We constrain the properties of massive binaries by comparing radial velocity data on early-type stars in Cygnus OB2 with the expectations of Monte Carlo models. Our comparisons test several popular prescriptions for massive binary parameters. We explore a range of true binary fraction, F, a range of power-law slopes, ?, describing the distribution of companion masses between the limits qlow and 1, and a range of power-law slopes, ?, describing the distribution of orbital separations between the limits rin and rout. We also consider distributions of secondary masses described by a Miller-Scalo type IMF and by a two-component IMF that includes a substantial ``twin'' population with M2 M1. Several seemingly disparate prescriptions for massive binary characteristics can be reconciled by adopting carefully chosen values for F, rin, and rout. We show that binary fractions F < 0.7 are less probable than F ? 0.8 for reasonable choices of rin and rout. Thus, the true binary fraction is high. For F = 1.0 and a distribution of orbital separations near the canonical Opik's law distribution (i.e., flat; ? = 0), the power-law slope of the mass ratio distribution is ? = -0.6 to 0.0. For F 0.8, ? is somewhat larger, in the range -0.4 to 1.0. In any case, the secondary star mass function is inconsistent with a Miller-Scalo-like IMF unless the lower end is truncated below ~2-4 M?. In other words, massive stars preferentially have massive companions. The best-fitting models are described by a Salpeter or Miller-Scalo IMF for 60% of secondary star masses with the other ~40% of secondaries having M2 M1, i.e., twins. These model parameters simultaneously predict the fraction of Type Ib/c supernovae to be 30%-40% of all core-collapse supernovae, in agreement with recent observational estimates.

https://iopscience.iop.org/article/10.1086/522073/pdf

A New Look at the Binary Characteristics of Massive Stars

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, 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 more » 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{sup –1} attributed to atmospheric fluctuations. « less

http://iopscience.iop.org/article/10.1088/0067-0049/213/2/34/pdf

Toward complete statistics of massive binary stars: penultimate results from the cygnus ob2 radial velocity survey

We constrain the properties of massive binaries by comparing radial velocity data of Cygnus OB2 with Monte Carlo models. Our comparisons test several popular prescriptions for massive binary parameters. We explore a range of true binary fraction, F, a range of power-law slopes, \alpha, describing the distribution of companion masses, and a range of power-law slopes, \beta, describing the distribution of orbital separations. We also consider distributions of secondary masses described by a Miller-Scalo type initial mass function and by a two-component IMF that includes a substantial ``twin'' population with M_2 ~ M_1. We show that binary fractions F 0.8. Thus, the true binary fraction is high. For F=1.0 and a distribution of orbital separations near the canonical Opik's Law distribution (i.e., flat; \beta=0), the power law slope of the mass ratio distribution is \alpha= -0.6 - 0.0. For F~0.8, \alpha is somewhat larger, in the range -0.4 - 1.0. In any case, the secondary star mass function is inconsistent with a Miller-Scalo -like IMF unless the lower end is truncated below ~ 2--4 solar masses. In other words, massive stars preferentially have massive companions. The best fitting models are described by a Salpeter or Miller-Scalo IMF for 60% of secondary star masses with the other 40% of secondaries having M_2 ~ M_1, i.e., ``twins''. These best-fitting model parameters simultaneously predict the fraction of type Ib/c supernovae to be 30-40% of all core-collapse supernovae, in agreement with recent observational estimates.

https://arxiv.org/pdf/astro-ph/0605069.pdf

▪ Abstract Stars over essentially the whole mass domain can become pulsationally unstable during various stages of their evolution. They will appear as variable stars with characteristics that are ...

/pdf/stellar-pulsations-across-the-hr-diagram-part-1-4e9rm5u5il.pdf

STELLAR PULSATIONS ACROSS THE HR DIAGRAM: Part 1

We measured the radial-velocity curve of HD 77581, the B-supergiant companion of the X-ray pulsar Vela X-1, using 183 high-resolution optical spectra obtained in a nine-month campaign. We derive radial-velocity amplitudes for dierent lines and wavelength regions, and nd all are consistent with each other, as well as with values found in previous analyses. We show that one apparent exception, an anomalously low value derived from ultra-violet spectra obtained with the International Ultraviolet Explorer, was due to an error in the analysis procedures. We re-analyse all IUE spectra, and combine the resulting velocities with the ones derived from the new optical spectra presented here, as well as those derived from optical spectra published earlier. As in previous analyses, the radial velocities show strong deviations from those expected for a pure Keplerian orbit, with root- mean-square amplitudes of 7k m s 1 for strong lines of Si iv and N iii near 4100 A, and up to20 km s 1 for weaker lines of N ii and Al iii near 5700 A. The deviations likely are related to the pronounced line-prole variations seen in our spectra. Our hope was that the deviations would average out when a sucient number of spectra were added together. It turns out, however, that systematic deviations as a function of orbital phase are present as well, at the 3 km s 1 level, with the largest deviations occurring near inferior conjunction of the neutron star and near the phase of maximum approaching velocity. While the former might be due to a photo-ionisation wake, for which we observe direct evidence in the proles of H and H, the latter has no straightforward explanation. As a result, our best estimate of the radial-velocity amplitude, Kopt =2 1:7 1: 6k m s 1 , has an uncertainty not much reduced to that found in previous analyses, in which the influence of the systematic, phase-locked deviations had not been taken into account. Combining our velocity amplitude with the accurate orbital elements of the X-ray pulsar, we infer Mns sin 3 i =1 :78 0:15 M ??? .

/pdf/the-mass-of-the-neutron-star-in-vela-x-1-2nq5pxbe7q.pdf

G. D. Penrod

Papers

Detection of high-order nonradial oscillations on the rapid rotator Zeta Ophiuchi and their link with Be type outbursts