An analytical model of eclipsing binary star systems
Model of eclipsing binary star system based on digital computers
Wood, D. B.↗
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An analytic model of eclipsing binary star systems
Analytical model of eclipsing binary star systems, testing validity through numerical integration error analysis
Wood, D. B.↗
Terrestrial Planet Formation in Binary Star Systems
Most stars reside in multiple star systems; however, virtually all models of planetary growth have assumed an isolated single star. Numerical simulations of the collapse of molecular cloud cores to form binary stars suggest that disks will form within such systems. Observations indirectly suggest disk material around one or both components within young binary star systems. If planets form at the right places within such circumstellar disks, they can remain in stable orbits within the binary star systems for eons. We are simulating the late stages of growth of terrestrial planets within binary star systems, using a new, ultrafast, symplectic integrator that we have developed for this purpose. We show that the late stages of terrestrial planet formation can indeed take place in a wide variety of binary systems and we have begun to delineate the range of parameter space for which this statement is true. Results of our initial simulations of planetary growth around each star in the alpha Centauri system and other 'wide' binary systems, as well as around both stars in very close binary systems, will be presented.
Lissauer, Jack J.↗
Terrestrial Planet Formation in Binary Star Systems
Most stars reside in binary/multiple star systems; however, previous models of planet formation have studied growth of bodies orbiting an isolated single star. Disk material has been observed around one or both components of various young close binary star systems. If planets form at the right places within such disks, they can remain dynamically stable for very long times. We have simulated the late stages of growth of terrestrial planets in both circumbinary disks around 'close' binary star systems with stellar separations ($a_B$) in the range 0.05 AU $\le a_B \le$ 0.4 AU and binary eccentricities in the range $0 \le e \le 0.8$ and circumstellar disks around individual stars with binary separations of tens of AU. The initial disk of planetary embryos is the same as that used for simulating the late stages of terrestrial planet growth within our Solar System and around individual stars in the Alpha Centauri system (Quintana et al. 2002, A.J., 576, 982); giant planets analogous to Jupiter and Saturn are included if their orbits are stable. The planetary systems formed around close binaries with stellar apastron distances less than or equal to 0.2 AU with small stellar eccentricities are very similar to those formed in the Sun-Jupiter-Saturn, whereas planetary systems formed around binaries with larger maximum separations tend to be sparser, with fewer planets, especially interior to 1 AU. Likewise, when the binary periastron exceeds 10 AU, terrestrial planets can form over essentially the entire range of orbits allowed for single stars with Jupiter-like planets, although fewer terrestrial planets tend to form within high eccentricity binary systems. As the binary periastron decreases, the radial extent of the terrestrial planet systems is reduced accordingly. When the periastron is 5 AU, the formation of Earth-like planets near 1 AU is compromised.
Lissauer, J. J.↗
A computer program for modeling non-spherical eclipsing binary star systems
The accurate analysis of eclipsing binary light curves is fundamental to obtaining information on the physical properties of stars. The model described accounts for the important geometric and photometric distortions such as rotational and tidal distortion, gravity brightening, and reflection effect. This permits a more accurate analysis of interacting eclipsing star systems. The model is designed to be useful to anyone with moderate computing resources. The programs, written in FORTRAN 4 for the IBM 360, consume about 80k bytes of core. The FORTRAN program listings are provided, and the computational aspects are described in some detail.
Wood, D. B.↗
RY Scuti: Infrared and radio observations of the mass-loss wind of a massive binary star system
We report infrared (IR) imaging, IR photometry, IR spectroscopy, optical/IR photopolarimetry, and Very Large Array (VLA) radio observations of the peculiar binary star RY Scuti. These observations provide an unprecedented view of the detailed spatial structure of the equatorial mass-loss wind of a massive, luminous, 'overcontact' binary system. The binary star (0.43 AU separation) is surrounded by a flattened equatorial disk with an outer radius of approximately = 3 x 10(exp 16) cm (2000 AU) that emits strongly in the IR and radio. The inside of the disk is ionized and emits free-free radiation from hydrogen and 12.8 micrometers forbidden-line emission from (Ne II); the outside of the disk emits thermal radiation from silicate dust. Radio continuum emission is also produced in a compact H II region surrounding the binary. The dust may have a polycyclic aromatic hydrocarbon (PAH) component. We use a rudimentary geometric model in which the thermal IR and radio emission from the disk are assumed to arise in a pair of concentric toroidal rings to estimate the physical properties of the disk. The mean radius of the ionized gas toroid is approximately = 1.3 x 10(exp 16) cm (870 AU), and the mean radius of the dust toroid is approximately = 2.2 x 10(exp 16) cm (1470 AU). RY Scuti has a small intrinsic polarization, with the electric vector perpendicular to the equatorial disk, that is probably caused by electron scattering from hot gas close to the central binary. We conclude that neon in the nebula is overabundant with respect to hydrogen and helium by a factor of between 1.6 and 10. Our IR/radio image data suggest that the circumstellar disk is part of an extensive radiation driven mass-loss outflow that is strongly confined to the equatorial plane of the binary system. The sharp spatial separation of the outer dust torous from the inner ionized gas torus confirms earlier suggestions that dust formation in the circumstellar ejecta of very hot stars must occur in regions that are shielded from the hard radiation field.
Gehrz, R. D.↗
The Binary INformation from Open Clusters Using SEDs (BINOCS) Project: Reliable Photometric Mass Determinations of Binary Star Systems in Clusters
We introduce a new binary detection technique, Binary INformation from Open Clusters using SEDs (binocs), which we show is able to determine reliable stellar multiplicity and masses over a much larger mass range than current approaches. This new technique determines accurate component masses of binary and single systems of the open clusters’ main sequence by comparing observed magnitudes from multiple photometric filters to synthetic star spectral energy distributions (SEDs), allowing us to systematically probe the binary population for low-mass stars in clusters for eight well-studied open clusters. We provide new deep, infrared photometric catalogs (1.2–8.0 μm) for the key open clusters NGC 1960 (M36), NGC 2099 (M37), NGC 2420, and NGC 2682 (M67), using observations from NOAO/NEWFIRM and Spitzer/IRAC. Using these deep multiwavelength catalogs, the binocs method is applied to these clusters to determine accurate component masses for unresolved cluster binaries. We explore binary fractions as a function of cluster age, Galactic location, and metallicity.
47 OTHER INSTRUMENTATION↗
White dwarfs in Be star binary systems
An evaluation is made of possible reasons for the persistent inability to identify white dwarf stars in the Be binary systems. It is noted that many Be stars exhibiting large optical enhancements may be Be + WD and Be + He systems, and that observations of pulsations in the H-alpha emission, as well as observation of time delays between enhancements of optical line and continuum, can identify such systems.
Apparao, K. M. V.↗
SIM Lite Detection of Habitable Planets in P-Type Binary-Planetary Systems
Close binary stars like spectroscopic binaries create a completely different environment than single stars for the evolution of a protoplanetary disk. Dynamical interactions between one star and protoplanets in such systems provide more challenges for theorists to model giant planet migration and formation of multiple planets. For habitable planets the majority of host stars are in binary star systems. So far only a small amount of Jupiter-size planets have been discovered in binary stars, whose minimum separations are 20 AU and the median value is about 1000 AU (because of difficulties in radial velocity measurements). The SIM Lite mission, a space-based astrometric observatory, has a unique capability to detect habitable planets in binary star systems. This work analyzed responses of the optical system to the field stop for companion stars and demonstrated that SIM Lite can observe exoplanets in visual binaries with small angular separations. In particular we investigated the issues for the search for terrestrial planets in P-type binary-planetary systems, where the planets move around both stars in a relatively distant orbit.
Pan, Xiaopei↗
All-sky search in early O3 LIGO data for continuous gravitational-wave signals from unknown neutron stars in binary systems
Rapidly spinning neutron stars are promising sources of continuous gravitational waves. Detecting such a signal would allow probing of the physical properties of matter under extreme conditions. A significant fraction of the known pulsar population belongs to binary systems. Searching for unknown neutron stars in binary systems requires specialized algorithms to address unknown orbital frequency modulations. We present a search for continuous gravitational waves emitted by neutron stars in binary systems in early data from the third observing run of the Advanced LIGO and Advanced Virgo detectors using the semicoherent, GPU-accelerated, binaryskyhough pipeline. The search analyzes the most sensitive frequency band of the LIGO detectors, 50–300 Hz. Binary orbital parameters are split into four regions, comprising orbital periods of three to 45 days and projected semimajor axes of two to 40 light seconds. No detections are reported. We estimate the sensitivity of the search using simulated continuous wave signals, achieving the most sensitive results to date across the analyzed parameter space.
Gravitation↗
Synchronization of magnetic stars in binary systems
Asynchronous rotation of magnetic stars in close binary systems drives substantial field-aligned electrical currents between the magnetic star and its companion. The resulting magnetohydrodynamic torque is able to account for the heretofore unexplained synchronous rotation of the strongly magnetic degenerate dwarf component in systems like AM Her, VV Pup, AN UMa, and EF Eri as well as the magnetic A type component in systems like HD 98088 and 41 Tauri. The electric fields produced by even a small asynchronism are large and may accelerate some electrons to high energies, producing radio emission. The total energy dissipation rate in systems with degenerate dwarf spin periods as short as 1 minute may reach 10 to the 33rd ergs/s. Total luminosities of this order may be a characteristic feature of such systems.
Lamb, F. K.↗
X-Ray Emission from "Uranium" Stars
The project aims to secure XMM observations of two targets with extremely low abundances of the majority of heavy elements (e.g., log[Fe/H] $\sim$-4), but that show absorption lines of uranium. The presence of an r-process element such as uranium requires a binary star system in which the companion underwent a supernova explosion. A binary star system raises the distinct possibility of the existence of a compact object, most likely a neutron star, in the binary, assuming it survived the supernova blast. The presence of a compact object then suggests X-ray emission if sufficient matter accretes to the compact object. The observations were completed less than one year ago following a series of reobservations to correct for significant flaring that occurred during the original observations. The ROSAT all-sky survey was used to report on the initial assessment of X-ray emission from these objects; only upper limits were reported. These upper limits were used to justify the XMM observing time, but with the expectation that upper limits would merely be pushed lower. The data analysis hinges critically on the quality and degree of precision with which the background is handled. During the past year, I have spent some time learning the ins and outs of XMM data analysis. In the coming year, I can apply that learning to the analysis of the 'uranium' stars.
Schlegel, Eric↗
Infrared stars in binary systems
The peculiar F-type supergiant HD 101584, which has a large and unusual infrared excess, is discussed along with the possibility that the infrared radiation could be accounted for by a cool companion. The peculiar F supergiants 89 Her, v Sgr, and R CrB are also considered as possible binary systems containing an infrared star. It is pointed out that all four of these stars have infrared excesses with characteristics similar to the infrared radiation from several cool objects which are known single stars.
Humphreys, R. M.↗
Enabling High-Contrast Imaging of Binary Stars With the Roman Space Telescope Coronagraph Instrument
A large fraction of Sun-like stars is contained in binary systems, in fact within 10 pc there are 67 FGK stars, out of which 42 belong to a multi-star system, and 28 have companion leak that is greater than 1e-9 contrast, assuming typical Hubble-quality space optics. Currently, those binary stars are not included in the Roman Space Telescope Coronagraph Instrument target list, but they could be observed if high-contrast imaging around binary star systems using Roman was possible. The Multi-Star Wavefront Control (MSWC) algorithm can be used to suppress companion star leakage. If the targets have angular separations larger than the Nyquist controllable region of the Deformable Mirror, MSWC must operate in its Super-Nyquist (SN) mode. This mode requires a target star replica within the SN region in order to provide the ability to null speckles at SN angular separations. For the case of Roman, more than half of the targets that can be observed using MSWC, including Alpha Centauri, have angular separations larger than the Nyquist controllable region of the 48x48 actuator Deformable Mirror (DM) to be used. In this paper, we describe how super-Nyquist MSWC can be implemented in Roman CGI adding a mild grating on a replica of the Wide-field Shaped Pupil mask, which would use a spare space in the Shaped Pupil Active Mechanism. We present the feasibility analysis, simulation results, and discuss the latest results on MSWC experiment from three different laboratories at NASA Ames, the Jet Propulsion Laboratory, and the Subaru telescope.
Prada, Camilo Mejia↗
Multi-Star Wavefront Control for the Wide-Field Infrared Survey Telescope
The Wide-Field Infrared Survey Telescope (WFIRST) is planned to have a coronagraphic instrument (CGI) to enable high-contrast direct imaging of exoplanets around nearby stars. The majority of nearby FGK stars are located in multi-star systems, including the Alpha Centauri stars which may represent the best quality targets for the CGI on account of their proximity and brightness potentially allowing the direct imaging of rocky planets. However, a binary system exhibits additional leakage from the off-axis companion star that may be brighter than the target exoplanet. Multi-Star Wavefront Control (MSWC) is a wavefront-control technique that allows suppression of starlight of both stars in a binary system thus enabling direct imaging of circumstellar planets in binary star systems such as Alpha Centauri. We explore the capabilities of the WFIRST CGI instrument to directly image multi-star systems using MSWC. We consider several simulated scenarios using the WFIRST CGI's Shaped Pupil Coronagraph Disk Mask. First, we consider close binaries such as Mu Cassiopeia that require no modifications to the WFIRST CGI instrument and can be implemented as a purely algorithmic solution. Second, we consider wide binaries such as Alpha Centauri that require a diffraction grating to enable suppression of the off-axis starlight leakage at Super-Nyquist separations. We demonstrate via simulation dark holes in 10 percent broadband compatible with the WFIRST CGI.
Sirbu, Dan↗
Demonstration of Multi-Star Wavefront Control for WFIRST, Habex, and LUVOIR
Coronagraphic instruments will enable direct imaging of dim planetary companions around nearby stars. The majority of nearby FGK stars are located in multi-star systems, including the Alpha Centauri stars, which may represent the best quality targets available for spectroscopic characterization due to their proximity and brightness. However, a binary system exhibits additional leakage from the o -axis companion star that may be brighter than the target exoplanet. Multi-Star Wavefront Control (MSWC) is a wavefront-control technique that allows simultaneous suppression of starlight of both stars in a binary system. MSWC would thus enable direct imaging of circumstellar planets in binary star systems such as Alpha Centauri. MSWC is compatible with a wide suite of planned coronagraphic instruments for future space missions. As part of the technology demonstration e orts for MSWC, the rst milestone results are presented here demonstrating (via computer simulations), high-contrast imaging capabilities of multi-star systems for several instruments including: [1] the upcoming WFIRST and its CGI demonstrator, [2] the HABitable Worlds EXplorer (Habex) mission concept, [3] the segmented Large UV/Optical/IR (LUVOIR) mission concept, and [4] a small-aperture Alpha Centauri direct-imager mission concept. For each of these missions, a baseline coronagraph option planned for the mission will be adopted and instrument baseline performance will be compared for single-star wavefront control.
Sirbu, Dan↗
Types of Information Expected from a Photometric Search for Extra-Solar Planets
The current theory postulates that planets are a consequence of the formation of stars from viscous accretion disks. Condensation from the hotter, inner portion of the accretion disk favors the formation of small rocky planets in the inner portion and the formation of gas giants in the cuter, cooler part. Consequently, terrestrial-type planets in inner orbits must be commonplace (Wetheril 1991). From the geometry of the situation (Borucki and Summers 1984), it can be shown that 1% of those planetary systems that resemble our solar system should show transits for Earth-sized (or larger) planets. Thus a photometric satellite that uses a wide field of view telescope and a large CCD array to simultaneously monitor 5000 target stars should detect 50 planetary systems. To verify that regularly recurring transits are occurring rather than statistical fluctuations of the stellar flux, demands observations that extend over several orbital periods so that the constancy of the orbital period, signal amplitude, and duration can be measured. Therefore, to examine the region from Mercury's orbit to that of the Earth requires a duration of three years whereas a search out to the orbit of mars requires about six years. The results of the observations should provide estimates of the distributions of planetary size and orbital radius, and the frequency of planetary systems that have Earth-sized planets in inner orbits. Because approximately one half of the star systems observed will be binary systems, the frequency of planetary systems orbit ' ing either one or both of the stars can also be determined. Furthermore, the complexity of the photometric signature of a planet transiting a pair of stars provides enough information to estimate the eccentricities of the planetary orbits. In summary, the statistical evidence from a photometric search of solar-like stars should be able to either confirm or deny the applicability of the current theory of planet formation and provide new information about the stability of planetary orbits in binary star systems.
Borucki, William↗
Radio emission from binary stars
Radio emission from binary star systems; characteristics of the binary systems inferred from the radio observations; and the reasons for the activity are reviewed. Binary stars with two main sequence stars, with one normal star and a white dwarf, and those containing a neutron star or a black hole are described. Energy may be directly available as matter falls into the potential well of a compact object. Electromagnetic induction effects may occur due to relative motions of magnetic fields and matter. By enforcing rapid rotation, binaries can induce strong dynamo action and hence generate free energy in the form of intense, complex, evolving magnetic fields. Whatever the source of energy, the observations at radio and X-ray wavelengths demonstrate that electrons are accelerated to high energies (mildly relativistic and, ultrarelativistic). Observed or inferred radio brightness temperatures range up to 10 to the 15th power K or more, implying coherent emission for sources brighter than 10 billion K.
Dulk, George A.↗