Characterization of very wide companion candidates to young stars with planets and disks

Abstract

Discovering wide companions of stellar systems allows us to constrain the dynamical environment and age of the latter. We studied four probable wide companions of four different stellar systems. The candidates were selected mainly based on their similar kinematic properties to the central star using Gaia DR2. The central stars are V4046 Sgr, HIP 74865, HIP 65426, and HIP 73145, and their probable wide companions are 2MASS J18152222-3249329, 2MASS J15174874-3028484, 2MASS J13242119-5129503, and 2MASS J14571503-3543505 respectively. V4046 Sgr is a member of β-Pictoris Moving Group while the rest of the stellar systems are acknowledged as members of the Scorpius-Centaurus association. The selected stellar systems are particularly interesting because all of them are already known to possess a low-mass companion and/or a spatially resolved disk. Identifying wider companions of these stars can improve their eligibility as benchmarks for understanding the formation channels of various triple systems, and can help us to determine the orbits of their possibly undiscovered inner, wider companions in case of higher multiplicity. By analyzing the X-shooter spectra of the wide companion candidates of these stars, we obtained their stellar parameters and determined their ages. We find that 2MASS J15174874-3028484 (0.11 M<SUB>⊙</SUB>, 7.4 ± 0.5 Myr), an already recognized pre-main sequence (PMS) member of Scorpius-Centaurus association, is a highly probable wide companion of HIP 74865. 2MASS J13242119-5129503 (0.04 M<SUB>⊙</SUB>, 16 ± 2.2 Myr) is ruled out as a plausible wide companion of HIP 65426, but confirmed to be a new sub-stellar member of the Scorpius-Centaurus association. 2MASS J14571503-3543505 (0.02 M<SUB>⊙</SUB>, 17.75 ± 4.15 Myr) is a probable sub-stellar member of the same association, but we cannot confirm whether or not it is gravitationally bound to HIP 73145. 2MASS J18152222-3249329 (0.3 M<SUB>⊙</SUB>, older than 150 Myr) is determined to be a mildly active main sequence star, much older than members of β-Pictoris Moving Group, and unbound to V4046 Sgr despite their similar kinematic features. PMS wide companions such as 2MASS J15174874-3028484 might have formed through cascade fragmentation of their natal molecular core, hinting at high multiplicity in shorter separations which can be confirmed with future observations. <P />Based on observations collected at the European Southern Observatory at Paranal, under program 103.C-0200(A), and archive data from 074.C-0037(A) and 082.C-0390(A).