Search Results - (Author, Cooperation:P. Molaro)

2011-09-03

Nature Publishing Group (NPG)

0028-0836

1476-4687

Biology

Chemistry and Pharmacology

Medicine

Natural Sciences in General

Physics

1476-4687

Nature Archives 1869 - 2009

Biology

Chemistry and Pharmacology

Medicine

Natural Sciences in General

Physics

[Auszug] The ages of the oldest stars in the Galaxy indicate when star formation began, and provide a minimum age for the Universe. Radioactive dating of meteoritic material and stars relies on comparing the present abundance ratios of radioactive and stable nuclear species to the theoretically ...

Electronic Resource

0273-1177

Elsevier Journal Backfiles on ScienceDirect 1907 - 2002

Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics

Physics

Electronic Resource

0273-1177

Elsevier Journal Backfiles on ScienceDirect 1907 - 2002

Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics

Physics

Electronic Resource

1572-946X

Springer Online Journal Archives 1860-2000

Physics

Abstract In this paper we present the first results of the analysis of intermediate resolution (Δλ ∼ 3.5 Å) spectra of giants of the Sagittarius dwarf galaxy acquired using the ESO NTT telescope. From the deep CCD photometry of Marconi et al. (1998a) we have selected a sample of giants representative of the metallicity spread suggested by the comparison of the colour-magnitude diagram of Sagittarius with those of galactic globular clusters. The spectra have been used to measure radial velocities, to confirm the membership to Sagittarius, and to provide a metallicity estimate by using spectral synthesis techniques. The analyzed stars show a spread in metallicities in the range −1.0≤ [Fe/H]≤ +0.7, some 0.5 dex more metal-rich than the photometric estimates.

Electronic Resource

1572-946X

Springer Online Journal Archives 1860-2000

Physics

Abstract We present a study of the [α/Fe-peak] and [N/α] abundance ratios in Damped Lyα (DLA) systems. By using ratios of undepleted elements ([S/Zn] and [N/S]) or when abundances of refractory elements are corrected by dust depletion ([Si/Fe]corr), the resulting ratios do not resemble those observed in the Galactic metal-poor stars, showing instead similarities with those ratios observed in dwarf galaxies. These results challenge the idea that these absorbers are the progenitors of the present-day spiral galaxies, and suggest an origin in low-mass galaxies for the systems up to now investigated.

Electronic Resource

1572-946X

Springer Online Journal Archives 1860-2000

Physics

Abstract We outline a method to explore the column density of the Local Interstellar Medium (LISM) using absorptions in the resonance H and K lines of Mgii. The intrinsic strengths of these lines in the temperature and density conditions prevailing in warm clouds (T eff〈104 K) in the LISM allows them to be used to explore many lines of sight where lines such a NaD and Caii H and K are too weak, but where Lα is saturated. The number of measurable lines-of-sight is greatly enhanced by using cool stars as the background emitters, but this implies reliable separation of the LISM components from stellar chromospheric selfabsorptions. We explain how to do this, and how to use a combination of column density and radial velocity data to measure the spatial extent and the physical parameters of the single cloud in which the Sun is embedded. This proves to be an oblate spheroid, of characteristic diameter 8 pc, withT eff ∼ 104 K,n(Hi) of 0.1 cm−3 and a mass 〈5M ⊙, streaming in the LSR from a point 1″=4°,B″=+16° with velocity equal to 16 km s−1, and is surrounded by the much hotter lower density ionized gas of the local supernova bubble.

Electronic Resource

1572-946X

Springer Online Journal Archives 1860-2000

Physics

Abstract A very low upper limit of 0.15 mÅ for the interstellar λ6707 Å Lii line has been recently derived towards the SN1987a by Baade and Magain (1988). This value corresponds toN(Li)〈1.4×1011 cm−2 and gives [Li/H]〈5.4×10−11 assumingN(Hi)=2.6×1021 cm−2 for the hydrogen column density in the LMC towards SN1987a. This value is lower than the Li abundance found in the Population II stars and lower than the minimum abundance allowed in the framework of the standard Big-Bang theory. We indirectly estimate the Li depletion usingKi observations and show that a depletion of 1.2 dex is plausible. Therefore, an interstellar abundance [Li/H] as high as 0.8×10−9 cannot be excluded. Any improvement in the above-mentioned upper limit will place important constraints on current theories for lithium nucleosynthesis. High-resolution IUE spectra of the SN1987a have been analysed in search for IS 1362 ÅBii resonance lines. A minimum detectable equivalent width of 22 mÅ has been found, that impliesN(B)〈1.2×10−12 cm−2 and [B/H]〈4.7×10−10 cm−2, i.e., comparable to the solar value of [B/H]=4×10−10. This limit is the most stringent derived so far for an external galaxy, and suggests that the rate of spallation processes in the LMC has not been higher than in our own Galaxy.

Electronic Resource

1572-9672

Springer Online Journal Archives 1860-2000

Physics

Abstract Ongoing spectroscopy and photometry of stars selected in the HK objective-prism/interference-filter survey of Beers and colleagues has resulted in the identification of many hundreds of additional stars in the halo (and possibly the thick disk) of the Galaxy with abundances [Fe/H] ≤ -2.0. A new calibration of the technique for estimation of metal abundance based on a CaII K index as a function of broadband B - V color is applied to obtain metallicities for stars observed with the SSO 2.3m and INT 2.5m telescopes. This new data is combined with other samples of extremely metal-deficient stars (Ryan and Norris, 1991a; Beers et al., 1992; Carney et al., 1994) to form a large database of objects of low metallicity. The combined sample is examined and compared with expectations derived from a Simple Model of Galactic chemical evolution. There appears to be a statistically-significant deficit of stars more metal-weak than [Fe/H] = -3.0. An abundance of [Fe/H] ≈ -4.0 can be taken as the low-metallicity limit for presently-observable stars in the Galaxy.

Electronic Resource