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Appendix A: Discussion of individual targets

HIP 9892 = HD 13183: member of Tucana association, classified as a long-period SB by Guenther & Esposito (2007). No orbital solution is available.

HIP 12545 = BD +05 0378: member of β Pic moving group. Identifed as SB1 in Song et al. (2003) (peak-to-valley variation of 20 km s^-1, no orbital solution provided). However, Bailey et al. (2012) found no evidence for large RV variations from their monitoring over 600 days (14 epochs, scatter of 179 m/s). These observations might be explained by a high-eccentricity orbit.

UX For = HIP 12716 = HD 17084: triple system formed by a close SB2 (orbital period 0.9548 d, mass ratio 1.371; Washuettl & Strassmeier 2001) and an outer component, resolved by Hartkopf et al. (2012) and our own NACO observations, which is likely responsible of the proper motion difference between Hipparcos and historical proper motions (Makarov & Kaplan 2005). The large activity levels are likely due to tidal locking of the inner components, as the Lithium equivalent width (Li EW) is similar to that of the Hyades. The presence of the third component significantly limits the parameter space of possible planets around the central pair.

HIP 16853 = HD 22705: member of Tucana association. Astrometric orbit and parallax adopted from Makarov (2007).

V1136 Tau = CHR 14 = HD 284163 = HIP 19591: triple system, member of the Hyades. A 2.39 d RV orbit has been derived by Griffin & Gunn (1981), with indication of the presence of a tertiary companion from the presence in the spectra of an additional system of lines at constant radial velocity. The inner pair was resolved as SB2 thanks to NIR RVs by Bender & Simon (2008), yielding a mass ratio of 0.68 ± 0.03. The third component was visually resolved allowing a preliminary estimate of the orbit (Malkov et al. 2012). The tertiary component is also identified in our NACO images (see Sect. 4).

TYC 5907-1244-1 = BD-20 951: member of Tucana associaton and SB2 following Torres et al. (2008). No orbital solution is available.

AF Lep = HIP 25486 = HD 35850: member of β Pic moving group. Reported as SB2 in Nordström et al. (2004), with mass ratio between the components of 0.72. Details of orbital solution not provided.

HIP 25709 = HD 36329: member of Columba association, was reported as a SB2 with similar components by Torres et al. (2008). The orbital solution is not available.

XZ Pic = HIP 27134 = CD-59 1125: short-period SB1 according to sparse RV measurements (Dall et al. 2007; Torres et al. 2006; Cutispoto et al. 1999). Age indicators based on activity and rotation are likely biased by tidal locking between the components. The lithium in the spectrum indicates an age of about 300 Myr.

26 Gem = HIP 32104 = HD 48097 = HR 2466: member of Columba association according to Zuckerman et al. (2011) and Malo et al. (2013). Spectroscopic (Galland et al. 2005) and astrometric (Hipparcos orbital solution) binary. Combining the spectroscopic solution with the inclination from Hipparcos results in a companion mass of 0.51 M_⊙ at 1.87 AU. The secondary is most likely responsbile for the X-ray emission from the system.

Alhena = γ Gem = HIP 31681 = HD 47105: spectroscopic, astrometric and close visual binary. The constraints on orbital solution derived from our own observations are presented in Sect. 4.4. The isochrone fitting yields an age of 300 Myr and the X-ray emission (assuming it comes from the late-type secondary) is consistent with such an estimate. The space velocities are close to those of the Ursa Major association.

TYC 8104-0991-1 = CD-45 2654: SB3 discovered by Torres et al. (2006), but no additional information is available on the binary parameters. The large Li EW indidates an age of about 100 Myr.

EM Cha = RECX7: SB2, member of η Cha open cluster. Masses and orbital parameters from Lyo et al. (2003) (eccentricity not provided, we assume 0.0 due the short period). The orbital period is equal to the photometric period, suggesting the occurrence of tidal locking.

TYC 8569-3597-1 = CD-53 2515: member of Carina MG and SB2 with a period of 24.06 days (Torres et al. 2008). Distance from Torres et al. (2008).

GS Leo = HIP 46637 = HD 82159: triple system, formed by a close pair and an outer component. The latter was observed by Chauvin et al. (2014). Stellar and binary parameters from Desidera et al. (2014).

TYC 9399-2452-1 = HD 81485B: the SB2 HD 81485B (Covino et al. 1997) is part of a quadruple system with HD 81485A and its close visual companion at 9′′~ 500 AU projected separation at the trigonometric distance of HD 81485A. The SB2 component shows exceptional high levels of chromospheric activity, while the primary is only moderately active (Desidera et al. 2006). This, together with the Li EW comparable with that of the Hyades (Torres et al. 2006), indicates an age of about 800 Myr and probable tidal-locking of the SB2 component. The very young age for the primary (14 Myr) derived from isochrone fitting by Neuhauser & Brandner (1998) is probably due to the unrecognized (at that time) multiplicity of A, that is actually overluminous by about 0.5 mag in K-band with respect to the individual Aa component. Finally, we note discrepant trigonometric parallaxes between the two reductions of Hipparcos data.

HIP 47760 = HD 84323: star flagged as SB1 in Cutispoto et al. (2002) without further details. No orbital solution is available. The Li EW larger than Pleiades of similar colors and similar to that of member of Tucana association but the lack of system RV prevents a proper evaluation of MG membership. The BANYAN II online tool (Gagné et al. 2014) without using RV information does not support membership in any of the MG considered in that work. We adopt an age of 30 Myr.

TYC 6604-0118-1 = CD-22 7788 = BD-21 2961: short-period (1.83 d) SB2 (Torres et al. 2003). The Li EW indicate an age pf about 100 Myr and the kinematic parameters are compatible with such a moderately young age. The close pair has a wide common proper motion companion (2MASS J09590930-2239582) at 26′′ projected separation.

HS Lup = HIP 74049 = HD 133822: SB2 with period 17.83 d (Evans 1961). There is independent evidence that the star is rather young, as it is active with a possible rotation period which is different from the orbital one (Helt & Jensen 1989) and shows lithium intermediate between that of members of Hyades and Pleiadesof similar color. We adopt an age of 250 Myr.

HIP 76629 = HD 139084 = V343 Nor: triple system, member of β Pic MG. Evidence of RV variability is derived in the literature from Guenther & Esposito (2007) and Torres et al. (2006). Including RVs measured on archival FEROS and HARPS spectra, we derived a tentative orbital solution with a period of about 4.5 years and moderate eccentricity (0.5–0.6). The corresponding minimum mass of the companion is 0.11 M_⊙. There is an additional companion, the M5Ve star HD 139084B at 10′′.

HIP 78416 = HD 143215: triple system, formed by an SB2 system discovered by Desidera et al. (2006) and a wide companion at 6.̋55 (550 AU projected separation). The system is formed by three stars with similar masses. The large X-ray emission might be due to fast rotation due to tidal circularization. However, the isolated secondary also shows a fast rotational velocity, Ca II HK emission level similar to Pleiades, and a Lithium 6708 Å line stronger than Pleiades stars of similar color. Li lines are clearly visible and well separated also in the SB2 component. The star is at a distance of 84 ± 12 pc in front of the Lupus cloud. The kinematical parameters and the space position are compatible with those of Upper Centaurus Lupus (UCL) group. The age resulting from lithium is also fully compatible with UCL membership.

BS Ind = HIP 105404 = HD 202917: this is a spectroscopic binary with P = 3.3 yr and e = 0.6, in which the primary is found to be itself an eclipsing binary with P = 0.43 days. The components of the eclipsing system are likely late K- or early M-type stars, with a total mass of about 0.9 M_⊙, while the wider spectroscopic companion is a K0V-type star of 0.8 M_⊙ (see Guenther et al. 2005, for all the details). Membership to Tuc-Hor association was supported by Zuckerman & Song (2004) and Malo et al. (2013) but rejected by Torres et al. (2008). The Li EW suggests an age as young as 10 Myr but should be taken with caution because of the composite nature of the system. We adopt Tuc-Hor membership and its age.

IK Peg = HIP 105860 = HD 204188: single-lined SB with a massive white dwarf companion (Wonnacott et al. 1993). The system should have evolved through the common envelope phase, rendering it challenging to estimate the original configuration and the age of the system (Davis et al. 2010). The position of the primary close to the zero-age main sequence, the large mass and hot temperature of the white dwarf, and the young-disk kinematics support a moderately young age. Trilling et al. (2007) adopt an age of 100 Myr. The primary is also a δ Scu pulsating variable.

δCap = HIP 107556 = HD 207098 = GJ 837: short-period spectroscopic and semi-detached eclipsing binary. Orbit from SB9: P = 1.02 d, e = 0.01, K1 = 70.80 km s^-1. In the catalog of semi-detached binaries (Surkova & Svechnikov 2004) individual masses and radii M_A = 1.50, M_B = 0.56, R_A = 1.85, R_B = 1.56 are listed. The large X-ray luminosity of the system is likely due to tidal-spin up of the late type secondary. An age of 540 Myr is derived by Nielsen et al. (2013). However, it is highly uncertain. Furthermore, the position on CMD and then age from iscochrone may have been altered by mass trasfer process. The kinematic parameters are compatible with a young age.

CS Gru = HIP 109901 = HD 211087: lithium-rich K-type dwarf identified as SB1 (RMS of RV 37 km/s, 4 measurements) in SACY. The possibility of a tidally-locked binary can not be excluded from current data, but the large lithium EW indicates an age of about 100 Myr. The large uncertainty in the kinematic parameters due to the RV variability prevents a proper evaluation of membership to associations.

TYC 6386-0896-1 = HD 215341: SB2 discovered by Christian et al. (2002); the orbital solution is not available. The very large coronal and chromospheric activity are likely due to tidal locking, while Lithium is within the locus of Pleides stars. We adopt an age of 150 Myr.

© ESO, 2014