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At least 127 records · Page 7
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NASA NTRS1972

Ultraviolet photometry of Nova Serpentis 1970

The appearance of the bright nova, Nova Serpentis 1970, provided the first opportunity to obtain spectrophotometric observations of a nova in the vacuum ultraviolet. OAO-2 carried out systematic measurements from shortly after outburst on through the first sixty days of nova activity. This data consist of filter photometry and spectral scans. General characteristics of the light and spectral variations in the ultraviolet exhibited by this set of data are described.

Code, A. D.↗
NASA NTRS1974

CNO abundances and hydrodynamic models of the nova outburst. II - 1.00 solar mass models with enhanced carbon and oxygen

Results of a computation of a variety of evolutionary sequences involving thermonuclear runaways in the hydrogen-rich envelopes of 1.00-solar-mass carbon-oxygen white dwarfs. The evidence concerning the location of the outburst in the nova system is reexamined, and it is concluded that the white dwarf is the seat of the outburst. An order-of-magnitude argument is presented which indicates that for a 1.00-solar-mass white dwarf it is impossible to achieve mass ejection without an energy generation of approximately 10 to the 16th ergs/g/sec. A description is given of models with low nuclear enhancements that do not produce an outburst, although their evolution has certain implications for the cause of the dwarf-nova outburst. The results for models that produced a nova outburst are then presented, and on the basis of these results it is found possible to explain continuous ejection, Kukarkin and Parenago's (1934) relationship, and other gross features of the nova phenomena.

Starrfield, S.↗
NASA NTRS1976

Grains of anomalous isotopic composition from novae

The effects of grain formation in nova ejecta are studied in order to model the optical and infrared luminosities schematically and to identify the anomalies of isotopic composition that should be present in large abundance in these grains. The large carbon concentration makes rapid and efficient grain formation possible and accounts for the peculiar luminosities observed in Nova Serpentis 1970. In the anticipated range of nova conditions, rapid addition of hot protons during the outburst produces large overabundances of C-13, O-18, Na-22, Al-26, Si-30, and perhaps others. Anomalous C-14 is expected subsequent to the C-13(alpha, n)O-16 reaction, and will be trapped in grains formed by subsequent atmospheric loss. Each of these anomalies may have been detected on the moon (due to accretion of interstellar dust) or in carbonaceous chondrites. Perhaps nova grains are responsible.

Clayton, D. D.↗
NASA NTRS1976

Search for X-ray emission from Nova Cygni 1975

A search for X-rays from Nova Cygni 1975 was carried out before, during, and after the time of optical maximum. No X-rays were detected over the spectral range 0.1-50 keV. On the basis of these results a strong upper limit of .0001 has been placed on the ratio of X-ray to optical luminosity for this nova, consistent with effective temperatures of about 10,000 K. If Nova Cygni 1975 is a virgin nova, its low mass exchange rate would imply that any associated X-ray emission would not be detectable by present techniques.

Hoffman, J. A.↗
NASA NTRS1977

Copernicus observations of Nova Cygni 1975

Near-ultraviolet radiation from Nova Cygni 1975 was detected by the Copernicus satellite on five occasions from 1975 September 1 to 1975 September 9. The nova was not seen in the UV after this date. The principal result was the observation of a broad emission feature from the Mg II doublet at 2800 A. The absence of strong UV radiation at shorter wavelengths suggests that these lines are produced by collisional excitation in the outer layers of an expanding shell with electron temperature of approximately 4000 K. The absence of observed emission lines from highly ionized species indicates that the amount of material with log T between 4.4 and 5.7 is less than 0.001 times that which produces the Mg II emission. The continuum flux in the near-UV decreased as the nova evolved, showing that the total luminosity decreased as the nova faded in the visible.

Jenkins, E. B.↗
NASA NTRS1977

CNO nucleosynthesis and the nova outburst

Predictions for CNO nucleosynthesis by the classical nova outburst are presented. Properties of the nova phenomenon pertinent to the production of CNO isotopes are discussed, the effect of beta(+) unstable nuclei on outburst evolution is examined, and the need for enhanced CNO nuclei in the envelope is described. Possible mechanisms for producing such enhancement are considered, and recent observations of enhanced CNO nuclei in nova ejecta are reviewed. Results of model evolutionary calculations are outlined which show that a thermonuclear runaway in the hydrogen envelope of a carbon-oxygen white dwarf can reproduce the gross features of the classical nova outburst, that the behavior of the outburst depends at least on the hydrogen-envelope mass and the degree of CNO enhancement, and that all degrees of isotopic enhancement result in an outburst that may be compared with observed events. Two enhancement mechanisms are identified, both of which involve mixing in the envelope.

Starrfield, S.↗
NASA NTRS1980

The evolution of the dust shell of Nova Serpentis 1978

Photometric measurements of Nova Serpentis 1978 from V to 19.5 microns covering the first 240 days of the nova's development are reported. A free-free expansion phase was followed by the condensation of a dust shell that became optically thick at both visible and infrared wavelengths. Carbon grains grew to radii of approximately 0.3 microns during the condensation period. The grains appeared to sputter or evaporate for a period of approximately 100 days following infrared maximum. It is found that the condensed carbon comprised 2% of the ejected mass, which implies that carbon abundance was enhanced in the nova shell. The angular expansion rate of the shell yields a distance of approximately 5 kpc and a luminosity of approximately 3000 solar luminosities for Nova Serpentis 1978.

Gehrz, R. D.↗
NASA NTRS1981

Ultraviolet spectroscopy of the recurrent nova U Scorpii during outburst

Observations of the recurrent nova U Sco during the 1979 outburst are presented, and the spectral evolution is found to differ from that of other recurrent novas. Spectra are dominated by emission lines, and the strong forbidden-line emission characteristic is conspicuously absent. A method to determine masses of nova shells is outlined, and an analysis of the emission lines shows an enrichment in N relative to C and O, and that the nova ejecta are rich in He relative to H. Optical spectra of U Sco obtained following its return to quiescence show predominantly He II emission lines, which suggests an enrichment of the preoutburst gas in He, and thus the presence of a highly evolved companion.

Williams, R. E.↗
NASA NTRS1986

Mass transfer in cataclysmic variables - Clues from the dwarf nova period distribution

Evidence is presented in support of the hypothesis that the mean mass-transfer rate at a given orbital period is not continuous across the 2-3 hr gap in the orbital period distribution for cataclysmic variables. It is pointed out that although dwarf novae comprise nearly half (48 percent) of all disk systems with orbital periods less than 10 hr, only three systems out of the 22 with periods between 3 and 4 hr appear to be dwarf novae. The overall orbital period distribution for dwarf novae in conjunction with the predictions from current theories of dwarf nova eruptions are used to argue that mass-transfer rates must be generally higher for systems with orbital periods greater than 3 hr relative to systems with periods less than 2 hr. It is further argued that the mean mass-transfer rate at a given orbital period cannot increase more steeply than P exp 1.7 unless the white dwarf mass is positively correlated with orbital period.

Shafter, A. W.↗
NASA NTRS1986

The space density of classical novae

A survey for Galactic plane ultraviolet-excess objects has been performed to obtain a statistically complete sample of cataclysmic variables from which to derive a space density. Six previously cataloged objects were recovered in the survey area of about 1000 sq deg, while one new nova was found, and two candidate cataclysmic variables were discovered. The resultant space densities of dwarf and novalike variables are consistent with previous determinations, while the nova space density is in good agreement with the recent determination of Patterson (1984), but is considerably lower than that of Bath and Shaviv (1978). However, if novae fade considerably between outbursts, as seems to be the case for the oldest recovered nova, CK Vulpeculae (1670), then the space density derived here may be greatly underestimated.

Downes, R. A.↗
NASA NTRS1986

Classical novae detected in the IRAS survey

Of the four classical novae presently identified as having accurately known optical positions with counterparts in the IRAS Point Source Catalog, two correspond to events observed by IRAS within one year of their respective optical maxima; these are noted to be the first classical novae detected at IR wavelengths longer than 20 microns. The novae are Sgr 1982, Mus 1983, FH Ser (1970) and HR Del (1967), of which the latter two were also detected by IRAS. Mus 1983 is noted to have IR emission characteristics that are consistent with a free-free spectrum, as opposed to dust emission. The behavior of this and the Sgr 1982 nova is consistent with a previously suggested correlation between the inferred mass of heated dust and luminosity/speed class.

Dinerstein, Harriet L.↗
NASA NTRS1987

The unusual radio outburst of Nova Vulpeculae 1984 No. 2

Multifrequency radio monitoring of Nova Vulpeculae 1984 No. 2 has revealed a unique radio light curve, exhibiting a strong outburst which precedes the appearance of normal radio emission from the principal ejecta of the nova by at least 100 days. The early emission is extremely optically-thick and has brightness temperature in excess of 100,000 K. A model is discussed in which the radiation is produced by a strong shock propagating outward through the principal ejecta of the nova, as a result of an interaction with a later, high velocity wind from the central source. It is shown that the general features of the radio light curve can be explained by the presence of a central wind with a mass loss rate of about 0.00001 solar masses/yr, lasting for a period of 200 to 300 days after the optical outburst. The first radio map of nova ejecta shortly after outburst is presented. Comparison of the angular expansion rate to the ejection velocity implies a distance of 3.6 kpc, and preliminary analysis of the main outburst emission indicates a mass and kinetic energy of the ejecta respectively of about 0.0008 solar masses and 8 x 10 to the 45th erg.

Taylor, A. R.↗
NASA NTRS1988

Light echoes - Novae

The sudden brilliance of a nova eruption will be reflected on surrounding dust grains to create a phantom nebula. Previous searches for these light echoes have used relatively short exposures with photograhic detectors. This paper reports on a search around eight recent novae with long exposures using a CCD camera. Despite an increase of sensitivity by over an order of magnitude, no light echoes were detected. It is found that the average grain density must be less than about 10 to the -9th per cu cm for distances from 0.1 pc to 1000 pc from the novae. The light echo around Nova Persei 1901 was caused by reflection off clouds with grain densities of several times 10 to the -9th per cu cm which are at distances between 0.1 pc and 10 pc. Echoes from dust in a circumstellar shell or ejected during a previous eruption will be effectively unobservable.

Schaefer, Bradley E.↗
NASA NTRS1988

A survey of IRAS data on 41 classical novae

The IRAS database has been searched for detections of 41 classical novae using coadditions of survey scans; 15 were detected. IRAS temporal observations of novae in outburst are discussed. The observed long-wavelength infrared distributions of DQ Her, and possibly HR Del, can be explained by emission from small (a of about 0.1 microns) dust grains heated by the central object. An alternative explanation for the energy distributions of DQ Her and HR Del is emission from fine-structure lines. FH Ser and LW Ser display energy distributions that have color temperatures much too hot to be due to heating of dust by the central source in any plausible scenario. Line emission is probably the best explanation of their observed energy distributions. The novae NQ Vul and LV Vul have energy distributions that may be contaminated by emission from galactic cirrus. The unusual object PL 1547.3-5612 exhibits an energy distribution that does not resemble those of planetary nebulae or other novae detected in this sample. An IRAS low-resolution spectrum of RR Tel shows the 10-micron silicate emission feature.

Harrison, T. E.↗
NASA NTRS1988

Observations and simulations of recurrent novae: U Sco and V394 CrA

Observations and analysis of the Aug. 1987 outburst of the recurrent nova V394 CrA are presented. This nova is extremely fast and its outburst characteristics closely resemble those of the recurrent nova U Sco. Hydrodynamic simulations of the outbursts of recurrent novae were performed. Results as applied to the outbursts of V394 CrA and U Sco are summarized.

Starrfield, S.↗
NASA NTRS1988

A real light echo - Nova Persei 1901

Observations of Nova Persei 1901, a light echo from SN 1987A, are reviewed. The large broken outer ring and bright inner ring of the nova are examined. The outer ring has been shown to increase its radius at a speed of about 11 arcmin/year. Since the distance to Nova Persei 1901 is about 400-600 pc, the apparent projected velocity of expansion is about 4-5 c, making the nova the first observed superluminal cosmic source.

Felten, J. E.↗
NASA NTRS1989

CCD observations of old nova fields

The discovery of CK Vulpeculae (Nova 1670) has prompted a major review of ideas concerning the long-term development of novae. Unfortunately, there are very few recovered novae old enough to provide confirmation (or rejection) of the new 'hibernation' scenario. CCD images of seven old nova fields, and R band photometry for four fields, have been obtained in an attempt to recover these objects in quiescence. A strong candidate for U Leonis, and a possible counterpart for T Bootis, are found. For three other fields, weak candidates have been found. Finding charts and colors are presented for the seven fields observed. The R light curves of U Leo, indicating an orbital period of 192.5 or 385.0 min, are shown.

Downes, Ronald A.↗
NASA NTRS1990

The infrared coronal lines of recent novae

IR coronal line emissions are reported in the novae V1819 Cyg and V827 Her; high-resolution near-IR spectra of coronal line emission in the nova QU Vul have also been obtained, increasing the number of known IR coronal line novae from two to four. Each of the four is found to be characterized by approximately the same Si VI/Si VII line-intensity ratio, which indicates a common coronal-zone electron temperature of 300,000 K. The coronal-line novae are noted to possess a remarkably similar near-IR spectrum, suggesting that their coronal line emission will only occasionally be observed at optical wavelengths.

Greenhouse, Matthew A.↗