Search for associations containing young stars (SACY)

Abstract

Context. The young associations offer us one of the best opportunities to study the properties of young stellar and substellar objects and to directly image planets thanks to their proximity (<200 pc) and age (≈5−150 Myr). However, many previous works have been limited to identifying the brighter, more active members (≈1 M ) owing to photometric survey sensitivities limiting the detections of lower mass objects. Aims. We search the field of view of 542 previously identified members of the young associations to identify wide or extremely wide (1000−100 000 au in physical separation) companions. Methods. We combined 2MASS near-infrared photometry (J, H, K) with proper motion values (from UCAC4, PPMXL, NOMAD) to identify companions in the field of view of known members. We collated further photometry and spectroscopy from the literature and conducted our own high-resolution spectroscopic observations for a subsample of candidate members. This complementary information allowed us to assess the efficiency of our method. Results. We identified 84 targets (45: 0.2−1.3 M , 17: 0.08−0.2 M , 22: <0.08 M ) in our analysis, ten of which have been identified from spectroscopic analysis in previous young association works. For 33 of these 84, we were able to further assess their membership using a variety of properties (X-ray emission, UV excess, H α , lithium and K I equivalent widths, radial velocities, and CaH indices). We derive a success rate of 76-88% for this technique based on the consistency of these properties. Conclusions. Once confirmed, the targets identified in this work would significantly improve our knowledge of the lower mass end of the young associations. Additionally, these targets would make an ideal new sample for the identification and study of planets around nearby young stars. Given the predicted substellar mass of the majority of these new candidate members and their proximity, high-contrast imaging techniques would facilitate the search for new low-mass planets.

TheβPictoris association: Catalog of photometric rotational periods of low-mass members and candidate members

“…, and then by Torres et al (2006) and Lépine & Simon (2009). The membership was recently confirmed by Binks & Jeffries (2014, Riedel et al (2014), and Elliott et al (2016). Our LS and CLEAN analyses of ASAS time series revealed two possible rotation periods: P = 6.43 d and P = 1.22 d (see Fig.…”

“…Based on 12 epochs of astrometric observations (where the observed separation ranges from 0.095 to 0.307 ), Janson et al (2014) estimated an orbital period of 30 yr. The membership of the β Pictoris association was first proposed by Zuckerman et al (2001), , then by Torres et al (2008) and confirmed by Binks & Jeffries (2014, and by Elliott et al (2016). Scholz et al (2007) measured a projected rotational velocity v sin i = 5.3 km s −1 .…”

“…Bell et al (2015) consider this star a member of the 32 Ori group with an estimated age of 22 ± 4 Myr. Elliott et al (2016) found this star to be component of a hierarchical triple system together with the common proper motion stars TYC 112 917 1 and 2MASS 05195327+0617258. Kiraga (2012) measured a photometric rotation period P = 2.18 d and a light curve amplitude ∆V = 0.09 mag from ASAS data.…”

“…On the other hand, Malo et al did not detect any Li line, noticing that it is detectable in similar T eff members. This system is found by Elliott et al (2016) to have the star 2MASS J01373545-0645375 as common proper motion companion at a separation of 14635 AU. Interestingly, this system has been identified by Alonso-Floriano et al (2011) as the wide proper-motion companion (ρ = 612 ) of EX Cet, which is a BY Dra-type star in the Her-Lyr moving group with an age of about 200 Myr at the same distance d = 24 pc.…”

Young, active radio stars in the AB Doradus moving group

“…The age of the HD 160934 system predicted by the models in Fig. 7 is between 15 Myr and 60 Myr, near the young estimates of the age of the AB Dor-MG. Age estimates of the AB Dor-MG range from 50−120 Myr (Malo et al 2013), 70 Myr (Zuckerman et al 2011), 70−120 Myr (Gagné et al 2014), 100−150 Myr (Elliott et al 2016), and 130−200 Myr (Bell et al 2015). It should be mentioned that the possibility that HD 160934 does not belong to the AB Dor-MG cannot be ruled out.…”