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NASA NTRS1983

HD 207739 - A strange composite star

This star, classified F8 IIe + B:, has a very unusual ultraviolet spectrum, with abnormally strong and numerous absorption features in the far-UV and exceptionally strong Mg II emission. There is some resemblance to shell and pre-main-sequence B stars, but it more closely matches the strange spectra of the eclipsing systems VV Cep and SX Cas, and it probably has considerable circumstellar material at fairly high temperature. HD 207739 is probably an interacting binary and needs to be monitored for light and velocity variations.

Parsons, S. B.↗

NASA NTRS1989

Sources of gravitational waves

Sources of low frequency gravitational radiation are reviewed from an astrophysical point of view. Cosmological sources include the formation of massive black holes in galactic nuclei, the capture by such holes of neutron stars, the coalescence of orbiting pairs of giant black holes, and various means of producing a stochastic background of gravitational waves in the early universe. Sources local to our Galaxy include various kinds of close binaries and coalescing binaries. Gravitational wave astronomy can provide information that no other form of observing can supply; in particular, the positive identification of a cosmological background originating in the early universe would be an event as significant as was the detection of the cosmic microwave background.

Schutz, Bernard F.↗

NASA NTRS1982

Mass flow due to heating in a binary system - Application to U Cephei

The possibility of mass flow due to the heating of the cooler component in a close binary system has been investigated. The heating may be caused by irradiation from the hotter companion or by other mechanisms such as the spacial coincidence of non-linear 'g-mode' oscillations in the cooler star. The 2.4-day period binary U Cep, in which gas streaming has been observed, has been chosen for model calculations. Preliminary results show that such a heating of the lower atmosphere of the cooler star could lead to mass flow at an average rate of 10 to the -9th - 10 to the -7th solar mass per year without the star necessarily filling its critical Roche surface.

Kondo, Y.↗

NASA NTRS1990

Dynamics of groups around interacting double ellipticals: Measuring dark matter haloes

Binary galaxies, as binary stars, are important to measure masses, as suggested by Page (1952). Because three orbit parameters are measurable for galaxies at one instant of time, severe uncertainties remain in the orbit and mass determinations. These uncertainties can partly be overcome by statistical studies of selected samples and/or n-body simulations. Close double galaxies (and isolated galaxies) could also be useful to estimate dynamical masses if we can find test particles around them. Interacting elliptical pairs or dumb-bell galaxies are found with a large range, between 0-1200 km s(exp -1), of relative radial velocities. Standard 2-body orbit calculations, highly uncertain due to projection factors, suggest for the largest velocity differences very large galaxy masses, if the systems are bound and stationary. However, recent n-body simulations model these binaries as galaxies captured from hyperbolic orbits, requiring masses of order a few times 10(exp 11) solar maximum (Borne et al. 1988), but producing systems that are short lived. A different picture appears when we study observationally the dynamical mass of interacting double ellipticals using faint satellite galaxies. These satellites contribute little luminosity and, presumably, little mass to the system. The authors present results of two such groups, basically forming systems of test particles, around the dumb-bells NGC 4782/3 and IC 5049. They also briefly discuss the satellite group around the central dumb-bell in the cluster Sersic 40/6. Apparently, they detect large quantities of dark matter in the vicinity of these dumb-bell galaxies, because the system masses of approx. 4.5 times 10(exp 13) solar mass and 8 times 10(exp 13) solar mass for NGC 4782/3 and IC 5049, respectively, are quite high. Likewise, the mass of the Sersic 40/6 inner core is 7 times 10(exp 13) solar mass. The possibility that a common massive dark matter halo increases the merging times of these types of galaxies is suggested. Here, the authors assume H sub o = 100 km s (exp -1) Mpc(exp -1).

Quintana, H.↗

NASA NTRS1993

Hard apex transition in quasi-periodic oscillators - Closing of the accretion gap

We propose that the 'hard apex' transition in the X-ray two-color diagrams for low-mass X-ray binaries exhibiting quasi-periodic oscillation is associated with closure of a gap between the accretion disk and the star. At low accretion rates, gas crosses this gap intermittently. However, when the mass accretion rate increases, the disk thickens and its inner edge touches the star, thus forming a boundary layer through which the gas flows steadily. This explanation is viable provided that the equation of state of nuclear matter is not significantly harder than the Bethe-Johnson I prescription. Accretion gap scenarios are possibly distinguishable from models which invoke a small magnetosphere around the neutron star, in that they preclude large stellar magnetic fields and associate the high-frequency (horizontal-branch) oscillations with different sites.

Biehle, Garrett T.↗

NASA NTRS1982

Nodding motions of accretion rings and disks - A short-term period in SS 433

It is pointed out that accretion disks and rings in mass transfer binaries have been observed spectroscopically and calculated theoretically for many years. The present investigation is partly based on the availability of several years of spectroscopic observations of the Doppler shifts of the moving lines in SS433. A formalism is presented to compute frequencies and amplitudes of short-term 'nodding' motions in precessing accretion disks in close binary systems. This formalism is applied to an analysis of the moving-line Doppler shifts in SS433. The 35d X-ray cycle of Hercules X-1 is also discussed. In the considered model, the companion star exerts a gravitational torque on the disk rim. Averaged over the binary orbit, this yields a steady torque which results in the mean driven counterprecession of the disk.

Katz, J. I.↗

NASA NTRS1993

VVNRS: Variable phenomena in VV Cephei

The current research project (VVNRS) involves VV Cephei, which is a binary system in which a 20 solar mass main sequence star orbits within the extended atmosphere of the 40 solar mass M-type supergiant primary. Although the period of the system is 20.3 years, the components are close enough for a stream of matter from the primary to form an accretion disk around the hot secondary. We had previously completed an ADP-sponsored study of twelve years of archival spectra of this system and were surprised to find intermittent changes in the line profiles of the chromosphere-like absorption spectrum. This we think may be related to the accretion process. The previously existing spectra were not closely spaced enough in time to clearly delineate the nature of these changes. Therefore, we proposed and were granted eleven half-shifts to obtain closely spaced IUE spectra during IUE's 14th year of operations (1991/1992).

Stencel, Robert E.↗

NASA NTRS2005

A Search for Transiting Neptune-Mass Extrasolar Planets in High-Precision Photometry of Solar-Type Stars

Tennessee State University operates several automatic photometric telescopes (APTs) at Fairborn Observatory in southern Arizona. Four 0.8 m APTs have been dedicated to measuring subtle luminosity variations that accompany magnetic cycles in solar-type stars. Over 1000 program and comparison stars have been observed every clear night in this program for up to 12 years with a precision of approximately 0.0015 mag for a single observation. We have developed a transit-search algorithm, based on fitting a computed transit template for each trial period, and have used it to search our photometric database for transits of unknown companions. Extensive simulations with the APT data have shown that we can reliably recover transits with periods under 10 days as long as the transits have a depth of at least 0.0024 mag, or about 1.6 times the scatter in the photometric observations. Thus, due to our high photometric precision, we are sensitive to transits of possible short-period Neptune-mass planets that likely would have escaped detection by current radial velocity techniques. Our search of the APT data sets for 1087 program and comparison stars revealed no new transiting planets. However, the detection of several unknown grazing eclipsing binaries from among our comparison stars, with eclipse depths of only a few millimags, illustrates the success of our technique. We have used this negative result to place limits on the frequency of Neptune-mass planets in close orbits around solar-type stars in the Sun's vicinity.

Henry, Stephen M.↗

NASA NTRS2022

Testing Lyα Emission-line Reconstruction Routines at Multiple Velocities in One System

The 1215.67 Å H ו Lyα emission line dominates the ultraviolet flux of low-mass stars, including the majority of known exoplanet hosts. Unfortunately, strong attenuation by the interstellar medium (ISM) obscures the line core in most stars, requiring the intrinsic Lyα flux to be reconstructed based on fits to the line wings. We present a test of the widely used Lyα emission-line reconstruction code ւʏᴀᴘʏ using phase-resolved, medium-resolution STIS G140M observations of the close white dwarf–M dwarf binary EG UMa. The Doppler shifts induced by the binary orbital motion move the Lyα emission line in and out of the region of strong ISM attenuation. Reconstructions of each spectrum should produce the same Lyα profile regardless of phase, under the well-justified assumption that there is no intrinsic line variability between observations. Instead, we find that the reconstructions underestimate the Lyα flux by almost a factor of 2 for the lowest velocity, most attenuated spectrum, due to a degeneracy between the intrinsic Lyα and ISM profiles. Our results imply that many stellar Lyα fluxes derived from G140M spectra reported in the literature may be underestimated, with potential consequences for, for example, estimates of extreme-ultraviolet stellar spectra and ultraviolet inputs into simulations of exoplanet atmospheres.

M dwarf stars↗

NASA NTRS1972

Underluminosity and magnetic fields in Beta Lyrae

A combination of available observational data for Beta Lyrae and theoretical models of evolution in close binary systems in used to show that the minimum underluminosity of the dark secondary component of this system is 1 to 4 mag. It is demonstrated that magnetic fields are probably relatively weak in massive main-sequence stars, including the two stellar components of Beta Lyrae, and therefore that a strong magnetic field is not a likely explanation for the underluminosity of the secondary component of Beta Lyrae.

Stothers, R.↗

NASA NTRS1981

A study of the Mg II k line in Beta Persei

Spectral scans of the Mg II k line in Beta Per were obtained with Copernicus during two primary eclipses. A brief description of observation in a short frame mode is given. The observed data are compared with computed line profiles based on the eclipse geometry of spherical stars. It is shown that a nonuniform circumstellar envelope, or cloud, probably is present. In one scan, a red-shifted line of P Cygni-type profile appeared, indicating the occurrence of an unusual event in the close binary system.

Chen, K.-Y.↗

NASA NTRS1993

Determination and characterization of the Hubble Space Telescope pointing stability

The Hubble Space Telescope (HST) was designed to maintian a pointing stability (jitter) of 0.007 arc seconds rms throughout every observing period, which can last from a few seconds to several orbits. On-orbit measurements indicate that the hardware excitation induced by the reaction wheels. gyros, high gain antennae, science instrument mechanisms and tape recorders are well within specifications. Unexpectedly, the solar arrays because the dominant source of jitter. Every passage through an orbital terminator produces vibrations which emanate from the solar arrays due to thermal effects, which affect the relative positional stability. Broadband frequencies centered about 0.11 and 0.65 Hz were detected in the frequency content of the vehicle jitter. On-board modifications to the control law have attenuated the disturbance torques and reduced the vehicle jitter close to specification. Replacement of the solar arrays in December, 1993, should eliminate the torque distubances. Astrometric science observations are extremely susceptible to corruption from vehicle jitter. The removal of vehicle jitter from astrometric Transfer function scans of binary stars is explained in detail. A binary star separation of 16 milli-seconds of arc has been achieved, a separation resolution of 10 to 12 milli-seconds of arc appears feasible, with a binary star magnitude of 9 m(sub V). The achievement of this resolution is in part due to vehicle jitter removal. Comparison of vehicle jitter measurements from the position path of the vehicle control law, or from the guiding Fine Guidance Sensors (FGS), are shown to be equivalent to approximately 0.001 arc second.

Bradley, A. J.↗

NASA NTRS1985

Are galactic bulge X-ray burst sources leftovers of distupted globular clusters

Since approximately 1979, it is known that galactic bulge X-ray sources are low-mass binary systems, and that the X-ray bursters are a subset of the bulge sources. Grindlay and Hertz (1983) reported on the close proximity (in four of twelve cases) of an X-ray burst source and a normal star. The two authors believe that these alignments are not coincidental. They suggest that the normal star is surviving giant in a disrupted globular cluster core, of which the X-ray source would also be a member. The present investigation has the objective to show that Grindlay and Hertz made an error in their statistical analysis of a factor of approximately 10. It is, thus, believed that there is insufficient evidence for the conclusion reported by Grindlay and Hertz. On the basis of the present investigation, it is concluded that there exists at present no statistically significant observational evidence that X-ray bursters, presently located outside globular clusters, were formed in globular clusters.

Van Paradijs, J.↗

NASA NTRS1993

The multiplicity of T Tauri stars in the star forming regions Taurus-Auriga and Ophiuchus-Scorpius: A 2.2 micron speckle imaging survey

We present the results of a magnitude limited (K less than = 8.5 mag) speckle imaging survey of 69 T Tauri stars in the star forming regions Taurus-Auriga and Ophiuchus-Scorpius. Thirty-three companion stars were found with separations ranging from 0.07 sec to 2.5 sec, nine are new detections. This survey reveals a distinction between the classical T Tauri stars (CTTS) and the weak-lined T Tauri stars (WTTS) based on the binary star frequency as a function of separation: the WTTS binary star distribution is enhanced at the closer separations (less than 50 AU) relative to the CTTS binary star distribution. We suggest that the nearby companion stars shorten the accretion time scale in multiple star systems, thereby accounting for the presence of WTTS that are coeval with many CTTS. The binary star frequency in the projected linear separation range 16 to 252 AU for T Tauri stars (60 (+/- 17)%) is a factor of 4 greater than that of the solar-type main-sequence stars (16(+/- 3)%). Given the limited separation range of this survey, the rate at which binaries are detected suggests that most, if not all, T Tauri stars have companions. We propose that the observed overabundance of companions of T Tauri stars is an evolutionary effect, in which triple and higher order T Tauri stars are disrupted by close encounters with another star or system of stars.

Ghez, A. M.↗

NASA NTRS2008

Multi-Satellite Observations of Cygnus X-1 to Study the Focused Wind and Absorption Dips

High-mass X-ray binary systems are powered by the stellar wind of their donor stars. The X-ray state of Cygnus X-1 is correlated with the properties of the wind which defines the environment of mass accretion. Chandra-HETGS observations close to orbital phase 0 allow for an analysis of the photoionzed stellar wind at high resolution, but because of the strong variability due to soft X-ray absorption dips, simultaneous multi-satellite observations are required to track and understand the continuum, too. Besides an earlier joint Chandra and RXTE observation, we present first results from a recent campaign which represents the best broad-band spectrum of Cyg X-1 ever achieved: On 2008 April 18/19 we observed this source with XMM-Newton, Chandra, Suzaku, RXTE, INTEGRAL, Swift, and AGILE in X- and gamma-rays, as well as with VLA in the radio. After superior conjunction of the black hole, we detect soft X-ray absorption dips likely due to clumps in the focused wind covering greater than or equal to 95% of the X-ray source, with column densities likely to be of several 10(exp 23) cm(exp -2), which also affect photon energies above 20 keV via Compton scattering.

Hanke, Manfred↗

NASA NTRS2011

Constraining the Properties of the Eta Carinae System via 3-D SPH Models of Space-Based Observations: The Absolute Orientation of the Binary Orbit

The extremely massive (> 90 Stellar Mass) and luminous (= 5 x 10(exp 6) Stellar Luminosity) star Eta Carinae, with its spectacular bipolar "Homunculus" nebula, comprises one of the most remarkable and intensely observed stellar systems in the Galaxy. However, many of its underlying physical parameters remain unknown. Multiwavelength variations observed to occur every 5.54 years are interpreted as being due to the collision of a massive wind from the primary star with the fast, less dense wind of a hot companion star in a highly elliptical (e approx. 0.9) orbit. Using three-dimensional (3-D) Smoothed Particle Hydrodynamics (SPH) simulations of the binary wind-wind collision, together with radiative transfer codes, we compute synthetic spectral images of [Fe III] emission line structures and compare them to existing Hubble Space Telescope/Space Telescope Imaging Spectrograph (HST/STIS) observations. We are thus able, for the first time, to tightly constrain the absolute orientation of the binary orbit on the sky. An orbit with an inclination of approx. 40deg, an argument of periapsis omega approx. 255deg, and a projected orbital axis with a position angle of approx. 312deg east of north provides the best fit to the observations, implying that the orbital axis is closely aligned in 3-D space with the Homunculus symmetry axis, and that the companion star orbits clockwise on the sky relative to the primary.

Madura, Thomas I.↗

NASA NTRS1986

Can comet clouds around neutron stars explain gamma-ray bursts?

The proposal of Harwit and Salpeter (1973) that gamma-ray bursts are due to impacts of comets onto neutron stars is examined further. It is assumed that most stars are formed with comet clouds similar to the Oort comet cloud which surrounds the sun, and it is suggested that there are at least four mechanisms by wich neutron stars may be formed while retaining their comet clouds: a spherically symmetric supernova explosion in an isolated star, accretion-induced collapse of a white dwarf in a cataclysmic variable with a very low mass secondary, accretion-induced collapse of a white dwarf in a wide binary with a low-mass giant companion, and coalescence of a close binary composed of two white dwarfs. Estimates are given of the cometary impact rates for such systems. It is suggested that if the wide binary scenario is correct, optical bursts may arise from the impact of comets onto the white dwarf remnant of the giant companion.

Tremaine, S.↗

NASA NTRS1992

The variable Herbig Ae Star HR 5999. X - Its photometric 'pulse-shaped' variability

We present additional photometric observations (Stromgren y filter) of the Herbig Ae Star HR 5999. This new set of data, composed of 282 data points covering April 1983 to August 1989, was used in conjunction with the 362 data points compiled by Baade and Stahl (1989). Our aim was to detect single or multiple periods in the integrated set of data spanning nearly 20 yr. Through the use of series analysis techniques, and by removing any linear component present in the raw data, we were able to detect weak peaks in the power spectra (in the order of intensity the strongest peaks are at 301 and 113 d) which were not self-evident in the phase diagrams. The overall picture of the data shows a small linear component, which is more noticeable in the new set of data, indicating that the recent maxima appear brighter. By a detailed analysis of the full light curve we were able to detect the presence of well-defined 'pulses' or bursts. Further Gaussian fits of these bursts indicated that the pulses are relatively rapid, of the order of 10 d, with some of them being closely spaced. No periodicity was found for the pulses. A possible explanation of these aperiodic outbursts is that they detect a flow of matter accompanied by magnetic field disturbances originated from the interior of the star, unlike those originating externally such as binary perturbations, which tend to be periodic.

Perez, M. R.↗