Engineering Papers⌕ Search

Engineering topics

Lamb, D. Q.

Publications and source records attributed to Lamb, D. Q..

51 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS1983

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.↗
NASA NTRS1983

Spin-up and magnetic fields in DQ Her stars

A detailed comparison of the spin-up behavior of the recently discovered faint long-period X-ray sources, using the accretion torque theory of Ghosh and Lamb has been carried out. It is confirmed that these sources are degenerate dwarfs. It is found that they have magnetic fields B about 1 billion G, an order of magnitude smaller than those of AM Her stars. On this basis, it is predicted that they will show significant polarization in the infrared.

Lamb, D. Q.↗
NASA NTRS1983

X-ray emission from cataclysmic variables

X-ray observations of cataclysmic variables and theoretical work on X-ray emission from them are reviewed, emphasizing recent developments. Observations of luminosities and space densities, X-ray spectra and temporal behavior, and X-ray emitting cataclysmic variables in globular clusters are addressed. The relationship of disk and radial accretion to X-ray emission is qualitatively considered, and the spectra and correlation between spectral temperature and luminosity are examined for magnetic and nonmagnetic stars. The relationship between ionization structure and line features is summarized, and nuclear burning and electron conduction are briefly addressed. Important issues concerning X-ray emission from cataclysmic variables are discussed, including magnetic fields, the origin of hard and soft X-rays, the soft X-ray puzzle in AM Her stars, nuclear burning, long-period pulsing sources, cyclotron-dominated sources, high-luminosity sources, and the stability of accretion flow.

Lamb, D. Q.↗
NASA NTRS1982

Fundamental studies in X-ray astrophysics

An analytical model calculation of the ionization structure of matter accreting onto a degenerate dwarf was carried out. Self-consistent values of the various parameters are used. The possibility of nuclear burning of the accreting matter is included. We find the blackbody radiation emitted from the stellar surface keeps hydrogen and helium ionized out to distances much larger than a typical binary separation. Except for low mass stars or high accretion rates, the assumption of complete ionization of the elements heavier than helium is a good first approximation. For low mass stars or high accretion rates the validity of assuming complete ionization depends sensitivity on the distribution of matter in the binary system.

Lamb, D. Q.↗
NASA NTRS1982

X-ray and UV radiation from accreting nonmagnetic degenerate dwarfs. II

Numerical calculations of X-ray and UV emission from accreting nonmagnetic degenerate dwarfs are reported, which span the entire range of accretion rates and stellar masses. Calculations include the effects of bremsstrahlung, Compton cooling, radiation pressure, albedo of the stellar surface, Compton degradation and free-free abscription of the X-ray spectrum by the accreting matter. Maximum X-ray luminosity for degenerate dwarfs undergoing spherical accretion is found to be 2.2 x 10 to the 36th ergs/s, which is little changed if accretion occurs radially over only a fraction of the stellar surface, so that the emitted radiation escapes without significant scattering. The temperature characterizing the X-ray spectra produced by degenerate dwarfs strongly depends on the stellar mass and the accretion rate, and it is suggested that the correlation between spectral temperature and luminosity is an important signature of degenerate X-ray sources.

Kylafis, N. D.↗
NASA NTRS1981

Continuum and line spectra of degenerate dwarf X-ray sources

Recent observations of X-ray sources are summarized. Unresolved issues concerning these sources are discussed and an outline of the kinds of X-ray observations that would best advance the understanding of these sources is presented.

Lamb, D. Q.↗
NASA NTRS1981

Neutron star evolution and results from the Einstein X-ray Observatory

The evolution of neutron stars is reexamined using current knowledge of their structure and the available microphysics, including general relativistic effects, improved opacities, and cooling by the emission of neutrinos from a pion condensate or from free quarks. Theoretical cooling curves are compared with observations performed with the Einstein X-ray Observatory. It is found that current soft X-ray observations of pulsars and young supernova remnants do not require stars with a pion condensate or free quarks.

Van Riper, K. A.↗
NASA NTRS1980

The optical identification of H2252-035 with a cataclysmic variable

An improved position is presented for the X-ray source H2252-033 using the Ariel V Sky Survey Instrument, and precise positioning using the Scanning Modulation Collimator on HEAO-1. The source is identified optically with a 13th magnitude emission-line object, which is probably a white dwarf binary with a well formed accretion disk, with similarities to the dwarf novae (e.g., SS Cyg) at minimum.

Griffiths, R. E.↗
NASA NTRS1980

Evidence for the degenerate dwarf nature of Cygnus X-2

Observations of Cygnus X-2 using the Copernicus satellite have revealed a novel relationship between the spectral hardness and the intensity of this source in the 3-8 keV band. This behavior is very similar to that predicted for a spherically accreting nonmagnetic degenerate dwarf. The data, interpreted in terms of this model, determine solar mass, luminosity, and the distance for Cyg X-2; these parameters are at variance with the values derived from optical observations of the system. The implications of this discrepancy for the understanding of the source are examined.

Branduardi, G.↗
NASA NTRS1980

X-ray spectra of accreting degenerate stars

X-ray emission from accreting nonmagnetic degenerate dwarfs is discussed. Emphasis is placed on the numerical calculations by Kylafis and Lamb (1979) with regard to the entire range of accretion rates and stellar masses. It is concluded that at moderate and high accretion rates the spectral temperature varies dramatically and the star exhibits a pronounced correlation between X-ray spectral temperature and luminosity. Also considered are the results of Lamb and Masters (1979) of calculations of high-harmonic cyclotron emission from a hot plasma, from which they developed a model of X-ray and UV emission from accreting magnetic degenerate dwarfs. It is found that the position and relative strength of the spectral components change with variations in the accretion rate and differ for different magnetic fields; in addition, magnetic degenerate dwarfs are predicted to be strong UV sources with only a few percent of the total accretion luminosity ordinarily appearing as soft and hard X-rays.

Kylafis, N. D.↗
NASA NTRS1979

Degenerate dwarf X-ray sources

X-ray emission by accreting degenerate dwarfs is examined qualitatively, considering bremsstrahlung and cyclotron fluxes and cooling. Also discussed are strongly magnetic degenerate dwarfs, which are characterized by a blackbody-limited UV cyclotron component and a hard X-ray bremsstrahlung component, both produced by the hot emission region, and a hard UV or soft X-ray blackbody component produced by cyclotron and bremsstrahlung photons. With regard to nonmagnetic and weakly magnetic degenerate dwarfs, it is concluded that degenerate dwarfs can produce larger luminosities than earlier estimates indicated, that even high mass stars can produce low temperature (less than 10 keV) X-ray spectra, and, for moderate and high accretion rates and high (greater than 1.2 solar masses) stellar masses, the spectra exhibit a high energy tail. Individual sources of each type of dwarf are considered, such as the AM Her, DQ Her and SS Cyg classes as well as Cyg X-2 and the Sco X-1 class, and the number of such sources in the Galaxy is estimated.

Lamb, D. Q.↗
NASA NTRS1979

X-ray emission from degenerate dwarfs

Theoretical studies of magnetic and nonmagnetic degenerate dwarf X-ray sources are reviewed. It is shown that the physical properties of X-ray sources, such as mass, magnetic field strength, and intrinsic luminosity, may be determined from the qualitative features of their X-ray spectra and from correlations between their X-ray luminosity and spectral temperature.

Kylafis, N. D.↗