SEARCH · Search NASA
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.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
Low dispersion IUE spectra of 3 cataclysmic variables (V442 Oph, V794 Aq1 and H2215-086) are discussed in terms of current disk models. The range of continuum fluxes, line emission and disk parameters of these three novalike systems are compared with past observations of dwarf novae at outburst and quiescence. Evidence of variability on orbital time scales is presented for V442 Oph and H2215-086.
Observations of V794 Aql have revealed features that are consistent with its inclusion in the class of cataclysmic variables. The features include: (1) a 0.1-4.5 keV luminosity of 5 x 10 to the 30th ergs/sec for a d-value of 100 pc, with a hardness ratio of 11; (2) blue colors; (3) 0.5 mag variability on 40-min time scales, and 3.0 mag variability on the time scale of one day; and (4) a weak He II 4686 A, which argues against classification of V794 Aql as an AM Her-type variable. It is predicted that V794 Aql has a period shorter than six hours, with a strong possibility for eclipses, and is a strong UV emission source.
The variable spectrum of BE Ursae Majoris, which is similar to that of the cataclysmic variables (CVs), shows (1) an emission-line spectrum with the high-excitation CN 4650 A blend as the strongest optical feature, weaker H and He lines, and a strong Balmer jump, and (2) an absorption spectrum dominated by He. Although the object shows no evidence of photometric variability on either short or long time-scales, it has been shown by Kurochkin (1964, 1971) to have a 2.29-day, sinusoidal, 1.5-mag variation. The luminosity is dominated by a UV power-law component, though the 4000-10000 A continuum is flat. The hypothesis that this object is an active mass transfer binary is not supported by its photometric behavior, energy distribution and long period, despite the spectroscopic variability. Nevertheless, three components whose nature is not understood remain: (1) an ultraviolet source whose energy distribution is explainable neither by a uniform temperature primary star nor by an accretion disk; (2) a reprocessed component powered by the UV star; and (3) a component similar to a CV disk, producing the optically thick Balmer lines.
Cataclysmic variables (CVs) as a class are defined by their optical properties, in particular the amplitudes and frequency of their outbursts. The availability of the Imaging Proportional Counter (IPC) on the Einstein Laboratory has increased significantly the number of CVs which can be studied on the basis of X-ray observations. In this connection, Becker and Marshall (1981) and Cordova et al. (1980) have surveyed 20 CVs and detected 70% of them. A description is presented of observations of an additional 12 CVs, and the properties of the combined set of 32 CVs are discussed. It is found that the CVs do not have any distinguishing X-ray characteristics. The IPC data alone cannot be used to determine to which category of CVs a particular source belongs, or even to identify an object as a CV. On the other hand, the optical observations are essential for estimating the X-ray luminosity from the IPC data.
Photometry and spectroscopy of a new cataclysmic variable star, Lanning 10 are presented. The star is shown to be an eclipsing binary with a 7h 42m orbital period. Blue flickering is observed to occur on a time scale of 10 minutes. The light curve is analyzed with a numerical simulation of the eclipse of the accretion disk by the lobe-filling star. The disk nearly spans the Roche lobe of the white dwarf, and its surface brightness is a steep function of radius. Spectra show broad H alpha and He I 6678 A emission lines from the accretion disk and a weak absorption feature from the red dwarf. Radial velocity measurements of the H alpha emission line vary systematically with binary phase. The observed velocity amplitude 240 km/s, gives the mass function 0.46 solar masses. A phase shift of the velocity curve relative to the eclipse ephemeris indicates that a brightness asymmetry exists in the inner parts of the disk.
International Ultraviolet Explorer observations of the recently discovered AM Herculis type cataclysmic variable E1405-451 reveal a UV spectrum (1000-3000 A) similar to the other members of the type. The continuum flux distribution rises steeply at short wavelength and shows the effects of interstellar extinction. Best fit parameters for a blackbody spectrum are T = 25,500 + or - 2300 K with E(B-V) = 0.13 + or - 0.05. Many strong emission lines appear in the spectrum with similar intensities to those in AM Her. C IV 1550 and He II 1640 show some sign of a P Cygni profile. If these profiles are truly P Cygni, they indicate the intriguing possibility of a magnetically confined, radiatively driven wind present in all AM Her systems but only observable in a subset with an orientation like E1405-451.
The four years of IUE operation have revealed that the ultraviolet region of the spectrum contributes a dominant share of the emerging energy from cataclysmic variables and provides important clues to the physical nature of these systems. The implications of the continuum flux distributions and line spectra for the determination of the accretion rates and mass loss rats are considered.
Photoionization models are presented for the relative abundances of Si IV, C IV, and N V as a function of the ionization parameter and shape of the ionizing continuum spectrum in the EUV and X-ray energy range. These models are applied to the interpretation of the UV resonance lines observed from the cataclysmic variable TW Virginis by Cordova and Mason. The observed lines are assumed to be formed in gas flowing supersonically out from the continuum source in the form of a stellar wind. It is shown that the shape of the ionizing spectrum can be determined without assuming that the outflow is spherical by fitting to ratios of the line strengths. Models which fit the observed ratios include an X-ray continuum with a low-energy cutoff and may also include a lower luminosity component in the EUV spectral region. Under the added assumption of spherical outflow the derived ionization parameter for the X-ray component can be used to constrain the total mass flux in the wind.
The results of a program of observations of the cataclysmic variable V442 Oph from UV to IR wavelengths are reported. The observations comprise IUE SWP and LWR-camera spectra from October, 1981; UBVr and R photometry at Manastash Ridge Observatory from August, 1980; UBV photometry and IR measurements at Kitt Peak from July, 1981; and Coudespectroscopy at Mt. Wilson from June, 1980, and at Mt Lemmon from July, 1982. Tables of data, plots of H-alpha and He-II radial velocity, sample spectra, light curves, and a log-log diagram of F(lambda) vs lambda are given. Flux-ratio analysis of the IR data indicates a disk with very little optically thin material anad an outer-edge temperature of about 7920 K. The calculated period (3.37 h) and mass-accretion rate (1 x 10 to the -8th solar mass/yr) are compared to those of similar objects, and V442 Oph is found to be similar in this respect to systems like H2252-035. Its lack of a rotational period and the weakness of the optical and UV line emissions, however, are more like the old nova V603 Aql.
Spectroscopic observations of 69 cataclysmic variables are presented. Representative spectra, accurate coordinates, and finding charts are given for each object. Line strengths, equivalent widths, and line widths for all emission lines in 153 spectra are tabulated. The spectra are discussed briefly, and notes to selected objects are given.
The paper presents a photometric and spectrophotometric analysis of a new eclipsing cataclysmic variable, PG 1012-029, with an orbital period of 3 hr 14 minutes 18.7 s. The eclipse depth reaches 1.9 mag, is rounded at minimum, and shows a prolonged egress 'shoulder', as found for UX UMa and some other eclipsing systems. The spectrum shows strong high-excitation lines at optical and UV wavelengths. A large fraction of the He II flux disappears during the eclipse, when the hydrogen spectrum fits a cooler temperature, and the continuum reddens. This behavior is attributed to eclipse of the hotter inner disk region.
Spectroscopic and photometric observations of T Leo which reveal the object to be an ultrashort period dwarf nova are presented. In particular, the analysis indicates that T Leo has an orbital period of 84.69936 (plus or minus 0.00068) minutes, which is the third shortest orbital period of any known cataclysmic variable and the shortest known for any U Gem type dwarf nova. These observations enable the placement of upper limits of 0.19 and 0.4 solar mass on the mass of the red dwarf and white dwarf, respectively. The overall energy distribution is relatively flat (f-sub-lambda approximately constant) which is consistent with a low mass accretion rate. The models of Williams and Ferguson (1982) suggest that the mass accretion rate is about 10 to the -10th solar mass/yr. A narrow peak component of H-alpha is observed, the phasing of which cannot be explained by the canonical hot spot model. Possible explanations for its origin are presented and discussed. It is predicted that future observations of T Leo may reveal the object to be a SU UMa type dwarf nova.
This paper presents the results of an X-ray survey of 31 known or suspected cataclysmic variables. Eighteen of these close binary systems are detected with inferred luminosities in the 0.1-4.0 keV band of between 10 to the 30th and 10 to the 32nd erg/sec. The majority have relatively hard X-ray spectra (kT greater than 2 keV) irrespective of luminosity state. Of seven dwarf novae observed during optical outbursts only U Gem exhibited enhanced ultrasoft X-ray emission (kT of about 10 eV) in addition to weak, hard X-ray emission. Variability of the X-ray flux is observed in many of these stars, on time-scales ranging from tens of seconds to hours. The contribution to the flux from extended X-ray emission is investigated for SU UMa and GK Per. Several possibilities for the origin of the hard X-rays are considered.
The observational data for the 124 cataclysmic and low-mass X-ray binaries of known orbital period are compiled. It is found that the eruption properties are very well correlated with the orbital periods, in a manner that suggests that the mass transfer is the all-important determinant of evolution and of the eruptive behavior. Transfer rates of 10 to the -11th to 10 to the -7th solar mass/year are found, which are well correlated with orbital period. It is concluded that the mechanism which drives these systems is the magnetic braking of the secondary's rotation by its own stellar wind, coupled with the enforcement of synchronous rotation by tidal friction. This permits CVs to lose sufficient angular momentum to begin mass transfer in a reasonable time and drives the mass transfer at a high rate once it begins. An account of the long-lived phases of CV evolution is given.
Theoretical models explaining the hard-X-ray, soft-X-ray, and EUV emission of accretion-disk cataclysmic variables in terms of the disk boundary layer (DBL) are developed on the basis of a survey of the published observational data. The data are compared with model predictions in graphs for systems with high or low (greater than or less than 10-Pg/s) accretion rates. Good agreement is obtained both at low accretion rates, where an optically thin rarefied hot (Te = 10 to the 8th K) DBL radiates most of its energy as hard X-rays, and at high accretion rates, where an optically thick 100,000-K DBL radiates most of its energy in the EUV and as soft X-rays. Detailed analysis of the old nova V603 Aql suggests that previous models predicting more detections of soft-X-ray/EUV emissions from thick-DBL objects (Ferland et al., 1982) used inappropriate dwarf masses, interstellar column densities, or classical-nova space densities.
A study of 11 cataclysmic variables in the UV, optical and IR ranges has indicated that the alpha index of the UV flux distribution for five systems at quiescence is relatively flat and constrained, implying a narrow range in mass transfer rate. This may be correlated with the mechanism for mass transfer in short orbital period systems. Near maximum light, the alpha index is steep and consistent with steady state models.
The relevance of the long term quasi-static evolution of accreting white dwarfs to the outbursts of Z Andromeda-like symbiotics; the masses and accretion rates of classical nova white dwarfs; and the observed properties of white dwarfs detected optically and with IUE in low M dot cataclysmic variables is discussed. A surface luminosity versus time plot for a massive, hot white dwarf bears a remarkable similarity to the outburst behavior of the hot blue source in Z Andromeda. The long term quasi-static models of hot accreting white dwarfs provide convenient constraints on the theoretically permissible parameters to give a dynamical (nova-like) outburst of classic white dwarfs.
Two X-ray emitting cataclysmic variables were discovered as a result of a program to identify faint X-ray sources located by the HEAO-A3 modulation collimator experiment. The objects, H0534-581 and 1H0542-407, have similar high excitation spectra with intense emission lines showing broad and narrow components. Photometry shows that H0534-581 and 1H0542-407 have average magnitudes of V=14.9 and 15.7 respectively, leading to Lx/Lopt ratios of 1.5 (typical of dwarf novae in quiescence). While pronounced variability of delta B or = 1.5 mag is observed from both systems, there is no clear evidence for repeatable orbital periods between 1 and 4 hr.