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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 271 records · Page 15
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NASA NTRS1975

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.

Sparks, W. M.↗
NASA NTRS1976

An unusually strong radio outburst in Algol - VLBI observations

For 8 hours during a strong radio flare on Jan. 15, 16, 1975, the close binary system Beta Persei (Algol) was observed with a three-station VLBI array operating at 7850 MHz. The size of the radio source was estimated to have been about 1.7 milliarcsec (0.05 AU), based on a model of a uniformly bright disk. The corresponding brightness temperature was nearly 10 billion K, indicating that the emission was probably nonthermal. There was no evidence for expansion of the source; the upper limit on the rate of any expansion was 100 km/s. The position of the Algol radio source with respect to an extragalactic reference frame was also determined from these observations with an uncertainty of about 0.1 arcsec in each coordinate.

Clark, T. A.↗
NASA NTRS1976

CNO abundances and hydrodynamic models of the nova outburst. IV - 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 nondegenerate 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 larger than the semimajor axis of the binary system. The CNO overabundances in novae reported by various observers are strongly suggestive of the proposed nova mechanism. Implications of the upper limits on C-13 and N-15 found in DQ Her are discussed.

Sparks, W. M.↗
NASA NTRS1976

Recurrent X-ray outbursts from Aquila X-1

Aquila X-1 observations by the All Sky Monitor on Ariel 5 are presented. Data is compared with that obtained by rocket survey, and by the Uhuru, OSO 7, and OAO 3 satellites. The variability of brightness is discussed as a connection between dwarf novae and long term transient X ray sources.

Kaluzienski, L. J.↗
NASA NTRS1977

Recurrent X-ray outbursts from Aquila X-1

Ariel V All-Sky Monitor observations of Aql X-1 are reported and compared with previous observations that indicate the existence of 'low' and 'high' intensity states. All the data considered are shown to be consistent with flaring episodes having a mean flare interval of 435 days with an rms scatter of about 10%. It is suggested that the observations are most easily interpreted in terms of an 'X-ray dwarf nova' binary of the type proposed for the transient X-ray source A0620-00. Constraints on more detailed features of the source model are discussed.

Kaluzienski, L. J.↗
NASA NTRS1978

CNO abundances and hydrodynamic studies of the Nova outburst. V - 1.00-solar-mass models with small mass envelopes

The paper reports on an investigation into the consequences of thermonuclear runaways in accreted hydrogen envelopes of 100 millionths of a solar mass on 1-solar-mass white dwarfs. These evolutionary sequences predict that from 10 to 50 millionths of a solar mass will be ejected with speeds from 300 to 3800 km/s (kinetic energies of 10 to the 44th-45th power ergs). Absolute visual magnitudes as high as -8.1 are attained, well within the observed range for fast novae. In addition, the shapes of the theoretical light curves are more reminiscent of an observed fast-nova light curve than those in earlier studies. The ejected material is strongly enhanced in the products of incomplete CNO burning; the most abundant of the ejected nuclei is C-13, followed by N-14 and C-12. The differences from previous studies are attributable to the lower peak temperatures reached in these sequences. These models also produce a large overabundance of Li-7, suggesting that novae may represent significant contributors to the galactic enrichment of this nucleus.

Starrfield, S.↗
NASA NTRS1980

A probable 1970 hard X-ray outburst by 4U0041+32

Balloon observations of a hard X-ray burst in 1970 most likely associated with the highly variable high-latitude X-ray source 4U 0041+32 are reported. The observation of X-ray flux at a density of about 0.06 photons/sq cm per sec from a previously unknown source at r.a. O h 45 min, dec 33 + or - 3 deg was made by a scintillation telescope on February 4, 1970. The spectrum was found to be very hard between 25 and 300 keV, with radiation in the form of a well-collimated beam causing the excess counting rate over a period of 30 min. Further observations on September 25, 1970 indicated the object had faded to an intensity below 0.01 photons/sq cm per sec. The power law spectrum obtained during the February burst is observed to differ from those of other hard transients and hard compact binary X-ray sources by the fact that it extends to 300 keV, its apparent lack of pulsation and its not being associated with an early-type giant or supergiant companion.

Laros, J. G.↗
NASA NTRS1980

IUE observations of WZ Sagittae in outburst

Preliminary results of the analysis of the low resolution spectra from the recurring nova WZ Sagittae are discussed with reference to the similarity between WZ Sge and dwarf novae and the applicability of accretion disk models. It is found that the spectrum observed on Dec. 1, 1978, is in very good agreement with a simple steady-state disk model of Lynden-Bell (1969) which predicts a power law spectrum over a limited range of frequency. Analysis of the observations within the framework of this model gives a value of the mass of the white dwarf larger than that estimated by Robinson et al (1978).

Holm, A. V.↗