Search for associations containing young stars (SACY)

Abstract

The young associations offer us one of the best opportunities to study the\nproperties of young stellar and substellar objects and to directly image\nplanets thanks to their proximity ($<$200 pc) and age ($\\approx$5-150 Myr).\nHowever, many previous works have been limited to identifying the brighter,\nmore active members ($\\approx$1 M$_\\odot$) owing to photometric survey\nsensitivities limiting the detections of lower mass objects. We search the\nfield of view of 542 previously identified members of the young associations to\nidentify wide or extremely wide (1000-100,000 au in physical separation)\ncompanions. We combined 2MASS near-infrared photometry ($J$, $H$, $K$) with\nproper motion values (from UCAC4, PPMXL, NOMAD) to identify companions in the\nfield of view of known members. We collated further photometry and spectroscopy\nfrom the literature and conducted our own high-resolution spectroscopic\nobservations for a subsample of candidate members. This complementary\ninformation allowed us to assess the efficiency of our method. We identified 84\ntargets (45: 0.2-1.3 M$_\\odot$, 17: 0.08-0.2 M$_\\odot$, 22: $<$0.08 M$_\\odot$)\nin our analysis, ten of which have been identified from spectroscopic analysis\nin previous young association works. For 33 of these 84, we were able to\nfurther assess their membership using a variety of properties (X-ray emission,\nUV excess, H$_\\alpha$, lithium and K I equivalent widths, radial velocities,\nand CaH indices). We derive a success rate of 76-88% for this technique based\non the consistency of these properties. Once confirmed, the targets identified\nin this work would significantly improve our knowledge of the lower mass end of\nthe young associations. Additionally, these targets would make an ideal new\nsample for the identification and study of planets around nearby young stars.\n