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 = /M1. 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 20 days (separations a 0.4 au), the binaries have small eccentricities e 0.4, favor modest mass ratios , and exhibit a small excess of twins q > 0.95. Second, the companion frequency peaks at intermediate periods log P (days) 3.5 (a 10 au), where the binaries have mass ratios weighted toward small values q 0.2-0.3 and follow a Maxwellian "thermal" eccentricity distribution. Finally, companions with long orbital periods log P (days) 5.5-7.5 (a 200-5000 au) are outer tertiary components in hierarchical triples and have a mass ratio distribution across q 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 to the corrected distributions, which can be incorporated into binary population synthesis studies.
ABSTRACT
The Roche lobe formalism describes mass transfer from one star to another. We develop an extension to hierarchical triples, considering the case in which a star donates mass to a companion ...which is itself a binary. The L1 point moves as the inner binary rotates, and the Roche lobe pulsates with the period of the inner binary. Signatures of mass transfer may therefore be imprinted with the orbital period of the inner binary. For some system parameters, the pulsing Roche lobe can drive mass transfer at high rates. Systems undergoing this type of mass transfer include those with inner binaries consisting of compact objects that will eventually merge, as well as progenitors of Type Ia supernovae.
ABSTRACT
The community may be on the verge of detecting low-frequency gravitational waves from massive black hole binaries (MBHBs), but no examples of binary active galactic nuclei (AGN) have been ...confirmed. Because MBHBs are intrinsically rare, the most promising detection methods utilize photometric data from all-sky surveys. Gravitational self-lensing has recently been proposed as a method of detecting AGN in close separation binaries. In this study, we calculate the detectability of lensing signatures in realistic populations of simulated MBHBs. Within our model assumptions, we find that VRO’s LSST should be able to detect tens to hundreds of self-lensing binaries, with the rate uncertainty depending primarily on the orientation of AGN discs relative to their binary orbits. Roughly a quarter of lensing detectable systems should also show detectable Doppler boosting signatures. If AGN discs tend to be aligned with the orbit, lensing signatures are very nearly achromatic, while in misaligned configurations, the bluer optical bands are lensed more than redder ones. Whether substantial obscuring material (e.g. a dusty torus) will be present in close binaries remains uncertain, but our estimates suggest that a substantial fraction of systems would still be observable in this case.
ABSTRACT We analyze 221 eclipsing binaries (EBs) in the Large Magellanic Cloud with B-type main-sequence (MS) primaries (M1 4-14 ) and orbital periods P = 20-50 days that were photometrically ...monitored by the Optical Gravitational Lensing Experiment. We utilize our three-stage automated pipeline to (1) classify all 221 EBs, (2) fit physical models to the light curves of 130 detached well-defined EBs from which unique parameters can be determined, and (3) recover the intrinsic binary statistics by correcting for selection effects. We uncover two statistically significant trends with age. First, younger EBs tend to reside in dustier environments with larger photometric extinctions, an empirical relation that can be implemented when modeling stellar populations. Second, younger EBs generally have large eccentricities. This demonstrates that massive binaries at moderate orbital periods are born with a Maxwellian "thermal" orbital velocity distribution, which indicates they formed via dynamical interactions. In addition, the age-eccentricity anticorrelation provides a direct constraint for tidal evolution in highly eccentric binaries containing hot MS stars with radiative envelopes. The intrinsic fraction of B-type MS stars with stellar companions q = M2/M1 > 0.2 and orbital periods P = 20-50 days is (7 2)%. We find early-type binaries at P = 20-50 days are weighted significantly toward small mass ratios q 0.2-0.3, which is different than the results from previous observations of closer binaries with P < 20 days. This indicates that early-type binaries at slightly wider orbital separations have experienced substantially less competitive accretion and coevolution during their formation in the circumbinary disk.
Early B-type main-sequence (MS) stars (M sub(1) approx = 5-16 M sub(middot in circle)) with closely orbiting low-mass stellar companions (q = M sub(2)/M sub(1) < 0.25) can evolve to produce Type Ia ...supernovae, low-mass X-ray binaries, and millisecond pulsars. However, the formation mechanism and intrinsic frequency of such close extreme mass-ratio binaries have been debated, especially considering none have hitherto been detected. Utilizing observations of the Large Magellanic Cloud galaxy conducted by the Optical Gravitational Lensing Experiment, we have discovered a new class of eclipsing binaries in which a luminous B-type MS star irradiates a closely orbiting low-mass pre-MS companion that has not yet fully formed. The primordial pre-MS companions have large radii and discernibly reflect much of the light they intercept from the B-type MS primaries ( Delta I sub(refl) approx = 0.02-0.14 mag). For the 18 definitive MS + pre-MS eclipsing binaries in our sample with good model fits to the observed light-curves, we measure short orbital periods P = 3.0-8.5 days, young ages tau approx = 0.6-8 Myr, and small secondary masses M sub(2) approx = 0.8-2.4 M sub(middot in circle) (q approx = 0.07-0.36). The majority of these nascent eclipsing binaries are still associated with stellar nurseries, e.g., the system with the deepest eclipse Delta I sub(1) = 2.8 mag and youngest age tau = 0.6 + or - 0.4 Myr is embedded in the bright H II region 30 Doradus. After correcting for selection effects, we find that (2.0 + or - 0.6)% of B-type MS stars have companions with short orbital periods P = 3.0-8.5 days and extreme mass ratios q approx = 0.06-0.25. This is approx =10 times greater than that observed for solar-type MS primaries. We discuss how these new eclipsing binaries provide invaluable insights, diagnostics, and challenges for the formation and evolution of stars, binaries, and H II regions.
ABSTRACT
We examine the light curves of two quasars, motivated by recent suggestions that a supermassive black hole binary (SMBHB) can exhibit sharp lensing spikes. We model the variability of each ...light curve as due to a combination of two relativistic effects: the orbital relativistic Doppler boost and gravitational binary self-lensing. In order to model each system, we extend previous Doppler plus self-lensing models to include eccentricity. The first quasar is identified in optical data as a binary candidate with a 20-yr period (Ark 120), and shows a prominent spike. For this source, we rule out the lensing hypothesis and disfavour the Doppler-boost hypothesis due to discrepancies in the measured versus recovered values of the binary mass and optical spectral slope. The second source, which we nickname Spikey, is the rare case of an active galactic nucleus identified in Kepler’s high-quality, high-cadence photometric data. For this source, we find a model, consisting of a combination of Doppler modulation and a narrow symmetric lensing spike, consistent with an eccentric SMBHB with a mass of $M_{\text{tot}} = 3\times 10^{7} {\, \mathrm{M}_{\odot }}$, rest-frame orbital period T = 418 d, eccentricity e = 0.5, and seen at an inclination of 8○ from edge-on. This interpretation can be tested by monitoring Spikey for periodic behaviour and recurring flares in the next few years. In preparation for such monitoring, we present the first X-ray observations of this object taken by the Neil Gehrels Swift Observatory.
Abstract
Nearly 150 massive black hole binary (MBHB) candidates at sub-pc orbital separations have been reported in recent literature. Nevertheless, the definitive detection of even a single such ...object remains elusive. If at least one of the black holes is accreting, the light emitted from its accretion disc will be lensed by the other black hole for binary orbital inclinations near to the line of sight. This binary self-lensing could provide a unique signature of compact MBHB systems. We show that, for MBHBs with masses in the range 106–1010 M⊙ and with orbital periods less than ∼10 yr, strong lensing events should occur in one to 10s of per cent of MBHB systems that are monitored for an entire orbit. Lensing events will last from days for the less massive, shorter period MBHBs to a year for the most massive ∼10 year orbital period MBHBs. At small inclinations of the binary orbit to the line of sight, lensing must occur and will be accompanied by periodicity due to the relativistic Doppler boost. Flares at the same phase as the otherwise average flux of the Doppler modulation would be a smoking gun signature of self-lensing and can be used to constrain binary parameters. For MBHBs with separation ≳100 Schwarzschild radii, we show that finite-sized source effects could serve as a probe of MBH accretion disc structure. Finally, we stress that our lensing probability estimate implies that ∼10 of the known MBHB candidates identified through quasar periodicity should exhibit strong lensing flares.
All stellar-mass black holes have hitherto been identified by X-rays emitted from gas that is accreting onto the black hole from a companion star. These systems are all binaries with a black-hole ...mass that is less than 30 times that of the Sun
. Theory predicts, however, that X-ray-emitting systems form a minority of the total population of star-black-hole binaries
. When the black hole is not accreting gas, it can be found through radial-velocity measurements of the motion of the companion star. Here we report radial-velocity measurements taken over two years of the Galactic B-type star, LB-1. We find that the motion of the B star and an accompanying Hα emission line require the presence of a dark companion with a mass of Formula: see text solar masses, which can only be a black hole. The long orbital period of 78.9 days shows that this is a wide binary system. Gravitational-wave experiments have detected black holes of similar mass, but the formation of such massive ones in a high-metallicity environment would be extremely challenging within current stellar evolution theories.
ABSTRACT
We explore a unique electromagnetic signature of stellar-mass compact-object binaries long before they are detectable in gravitational waves. We show that gravitational lensing of light ...emitting components of a compact-object binary, by the other binary component, could be detectable in the nearby Universe. This periodic lensing signature could be detected from present and future X-ray observations, identifying the progenitors of binaries that merge in the LIGO band, and also unveiling populations that do not merge, thus providing a tracer of the compact-object binary population in an enigmatic portion of its life. We argue that periodically repeating lensing flares could be observed for ≲100 ks orbital-period binaries with the future Lynx X-ray mission, possibly concurrent with gravitational wave emission in the LISA band. Binaries with longer orbital periods could be more common and be detectable as single lensing flares, though with reliance on a model for the flare that can be tested by observations of succeeding flares. Non-detection of such events, even with existing X-ray observations, will help to constrain the population of EM bright compact-object binaries.
We investigated the time-variability and spectral properties of the eclipsing X-ray source Circinus Galaxy X-1 (GG X-1), using Chandra, XMM-Newton and ROSAT. We phase-connected the light curves ...observed over 20 yr, and we obtained a best-fitting period P = (25,970.0 0.1) s 7.2 hr, and a period derivative P ˙ P = ( 10.2 4.6 ) × 10 − 7 yr−1. The X-ray light curve shows asymmetric eclipses, with sharp ingresses and slow, irregular egresses. The eclipse profile and duration vary substantially from cycle to cycle. We show that the X-ray spectra are consistent with a power-law-like component, which is absorbed by neutral and ionized Compton-thin material, and by a Compton-thick, partial-covering medium, which is responsible for the irregular dips. The high X-ray/optical flux ratio rules out the possibility that CG X-1 is a foreground Cataclysmic Variable. In agreement with previous studies, we conclude that it is the first example of a compact ultraluminous X-ray source fed by a Wolf-Rayet star or stripped Helium star. Its unocculted luminosity varies between 4 × 1039 erg s−1 and 3 × 1040 erg s−1. Both the donor star and the super-Eddington compact object drive powerful outflows. We suggest that the occulting clouds are produced in the wind-wind collision region and in the bow shock in front of the compact object. Among the rare sample of Wolf-Rayet X-ray binaries, CG X-1 is an exceptional target for studies of supercritical accretion and close binary evolution; it is also a likely progenitor of gravitational wave events.
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