Search for associations containing young stars (SACY) V. Is multiplicity universal? Tight multiple systems

Context. Dynamically undisrupted, young populations of stars are crucial in studying the role of multiplicity in relation to star formation, Loose nearby associations provide us with a great sample of close (<150 pc) pre-main sequence (PMS) stars across the very important age range (approximate to 15-70 Myr) to conduct such research. Aims. We characterize the short period multiplicity fraction of the search for associations containing young stars (SACY) sample. accounting for any identifiable bias in our techniques and present the role of multiplicity fractions of the SACY sample in the context of star formation. Methods. Using the cross-correlation technique we identified double-lined and triple-lined spectroscopic systems (SB2/SB3s), in addition to this we computed radial velocity (RV) values for our subsample of SACY targets using several epochs of Fiber-fed Extended Range Optical Spectrograph (FEROS) and Ultraviolet and Visual Echelle Spectrograph (LIVES) data. These values were used to revise the membership of each association that was then combined with archival data to determine significant RV variations across different data epochs characteristic of multiplicity: single-lined multiple systems (SB1). Results. We identified seven new multiple systems (SB1s: 5. SB2s: 2). We find no significant difference between the short period multiplicity fraction (F-m) of the SACY sample and that of close star forming regions (approximate to 1-2 Myr) and the field (F-m <= 10%). These are seen both as a function of age and as a function of primary mass, M-1, in the ranges P [1:200 day] and M-2 [0.08 M-circle dot-M-1] 08 respectively. Conclusions. Our results are consistent with the picture of universal star formation, when compared to the field and close star-forming regions (SERs). We comment on the implications of the relationship between increasing multiplicity fraction with the primary mass within the close companion range in relation to star formation.