Loss ◽  
Mass Loss Rate ◽  
Dust Emission ◽  
Evolutionary Model ◽  
Asymptotic Giant Branch ◽  
Asymptotic Giant Branch Stars ◽  
Near Ir ◽  
Low Metallicity ◽  
Bolometric Correction ◽  
Giant Branch Stars

We present the most comprehensive red supergiant (RSG) sample for the Small Magellanic Cloud (SMC) to date, including 1239 RSG candidates. The initial sample was derived based on a source catalog for the SMC with conservative ranking. Additional spectroscopic RSGs were retrieved from the literature, and RSG candidates were selected based on the inspection of Gaia and 2MASS color-magnitude diagrams (CMDs). We estimate that there are in total ∼1800 or more RSGs in the SMC. We purify the sample by studying the infrared CMDs and the variability of the objects, though there is still an ambiguity between asymptotic giant branch stars (AGBs) and RSGs at the red end of our sample. One heavily obscured target was identified based on multiple near-IR and mid-IR (MIR) CMDs. The investigation of color-color diagrams shows that there are fewer RSGs candidates (∼4%) showing PAH emission features compared to the Milky Way and LMC (∼15%). The MIR variability of RSG sample increases with luminosity. We separate the RSG sample into two subsamples (risky and safe), and identify one M5e AGB star in the risky subsample based on simultaneous inspection of variabilities, luminosities, and colors. The degeneracy of mass loss rate (MLR), variability, and luminosity of the RSG sample is discussed, indicating that most of the targets with high variability are also the bright ones with high MLR. Some targets show excessive dust emission, which may be related to previous episodic mass loss events. We also roughly estimate the total gas and dust budget produced by entire RSG population as ∼1.9−1.1+2.4 × 10−6 M⊙ yr−1 in the most conservative case, according to the derived MLR from IRAC1–IRAC4 color. Based on the MIST models, we derive a linear relation between Teff and observed J − KS color with reddening correction for the RSG sample. By using a constant bolometric correction and this relation, the Geneva evolutionary model is compared with our RSG sample, showing a good agreement and a lower initial mass limit of ∼7 M⊙ for the RSG population. Finally, we compare the RSG sample in the SMC and the LMC. Despite the incompleteness of LMC sample in the faint end, the result indicates that the LMC sample always shows redder color (except for the IRAC1–IRAC2 and WISE1–WISE2 colors due to CO absorption) and higher variability than the SMC sample, which is likely due to a positive relation between MLR, variability and the metallicity.

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 Dust Formation in Stellar Photospheres

2000 ◽  
Vol 177 ◽  
pp. 313-324
Author(s):  
Takashi Tsuji
Keyword(s):  
Mass Loss ◽  
Radiation Pressure ◽  
Brown Dwarfs ◽  
Asymptotic Giant Branch ◽  
Dust Formation ◽  
Circumstellar Envelope ◽  
Asymptotic Giant Branch Stars ◽  
Carbon Stars ◽  
Pulsating Stars ◽  
Giant Branch Stars

We examine whether dust forms in the photospheres of carbon-rich stars by referring to the case of red and brown dwarfs for which some observational clues on dust formation are now known. Dust may form in the photospheres of dwarf carbon stars and produce significant effects on both their structure and spectra. In carbon-rich asymptotic giant branch stars, dust probably forms in the photosphere, if not in the circumstellar envelope, and radiation pressure on dust is sufficient to expel the matter directly from the photosphere. This fact may play some role in mass-loss from cool luminous stars in general, including non-pulsating stars for which no successful mechanism of mass-loss was known.

scholarly journals The long secondary periods in semi-regular variables

2004 ◽  
Vol 193 ◽  
pp. 322-326
Author(s):  
P.R. Wood ◽  
A.E. Olivier ◽  
S.D. Kawaler
Keyword(s):  
Radial Velocity ◽  
Large Amplitude ◽  
Small Amplitude ◽  
Light Curves ◽  
Asymptotic Giant Branch ◽  
Asymptotic Giant Branch Stars ◽  
Red Giant ◽  
Eccentric Motion ◽  
Giant Branch Stars ◽  
Nonradial Pulsation

AbstractAbout 25% of variable asymptotic giant branch stars in the LMC have light curves that are modulated by a long secondary period of length ~ 1–4 yr. Solar-vicinity analogs of these stars show radial velocity curves that are asymmetric and of small amplitude (~3–5km s−1). Possible explanations for the photometric and radial velocity variations include: eccentric motion of an orbiting companion of mass ~0.1 M⊙; radial and nonradial pulsation; rotation of an ellipsoidal-shaped red giant; episodic dust ejection; and star spot cycles. We find that there are severe difficulties with each of these models. Thus, the long secondary periods are the only unexplained type of large-amplitude stellar variability known at this time.

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