Massive binaries in the Cepheus OB2/3 region

Abstract

Context. Two different formation scenarios for stars of masses larger than 10 M exist. Although simulations within both scenarios are capable of producing stars up to the highest observed masses, the relevance of the two formation scenarios for massive star-formation is not yet clear. Aims. We aim to detect companions to massive stars to constrain the binary parameters of the multiple systems. These findings will help to constrain the formation of massive stars. Methods. We performed z -band observations of massive and intermediate-mass stars in the Cep OB2/3 associations with the Lucky imaging camera AstraLux on the 2.2 m telescope of the Calar Alto observatory. The analysis aimed at detecting binary systems with separations out to 2. 2 (∼1700 AU), the inner limit depending on the contrast. The maximum contrast of 7 mag in z (corresponding to a mass contrast of 17:1 versus an O9V primary) requires a minimum separation of 0. 7 (∼550 AU). Results. We found 28 new companions for our sample of 148 intermediate-mass and massive stars in Cep OB2/3. The companion star fraction of the massive stars is 0.7; about 50% of the systems are triples. The mass function of the companions to the massive stars is strongly top-heavy. We found that the sample parameters closely agreed with those found in the Orion Trapezium cluster. Conclusions. The multiplicity of massive stars seems to be significantly higher than that of intermediate-mass stars, independently of the environment. The comparison of our findings with the theories of massive star-formation favor the formation of massive stars by the fragmentation of proto-stellar cores combined with competitive accretion.

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

“…We note that Duchêne et al (2001) conclude that sample data alone, which is smaller than our combined sample, are consistent with γ=−2.35. Meanwhile, Peter et al (2012) report γ≈−1.0, which is inconsistent with random pairings drawn from a Salpeter IMF. However, Peter et al (2012) fit this exponent down to extreme mass ratios q0.05 where the secondary masses M 2 0.5 M e are no longer expected to follow a Salpeter-like slope.…”

“…Companions to early-type stars can therefore be visually resolved only at larger orbital separations a20 au, i.e., P10 days, even with speckle interferometry (Mason et al 1998(Mason et al , 2009Preibisch et al 1999), adaptive optics (Duchêne et al 2001;Shatsky & Tokovinin 2002;Sana et al 2014), lucky imaging (Peter et al 2012), and space-based observations (Caballero-Nieves et al 2014; Aldoretta et al 2015). MS binaries with large brightness contrasts Δm4mag, and therefore small mass ratios q=M comp /M 1 0.3, can only be detected at even longer orbital periods P10 5 days (see purple region in our Figure 1).…”

“…have projected separations 0 45-1 5 and brightness contrasts Δz′<4.3mag (λ≈900 nm). We adopt the mass ratios presented in Figure 10 of Peter et al (2012) for our nine selected VBs with B0-B2 primaries. For the two systems with B3 primaries, we utilize the relation between Δz′ and q calculated in Peter et al (2012).…”

“…We adopt the mass ratios presented in Figure 10 of Peter et al (2012) for our nine selected VBs with B0-B2 primaries. For the two systems with B3 primaries, we utilize the relation between Δz′ and q calculated in Peter et al (2012). Specifically, we estimate q=0.10 for BD+612218 (Δz′=4.3 mag) and q=0.12 for HD239649 (Δz′=4.2 mag).…”

“…Of the eight companions,  = 3 q large ,B have large mass ratios q>0.3. In Figure 22, we display the cumulative distribution of mass ratios for the  comp =  comp,A +  comp,B =5+8=13 binaries we selected from Duchêne et al (2001) and Peter et al (2012). We measure an excess twin fraction  < 0.10 twin that is consistent with zero ( Table 9).…”