Search for associations containing young stars (SACY)

Abstract

Context. Nearby young associations offer one of the best opportunities for a detailed study of the properties of young stellar and substellar objects thanks to their proximity (<200 pc) and age (∼5−150 Myr). Previous works have identified spectroscopic (<5 au) binaries, close (5−1000 au) visual binaries, and wide or extremely wide (1000−100 000 au) binaries in the young associations. In most of the previous analyses, single-lined spectroscopic binaries (SB1) were identified based on radial velocities variations. However, this apparent variation may also be caused by mechanisms unrelated to multiplicity. Aims. We seek to update the spectroscopy binary fraction of the Search for Associations Containing Young stars (SACY) sample, taking into consideration all possible biases in our identification of binary candidates, such as activity and rotation. Methods. Using high-resolution spectroscopic observations, we produced ∼1300 cross-correlation functions (CCFs) to disentangle the previously mentioned sources of contamination. The radial velocity values we obtained were cross-matched with the literature and then used to revise and update the spectroscopic binary (SB) fraction in each object of the SACY association. In order to better describe the CCF profile, we calculated a set of high-order cross-correlation features to determine the origin of the variations in radial velocities. Results. We identified 68 SB candidates from our sample of 410 objects. Our results hint that at the possibility that the youngest associations have a higher SB fraction. Specifically, we found sensitivity-corrected SB fractions of 22−11+15% for ϵ Cha, 31−14+16% for TW Hya and 32−8+9% for β Pictoris, in contrast to the five oldest associations we have sampled (∼35−125 Myr) which are ∼10% or lower. This result seems independent of the methodology used to asses membership to the associations. Conclusions. The new CCF analysis, radial velocity estimates, and SB candidates are particularly relevant for membership revision of targets in young stellar associations. These targets would be ideal candidates for follow-up campaigns using high-resolution techniques to confirm binarity, resolve orbits, and, ideally, calculate dynamical masses. Additionally, if the results on the SB fraction in the youngest associations were confirmed, it could hint at a non-universal multiplicity among SACY associations.

Dynamical Mass of the Young Substellar Companion HD 984 B

“…This projected rotational velocity fromWhite et al (2007) is consistent within 2σ with a recent measurement of v sin i = 39.3± 1.5 km/s fromZúñiga-Fernández et al (2021).…”

“…The goal of these observations is to measure or constrain the radial component of the acceleration induced by HD 984 B on its host star. Measuring precise RVs of HD 984 is challenging due to its early spectral type (F7), fast rotation (v sin i = 39.3 ± 1.5 km/s; Zúñiga-Fernández et al 2021), and young age. Near-IR spectrographs like HPF have been shown to reduce activity-induced jitter by a factor of ≈2 − 3 compared to optical spectrographs (Crockett et al 2012;Gagné et al 2016;Tran et al 2021) by sampling wavelengths where starspot-to-photosphere contrasts are reduced.…”

Constraining masses and separations of unseen companions to five accelerating nearby stars

“…HIP 88399 (HD 164249) is a F6 star (Torres et al 2006) with a mass of 1.29 M (Zúñiga-Fernández et al 2021), located at a distance of 49.30±0.06 pc from the Sun (Gaia Collaboration et al 2021). It is part of the β Pictoris moving group (e.g., Messina et al 2017) and has an estimated age of 24±5 Myr (Desidera et al 2021).…”

“…It is part of the β Pictoris moving group (e.g., Messina et al 2017) and has an estimated age of 24±5 Myr (Desidera et al 2021). HIP 88399 has a known companion, HD 164249 B, an M2 star with an estimated mass of 0.54 M (Zúñiga-Fernández et al 2021) and a separation of ∼6.5 corresponding to ∼323 au at the distance of the system (Pawellek et al 2021). IR excess was detected using both WISE (Wright et al 2010), Spitzer (Chen et al 2014) and Herschel (Eiroa et al 2013) data, hinting toward the presence of debris disk.…”

The HD 98800 quadruple pre-main sequence system

“…The spectra are not given in the barycentre reference frame; a correction was therefore applied after retrieving the data. The RVs were determined from the CCF of the spectra with a CORAVEL-type G2 numerical mask using a standalone CCF tool 9 (for further details, see Zúñiga-Fernández et al 2021). The spectra from ELODIE show Notes.…”