A debate has arisen concerning the fundamental nature of luminous blue variables (LBVs) and their role in stellar evolution. While Smith & Tombleson proposed that their isolated environments indicate that LBVs must be largely the product of binary evolution, Humphreys et al. have recently expressed the view that the traditional single-star view still holds if one appropriately selects a subsample of LBVs. This paper finds the claim of Humphreys et al. to be quantitatively unjustified. A statistical test of 'candidate' as opposed to 'confirmed' LBVs shows no significant difference (<1 sigma) between their environments. Even if the sample is further subdivided as proposed, the three most luminous LBVs are spatially dispersed similar to late O-type dwarfs, which have much longer median lifetimes than expected for classical LBVs. The lower luminosity LBVs have a distribution associated with red supergiants (RSGs), but these RSGs are dominated by stars of 10-15 M-circle dot initial mass, with much longer lifetimes than expected for those lower luminosity LBVs. If one's view is restricted to the highest luminosity LBVs, then the appropriate comparison is with early O-type stars that are their presumed progenitors; when this is done, it is clear that even the high-luminosity LBVs are more dispersed than expected. Humphreys et al. also suggest that velocities of LBVs support the single-star view, being inconsistent with runaways. A quantitative analysis of the radial velocity distribution of LBVS in M31 and M33 contradicts this; modest runway speeds expected from mass gainers in binary evolution are consistent with the observed velocities, although the data lack the precision to discriminate.

Classical Cepheids, like binary stars, are laboratories for stellar evolution and Cepheids in binary systems are especially powerful ones. About one-third of Galactic Cepheids are known to have companions and Cepheids in eclipsing binary systems have recently been discovered in the Large Magellanic Cloud (LMC). However, there are no known Galactic binary Cepheids with orbital periods less than one year. We compute population synthesis models of binary Cepheids to compare to the observed period and eccentricity distributions of Galactic Cepheids as well as to the number of observed eclipsing binary Cepheids in the LMC. We find that our population synthesis models are consistent with observed binary properties of Cepheids. Furthermore, we show that binary interaction on the red giant branch prevents some red giant stars from becoming classical Cepheids. Such interactions suggest that the binary fraction of Cepheids should be significantly less than that of their main-sequence progenitors, and that almost all binary Cepheids have orbital periods longer than one year. If the Galactic Cepheid spectroscopic binary fraction is about 35%, then the spectroscopic binary fraction of their intermediate mass main sequence progenitors is about 40- 45%.

The Galactic blue supergiant SBW1 with its circumstellar ring nebula represents the best known analogue of the progenitor of SN 1987A. High-resolution imaging has shown H alpha and infrared structures arising in an ionized flow that partly fills the ring's interior. To constrain the influence of the stellar wind on this structure, we obtained an ultraviolet (UV) spectrum of the central star of SBW1 with the Hubble Space Telescope Cosmic Origins Spectrograph. The UV spectrum shows none of the typical wind signatures, indicating a very low mass-loss rate. Radiative transfer models suggest an extremely low rate below 10(-10) M-circle dot yr(-1), although we find that cooling time-scales probably become comparable to (or longer than) the flow time below 10(-8) M-circle dot yr(-1). We therefore adopt this latter value as a conservative upper limit. For the central star, the model yields T-eff = 21 000 +/- 1000 K, log(g(eff)) = 3.0, L similar or equal to 5 x 10(4) L-circle dot, and roughly Solar composition except for enhanced N abundance. SBW1' s very low mass-loss rate may hinder the wind's ability to shape its nebula and to shed angular momentum. The spin-down time-scale for magnetic breaking is more than 500 times longer than the age of the ring. This, combined with the star's slow rotation rate, constrains merger scenarios to form ring nebulae. The mass-loss rate is at least 10 times lower than expected from mass-loss recipes, without any account of clumping. The physical explanation for why SBW1' s wind is so weak presents an interesting mystery.

We combine precision radial velocity data from four different published works of the stars in the Leo II dwarf spheroidal galaxy. This yields a data set that spans 19 years, has 14 different epochs of observation, and contains 372 unique red giant branch stars, 196 of which have repeat observations. Using this multi-epoch data set, we constrain the binary fraction for Leo II. We generate a suite of Monte Carlo simulations that test different binary fractions using Bayesian analysis and determine that the binary fraction for Leo II ranges from 0.30(-0.10)(+0.09) to 0.34(-0.11)(+0.11), depending on the distributions of binary orbital parameters assumed. This value is smaller than what has been found for the solar neighborhood (similar to 0.4-0.6) but falls within the wide range of values that have been inferred for other dwarf spheroidals (0.14-0.69). The distribution of orbital periods has the greatest impact on the binary fraction results. If the fraction we find in Leo II is present in low-mass ultra-faints, it can artificially inflate the velocity dispersion of those systems and cause them to appear more dark matter rich than in actuality. For a galaxy with an intrinsic dispersion of 1 km s(-1) and an observational sample of 100 stars, the dispersion can be increased by a factor of 1.5-2 for Leo II-like binary fractions or by a factor of three. for binary fractions on the higher end of what has been seen in other dwarf spheroidals.

We compile observations of early-type binaries identified via spectroscopy, eclipses, long-baseline interferometry, adaptive optics, common proper motion, etc. Each observational technique is sensitive to companions across a narrow parameter space of orbital periods P and mass ratios q. =. M-comp/M-1. After combining the samples from the various surveys and correcting for their respective selection effects, we find that the properties of companions to O-type and B-type main-sequence (MS) stars differ among three regimes. First, at short orbital periods P less than or similar to 20. days (separations a less than or similar to 0.4 au), the binaries have small eccentricities e... 0.4, favor modest mass ratios < q > less than or similar to 0.5, and exhibit a small excess of twins q. >. 0.95. Second, the companion frequency peaks at intermediate periods log P (days). approximate to. 3.5 (a approximate to 10 au), where the binaries have mass ratios weighted toward small values q. approximate to 0.2-0.3 and follow a Maxwellian " thermal" eccentricity distribution. Finally, companions with long orbital periods log P (days). approximate to 5.5-7.5 (a approximate to 200-5000 au) are outer tertiary components in hierarchical triples and have a mass ratio distribution across q. approximate to 0.1-1.0 that is nearly consistent with random pairings drawn from the initial mass function. We discuss these companion distributions and properties in the context of binary-star formation and evolution. We also reanalyze the binary statistics of solar-type MS primaries, taking into account that 30% +/-. 10% of single-lined spectroscopic binaries likely contain white dwarf companions instead of low-mass stellar secondaries. The mean frequency of stellar companions with q. >. 0.1 and log P (days). <. 8.0 per primary increases from 0.50. +/- 0.04 for solar-type MS primaries to 2.1. +/- 0.3 for O-type MS primaries. We fit joint probability density functions f (M-1, q, P, e) not equal f (M-1) f (q) f (P) f (e) to the corrected distributions, which can be incorporated into binary population synthesis studies.

The orbital parameters of binaries at intermediate periods (10(2)-10(3) d) are difficult to measure with conventional methods and are very incomplete. We have undertaken a new survey, applying our pulsation timing method to Kepler light curves of 2224 main-sequence A/F stars and found 341 non-eclipsing binaries. We calculate the orbital parameters for 317 PB1 systems (single-pulsator binaries) and 24 PB2s (double-pulsators), tripling the number of intermediate-mass binaries with full orbital solutions. The method reaches down to small mass ratios q approximate to 0.02 and yields a highly homogeneous sample. We parametrize the mass-ratio distribution using both inversion and Markov-Chain Monte Carlo forward-modelling techniques, and find it to be skewed towards low-mass companions, peaking at q approximate to 0.2. While solar-type primaries exhibit a brown dwarf desert across short and intermediate periods, we find a small but statistically significant (2.6 sigma) population of extreme-mass-ratio companions (q < 0.1) to our intermediate-mass primaries. Across periods of 100-1500 d and at q > 0.1, we measure the binary fraction of current A/F primaries to be 15.4 per cent +/- 1.4 per cent, though we find that a large fraction of the companions (21 per cent +/- 6 per cent) are white dwarfs in post-mass-transfer systems with primaries that are now blue stragglers, some of which are the progenitors of Type Ia supernovae, barium stars, symbiotics, and related phenomena. Excluding these white dwarfs, we determine the binary fraction of original A/F primaries to be 13.9 per cent +/- 2.1 per cent over the same parameter space. Combining our measurements with those in the literature, we find the binary fraction across these periods is a constant 5 per cent for primaries M-1 < 0.8 M-circle dot, but then increases linearly with log M-1, demonstrating that natal discs around more massive protostars M-1 greater than or similar to M-1(circle dot) become increasingly more prone to fragmentation. Finally, we find the eccentricity distribution of the main-sequence pairs to be much less eccentric than the thermal distribution.

Context. One of the key questions of the star formation problem is whether brown dwarfs (BDs) form in the manner of stars directly from the gravitational collapse of a molecular cloud core (star-like) or whether BDs and some very low-mass stars (VLMSs) constitute a separate population that forms alongside stars comparable to the population of planets, for example through circumstellar disk (peripheral) fragmentation. Aims. For young stars in Taurus-Auriga the binary fraction has been shown to be large with little dependence on primary mass above approximate to 0.2 M-circle dot, while for BDs the binary fraction is < 10%. Here we investigate a case in which BDs in Taurus formed dominantly, but not exclusively, through peripheral fragmentation, which naturally results in small binary fractions. The decline of the binary frequency in the transition region between star-like formation and peripheral formation is modelled. Methods. We employed a dynamical population synthesis model in which stellar binary formation is universal with a large binary fraction close to unity. Peripheral objects form separately in circumstellar disks with a distinctive initial mass function (IMF), their own orbital parameter distributions for binaries, and small binary fractions, according to observations and expectations from smoothed particle hydrodynamics (SPH) and grid-based computations. A small amount of dynamical processing of the stellar component was accounted for as appropriate for the low-density Taurus-Auriga embedded clusters. Results. The binary fraction declines strongly in the transition region between star-like and peripheral formation, exhibiting characteristic features. The location of these features and the steepness of this trend depend on the mass limits for star-like and peripheral formation. Such a trend might be unique to low density regions, such as Taurus, which host binary populations that are largely unprocessed dynamically in which the binary fraction is large for stars down to M-dwarfs and small for BDs. Conclusions. The existence of a strong decline in the binary fraction - primary mass diagram will become verifiable in future surveys on BD and VLMS binarity in the Taurus-Auriga star-forming region. The binary fraction -primary mass diagram is a diagnostic of the (non-)continuity of star formation along the mass scale, the separateness of the stellar and BD populations, and the dominant formation channel for BDs and BD binaries in regions of low stellar density hosting dynamically unprocessed populations.

Many young, massive stars are found in close binaries. Using population synthesis simulations. we predict the likelihood of a companion star being present when these massive stars end their lives as core-collapse supernovae (SNe). We focus on stripped-envelope SNe, whose progenitors have lost their outer hydrogen and possibly helium layers before explosion. We use these results to interpret new Hubble Space Telescope observations of the site of the broad-lined Type. Ic SN 2002ap, 14 years post-explosion. For a subsolar metallicity consistent with SN 2002ap, we expect a main-sequence (MS) companion present in about two thirds of all stripped-envelope SNe and a compact companion (likely a stripped helium star or a white dwarf/neutron star/black hole) in about 5% of cases. About a quarter of progenitors are single at explosion (originating from initially single stars, mergers, or disrupted systems). All of the latter scenarios require a massive progenitor, inconsistent with earlier studies of SN 2002ap. Our new, deeper upper limits exclude the presence of an MS companion star > 8-10 M., ruling out about 40% of all stripped-envelope SN channels. The most likely scenario for SN 2002ap includes nonconservative binary interaction of a primary star initially. 23 M.. Although unlikely (< 1% of the scenarios), we also discuss the possibility of an exotic reverse merger channel for broadlined Type. Ic events. Finally, we explore how our results depend on the metallicity and the model assumptions and discuss how additional searches for companions can constrain the physics that govern. the evolution of SN progenitors.

A planetary nebula (PN) consists of material, mainly gas, that has been ejected from a star on the asymptotic giant branch of its life cycle. This material emits electromagnetic radiation due to photoionization and recombination, collisional and radiative excitation or free-free radiation. The envelope of material moves outwards from the central star and may take one of a variety of shapes. These shapes are believed to be sculpted by the stellar wind, magnetic fields and interactions with a binary companion. However, within a time scale of as little as 10 000 years the nebula fades from view and merges with the interstellar medium.Similar variations in the shape of planetary nebulae (PNe) can be seen in both the Galactic Bulge and Disc and in the Magellanic Clouds. It is therefore reasonable to assume that the shaping process is universal. By classifying PNe by morphology and relating those shapes to other nebular properties we have attempted to derive information about that shaping process.We have used photometric narrowband observations of a sample of PNe listed in the Strasbourg-ESO Catalogue of Galactic Planetary Nebulae to investigate the relationship between PN morphology and the other PN characteristics. The high resolution images were made using ESO's New Technology Telescope and the Hubble Space Telescope. The information we could obtain directly from the observations was augmented by information in the literature in order to address that question. The observations were used to classify the morphologies of 154 PNe, to estimate the sizes of 138 of those nebulae that we considered to lie within the Galactic Bulge, to determine the orientations of 130 of those Bulge nebulae and to derive photometric fluxes for the 69 PNe which had observations of standard stars made during the same night. Information on central star binarity, nebular abundances and radial and expansion velocity was obtained from the literature.Our photometrically derived PNe line fluxes were used to verify 59 H-beta and 69 [OIII] catalogued values (which were obtained using spectroscopy). We found sufficient discrepancy between the values for 9 PNe to merit a further check taking place.We found no distinguishing relationship between PN morphology and any of PN size, radial velocity, or angular location within the Bulge. The abundances of He and O, and the N/O ratio, are generally lower in bipolar nebulae than in those nebulae with no apparent internal structure. We are unable to come to any conclusion as to a relationship between PN morphology and stellar metallicity.Given the short lifespan of PNe and the age of the Bulge it appears that almost all PNe in the Bulge must be associated with low mass stars. The high ratio of bipolar PNe we found in our Bulge sample suggests that, at least within the Bulge, bipolar nebulae are not necessarily associated with high mass stars. Our results show that unlike the orientations of other types of PNe the orientations of the bipolar nebulae in the Bulge are not randomly distributed. Measured to a line tip to tip along the lobes they peak and have their mean approximately along the Galactic Plane. This suggests that the bipolar PNe originate in a different environment from other morphological types, perhaps related to binary separation. However, we find that bipolarity does not imply common-envelope evolution. If the hypothesis that bipolar nebulae are formed in binary star systems is correct, binary systems in the Galactic Bulge have angular momentum vectors that are preferentially aligned along the Galactic Plane. As the orientation appears to be unrelated to lobe size and hence nebular age, the alignment implies that the non-random nature of the angular momentum vectors originated at the time the Bulge stellar population formed. We suggest that it is due to the direction and strength of the ambient magnetic fields.

Context. The structure of the inner parts of Be star disks (≲ 20 stellar radii) is well explained by the viscous decretion disk (VDD) model, which is able to reproduce the observable properties of most of the objects studied so far. The outer parts, on the other hand, are not observationally well-explored, as they are observable only at radio wavelengths. A steepening of the spectral slope somewhere between infrared and radio wavelengths was reported for several Be stars that were previously detected in the radio, but a convincing physical explanation for this trend has not yet been provided. Aims. We test the VDD model predictions for the extended parts of a sample of six Be disks that have been observed in the radio to address the question of whether the observed turndown in the spectral energy distribution (SED) can be explained in the framework of the VDD model, including recent theoretical development for truncated Be disks in binary systems. Methods. We combine new multi-wavelength radio observations from the Karl. G. Jansky Very Large Array (JVLA) and Atacama Pathfinder Experiment (APEX) with previously published radio data and archival SED measurements at ultraviolet, visual, and infrared wavelengths. The density structure of the disks, including their outer parts, is constrained by radiative transfer modeling of the observed spectrum using VDD model predictions. In the VDD model we include the presumed effects of possible tidal influence from faint binary companions. Results. For 5 out of 6 studied stars, the observed SED shows strong signs of SED turndown between far-IR and radio wavelengths. A VDD model that extends to large distances closely reproduces the observed SEDs up to far IR wavelengths, but fails to reproduce the radio SED. Using a truncated VDD model improves the fit, leading to a successful explanation of the SED turndown observed for the stars in our sample. The slope of the observed SEDs in the radio is however not well reproduced by disks that are simply cut off at a certain distance. Rather, some matter seems to extend beyond the truncation radius, where it still contributes to the observed SEDs, making the spectral slope in the radio shallower. This finding is in agreement with our current understanding of binary truncation from hydrodynamical simulations, in which the disk does extend past the truncation radius. Therefore, the most probable cause for the SED turndown is the presence of binary companions that remain undetected for most of our sources.