Sample within 100 parsec

Accurate parallaxes from the Hipparcos catalog have enabled detailed studies of stellar properties. Subgiants are of particular interest because they lie in an area where isochrones are well separated, enabling dependable age determination. We have initiated a project to obtain hires spectra of Hipparcos subgiants in a volume-limited sample within 100 pc. We obtain stellar properties and abundances via fully automatic analysis. We will use our results to constrain star formation history and chemical evolution in the solar neighborhood. We present initial results for our observed sample and discuss future development for this project. We select Hipparcos subgiants in the Northern Hemisphere within 100 pc with σ πo ≤ 0.1, as shown in Fig. 1. We exclude stars with known multiplicity or variability to avoid ambiguity in abundance and age analysis. A clean sample is essential to test the quality of the automated method itself. We use the ARC 3.5-m telescope at APO to obtain hires echelle spectra (R∼37,500) for our sample. We use standard IRAF techniques for spectrum extraction and calibration. By collecting our own data, we ensure a uniform sample with high SNR and consistency in data reduction. 2. Analysis We use automated gaussian fitting for clean absorption features to obtain equivalent widths. We employ MOOG (Sneden 2002) and Kurucz model atmospheres (Kurucz 1993) in a fully automated analysis to derive effective temperature (T e), spectroscopic surface gravity (log g s), microturbulent velocity (ξ), and iron abundance. Values of T e , log g s , and ξ are obtained by simultaneously solving for constant Fe I abundance across excitation potential and reduced equivalent width, and ionization balance between Fe I and Fe II. These solutions are used to obtain abundances for other elements. We use Bayesian estimation (Jørgensen & Lindegren 2005) of Padova isochrones (Girardi et al. 2002) to obtain age and mass.