The breakdown of nuclear quasi-equilibrium in highly compact binaries and the origin of the 2-3 hour gap in the orbital period distribution of cataclysmic variables
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Joss, P. C.↗
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Boundary layers in cataclysmic variables: The HEAO-1 X-ray constraints
The predictions of the boundary layer model for the X-ray emission from novae are summarized. A discrepancy between observations and theory in the X-ray observations is found. Constraints on the nature of the boundary layers in novae, based on the lack of detections of novae in the HEAO-1 soft X-ray survey are provided. Temperature and column densities for optically thick boundary layers in novae are estimated.
Jensen, K. A.↗
Boundary layers in cataclysmic variables - The HEAO 1 X-ray constraints
The predictions of the boundary layer model for the X-ray emission from novae are summarized. A discrepancy between observations and theory in the X-ray observations is found. Constraints on the nature of the boundary layers in novae, based on the lack of detections of novae in the HEAO-1 soft X-ray survey are provided. Temperature and column densities for optically thick boundary layers in novae are estimated. Previously announced in STAR as N84-13046
Jensen, K. A.↗
IR Geminorum - Indications of a massive white dwarf and a heated secondary in this new SU Majoris cataclysmic variable
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Shafter, A. W.↗
Inclination and orbital-phase-dependent resonance line-profile calculations applied to cataclysmic variable winds
The implications of IUE resonance-line profiles of novalike variables and dwarf novae in outburst for theoretical models in which these objects are formed in constant-ionization stellar winds are investigated theoretically, with a focus on the 1549-A line of C IV. The model proposed by Drew (1986) is extended and refined to account for arbitrary inclinations of the large opaque continuum-emitting disk and the presence of a dark binary companion; the data and results are presented in extensive diagrams and graphs and characterized in detail. Findings reported include a wind C(3+) number density an order of magnitude or more greater than the density of Si(3+) and N(4+) and wind mass-loss rates greater than about 10 to the -10th solar mass/yr.
Drew, J. E.↗
A photometric and spectroscopic comparison of the cataclysmic variables on the 2 sides of the period gap and at a specific orbital period
New and previously existing photometric colors and spectroscopic H and He line strengths are used to compare CV disk systems below the period gap (P=80-130 min) with those directly above (P=190-240 min). Significant differences are found in the mean U-B, V-J colors and in the H-beta equivalent widths on the two sides of the gap. A detailed comparison from UV-IR of 3 high inclination novalike systems with periods near 3.3 hr (PG1012-029, PG1030 + 590 and V1315 Aql) shows similar continuum distributions (and implied mass accretion rates) but large differences in high excitation lines (He III 640 A and 4686 A; C IV 1550 A).
Szkody, P.↗
The period and magnetic field distributions of cataclysmic variables - Implications for their evolution
Comparison of the period distributions of various classes of CVs confirms an extreme bias of the synchronous AM Her systems toward short orbital periods, while the DQ Her systems do not differ significantly from the distribution of nonmagnetic systems. This suggests either strong selection effects or enhanced evolution of the AM Her systems. There is as yet no obvious bimodality in either the magnetic field distributions of isolated white dwarfs or of CV primaries. However, clear differences between the two exist: the strongest being that magnetic primaries are overrepresented among short period CVs by more than an order of magnitude in comparison to the field white dwarfs.
Schmidt, G. D.↗
White dwarfs in cataclysmic variables - Low state IUE observations of V794 Aquilae, MR Serpentis, and AN Ursae Majoris
IUE low-dispersion observations of one novalike system (V794 Aql) and two AM Her systems (MR Ser and AN UMa) during low or intermediate-low accretion-rate states are reported. The decreased UV emission during these times was used to place limits on the white dwarf temperatures. When these results are added to the existing data on white dwarf temperatures, it appears that the white dwarfs in systems with normal high accretion rates and only occasional low-accretion-rate states remain hotter than the white dwarfs in systems with low average accretion rates.
Szkody, Paula↗
US 943 - A 19th mag eclipsing cataclysmic variable with a period of 2 hr 3.8 min
The high-latitude, V equals about 19.5, blue variable star US 943 is found to be an eclipsing binary with an orbital period of 2.06 hr. The light curve is dominated by an orbital hump which has an amplitude of 0.9 mag in V and is centered about 0.17 orbital cycles before the 1.5-mag deep eclipse. There is evidence that the eclipse has at least two components. The overall appearance of the star is that of a dwarf nova in quiescence, a conclusion that is supported by the observation of a subsequent bright state (V equals about 15) suggesting a dwarf nova outburst.
Howell, S. B.↗
The inter-outburst behavior of cataclysmic variables
Existing International Ultraviolet Explorer (IUE) and American Association of Variable Star Observers (AAVSO) archive data was used to accomplish a large scale study of what happens to the ultraviolet flux of accretion disk systems during the quiescent intervals between outbursts and how it relates to the preceding outburst characteristics of amplitude and width. The data sample involved multiple IUE observations for 16 dwarf novae and 8 novae along with existing optical coverage. Results indicate that most systems show correlated ultraviolet (UV) flux behavior with interoutburst phase, with 60 percent of the dwarf novae and 50 percent of the novae having decreasing flux trends while 33 percent of the dwarf novae and 38 percent of the novae show rising UV flux during the quiescent interval. All of the dwarf novae with decreasing UV fluxes at 1475A have orbital periods longer than 4.4 hours, while all (except BV Cen) with flat or rising fluxes at 1475A have orbital periods less than two hours. There are not widespread correlations of the UV fluxes with the amplitude of the preceding outburst and no correlations with the width of the outburst. From a small sample (7) that have relatively large quiescent V magnitude changes between the IUE observations, most show a strong correlation between the UV and optical continuum. Interpretation of the results is complicated by not being able to determine how much the white dwarf contributes to the ultraviolet flux. However, it is now evident that noticeable changes are occurring in the hot zones in accreting systems long after the outburst, and not only for systems that are dominated by the white dwarf. Whether these differences are due to different outburst mechanisms or to changes on white dwarfs which provide varying contributions to the UV flux remains to be determined.
Szkody, Paula↗
Magnetic fields in the accretion disks of cataclysmic variables
The radial transport of magnetic flux in CV accretion disks is considered. Turbulent diffusion in a disk with finite outer radius Rd leads to decay of large-scale magnetic fields, as magnetic flux can leak out at the outer edge of the disk. Numerical computations of the decay rate and magnetic structure are presented. It is shown that the decay time is significantly shorter than the accretion time. Centrifugally driven winds may be possible from the outer parts of the disk, provided there exist efficient dynamo processes which regenerate the field.
Van Ballegooijen, A. A.↗
The interoutburst behavior of cataclysmic variables
Existing IUE and AAVSO archive data were used to accomplish a large scale study of what happens to the UV flux of accretion disk systems during the quiescent intervals between outbursts, and how it relates to the preceding outburst characteristics of amplitude and width. The data sample involved multiple IUE observations for 16 dwarf novae and 8 novae along with existing optical coverage. Results indicate that most systems show correlated UV flux behavior with interoutburst phase, with 60 percent of the dwarf novae and 50 percent of the novae having decreasing flux trends while 33 percent of the dwarf novae and 38 percent of the novae show rising UV flux during the quiescent interval. All of the dwarf novae with decreasing UV fluxes at 1475 A have orbital periods longer than 4.4 hours, while all (except BV Cen) with flat or rising fluxes at 1475 A have orbital periods less than two hours. From a small sample (7) that have relatively large quiescent V magnitude changes between the IUE observations, most show a strong correlation between the UV and optical continuum. Interpretation of the results is complicated by not being able to determine how much the white dwarf contributes to the ultraviolet flux. However, it is now evident that noticeable changes are occurring in the hot zones in accreting systems long after the outburst, and not only for systems that are dominated by the white dwarf.
Szkody, Paula↗
PG0027 + 260 - An example of a class of cataclysmic binaries with mysterious, but consistent, behavior
This paper reports extensive optical observations on the PG0027 + 260 binary, carried out on August 1984 with the 1.3 McGraw-Hill telescope and Mark II spectrometer at Michigan-Dartmouth-MIT Observatory on Kitt Peak. It is shown that this object is an eclipsing novalike variable with an orbital period of 3.51 hr. The PG0027 + 260 displays several unexplained phenomena which are remarkably similar to those of the SW Sex, DW UMa, and V1315 Aql, which are eclipsing novalike stars with periods between 3 and 4 hrs. The eclipse of the PG0027 + 260 is modeled, and it is shown that, while the mean eclipse light curve is easy to match, there is no simple explanation for the variable depth.
Thorstensen, John R.↗
Cataclysmic variable evolution - Clues from the underlying white dwarf
This paper presents an update of determinations of the CV white dwarf effective-temperature, T(eff), together with an initial exploration of the possible implications and constraints on the CV lifetimes and evolution based on the ensemble of white dwarf T(eff) values as a function of orbital period. The CV dwarf luminosities are derived by using the T(eff) data and adopting the masses of individual CV white dwarfs determined by Webbink (1990). The present ensemble of empirically determined white dwarf effective temperatures reveals a distribution centered near 16,000 K, implying a mean lower limit total cooling lifetime of 5 x 10 to the 8th yr for the majority of CV degenerates. The two coolest CV degenerates, VV Puppis and St LMi, were found among the strongly magnetic AM Her CVs.
Sion, Edward M.↗
Magnetic moment distribution of magnetic cataclysmic variables
A simulation study is made of the relative numbers of the AM Herculis binaries and the intermediate polars as a function of the orbital period using random variables subject to suitable constraints to describe the various parameters. It is shown that the observations can be matched by a single distribution in the magnetic moment equals 0.7 +/- 0.3. For such an ensemble, the intermediate polars are distributed in the log(Porb) - log(Ps) diagram about the critical disk line but with a larger scatter than observed.
Wu, Kinwah↗
Rapid oscillations in cataclysmic variables. VII - GK Persei
The discovery of a stable short-period oscillation in the UV light curve of the old nova GK Persei during 1989-91 is reported. The period is consistent with the 351.34-second pulse period seen in hard X-rays, due to the rotation of the white dwarf. In blue light, a quasi-periodic signal appears in the low-frequency wings of the coherent signal. There is evidence for long-term spin-up of the white dwarf; the most probable mean rate is 0.0008 sec/yr.
Patterson, Joseph↗
Apollo 15 impact melts, the age of Imbrium, and the Earth-Moon impact cataclysm
The early impact history of the lunar surface is of critical importance in understanding the evolution of both the primitive Moon and the Earth, as well as the corresponding populations of planetesimals in Earth-crossing orbits. Two endmember hypotheses call for greatly dissimilar impact dynamics. One is a heavy continuous (declining) bombardment from about 4.5 Ga to 3.85 Ga. The other is that an intense but brief bombardment at about 3.85 +/- Ga was responsible for producing the visible lunar landforms and for the common 3.8-3.9 Ga ages of highland rocks. The Apennine Front, the main topographic ring of the Imbrium Basin, was sampled on the Apollo 15 mission. The Apollo 15 impact melts show a diversity of chemical compositions, indicating their origin in at least several different impact events. The few attempts at dating them have generally not produced convincing ages, despite their importance. Thus, we chose to investigate the ages of melt rock samples from the Apennine Front, because of their stratigraphic importance yet lack of previous age definition.
Ryder, Graham↗
Rapid oscillations in cataclysmic variables. IX - BG Canis Minoris (=3A 0729+103)
Results of a 10-yr photometric program on BG Canis Minoris, a novalike variable distinguished by the presence of a strictly coherent 913-s wave in its light curve, are presented. Long-term ephemerides for the orbital clock, which manifests itself through a 3.2-h light modulation, and the 913-s clock, are presented. The light curve exhibits a persistent 0.3 mag modulation at a period consistent with the 3.2-h spectroscopic period. Well-distributed timings of the orbital minima prove that the period is 0.1347486 day. It is inferred from the shape of the waveform and from the existence of X-ray dips with a sharp energy dependence that the modulation is caused by absorption. Power spectra of the nightly light curves show variable secondary features, in addition to the regular 913-s pulse. The 913-s period, presumably the first harmonic of the true white-dwarf spin period, is decreasing by 0.0022 s/yr.
Patterson, Joseph↗