The Palomar/MSU Nearby Star Spectroscopic Survey. III. Chromospheric Activity, M Dwarf Ages, and the Local Star Formation History

We present high-resolution echelle spectroscopy of 676 nearby M dwarfs. Our measurements include radial velocities, equivalent widths of important chromospheric emission lines, and rotational velocities for rapidly rotating stars. We identify several distinct groups by their Hα properties and investigate variations in chromospheric activity among early (M0–M2.5) and mid (M3–M6) dwarfs. Using a volume-limited sample together with a relationship between age and chromospheric activity, we show that the rate of star formation in the immediate solar neighborhood has been relatively constant over the last 4 Gyr. In particular, our results are inconsistent with recent large bursts of star formation. We use the correlation between Hα activity and age as a function of color to set constraints on the properties of L and T dwarf secondary components in binary systems. We also identify a number of interesting stars, including rapid rotators, radial velocity variables, and spectroscopic binaries.