The VLT-FLAMES Tarantula Survey. VIII. Multiplicity properties of the O-type star population
University of Amsterdam1, Utrecht University2, Space Telescope Science Institute3, Johns Hopkins University4, Queen's University Belfast5, UK Astronomy Technology Centre6, University of Edinburgh7, Spanish National Research Council8, Open University9, University of Sheffield10, University of La Laguna11, University of Cambridge12, University of Bonn13, Armagh Observatory14
TL;DR: In this paper, the multiplicity properties of the massive O-type star population were analyzed using multi-epoch spectroscopy and variability analysis to identify spectroscopic binaries.
Abstract: Aims. We analyze the multiplicity properties of the massive O-type star population. With 360 O-type stars, this is the largest homogeneous sample of massive stars analyzed to date. Methods. We use multi-epoch spectroscopy and variability analysis to identify spectroscopic binaries. We also use a Monte-Carlo method to correct for observational biases. Results. We observe a spectroscopic binary fraction of 0.35\pm0.03, which corresponds to the fraction of objects displaying statistically significant radial velocity variations with an amplitude of at least 20km/s. We compute the intrinsic binary fraction to be 0.51\pm0.04. We adopt power-laws to describe the intrinsic period and mass-ratio distributions: f_P ~ (log P)^\pi\ (with 0.15 7.8', i.e. approx117 pc) and among the O9.7 I/II objects are however significantly lower than expected from statistical fluctuations. Conclusions. Using simple evolutionary considerations, we estimate that over 50% of the current O star population in 30 Dor will exchange mass with its companion within a binary system. This shows that binary interaction is greatly affecting the evolution and fate of massive stars, and must be taken into account to correctly interpret unresolved populations of massive stars.
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TL;DR: The Modules for Experiments in Stellar Astrophysics (MESA) Isochrones and Stellar Tracks (MIST) project as discussed by the authors provides a set of stellar evolutionary tracks and isochrones computed using MESA, a state-of-the-art 1D stellar evolution package.
Abstract: This is the first of a series of papers presenting the Modules for Experiments in Stellar Astrophysics (MESA) Isochrones and Stellar Tracks (MIST) project, a new comprehensive set of stellar evolutionary tracks and isochrones computed using MESA, a state-of-the-art open-source 1D stellar evolution package. In this work, we present models with solar-scaled abundance ratios covering a wide range of ages ($5 \leq \rm \log(Age)\;[yr] \leq 10.3$), masses ($0.1 \leq M/M_{\odot} \leq 300$), and metallicities ($-2.0 \leq \rm [Z/H] \leq 0.5$). The models are self-consistently and continuously evolved from the pre-main sequence to the end of hydrogen burning, the white dwarf cooling sequence, or the end of carbon burning, depending on the initial mass. We also provide a grid of models evolved from the pre-main sequence to the end of core helium burning for $-4.0 \leq \rm [Z/H] < -2.0$. We showcase extensive comparisons with observational constraints as well as with some of the most widely used existing models in the literature. The evolutionary tracks and isochrones can be downloaded from the project website at this http URL
1,301 citations
Cites background from "The VLT-FLAMES Tarantula Survey. VI..."
...Multiplicity is extremely common among O- and B-type stars; binary mass exchange is believed to occur for & 70% of O-type stars and about a third of those stars will ultimately form a binary merger product (e.g., Chini et al. 2012; Sana et al. 2012, 2013; de Mink et al. 2014)....
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TL;DR: In this article, the authors summarize the current empirical knowledge of stellar multiplicity for Main Sequence stars and brown dwarfs, as well as among populations of Pre-Main Sequence stars, and embedded protostars.
Abstract: Stellar multiplicity is an ubiquitous outcome of the star formation process Characterizing the frequency and main characteristics of multiple systems and their dependencies on primary mass and environment is therefore a powerful tool to probe this process While early attempts were fraught with selection biases and limited completeness, instrumentation breakthroughs in the last two decades now enable robust analyses In this review, we summarize our current empirical knowledge of stellar multiplicity for Main Sequence stars and brown dwarfs, as well as among populations of Pre-Main Sequence stars and embedded protostars Clear trends as a function of both primary mass and stellar evolutionary stage are identified that will serve as a comparison basis for numerical and analytical models of star formation
1,261 citations
TL;DR: The Modules for Experiments in Stellar Astrophysics (MESA) Isochrones and Stellar Tracks (MIST) project as mentioned in this paper provides a set of stellar evolutionary tracks and isochrones computed using MESA, a state-of-the-art 1D stellar evolution package.
Abstract: This is the first of a series of papers presenting the Modules for Experiments in Stellar Astrophysics (MESA) Isochrones and Stellar Tracks (MIST) project, a new comprehensive set of stellar evolutionary tracks and isochrones computed using MESA, a state-of-the-art open-source 1D stellar evolution package. In this work, we present models with solar-scaled abundance ratios covering a wide range of ages ($5 \leq \rm \log(Age)\;[yr] \leq 10.3$), masses ($0.1 \leq M/M_{\odot} \leq 300$), and metallicities ($-2.0 \leq \rm [Z/H] \leq 0.5$). The models are self-consistently and continuously evolved from the pre-main sequence to the end of hydrogen burning, the white dwarf cooling sequence, or the end of carbon burning, depending on the initial mass. We also provide a grid of models evolved from the pre-main sequence to the end of core helium burning for $-4.0 \leq \rm [Z/H] < -2.0$. We showcase extensive comparisons with observational constraints as well as with some of the most widely used existing models in the literature. The evolutionary tracks and isochrones can be downloaded from the project website at this http URL
1,127 citations
TL;DR: In this article, the authors explore a newly proposed channel to create binary black holes of stellar origin, where mixing induced by rotation and tides transports the products of hydrogen burning throughout the stellar envelopes.
Abstract: We explore a newly proposed channel to create binary black holes of stellar origin. This scenario applies to massive, tight binaries where mixing induced by rotation and tides transports the products of hydrogen burning throughout the stellar envelopes. This slowly enriches the entire star with helium, preventing the build-up of an internal chemical gradient. The stars remain compact as they evolve nearly chemically homogeneously, eventually forming two black holes, which we estimate typically merge 4–11 Gyr after formation. Like other proposed channels, this evolutionary pathway suffers from significant theoretical uncertainties, but could be constrained in the near future by data from advanced ground-based gravitational-wave detectors. We perform Monte Carlo simulations of the expected merger rate over cosmic time to explore the implications and uncertainties. Our default model for this channel yields a local binary black hole merger rate of about 10 Gpc−3 yr−1 at redshift z = 0, peaking at twice this rate at z = 0.5. This means that this channel is competitive, in terms of expected rates, with the conventional formation scenarios that involve a common-envelope phase during isolated binary evolution or dynamical interaction in a dense cluster. The events from this channel may be distinguished by the preference for nearly equal-mass components and high masses, with typical total masses between 50 and 110 M⊙. Unlike the conventional isolated binary evolution scenario that involves shrinkage of the orbit during a common-envelope phase, short time delays are unlikely for this channel, implying that we do not expect mergers at high redshift.
496 citations
Cites result from "The VLT-FLAMES Tarantula Survey. VI..."
...The latter assumption is consistent with the observational data available so far, which show no statistically significant trends with metallicity or environment (e.g., Moe & Di Stefano 2013; Sana et al. 2013)....
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TL;DR: In this paper, the authors presented a new set of synthesis models for stellar populations obtained with Starburst99 and based on new stellar evolutionary tracks with rotation, which results in pronounced changes in the integrated spectral energy distribution of a population containing massive stars.
Abstract: We present a new set of synthesis models for stellar populations obtained with Starburst99 and based on new stellar evolutionary tracks with rotation. We discuss models with zero rotation velocity and with velocities of 40% of the break-up velocity on the zero-age main-sequence. These values are expected to bracket realistic rotation velocity distributions in stellar populations. The new rotating models for massive stars are more luminous and hotter due to a larger convective core and enhanced surface abundances. This results in pronounced changes in the integrated spectral energy distribution of a population containing massive stars. The changes are most significant at the shortest wavelengths where an increase of the ionizing luminosity by up to a factor of five is predicted. We also show that high equivalent widths of recombination lines may not necessarily indicate a very young age but can be achieved at ages as late as ~107 yr. Comparison of these two boundary cases (0% and 40% of the break-up velocity) will allow users to evaluate the effects of rotation and provide guidance for calibrating the stellar evolution models. We also introduce a new theoretical ultraviolet spectral library built from the Potsdam Wolf-Rayet atmospheres. Its purpose is to help identify signatures of Wolf-Rayet stars in the ultraviolet whose strength is sensitive to the particulars of the evolution models. The new models are available for solar and one-seventh solar metallicities. A complete suite of models can be generated on the Starburst99 Web site. The updated Starburst99 package can be retrieved from that Web site as well.
440 citations
References
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TL;DR: In this paper, the uncertainty inherent in any observational estimate of the IMF is investigated by studying the scatter introduced by Poisson noise and the dynamical evolution of star clusters, and it is found that this apparent scatter reproduces quite well the observed scatter in power-law index determinations, thus defining the fundamental limit within which any true variation becomes undetectable.
Abstract: A universal initial mass function (IMF) is not intuitive, but so far no convincing evidence for a variable IMF exists. The detection of systematic variations of the IMF with star-forming conditions would be the Rosetta Stone for star formation.
In this contribution an average or Galactic-field IMF is defined, stressing that there is evidence for a change in the power-law index at only two masses: near 0.5 M⊙ and near 0.08 M⊙. Using this supposed universal IMF, the uncertainty inherent in any observational estimate of the IMF is investigated by studying the scatter introduced by Poisson noise and the dynamical evolution of star clusters. It is found that this apparent scatter reproduces quite well the observed scatter in power-law index determinations, thus defining the fundamental limit within which any true variation becomes undetectable. The absence of evidence for a variable IMF means that any true variation of the IMF in well-studied populations must be smaller than this scatter.
Determinations of the power-law indices α are subject to systematic errors arising mostly from unresolved binaries. The systematic bias is quantified here, with the result that the single-star IMFs for young star clusters are systematically steeper by Δα≈0.5 between 0.1 and 1 M⊙ than the Galactic-field IMF, which is populated by, on average, about 5-Gyr-old stars. The MFs in globular clusters appear to be, on average, systematically flatter than the Galactic-field IMF (Piotto & Zoccali; Paresce & De Marchi), and the recent detection of ancient white-dwarf candidates in the Galactic halo and the absence of associated low-mass stars (Ibata et al.; Mendez & Minniti) suggest a radically different IMF for this ancient population. Star formation in higher metallicity environments thus appears to produce relatively more low-mass stars. While still tentative, this is an interesting trend, being consistent with a systematic variation of the IMF as expected from theoretical arguments.
6,784 citations
"The VLT-FLAMES Tarantula Survey. VI..." refers methods in this paper
...For each combination of π, κ and fbin in our grid, we draw populations of N = 360 primary stars using a Kroupa mass function (Kroupa 2001) between 15 and 80 M , covering thus the expected mass range of O-type stars....
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TL;DR: More than 70% of all massive stars will exchange mass with a companion, leading to a binary merger in one-third of the cases, greatly exceed previous estimates and imply that binary interaction dominates the evolution of massive stars, with implications for populations ofmassive stars and their supernovae.
Abstract: The presence of a nearby companion alters the evolution of massive stars in binary systems, leading to phenomena such as stellar mergers, x-ray binaries, and gamma-ray bursts. Unambiguous constraints on the fraction of massive stars affected by binary interaction were lacking. We simultaneously measured all relevant binary characteristics in a sample of Galactic massive O stars and quantified the frequency and nature of binary interactions. More than 70% of all massive stars will exchange mass with a companion, leading to a binary merger in one-third of the cases. These numbers greatly exceed previous estimates and imply that binary interaction dominates the evolution of massive stars, with implications for populations of massive stars and their supernovae.
1,779 citations
"The VLT-FLAMES Tarantula Survey. VI..." refers background or methods or result in this paper
...Second, Sana et al. (2012) studied the multiplicity properties of the O star populations in nearby young open clusters....
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...Indeed most of the detected binaries in 30 Dor have too few RV measurements to compute a meaningful orbital solution, precluding the direct approach used by Sana et al. (2012)....
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...The value of the period distribution index is remarkably close to the value πGOC = −0.55 ± 0.22 found in the O star population of Galactic open clusters (GOCs, Sana et al. 2012)....
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...The detected binary fraction predicted by the simulations is compared to the observed fraction using a Binomial distribution (Sana et al. 2012)....
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...Sana et al. (2012) used a Monte-Carlo method to retrieve the intrinsic multiplicity properties of O-type stars in nearby Galactic open clusters....
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TL;DR: In this paper, the authors present new or improved methods for calculating NLTE, line-blanketed model atmospheres for hot stars with winds (spectral types A to O), with particular emphasis on fast performance.
Abstract: We present new or improved methods for calculating NLTE, line-blanketed model atmospheres for hot stars with winds (spectral types A to O), with particular emphasis on fast performance These methods have been implemented into a previous, more simple version of the model atmosphere code F (Santolaya-Rey et al 1997) and allow us to spec- troscopically analyze large samples of massive stars in a reasonable time-scale, using state-of-the-art physics Although this updated version of the code has already been used in a number of recent investigations, the corresponding methods have not been explained in detail so far, and no rigorous comparison with results from alternative codes has been performed This paper intends to address both topics In particular, we describe our (partly approximate) approach to solve the equations of statistical equilibrium for those elements that are primarily responsible for line-blocking and blanketing, as well as an approximate treatment of the line-blocking itself, which is based on a simple statistical approach using suitable means of line opacities and emissivities Both methods are validated by specific tests Furthermore, we comment on our implementation of a consistent temperature structure In the second part, we concentrate on a detailed comparison with results from two codes used in alternative spectroscopical investigations, namely (Hillier & Miller 1998) and -Basic (Pauldrach et al 2001) All three codes predict almost identical temperature structures and fluxes for λ> 400 A, whereas at lower wavelengths a number of discrepancies are found Particularly in the He continua, where fluxes and corresponding numbers of ionizing photons react extremely sensitively to subtle differences in the models, we consider any uncritical use of these quantities (eg, in the context of nebula diagnostics) as unreliable Optical H/He lines as synthesized by are compared with results from , obtaining a remarkable coincidence, except for the He singlets in the temperature range between 36 000 to 41 000 K for dwarfs and between 31 000 to 35 000 K for supergiants, where predicts much weaker lines Consequences of these discrepancies are discussed Finally, suggestions are presented as to adequately parameterize model-grids for hot stars with winds, with only one additional parameter compared to standard grids from plane-parallel, hydrostatic models
458 citations
TL;DR: In this article, the fundamental parameters of a substantial number of eclipsing binaries of spectral types O and B in the Small Magellanic Cloud (SMC) were determined using spectroscopic data obtained from the 3.9m Anglo- Australian Telescope.
Abstract: We have conducted a programme to determine the fundamental parameters of a substantial number of eclipsing binaries of spectral types O and B in the Small Magellanic Cloud (SMC). New spectroscopic data, obtained with the two- degree- field (2dF) multi- object spectrograph on the 3.9- m Anglo- Australian Telescope, have been used in conjunction with photometry from the Optical Gravitational Lens Experiment (OGLE- II) data base of SMC eclipsing binaries. Previously we reported results for 10 systems; in this second and concluding paper we present spectral types, masses, radii, temperatures, surface gravities and luminosities for the components of a further 40 binaries. The uncertainties are typically +/- 10 per cent on masses, +/- 4 per cent on radii and +/- 0.07 on log L. The full sample of 50 OB- type eclipsing systems is the largest single set of fundamental parameters determined for high- mass binaries in any galaxy. We find that 21 of the systems studied are in detached configurations, 28 are in semidetached post- mass- transfer states, and one is a contact binary.The overall properties of the detached systems are consistent with theoretical models for the evolution of single stars with SMC metal abundances (Z similar or equal to 0.004); in particular, observed and evolutionary masses are in excellent agreement. Although there are no directly applicable published models, the overall properties of the semidetached systems are consistent with them being in the slow phase of mass transfer in case A. About 40 per cent of these semidetached systems show photometric evidence of orbital- phase- dependent absorption by a gas stream falling from the inner Lagrangian point on the secondary star towards the primary star. This sample demonstrates that case- A mass transfer is a common occurrence amongst high- mass binaries with initial orbital periods P less than or similar to 5 d, and that this slow phase has a comparable duration to the detached phase preceding it.Each system provides a primary distance indicator. We find a mean distance modulus to the SMC of 18.91 +/- 0.03 +/- 0.1 (internal and external uncertainties; D = 60.6 +/- 1.0 +/- 2.8 kpc). This value represents one of the most precise available determinations of the distance to the SMC.
429 citations
"The VLT-FLAMES Tarantula Survey. VI..." refers background in this paper
...Based on a smaller sample of 13 O+OB and 37 B+B eclipsing binaries (Harries et al. 2003; Hilditch et al. 2005), Pinsonneault & Stanek (2006) suggested the presence of a population of equal-mass (“twin”) binaries albeit Lucy (2006) argued that the considered sample was too small to draw…...
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TL;DR: A cosmological simulation in which the central 50 M⊙ clump breaks up into two cores having a mass ratio of two to one, with one fragment collapsing to densities of 10−8 grams per cubic centimeter is discussed.
Abstract: Previous high-resolution cosmological simulations predicted that the first stars to appear in the early universe were very massive and formed in isolation. Here, we discuss a cosmological simulation in which the central 50 M(o) (where M(o) is the mass of the Sun) clump breaks up into two cores having a mass ratio of two to one, with one fragment collapsing to densities of 10(-8) grams per cubic centimeter. The second fragment, at a distance of approximately 800 astronomical units, is also optically thick to its own cooling radiation from molecular hydrogen lines but is still able to cool via collision-induced emission. The two dense peaks will continue to accrete from the surrounding cold gas reservoir over a period of approximately 10(5) years and will likely form a binary star system.
416 citations
"The VLT-FLAMES Tarantula Survey. VI..." refers background in this paper
...Massive binaries are spectacular systems that may have been among the first objects that formed in the early universe (Turk et al. 2009; Stacy et al. 2012)....
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