Red giants

Carbon nanotubes (CNTs) as well as fullerenes are splendid gift brought to the Earth from the red giant carbon stars in the long-distant universe through the spectroscopy. Moreover, those belong to new carbon allotropes of the mesoscopic scale with well-defined structures. In particular, CNTs are considered to be the materials appropriate to realise intriguing characteristics related to the mesoscopic system based on their size and physicochemical properties. 

The evolution of a. star after it leaves the red-giant phase depends to some extent on its mass. If it is not more than about 1.4 M it may contract appreciably again and then enter an oscillatory phase of its life before becoming a white dwarf (p. 7). When core contraction following helium and carbon depletion raises the temperature above I0 K the y-ray.s in the stellar assembly become sufficiently energetic to promote the (endothermic) reaction Ne(y,a) 0. The a-paiticle released can penetrate the coulomb barrier of other neon nuclei to form " Mg in a strongly exothermic reaction ... 

Self-Test 1.3B A red giant is a late stage in the evolution of a star. The average wavelength maximum at 700. nm shows that a red giant cools as it dies. What is the surface temperature of a red giant ... 

During the red giant phase of stellar evolution, free neutrons are generated by reactions such as C(a,n) and Ne(a,n) Mg. (The (ot,n) notation signifies a nuclear reaction where an alpha particle combines with the first nucleus and a neutron is ejected to form the second nucleus.) The neutrons, having no charge, can interact with nuclei of any mass at the existing temperatures and can in principle build up the elements to Bi, the heaviest stable element. The steady source of neutrons in the interiors of stable, evolved stars produces what is known as the "s process," the buildup of heavy elements by the slow interaction with a low flux of neutrons. The more rapid "r process" occurs in... 

The core of the Earth consists mainly of iron. It can be comically considered as a particle of ash that came to rest. However, this will not last forever. The sun is a star in its first phase. In 4 billion years, it will develop into a red giant, which will also envelop the Earth. But there is still a long time before then. 

In about 4 billion years our sun will also develop into a red giant. The diameter will then reach the orbit of Mars, and the inner planets will cease to exist. 

When, many, many million years in the future, our sun expands in its Anal phase to become a red giant, the habitable zone of our solar system will shift by 1-2 AU, to the region where Triton, Pluto/Charon and the Kuiper Belt are found. This zone is referred to as the delayed gratification habitable zone . All the heavenly bodies in this zone contain water and organic material, so that chemical and molecular... 

Abstract. [La/Eu] and [Ba/Eu] for a sample of Barium stars were determined in order to evaluate the ratio of abundances of s- and r-elements. The results have been compared to previous work dealing with normal red giants and dwarfs with metallicities in the range -3 < [Fe/H] < +0.3. 

Barium stars were recognized as a distinct group of peculiar stars by [1], The objects initially included in this group were red giants of spectral type G and K, which showed strong lines of s-process elements, particularly Ba II and Sr II, as well as enhanced CH, CN and C2 bands. The discovery that HR 107, a dwarf star, shows a composition similar to that of a mild Barium giant by [6] has pushed the search for new Barium dwarfs. 

Fig. 1. (V,V-I) CMD for stars in NGC2324. Isochrones from [3] of log t = 8.60, 8.65 and 8.70 are overplotted. Open circles are red giant members confirmed from Coravel radial velocities.

Fig. 2. Unreddened Washington colour-colour diagram for 4 red giants confirmed from Coravel radial velocities. Isoabundance relations from [1] for 0.5 dex intervals from [Fe/H] = -1.0 to 0.0 are shown, except for the (M — Ti)o/(Ti — 22)0 diagram wherein isoabundance relations for 0.4 dex intervals from -0.8 to 0.0 are given.

The current status of HF abundances from infrared spectroscopy in samples of red-giants from different Galactic stellar populations are summarized in Figure 1. The abundance results displayed in this figure are from Cunha et al. (2003), plus new results for stars at the lowest metallicities, as well as two Orion pre-main-sequence stars. The run of fluorine with metallicity is now probed between oxygen abundances from roughly 7.7 to 8.7. 

A few comments can be drawn from the abundance results presented in Figure 1. The abundances obtained for the red giants in the globular cluster iv Cen-tauri seem to indicate the existence of a sharp decline in the [F/O] ratios as the metallicity approaches the lowest observed oxygen abundance in this globular... 

Abstract. I present preliminary results for a sample of 700 red giants in u> Cen, observed during the Ital-FLAMES Consortium GTO time in May 2003, for the Bologna Project on u Cen. Preliminary Fe and Ca abundances confirm previous results while the metal-poor and intermediate populations show a normal halo o-enhancement of [a/Fe] +0.3, the most metal-rich stars show a significantly lower [a/Fe] +0.1. If the metal-rich stars have evolved within the cluster in a process of self-enrichment, the only way to lower their a-enhancement would be SNe type la intervention. 

We have also measured the lithium abundances in the samples of unmixed and mixed stars [6]. When low mass stars, such as those in our sample, evolve through the red giant branch, the degree of dilution of the lithium increases as the convective zone penetrates deeper and thus we expect a decline of the lithium abundance. In the mixed stars the lithium has never been detected, the upper limit of the lithium abundance is log N(Li) < 0.0, on the contrary in all the unmixed stars but one, the lithium line is visible and log N(Li) is > 0.20. In these stars as expected, the lithium abundance decreases when the gravity decreases (Fig. 3-b). 

Abstract. From VLT/UT2 GIRAFFE GTO, we performed a lithium abundance survey along the red giant branch of the metal-rich globular cluster 47 TUC (NGC 104), in order to investigate the efficiency of extra mixing occurring at the RGB bump. 

The DART large programme at ESO made v ei and [Fe/H] measurements from FLAMES spectroscopy of 401 red giant branch (RGB) stars in the Sculptor (Scl) dSph [6]. The relatively high signal/noise, S/N ( 10-20 per pixel) resulted in both accurate metallicities ( 0.1 dex from internal errors) and radial velocities ( 2 km/s). This is the first time that a large sample of accurate velocities and metallicities have been measured in a dwarf galaxy. 

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