Search for associations containing young stars (SACY)

Abstract

Context. Dynamically undisrupted, young populations of stars are crucial in studying the role of multiplicity in relation to star formation. Loose nearby associations provide us with a great sample of close (<150 pc) pre-main sequence (PMS) stars across the very important age range (≈5−70 Myr) to conduct such research. Aims. We characterize the short period multiplicity fraction of the search for associations containing young stars (SACY) sample, accounting for any identifiable bias in our techniques and present the role of multiplicity fractions of the SACY sample in the context of star formation. Methods. Using the cross-correlation technique we identified double-lined and triple-lined spectroscopic systems (SB2/SB3s), in addition to this we computed radial velocity (RV) values for our subsample of SACY targets using several epochs of Fiber-fed Extended Range Optical Spectrograph (FEROS) and Ultraviolet and Visual Echelle Spectrograph (UVES) data. These values were used to revise the membership of each association that was then combined with archival data to determine significant RV variations across different data epochs characteristic of multiplicity; single-lined multiple systems (SB1). Results. We identified seven new multiple systems (SB1s: 5, SB2s: 2). We find no significant difference between the short period multiplicity fraction (F m ) of the SACY sample and that of close star-forming regions (≈1−2 Myr) and the field (F m ≤ 10%). These are seen both as a function of age and as a function of primary mass, M 1 , in the ranges P [1:200 day] and M 2 [0.08 M -M 1 ], respectively. Conclusions. Our results are consistent with the picture of universal star formation, when compared to the field and close star-forming regions (SFRs). We comment on the implications of the relationship between increasing multiplicity fraction with the primary mass within the close companion range in relation to star formation.

Search for associations containing young stars (SACY)

“…We collated high-probability members from a collection of prominent moving group works to date (Torres et al 2008;Zuckerman et al 2011;Malo et al 2014;Kraus et al 2014;Elliott et al 2014;Murphy & Lawson 2015), which cover a wide range of spectral types (B2-M5) and ages (∼5−150 Myr), totalling 542 targets in nine associations. A summary of the associations can be found in Table 1.…”

“…Of 198 primaries, 188 were initially identified correctly. Of the ten sources that were not identified, seven were known sources with two or more components in their photometry (such as HD 217379, identified as a triple-lined spectroscopic binary in Elliott et al 2014). These are rare cases, however we do not want to exclude any sources (companions also have a small probability of being in an SB3 configuration) and therefore we increased the upper limit on the magnitude (1.2 mag.).…”

“…ID: U033Hr). The radial velocities were computed using a binary mask (SpT: K0) to produce a cross-correlation function (CCF) as described in Queloz (1995), Elliott et al (2014). The spectroscopic quantities are shown in Table 3.…”

“…The work presented here forms part of larger project to study multiplicity in the young associations (Elliott et al 2014. These works have used the search for associations containing young stars (SACY) dataset.…”

A High-Precision Near-Infrared Survey for Radial Velocity Variable Low-Mass Stars Using Cshell and a Methane Gas Cell

“…Six others were already followed either at optical or NIR wavelengths, albeit at a 50 m s −1 precision (AGTri, ATMicA, ATMicB, auMic, BD+012447, V1005Ori; Paulson & Yelda 2006;Bailey et al 2012), and three targets benefited from a precise RV follow-up at optical wavelengths (BD+201790,εEridani, GJ3305AB; e.g., Campbell et al 1988;Figueira et al 2010;Elliott et al 2014;Hernán-Obispo et al 2015).…”