TOWARD COMPLETE STATISTICS OF MASSIVE BINARY STARS: PENULTIMATE RESULTS FROM THE CYGNUS OB2 RADIAL VELOCITY SURVEY

By H. Kobulnicky, D. Kiminki, M. Lundquist, J. Burke, James B. Chapman, E. Keller, K. Lester, E. Rolen, E. Topel, A. Bhattacharjee and 5 more. 2014

189 citations recorded by the source corpus.

We analyze orbital solutions for 48 massive multiple-star systems in the Cygnus OB2 association, 23 of which are newly presented here, to find that the observed distribution of orbital periods is approximately uniform in log P for P < 45 days, but it is not scale-free. Inflections in the cumulative distribution near 6 days, 14 days, and 45 days suggest key physical scales of ≃0.2, ≃0.4, and ≃1 A.U. where yet-to-be-identified phenomena create distinct features. No single power law provides a statistically compelling prescription, but if features are ignored, a power law with exponent β ≃ −0.22 provides a crude approximation over P = 1.4–2000 days, as does a piece-wise linear function with a break near 45 days. The cumulative period distribution flattens at P > 45 days, even after correction for completeness, indicating either a lower binary fraction or a shift toward low-mass companions. A high degree of similarity (91% likelihood) between the Cyg OB2 period distribution and that of other surveys suggests that the binary properties at P ≲ 25 days are determined by local physics of disk/clump fragmentation and are relatively insensitive to environmental and evolutionary factors. Fully 30% of the unbiased parent sample is a binary with period P < 45 days. Completeness corrections imply a binary fraction near 55% for P < 5000 days. The observed distribution of mass ratios 0.2 < q < 1 is consistent with uniform, while the observed distribution of eccentricities 0.1 < e < 0.6 is consistent with uniform plus an excess of e ≃ 0 systems. We identify six stars, all supergiants, that exhibit aperiodic velocity variations of ∼30 km s−1 attributed to atmospheric fluctuations.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/f1ae210f5d7a7afd24e48b6db963d58bc4632256

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In Astronomy and Astrophysics

1. Ilya Mandel
2. Michela Mapelli
3. Selma de Mink
4. D. Holz
5. N. Giacobbo
6. Stan Woosley
7. N. Langer
8. Mario Spera

In Instrumentation

1. Selma de Mink
2. Ilya Mandel
3. Robert G. Izzard
4. N. Langer
5. Stan Woosley
6. N. Smith
7. D. Holz
8. H. Sana

Citations in the corpus

• Lidov–Kozai Cycles with Gravitational Radiation: Merging Black Holes in Isolated Triple Systems (2016, result): “The log-uniform distribution for binary orbits (known as Öpik’s law) is roughly consistent with the results of Kobulnicky et al. (2014), derived from observations of 48 massive star systems in the Cygnus OB2 association;however, the assumption that the inner and outer orbit in a triple system can…”
• Delay-time distribution of core-collapse supernovae with late events resulting from binary interaction (2017, methodology): “(4) We adopt π = 0, also known as Öpik’s law (1924), for systems with primary masses up to 15 M (Kobulnicky et al. 2014; Moe & Di Stefano 2015).”
• ASTROPHYSICAL IMPLICATIONS OF THE BINARY BLACK HOLE MERGER GW150914 (2016, background): “The fact that the majority of massive stars are members of binary systems with a roughly flat mass-ratio distribution (Kobulnicky & Fryer 2007; Sana et al. 2012; Kobulnicky et al. 2014) provides the opportunity for BBH formation in isolated binary systems.”
• Luminous blue variables are antisocial: their isolation implies that they are kicked mass gainers in binary evolution (2014, background): “…in binary systems whose separation is small enough that they will exchange mass (Sana et al. 2012, 2008, 2009; Kiminki & Kobulnicky 2012; Kiminki et al. 2012; Kobulnicky et al. 2014; Chini et al. 2012; Mahy et al. 2009; Evans et al. 2006; De Becker et al. 2006; Garcia & Mermilliod 2001; Gies 1987).”
• The effect of pair-instability mass loss on black-hole mergers (2016, methodology): “Initial parameters for massive binary stars (progenitors of neutron stars and black holes; MZAMS & 7−10 M ) are guided by recent observations of O/B binaries (Sana et al. 2012; Kobulnicky et al. 2014).”
• Binary Black Hole Mergers from Field Triples: Properties, Rates, and the Impact of Stellar Evolution (2017, result): “This choice is consistent with observations of massive binary stars which indicate a nearly flat distribution of the mass ratio (e.g., Sana et al. 2012; Duchêne & Kraus 2013; Kobulnicky et al. 2014).”
• The chemically homogeneous evolutionary channel for binary black hole mergers: rates and properties of gravitational-wave events detectable by advanced LIGO (2016, background): “…of massive binary systems from a Kroupa initial mass function (IMF) for the primary star (Kroupa &Weidner 2003), a flat mass ratio distribution (e.g. Sana et al. 2012; Kobulnicky et al. 2014) and a distribution of orbital periods appropriate for O-type stars (Sana et al. 2012) as detailed in MdM16.”
• Merging binary black holes formed through chemically homogeneous evolution in short-period stellar binaries (2015, methodology): “We adopt a flat mass ratio distribution for q ∈ [0.1, 1], where q = m2/m1 (e.g. Sana et al. 2012; Kobulnicky et al. 2014).”
• Massive runaway and walkaway stars (2018, background): “Most young, unevolved massive stars have a nearby companion with which they form a close binary system (e.g., Sana et al. 2012; Chini et al. 2012; Kobulnicky et al. 2014; Almeida et al. 2017).”
• MODULES FOR EXPERIMENTS IN STELLAR ASTROPHYSICS (MESA): BINARIES, PULSATIONS, AND EXPLOSIONS (2015, background): “Recent surveys such as Raghavan et al. (2010) suggest 30% to 50% of solar-like systems in the Galactic disk are composed of binaries, where the binary fraction is higher for more massive stars (Sana et al. 2012; Kobulnicky et al. 2014).”
• Dawes Review 6: The Impact of Companions on Stellar Evolution (2016, background): “Another recent and important discovery is that most mainsequence, massive stars are in multiple systems, with ∼70% of them predicted to interact with their companion(s) dur- ing their lifetime (e.g., Sana et al. 2012a, Kiminki & Kobulnicky 2012, Kobulnicky et al. 2012, Kobulnicky et al. 2014).”
• Greatly Enhanced Merger Rates of Compact-object Binaries in Non-spherical Nuclear Star Clusters (2017, result): “This choice is consistent with the observed mass ratios of massive binary stars (Duchêne & Kraus 2013; Sana et al. 2012; Kobulnicky et al. 2014).”
• COMPACT BINARY MERGER RATES: COMPARISON WITH LIGO/VIRGO UPPER LIMITS (2015, background): “However, Kobulnicky & Fryer (2007) and later Kobulnicky et al. (2014) used limits from observations of massive stars and have not found similarly strong constraints; instead, they argue that the orbital parameters are still consistent with the old formulations.”
• The Close Binary Fraction of Solar-type Stars Is Strongly Anticorrelated with Metallicity (2018, methodology): “The measured companion frequency is flog P≈0.15–0.20 across log P(days)=0–2, according to observations of spectroscopic (Levato et al. 1987; Abt et al. 1990; Kobulnicky et al. 2014) and eclipsing (Moe & Di Stefano 2013, 2015) early-B binaries.”
• Mind Your Ps and Qs: The Interrelation between Period (P) and Mass-ratio (Q) Distributions of Binary Stars (2016, methodology): “Sana et al. (2012) and Kobulnicky et al. (2014) identified additional SB2s with q > 0.55 and P > 500 days, which confirms that spectroscopic observations can reveal moderate mass-ratio binaries at intermediate orbital periods.”