A multiplicity survey of chromospherically active and inactive stars

Surveys of three samples of solar-type stars, segregated by chromospheric e mission level, were made to determine their multiplicity fractions and to i nvestigate the evolution of multiplicity with age. In total, 245 stars were searched for companions with Delta V less than or equal to 3.0 and separat ions of 0." 035 to 1." 08 using optical speckle interferometry. By incorpor ating the visual micrometer survey for duplicity of the Lamont-Hussey Obser vatory, the angular coverage was extended to 5." 0 with no change in the De lta V limit. This magnitude difference allows mass ratios of 0.63 and large r to be detected throughout a search region of 2-127 AU for the stars obser ved. The 84 primaries observed in the chromospherically active sample are p resumably part of a young population and are found to have a multiplicity f raction of 17.9% +/- 4.6%. The sample of 118 inactive, presumably older, pr imaries were selected and observed using identical methods and are found to have a multiplicity fraction of only 8.5% +/- 2.7%. Given the known link b etween chromospheric activity and age, these results tentatively imply a de creasing stellar multiplicity fraction from 1 to 4 Gyr, the approximate age s of the two samples. Finally, only two of the 14 very active primaries obs erved were found to have a companion meeting the survey detection parameter s. In this case, many of the systems are either very young, or close, RS CV n type multiples that are unresolvable using the techniques employed here.