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NASA NTRS1991

A luminous X-ray binary in M82

Optical CCD imaging at the position of a bright X-ray point source just off the visible disk of the nearby irregular galaxy M82 constrain it to be an X-ray binary with a 0.2-4 keV X-ray luminosity of not less than 9 x 10 exp 38 ergs/sec. Assuming that the X-ray emission is due to a single object, then by asumming an Eddington limit appropriate for pure electron scattering, this luminosity requires a minimum primary mass of not less than 15 solar masses; thus, this X-ray source is a black hole candidate. If the brightest optical object detected inside the X-ray error circle at B about 22.2 is the secondary to the X-ray emitter, it is most likely an early type star making this system the most luminous massive X-ray binary system known.

Stocke, John T.↗

NASA NTRS1991

IUE spectra of the eclipsing binary NN Serpentis

Low-resolution SWP and LWP IUE spectra are used to fit the temperature and angular radius of the white dwarf in the detached eclipsing binary NN Ser. It is found that the redenning to the system has E(B-V) of 0.05 +/-0.05, the white dwarf temperature is 60,000 +/-10,000 K, and the age of the white dwarf is less than 10 exp 7. The shape of eclipse and the K-magnitude of the secondary star are used to constrain the inclination of the binary and the masses and radii of the two stars. The size of the secondary star relative to its Roche lobe and the age of the white dwarf indicate that mass transfer has not yet occurred and that the system is a precataclysmic variable rather than a cataclysmic variable which has entered the period gap. Fitting the observed magnitude of the sinusoidal modulation with a reprocessing model shows that only when i is approximately equal to 90 deg is the required temperature of the secondary star consistent with these results. For this solution the white dwarf temperature is also consistent with those obtained from the IUE spectra.

Wood, Janet H.↗

NASA NTRS1991

Doublet craters and the tidal disruption of binary asteroids

An evaluation is conducted of the possibility that the tidal disruption of a population of contact binary asteroids can account for terrestrial-impact 'doublet' craters. Detailed orbital integrations indicate that while such asteroids are often disrupted by tidal forces outside the Roche limit, the magnitude of the resulting separations is too small to account for the observed doublet craters. It is hypothesized that an initial population of km-scale earth-crossing objects encompassing 10-20 percent binaries must be responsible for doublet impacts, as may be verified by future observations of earth-approaching asteroids.

Melosh, H. J.↗

NASA NTRS1992

On the nature of the symbiotic binary AX Persei

Photometric and spectroscopic observations of the symbiotic binary AX Persei are presented. This system contains a red giant that fills its tidal lobe and transfers material into an accretion disk surrounding a low-mass main-sequence star. The stellar masses - 1 solar mass for the red giant and about 0.4 solar mass for the companion - suggest AX Per is poised to enter a common envelope phase of evolution. The disk luminosity increases from L(disk) about 100 solar luminosity in quiescence to L(disk) about 5700 solar luminosity in outburst for a distance of d = 2.5 kpc. Except for visual maximum, high ionization permitted emission lines - such as He II - imply an EUV luminosity comparable to the disk luminosity. High-energy photons emitted by a hot boundary layer between the disk and central star ionize a surrounding nebula to produce this permitted line emission. High ionization forbidden lines form in an extended, shock-excited region well out of the binary's orbital plane and may be associated with mass loss from the disk.

Mikolajewska, Joanna↗

NASA NTRS1992

Colliding winds from early-type stars in binary systems

The dynamics of the wind and shock structure formed by the wind collision in early-type binary systems is examined by means of a 2D hydrodynamics code, which self-consistently accounts for radiative cooling, and represents a significant improvement over previous attempts to model these systems. The X-ray luminosity and spectra of the shock-heated region, accounting for wind attenuation and the influence of different abundances on the resultant level and spectra of X-ray emission are calculated. A variety of dynamical instabilities that are found to dominate the intershock region is examined. These instabilities are found to be particularly important when postshock material is able to cool. These instabilities disrupt the postshock flow and add a time variability of order 10 percent to the X-ray luminosity. The X-ray spectrum of these systems is found to vary with the nuclear abundances of winds. These theoretical models are used to study several massive binary systems, in particular V444 Cyg and HD 193793.

Stevens, Ian R.↗

NASA NTRS1992

On the power spectra of the wind-fed X-ray binary pulsar GX 301 - 2

A phenomenological model of accretion which is applied to the wind-fed X-ray binary pulsar GX 301 - 2 is developed, assuming that the accretion onto the neutron star does not occur from a continuous flux of plasma, but from blobs of matter which are threaded by the magnetic field lines onto the magnetic polar caps of the neutron star. These 'lumps' are produced at the magnetospheric limit by magnetohydrodynamical instability, introducing a 'noise' in the accretion process, due to the discontinuity in the flux of matter onto the neutron star. This model is able to describe the change of slope observed in the continuum component of the power spectra of the X-ray binary pulsar GX 301 - 2, in the frequency range 0.01 - 0.1 Hz. The physical properties of the infalling blobs derived in the model are in agreement with the constraints imposed by observations.

Orlandini, Mauro↗

NASA NTRS1992

An astrometric study of the Mira variable R Leonis and the occultation binary 19 Leonis

The Multichannel Astrometric Photometer (MAP) was used to determine parallaxes of stars in the region centered on the Mira variable R Leonis. R Leonis, with a parallax of 8.3 +/- 1.0 mas (120 +/- 15 pc), is significantly closer than most recent estimates. At visual wavelengths, its mean physical diameter is 612 +/- 96 times that of the sun. The photocentric motion of R Leonis is not suggestive of either optical or orbital companions, excluding possible secondary components over a wide range of magnitudes as well as orbital periods of up to approximately one decade. Nineteen Leonis, an occultation-speckle binary with a well-determined orbit and a reference star in the R Leonis field, has a distance of 92.6 +/- 12 pc. The 15.2 yr period binary exhibits a slight perturbation during the 4 yr of MAP observations. The similar primary and secondary of this A7 Vn system are 2.41 +/- 0.96 and 2.31 +/- 0.92 solar masses, respectively.

Gatewood, George↗

NASA NTRS1992

Radio continuum and X-ray properties of the coronae of RS Canum Venaticorum and related active binary systems

Data from circular polarization measurements are reported which yield radio-continuum and X-ray characterizations of the coronae of active binaries including RS CVn. The circular polarization measurements are taken at 6 cm for 28 binary systems detected at flux densities of more than 0.7 mJy, and the data are examined in conjunction with those by Drake et al. (1989). Optical positions are derived for 8 RS CVn objects, three previous detections are confirmed, and seven sources are shown to have circular polarization at levels of 2-13 percent. A total of 49 X-ray sources are confirmed in a total of 190 positions, and the correlation between X-ray and radio emissions is analyzed. No observational evidence exists to support the notion that radio and X-ray emissions are due to nonthermal electrons, and the data provide evidence for and against thermal gyrosynchrotron radio emission.

Drake, Stephen A.↗

NASA NTRS1992

Long-term variability in low-mass X-ray binaries - A study using data from Vela 5B

A complete sample of low-mass X-ray binaries in uncrowded fields obtained from Vela 5B is studied here for periodic and aperiodic time variability on time scales of more than one day. The strong 176-day periodicity in X1820 - 303 is confirmed, and evidence is found for a significant 77-day period in Cyg X-2 and for variability on time scales of less than about 200 days in Cyg X-3. Limits are set on the possible amplitude of candidate periodicities in the literature for Ser X-1 and X0614 + 091. The evidence reported here suggests that while long-term cyclic variability is common among high-mass binaries, it is a rare occurrence in low-mass systems.

Smale, Alan P.↗

NASA NTRS1992

Dynamics of binary and planetary-system interaction with disks - Eccentricity changes

Protostellar and protoplanetary systems, as well as merging galactic nuclei, often interact tidally and resonantly with the astrophysical disks via gravity. Underlying our understanding of the formation processes of stars, planets, and some galaxies is a dynamical theory of such interactions. Its main goals are to determine the geometry of the binary-disk system and, through the torque calculations, the rate of change of orbital elements of the components. We present some recent developments in this field concentrating on eccentricity driving mechanisms in protoplanetary and protobinary systems. In those two types of systems the result of the interaction is opposite. A small body embedded in a disk suffers a decrease of orbital eccentricity, whereas newly formed binary stars surrounded by protostellar disks may undergo a significant orbital evolution increasing their eccentricities.

Atrymowicz, Pawel↗

NASA NTRS1992

Populations of low-mass black hole binaries

The evolution of a population of massive binaries with low-mass secondaries is considered by contrasting the fate of black hole-producing systems with those leaving neutron stars. It is found that the interacting black hole binaries may be even more common than the familiar neutron star LMXBs. Certain unusual expected systems are described, and a comparison with present observations is made to determine the accuracy of predictions of this scenario.

Romani, Roger W.↗

NASA NTRS1992

Tidal interactions of inspiraling compact binaries

We discuss the tidal interaction in neutron star-neutron star and neutron star-black hole binaries and argue that they will not be tidally locked during the gravitational inspiral. More specifically, we show that, for inspiraling neutron stars of mass greater than about 1.2 solar mass, the shortest possible tidal synchronization time exceeds the gravitational decay time, so that the neutron star cannot be tidally locked prior to tidal disruption, regardless of its internal viscosity. For smaller mass neutron stars, an implausibly large kinematic viscosity - nearly the speed of light times the stellar radius - is required for tidal locking. We also argue that the mass transfer which occurs when the neutron star reaches the tidal radius will be unstable in neutron star-black hole binaries, and the instability will destroy the neutron star in a few orbital periods. The implications of our work for the detection of these sources by LIGO and other gravitational wave observatories and for the gamma-ray burst scenarios of Paczynski (1986, 1991) are discussed.

Bildsten, Lars↗

NASA NTRS1992

The infrared counterpart of the eclipsing X-ray binary HO253 + 193

We report the identification of the infrared counterpart of the pulsating X-ray source HO253 + 193. It is a highly reddened star varying in K light with a period near 3 hr, but an apparent even-odd effect in the light curve implies that the true period is 6.06 hr. Together with the recent report of X-ray eclipses at the latter period, this establishes the close binary nature of the source. Infrared minimum occurs at X-ray minimum, certifying that the infrared variability arises from the tidal distortion of the lobe-filling secondary. The absence of a point source at radio wavelengths, plus the distance derived from the infrared data, suggests that the binary system is accidentally located behind the dense core of the molecular cloud Lynds 1457. The eclipses and pulsations in the X-ray light curve, coupled with the hard X-ray spectrum and low luminosity, demonstrate that HO253 + 193 contains an accreting magnetic white dwarf, and hence belongs to the 'DQ Herculis' class of cataclysmic variables.

Zuckerman, B.↗

NASA NTRS1992

Terrain tracking for lander guidance using binary phase-only spatial filters

We demonstrate the use of binary phase-only spatial filters (BPOFs) for tracking target sites through a sequence of gray-scale terrain images. The filters are demonstrated in a closed loop guidance system for a laboratory lander mockup. Images of a 3D terrain board taken by the lander's video camera are preprocessed to produce binary intensity contour maps of a simulated planetary surface. A BPOF is made from a section of the current preprocessed image centered on the exact desired landing site. After the lander has descended to a lower altitude, the BPOF is correlated with a new image. The position of the correlation peak is used in making the next filter and to guide the lander so as to recenter the landing site in the camera's view. We present testbed results of the accuracy with which a site may be tracted from orbit to landing, and the maximum scale, translation, and rotation which can be tolerated between subsequent images. Application of the results to NASA's proposed Mars Rover Sample Return (MRSR) and Mars Environmental Survey (MESUR) missions is discussed.

Reid, Max B.↗

NASA NTRS1993

Hydrodynamic instability and coalescence of close binary systems

The meaning of hydrodynamic instability of close binary systems is clarified, and the resulting large (but finite) value of the radial infall velocity near the end of the coalescence is estimated. Emphasis is placed on the case where the orbital decay is driven by gravitational radiation. A simple calculation of the orbital decay is presented for a simple generic model of a close binary.

Lai, Dong↗

NASA NTRS1993

RE 1016-053 - A pre-cataclysmic binary, and the first extreme ultraviolet and X-ray detections of a DAO white dwarf

Photometric observations and analysis of the optical, UV, EUV, and X-ray spectra are presented for the EUV/X-ray source RE 1016-53. Multiwavelength observations of RE 1016-53 point out that it is a precataclysmic binary. Optical spectra exhibit the steep blue continuum and Balmer absorption typical of a hot white dwarf, but there are bright, narrow emission lines of H I, He I, and Ca II superimposed on this. The white dwarf component, with T (eff) = 55,800 +/- 1000 K and log g = 7.81 +/- 0.007, dominates the spectrum from the optical to the EUV/X-ray. An He II 4686 A absorption line suggests that the white dwarf is a hydrogen-helium (DAO) hybrid star. Four of the five precataclysmic binaries with white dwarfs with T(eff) greater than 40,000 K appear to be DAOs. A mass of 0.57 +/- 0.003 solar mass has been derived.

Tweedy, R. W.↗

NASA NTRS1993

PG 0308 + 096 and PG 1026 + 002 - Two new short period binary stars resulting from common-envelope evolution

Ultraviolet spectroscopy, optical spectroscopy, and spectrophotometry have been used to study the excess UV stars PG 0308 + 096 and PG 1026 + 002. Both objects are short-period binary systems, each containing a DA white dwarf star and a dM star. Orbital periods of approximately 0.284 day for PG 0308 + 096, and aproximately 0.597 day for PG 1026, have been found by spectroscopic analysis of the H-alpha emission line. Ly-alpha and Balmer line profile fitting were used to estimate the mass of white dwarf stars; mass estimates for the dM stars are based on their spectral types. The orbital inclinations are derived from these masses, the periods, and amplitudes of the H-alpha radial velocity curves. The equivalent width of the H-alpha emission line, in each binary system, varies with the orbital phase in such a manner as to imply that it arises, in large part at least, from the hemisphere of the M star that faces the white dwarf star.

Saffer, Rex A.↗

NASA NTRS1993

Case study of binary and ternary synthetic discriminant function filters with similar in-class and out-of-class images

A simulation study is reported of the performance of two designs of ternary synthetic discriminant function (SDF) filters. The filters are compared to binary SDFs in terms of the probability of correct identification P(ID) between in-class and out-of-class image sets. Compared to binary synthetic discriminant function (BSDF) filters, both ternary SDF filters designs offer improved performance in P(ID) and thus allow extension of the maximum filter direction range when evaluated in the presence of white image noise. Larger distortion range filters translate to fewer correlations required to perform image identification, and thus higher system speed. The TSDF(SNR) filters had the highest of system performance, while TSDF(d) filters were able to improve discrimination to a degree, but their optimal designs had essentially the same SNR performance as the BSDF filters.

Downie, John D.↗