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.

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 DEEP MIXING IN EVOLVED STARS. II. INTERPRETING Li ABUNDANCES IN RED GIANT BRANCH AND ASYMPTOTIC GIANT BRANCH STARS

2011 ◽  
Vol 741 (1) ◽  
pp. 26 ◽  
Author(s):  
S. Palmerini ◽  
S. Cristallo ◽  
M. Busso ◽  
C. Abia ◽  
S. Uttenthaler ◽  
...  
Keyword(s):  
Asymptotic Giant Branch ◽  
Asymptotic Giant Branch Stars ◽  
Deep Mixing ◽  
Evolved Stars ◽  
Red Giant ◽  
Giant Branch Stars

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 Phase Lags in the Optical-Infrared Light Curves of Asymptotic Giant Branch Stars

2006 ◽  
Vol 131 (1) ◽  
pp. 612-620 ◽  
Author(s):  
Beverly J. Smith ◽  
Stephan D. Price ◽  
Amanda J. Moffett
Keyword(s):  
Light Curves ◽  
Asymptotic Giant Branch ◽  
Infrared Light ◽  
Asymptotic Giant Branch Stars ◽  
Phase Lags ◽  
Giant Branch Stars

scholarly journals The Stellar Populations of M32: Resolving the nearest elliptical with HST ACS/HRC

2009 ◽  
Vol 5 (S262) ◽  
pp. 135-138 ◽  
Author(s):  
Antonela Monachesi ◽  
S. C. Trager ◽  
Tod R. Lauer ◽  
Wendy Freedman ◽  
Alan Dressler ◽  
...  
Keyword(s):  
Stellar Population ◽  
Asymptotic Giant Branch ◽  
Asymptotic Giant Branch Stars ◽  
Horizontal Branch ◽  
Horizontal Branch Stars ◽  
Magnitude Diagram ◽  
Colour Distribution ◽  
Red Clump ◽  
Red Giant ◽  
Giant Branch Stars

AbstractWe present the deepest colour-magnitude diagram (CMD) of M32 to date, obtained from deep (F435W, F555W) photometry of HST ACS/HRC images. Due to the high resolution of our images, the small photometric errors, and the completeness level of our data we obtain the most detailed resolved photometric study of M32 to date. The CMD of M32 displays a wide colour distribution of red giant branch stars, mainly due to a metallicity spread, a strong red clump and bright asymptotic giant branch stars. The detection of a “blue plume” in M32 indicates the presence of a very young stellar population. There is not a noticeable presence of blue horizontal branch stars, suggesting that an old population with [Fe/H] < −1.5 does not significantly contribute to the light or mass of M32 in our observed fields.

scholarly journals The chemical evolution of the dwarf spheroidal galaxy Sextans

2020 ◽  
Vol 642 ◽  
pp. A176 ◽  
Author(s):  
R. Theler ◽  
P. Jablonka ◽  
R. Lucchesi ◽  
C. Lardo ◽  
P. North ◽  
...  
Keyword(s):  
Star Formation ◽  
Galaxy Evolution ◽  
Dwarf Galaxy ◽  
Small Mass ◽  
Asymptotic Giant Branch ◽  
Asymptotic Giant Branch Stars ◽  
Chemical Abundances ◽  
Low Metallicity ◽  
Red Giant ◽  
Giant Branch Stars

We present our analysis of the FLAMES dataset targeting the central 25′ region of the Sextans dwarf spheroidal galaxy (dSph). This dataset is the third major part of the high-resolution spectroscopic section of the ESO large program 171.B-0588(A) obtained by the Dwarf galaxy Abundances and Radial-velocities Team. Our sample is composed of red giant branch stars down to V ∼ 20.5 mag, the level of the horizontal branch in Sextans, and allows users to address questions related to both stellar nucleosynthesis and galaxy evolution. We provide metallicities for 81 stars, which cover the wide [Fe/H] = −3.2 to −1.5 dex range. The abundances of ten other elements are derived: Mg, Ca, Ti, Sc, Cr, Mn, Co, Ni, Ba, and Eu. Despite its small mass, Sextans is a chemically evolved system, showing evidence of a contribution from core-collapse and Type Ia supernovae as well as low-metallicity asymptotic giant branch stars (AGBs). This new FLAMES sample offers a sufficiently large number of stars with chemical abundances derived with high accuracy to firmly establish the existence of a plateau in [α/Fe] at ∼0.4 dex followed by a decrease above [Fe/H] ∼ −2 dex. These features reveal a close similarity with the Fornax and Sculptor dSphs despite their very different masses and star formation histories, suggesting that these three galaxies had very similar star formation efficiencies in their early formation phases, probably driven by the early accretion of smaller galactic fragments, until the UV-background heating impacted them in different ways. The parallel between the Sculptor and Sextans dSph is also striking when considering Ba and Eu. The same chemical trends can be seen in the metallicity region common to both galaxies, implying similar fractions of SNeIa and low-metallicity AGBs. Finally, as to the iron-peak elements, the decline of [Co/Fe] and [Ni/Fe] above [Fe/H] ∼ −2 implies that the production yields of Ni and Co in SNeIa are lower than that of Fe. The decrease in [Ni/Fe] favours models of SNeIa based on the explosion of double-degenerate sub-Chandrasekhar mass white dwarfs.

scholarly journals Magnetic Mixing in Red Giant and Asymptotic Giant Branch Stars

2008 ◽  
Vol 684 (1) ◽  
pp. L29-L32 ◽  
Author(s):  
J. Nordhaus ◽  
M. Busso ◽  
G. J. Wasserburg ◽  
E. G. Blackman ◽  
S. Palmerini
Keyword(s):  
Asymptotic Giant Branch ◽  
Asymptotic Giant Branch Stars ◽  
Magnetic Mixing ◽  
Red Giant ◽  
Giant Branch Stars

scholarly journals Grain Formation in the Winds of Cool Red Giant Stars

2000 ◽  
Vol 177 ◽  
pp. 337-347
Author(s):  
E. Sedlmayr ◽  
J. M. Winters
Keyword(s):  
Dynamical Behavior ◽  
Asymptotic Giant Branch ◽  
Dust Formation ◽  
Asymptotic Giant Branch Stars ◽  
Circumstellar Envelopes ◽  
Giant Stars ◽  
Grain Formation ◽  
Circumstellar Shell ◽  
Red Giant ◽  
Giant Branch Stars

The problem of dust formation in the circumstellar envelopes of Asymptotic Giant Branch stars is reviewed. Special emphasis is put on the consistent modelling of the dust-forming circumstellar shell, where due to a strong coupling the dust formation process governs the dynamical behavior of the object.

scholarly journals Nucleosynthesis in Red Giant Stars

2002 ◽  
Vol 187 ◽  
pp. 57-69
Author(s):  
Nami Mowlavi
Keyword(s):  
Asymptotic Giant Branch ◽  
Red Giants ◽  
Asymptotic Giant Branch Stars ◽  
Chemical Abundance ◽  
Chemical Abundances ◽  
Giant Stars ◽  
Intermediate Mass Stars ◽  
Standard Models ◽  
Red Giant ◽  
Giant Branch Stars

The production of elements from helium-3 to fluorine in low- and intermediate-mass stars is reviewed and compared to chemical abundances observed at the surface of both red giant branch and asymptotic giant branch stars. It is highlighted that, while the trends predicted by standard models are generally well confirmed, many chemical abundances observed at the surface of red giants require the operation of non-standard mixing in the stellar interior. In addition, chemical abundance predictions from presently available asymptotic giant branch models further suffer from the uncertainties affecting the third dredge-up phenomenon, the source of neutrons and the hot bottom burning process.

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