Solar neighbourhood

The solar neighbourhood thick disk stars that have been studied are all old... 

There are a number of important observational facts that we now have established for the stellar population of solar neighbourhood stars that have kinemat-... 

We have observed three subgiants HD 23249 (KO), HD 198149 (KO), HD 222404 (Kl) and three dwarfs HD 10780 (KO), HD 4628 (K2), HD 201091 (K5), on 2002 November 28 and 29, with the high-resolution cross-dispersed echelle spectrograph SOFIN, mounted on the Nordic Optical Telescope (NOT). They are in the solar neighbourhood (< 15 pc), are very bright (V < 6) and have modest projected rotational velocities (v sin i < 4 km s 1) to limit blends between spectral lines. They also do not present any evidence for emission (or a moderate one, as in the case of the three dwarfs) in the core of Ca II H and K lines. 

Abstract. High resolution spectral data of red clump stars towards the NGP have been obtained with the spectrograph Elodie at OHP stars. Nearby Hipparcos red clump stars were also observed. We determine the thin and thick properties kinematics and chemical abundances in the solar neighbourhood. We estimate the surface mass density of the galactic disk, we also determine the thin and thick disk chemical properties. 

Theory doesn t tell us what initial Li a star has, only what depletion it suffers. An accurate estimate of the initial Li abundance is therefore a pre-requisite before observations and models can be compared. The Sun is a unique exception, where we know the present abundance, A(Li) = 1.1 0.1 (where A(Li)= log[AT(Li)/AT(H)] + 12) and the initial abundance of A(Li)= 3.34 is obtained from meteorites. For recently born stars, the initial Li abundance is estimated from photospheric measurements in young T-Tauri stars, or from the hotter F stars of slightly older clusters, where theory suggests that no Li depletion can yet have taken place. Results vary from 3.0 < A(Li) < 3.4, somewhat dependent on assumed atmospheres, NLTE corrections and TeS scales [23,33]. It is of course quite possible that the initial Li, like Fe abundances in the solar neighbourhood, shows some cosmic scatter. Present observations certainly cannot rule this out, leading to about a 0.2 dex systematic uncertainty when comparing observations with Li depletion predictions. 

The result of all these processes is that the Sun was bom 4.6 Gyr ago with mass fractions X 0.70, Y 0.28, Z 0.02. These abundances (with perhaps a slightly lower value of Z) are also characteristic of the local ISM and young stars. The material in the solar neighbourhood is about 15 per cent gas (including dust which is about 1 per cent by mass of the gas) and about 85 per cent stars or compact remnants thereof these are white dwarfs (mainly), neutron stars and black holes. 

The most metal-deficient stars comprise field stars in the solar neighbourhood (where in some cases distances and luminosities can be found from parallaxes) and stars in globular clusters where the morphology of the HR diagram can be studied (Fig. 4.8). Such stars are of particular interest because their content of heavy elements (synthesized in still earlier generations of stars) is so low that they can... 

Since L /M — 1 (in cgs units), it follows from a comparison of equations (7.18) and (7.19) that, for exponential decay in bolometric luminosity, v-1 7 Gyr. Thus a single strong initial burst seems to be ruled out as a dominant contributor in the solar neighbourhood. 

The oxygen abundance then decreases more or less linearly from about 2 Z0 near the centre to Z0 in the solar neighbourhood, reaching about 0.3 Z0 at 20 kpc. 

It is therefore among the disk stars of the solar neighbourhood that one looks for quantitative evidence for an age-metallicity relation some relevant data are shown in Figs. 8.16, 8.17 and 8.41. 

Table 8.2. Model of chemical evolution of the disk in the solar neighbourhood...

A careful study of assumptions underlying chemical models for the solar neighbourhood and their comparison with observation was carried out by Thomas, Greggio and Bender (1998). They considered nucleosynthetic yields calculated... 

Fig. 8.39. Chemo-spectrophotometric evolution of the solar neighbourhood (left) and the whole Milky Way (right) as a function of time. Panels aA show the oxygen and iron abundances, bB the mass of stars and gas and the star formation rate, cC the extinction in B, V and K bands along a line of sight normal to the plane, dD the luminosity in solar units (taking extinction into account), eE the colour indices and fF the supernova rates. Note that panels aA are in linear units (see Fig. 8.16), while the others are all logarithmic. After Boissier and Prantzos (1999).

Fig. 11.3 for the LMC. Figure 11.4 shows the resulting age-metallicity relations unlike the solar neighbourhood, there seems to be a reasonably well-defined relationship, despite the lack of clusters (from which ages were mainly determined at the time) at intermediate ages. The SMC, which does not suffer such a gap, shows... 

Fig. 11.3. SFR history of the LMC assumed in our models. The full curve shows the bursting model, while the broken curve shows a smooth model with cw = 0.18, compared to co 0.3 for the solar neighbourhood. After Pagel and TautvaiSiehe (1998).

This parameter is nevertheless constrained by the relationship between the age and iron content of stars, the observed rate of supernova events (of the order of three per century), which is related to the current star formation rate, and the present gaseous fraction. After 10 billion years of evolution, the region of the Galaxy accessible to us, that is, the solar neighbourhood, still retains about 10% gas. 

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