出版社：SISSA, Scuola Internazionale Superiore di Studi Avanzati
摘要：A method for determining the abundance ratio of the a-elements (O, Mg, Si, Ca, Ti) with respect
to Fe (collectively parameterized as “[a/Fe]”) from medium-resolution (R = 2000) spectra is
explored. Results of a comparison with the ELODIE spectral library and from a noise injection
experiment suggest that an accuracy in [a/Fe] of about 0.1 dex for spectra with S/N 20/1 is
achievable. This technique is used to estimate [a/Fe] for a total of 39,167 spectrophotometric
and telluric calibration stars from the most recent public release of the Sloan Digital Sky Survey,
in order to study the a-abundance patterns in stars of the Galactic halo. Local space velocities
(U, V, W) and orbital parameters (such as Zmax, Rapo, Rperi, Vf , and eccentricity) are calculated
for this sample, and a total of 7590 potential halo stars are selected by applying cuts of Vf
80 km s−1, Zmax 1 kpc, and [Fe/H] –1.0. The sample is further divided into two groups: a
dissipative component (or inner halo) with stars having 40 Vf 80 km s−1 and Rapo < 16 kpc
and an accreted component (or outer halo) with stars having Vf < 40 km s−1 and Rapo 16 kpc.
Preliminary results for the comparison of the a abundance of these two samples are presented as
a first step toward understanding the assembly history of the halos of the Galaxy.
