3,748 research outputs found
CNO abundances and hydrodynamic models of the Nova outbursts. 4: Comparison with observations
A variety of observations of novae are discussed in light of theoretical models. It is proposed that the nearly constant bolometric luminosity of FH Ser originates in the non-degenerate hydrogen-burning region at the bottom of the hydrogen-rich envelope which remains after the primary ejection. The shift of the wavelength of peak emission from the visual to shortward of the ultraviolet is caused by the decrease of the photospheric radius of the remnant envelope as the bolometric luminosity stays nearly constant. The oscillations in the light curve of GK Per during the transition stage can be explained by a pulsation of the remnant envelope when it is the size of the Roche lobe. The CNO over-abundances in novae reported by various observers are strongly suggestive of this nova mechanism. Finally, the implications of the upper limits of C-13 and N-15 in DQ Her are discussed
Hydrodynamic models for novae with ejecta rich in oxygen, neon and magnesium
The characteristics of a new class of novae are identified and explained. This class consists of those objects that have been observed to eject material rich in oxygen, neon, magnesium, and aluminum at high velocities. We propose that for this class of novae the outburst is occurring not on a carbon-oxygen white dwarf but on an oxygen-neon-magnesium white dwarf which has evolved from a star which had a main sequence mass of approx. 8 solar masses to approx. 12 solar masses. An outburst was simulated by evolving 1.25 solar mass white dwarfs accreting hydrogen rich material at various rates. The effective enrichment of the envelope by ONeMg material from the core is simulated by enhancing oxygen in the accreted layers. The resulting evolutionary sequences can eject the entire accreted envelope plus core material at high velocities. They can also become super-Eddington at maximum bolometric luminosity. The expected frequency of such events (approx. 1/4) is in good agreement with the observed numbers of these novae
Thermonuclear runaways in thick hydrogen rich envelopes of neutron stars
A Lagrangian, fully implicit, one dimensional hydrodynamic computer code was used to evolve thermonuclear runaways in the accreted hydrogen rich envelopes of 1.0 Msub solar neutron stars with radii of 10 km and 20 km. Simulations produce outbursts which last from about 750 seconds to about one week. Peak effective temeratures and luninosities were 26 million K and 80 thousand Lsub solar for the 10 km study and 5.3 millison and 600 Lsub solar for the 20 km study. Hydrodynamic expansion on the 10 km neutron star produced a precursor lasting about one ten thousandth seconds
Numerical simulation of the magnetospheric gate model for X-ray bursters
A Lagrangian, fully implicit, one dimensional hydrodynamic computer code was used to investigate the evolution of a gas cloud impacting the surface of a 20 km, 1 Msub solar neutron star. This gas is initially at rest with respect to the surface of the neutron star, extends to 185 km above the surface, and is optically thick. The infall results in a burst which lasts about 0.1 seconds and reached a peak luminosity and effective temperature of 240,000 Lsub solar and 9 million; respectively. The burst was followed by a phase of oscillations with a period 0.2 seconds
Cryogenic thermocouple calibration tables
Thermocouple calibration standards are developed for low-temperature thermocouple materials. Thermovoltage, thermopower, and the thermopower derivative are presented in tabular and graphical form
A burst from a thermonuclear runaway on an ONeMg white dwarf
Studies which examine the consequences of accretion, at rates of 10(exp -9) solar mass/yr and 10(exp -10) solar mass/yr, onto an ONeMg white dwarf with a mass of 1.35 solar masses are performed. In these studies, a Lagrangian, hydrodynamic, one-dimensional computer code was used. The code now includes a network with 89 nuclei up to Ca-40, elemental diffusion, new opacities, and new equation of state. The initial abundance distribution corresponded to a mixture that was enriched to either 25, 50, or 75 percent in products of carbon burning. The remaining material in each case is assumed to have a solar composition. The evolution of the thermonuclear runaway in the 1.35 solar mass white dwarf, with M = 10(exp -9) solar mass, produced peak temperatures in the shell source exceeding 300 million degrees. The sequence produced significant amounts of Na-22 from proton captures onto Ne-20 and significant amounts of Al-26 from proton captures on Mg-24. This sequence ejected 5.2 x 10(exp -6) solar mass moving with speeds from approximately 100 km/s to 2300 km/s. When the mass accretion rate was decreased to 10(exp -10) solar mass, the resulting thermonuclear runaway produced a shock that moved through the outer envelope of the white dwarf and raised the surface luminosity to L greater than 10(exp 7) solar luminosity and the effective temperature to values exceeding 10(exp 7) K. The interaction of the material expanding from off of the white dwarf with the accretion disk should produce a burst of gamma-rays
Effect of gaseous and solid simulated jet plumes on a 040A space shuttle launch configuration at Mach numbers from 1.6 to 2.2
An experimental investigation was conducted in a 9- by 7-foot supersonic wind tunnel to determine the effect of plume-induced flow separation and aspiration effects due to operation of both the orbiter and the solid rocket motors on a 0.019-scale model of the launch configuration of the space shuttle vehicle. Longitudinal and lateral-directional stability data were obtained at Mach numbers of 1.6, 2.0, and 2.2 with and without the engines operating. The plumes exiting from the engines were simulated by a cold gas jet supplied by an auxiliary 200 atmosphere air supply system, and by solid body plume simulators. Comparisons of the aerodynamic effects produced by these two simulation procedures are presented. The data indicate that the parameters most significantly affected by the jet plumes are the pitching moment, the elevon control effectiveness, the axial force, and the orbiter wing loads
Cryogenic thermocouple tables
Cryogenic standardized thermocouple materials table
Morphology of the Nuclear Disk in M87
A deep, fuly sampled diffraction limited (FWHM ~ 70 mas) narrow-band image of
the central region in M87 was obtained with the Wide Filed and Planetary Camera
2 of the Hubble Space Telescope using the dithering technique. The
H-alpha+[NII] continuum subtracted image reveals a wealth of details in the
gaseous disk structure described earlier by Ford et al. (1994). The disk
morphology is dominated by a well defined three-arm spiral pattern. In
addition, the major spiral arms contain a large number of small "arclets"
covering a range of sizes (0.1-0.3 arcsec = 10-30 pc). The overall surface
brightness profile inside a radius ~1.5" (100 pc) is well represented by a
power-law I(mu) ~ mu^(-1.75), but when the central ~40 pc are excluded it can
be equally well fit by an exponential disk. The major axis position angle
remains constant at about PA_disk ~ 6 deg for the innermost ~1", implying the
disk is oriented nearly perpendicular to the synchrotron jet (PA_jet ~ 291
deg). At larger radial distances the isophotes twist, reflecting the gas
distribution in the filaments connecting to the disk outskirts. The ellipticity
within the same radial range is e = 0.2-0.4, which implies an inclination angle
of i~35 deg. The sense of rotation combined with the dust obscuration pattern
indicate that the spiral arms are trailing.Comment: 5 pages, 3 postscript figures, to appear in the Proceedings of the
M87 Workshop, Ringberg castle, Germany, 15-19 Sep 1997, also available from
http://jhufos.pha.jhu.edu/~zlatan/papers.htm
Will Jets Identify the Progenitors of Type Ia Supernovae?
We use the fact that a Type Ia supernova has been serendipitously discovered
near the jet of the active galaxy 3C 78 to examine the question of whether jets
can enhance accretion onto white dwarfs. One interesting outcome of such a
jet-induced accretion process is an enhanced rate of novae in the vicinity of
jets. We present results of observations of the jet in M87 which appear to have
indeed discovered 11 novae in close proximity to the jet. We show that a
confirmation of the relation between jets and novae and Type Ia supernovae can
finally identify the elusive progenitors of Type Ia supernovae.Comment: 10 pages, 3 figure
- …