Long-baseline interferometric multiplicity survey of the Sco-Cen OB association

Abstract

We present the first multiplicity-dedicated long baseline optical interferometric survey of the Scorpius-Centaurus-Lupus-Crux association. We used the Sydney University Stellar Interferometer to undertake a survey for new companions to 58 Sco-Cen Btype stars and have detected 24 companions at separations ranging from 7-130 mas, 14 of which are new detections. Furthermore, we use a Bayesian analysis and all available information in the literature to determine the multiplicity distribution of the 58 stars in our sample, showing that the companion frequency is F = 1.35 ± 0.25 and the mass ratio distribution is best described by q γ with γ = −0.46, agreeing with previous Sco-Cen high mass work and differing significantly from lower-mass stars in Tau-Aur. Based on our analysis, we estimate that among young B-type stars in moving groups, up to 23% are apparently single stars. This has strong implications for the understanding of high-mass star formation, which requires angular momentum dispersal through some mechanism such as formation of multiple systems.

Mind Your Ps and Qs: The Interrelation between Period (P) and Mass-ratio (Q) Distributions of Binary Stars

“…LBI is limited by the brightness contrasts Δm4mag between the binary components, and so the secondaries must be comparable in luminosity to the primaries in order to be detected. Unlike SB2s, which become biased toward moderate q with increasing P, the sensitivity of LBI is nearly constant with respect to orbital separation (see Figure 4 in Rizzuto et al 2013 and Figure 7 in Sana et al 2014). LBI can therefore provide an unbiased sample of companions with q0.3 and 2.3log P (days)4.3 (magenta region in our Figure 1).…”

“…05-0.10 (Abt et al 1990;Shatsky & Tokovinin 2002;Hinkley et al 2015;Moe & Di Stefano 2015a), which we exclude when quantifying our multiplicity statistics. Alternatively, other observational methods are sensitive to only companions with q0.3 (Evans et al 2013;Rizzuto et al 2013;Sana et al 2014, see Figure 1). For these surveys, we cannot determine g q small .…”

“…Certain channels of lowmass X-ray binaries, millisecond pulsars, and Type Ia supernovae are expected to derive from early-type MS primaries with low-mass companions q≈0.1-0.3 at initially moderate orbital periods P≈100-3000days (filled yellow region). We emphasize that only recent observations of eclipsing binaries (Moe & Di Stefano 2015a, 2015bred), companions identified via long-baseline interferometry (Rizzuto et al 2013;Sana et al 2014;magenta), and binaries with intermediatemass Cepheid primaries (Evans et al 2013(Evans et al , 2015; green) come close to probing this portion of the parameter space.…”

New constraints on the multiplicity of massive young stars in Upper Scorpius

“…Four objects (τ Sco, π Sco, ω Sco, χ Oph) do not show any sign for a companion in their visibilities, although Rizzuto et al (2013) detect a companion around τ Sco with a separation of ∼0.071 . However, the flux difference between this companion and the primary is ∼3 mag in the optical and might thus be out of our detection range in the near infrared.…”

“…AMBER is very well suited to finding these companions, because in the near-infrared the contrast between the bright B stars and secondary components is much less than in the optical. A similar approach has recently been followed by Rizzuto et al (2013) who obtained interferometric observations between 550 and 800 nm with the Sydney University Stellar Interferometer (SUSI) of all stars in Sco-Cen that were brighter than 5 mag in the visual.…”