Discovery of a new WZ Sagittae-type cataclysmic variable in the Kepler/K2 data
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R Ridden-Harper↗
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High-speed photometry of faint cataclysmic variables – IX. Targets from multiple transient surveys
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K Paterson↗
Measuring the Masses of Magnetic White Dwarfs: A NuSTAR Legacy Survey
The hard X-ray spectrum of magnetic cataclysmic variables can be modelled to provide a measurement of white dwarf mass. This method is complementary to radial velocity measurements, which depend on the (typically rather uncertain) binary inclination. Here we present results from a Legacy Survey of 19 magnetic cataclysmic variables with NuSTAR.We fit accretion column models to their 20–78 keV spectra and derive the white dwarf masses, finding a weighted average M(sub WD) = 0.77 ± 0.02 M(sub ⨀), with a standard deviation σ = 0.10 M(sub ⨀), when we include the masses derived from previous NuSTAR observations of seven additional magnetic cataclysmic variables. We find that the mass distribution of accreting magnetic white dwarfs is consistent with that of white dwarfs in non-magnetic cataclysmic variables. Both peak at a higher mass than the distributions of isolated white dwarfs and post-common-envelope binaries. We speculate as to why this might be the case, proposing that consequential angular momentum losses may play a role in accreting magnetic white dwarfs and/or that our knowledge of how the white dwarf mass changes over accretion–nova cycles may also be incomplete.
Novae↗
Models for various aspects of dwarf novae and nova-like stars
The first attempts to explain the nature of dwarf novae were based on the assumption of single-star phenomena, in which emission lines were assumed to be caused by circumstellar gas shells. The outburst behavior was tentatively ascribed to the kind of (also not understood) mechanism leading to nova outbursts. The realization that some, and possibly all, dwarf novae and nova-like stars (and novae) are binaries eventually led to models which bore more and more similarities to the modern interpretation on the basis of the Roche model. Not all cataclysmic variables are known binaries. In fact, with respect to the entire number of known objects, the proven binaries are still the minority, but all the brightest variables are in fact known to binaries. Not a single system is known which exhibits the usual characteristics of a cataclysmic variable and at the same time can be declared with certainty to be a single star. Two systems are known, the dwarf nova EY Cyg and the recurrent nova V1017 Sgr, in which, in spite of intensive search, no radial velocity variations have been found; but they still exhibit composite spectra consisting of a bright continuum, an emission spectrum, and a cool absorption spectrum. If the Roche model is correct, it is to be expected that a small percentage of objects is viewed pole-on, so orbital motions do not make themselves felt as Doppler shifts of spectral lines. So even these two systems support the hypothesis that all cataclysmic variables (with the possible exception of symbiotic stars) are binaries. In cataclysmic variables, it seems that the brightness changes observed in dwarf novae and nova-like stars in the optical and the UV are due directly to changes in the accretion disks. The study and understanding of accretion disks in these systems can bear potentially valuable consequences for many other fields in astronomy. The observed spectra of dwarf novae and nova-like stars comprise a fairly large range: pure emission spectra, pure absorption spectra, a mixture of both, asymmetric line profiles, very different slopes of the continuous flux distribution -- and one single system may exhibit all of these features at different times. Agreement and disagreement between computed and observed spectra should show whether or not the Roche model is applicable and where it probably will have to be modified and improved. Except for their outburst behavior and its immediate consequences, novae, dwarf novae, and nova-like stars cannot be physically distinguished from each other.
Ladous, Constanze↗
The nautre of dwarf novae and related systems
The high energy emissions from cataclysmic variables (interacting binary systems containing an accreting white dwarf) and the relationship of the high energy emission of these stars to their optical properties were investigated. The relationship of the cataclysmic binaries to the strong X-ray emitting binaries that contain a neutron star as the accreting star was examined. A soft X-ray survey of cataclysmic variable stars was carried out. Approximately 75% of all the sources observed were detected in short (2000 sec) observations. Relationships between the X-ray and optical luminosity and the dependence of this quantity on the subclass of the variable were investigated and constraints on the nature of these systems were provided.
Lampton, M.↗
Accreting degenerate dwarfs in close binary systems
Advances in the study of cataclysmic variables made during the past few years are reviewed. The classification of cataclysmic binaries and their dynamic properties are summarized. The hard and soft X-ray emission from these objects is discussed, and two alternative accretion geometries for producing this radiation from deep in the potential well of the degenerate dwarf are considered. The ultraviolet and optical spectrum is addressed, including disk emission and contributions from the companion star. Magnetic fields in cataclysmic variables are discussed, and the temporal behavior of these stars is addressed, including periodic modulations associated with orbital motion and rotation as well as flickering and pulsation reflecting the mass transfer process and the dynamics of matter near the surface of the accreting star. The outburst process is considered, including classical novae, recurrent novae, and dwarf novae.
Cordova, F. A.↗
Variable radio emission from the 4 Draconis system
The 4 Dra system, which contains an M3 giant and a cataclysmic binary, has been detected as a 6 cm radio source with the VLA. This radio emission is variable on time scales of weeks to months. A number of possible sources of the radio emission within the 4 Dra system are considered, and the observed time variability probably rules out optically thick free-free emission from the wind of the M3 giant as the dominant source. The major source of the observed radio emission is likely to be either the cataclysmic binary or shocked regions due to the interaction between the cataclysmic binary and the red giant wind.
Brown, Alexander↗
Far UV Observations of Interstellar Shocks
This grant covered analysis of Hopkins Ultraviolet Telescope data from the Astro-2 mission. The proposed research was aimed primarily at SNR shock waves, but the ASTRO-2 GO program was intended to make the GOs part of the instrument teams. The grant therefore covered extensive travel to Marshall Space Flight Center for mission simulations and the mission itself. In keeping with the unique nature of the ASTRO-2 GO program, I participated actively in the instrument team's investigations of HH objects and cataclysmic variables. Over the course of the Astro-2 mission, we obtained good observations of the supernova remnants SN1006 (1 position), Vela (3 positions), the Cygnus Loop (7 positions) and 0519-69 in the LMC (1 position) as part of this GI program, along with Puppis A (1 position), Vela (1 position), the Cygnus Loop (7 positions) and the Schweizer- Middleditch star (HUT PI program on SNRS). We also observed the Herbig-Haro object HH2 and about a dozen cataclysmic variables, including magnetic systems and dwarf novae. This GI grant covered modest travel for data analysis. We anticipate submitting papers on the non-radiative shock in northern Cygnus Loop, on the LMC Balmer-dominated remnant LMC 0519-69, on the radiative shocks in the Eastern Cygnus Loop (the XA region), and on the cataclysmic variable YZ Cnc over the course of the coming year. We have obtained extensive supporting data from ground-based telescopes for the Cygnus Loop spectra.
Raymond, John C.↗
Rosat X-Ray Observations
This grant has supported ongoing analysis of ROSAT X-Ray observations. Publications resulting in whole or in part from this grant include: X-Rays and Activity in Pre-Main Sequence Stars. The Rest of Orion: Low Mass Pre-Main Sequence Stars Outside the Orion Nebula. Star Formation in Orion (the Constellation). Discovery of a New Cataclysmic Variable System. An IDL-based ROSAT Data Analysis Package. The Long Period AM Her-like Cataclysmic Variable RXJ051541+0104.611. Discovery of A Nearby Isolated Neutron Star. A candidate isolated old neutron star. On the X-ray Position and Deep Optical Imaging of the Neutron Star Candidate RXJ1856.5-375411. The Spectral Energy Distribution of the Isolated Neutron Star RXJ185635-3754. A Most Unusual, Highly-X-ray-Variable Cataclysmic Variable.
Walter, F. M.↗
An Estimate of the Likelihood for a Climatically Significant Volcanic Eruption Within the Present Decade (2000-2009)
Since 1750, the number of cataclysmic volcanic eruptions (i.e., those having a volcanic explosivity index, or VEI, equal to 4 or larger) per decade is found to span 2-11, with 96% located in the tropics and extra-tropical Northern Hemisphere, A two-point moving average of the time series has higher values since the 1860s than before, measuring 8.00 in the 1910s (the highest value) and measuring 6.50 in the 1980s, the highest since the 18 1 0s' peak. On the basis of the usual behavior of the first difference of the two-point moving averages, one infers that the two-point moving average for the 1990s will measure about 6.50 +/- 1.00, implying that about 7 +/- 4 cataclysmic volcanic eruptions should be expected during the present decade (2000-2009). Because cataclysmic volcanic eruptions (especially, those having VEI equal to 5 or larger) nearly always have been associated with episodes of short-term global cooling, the occurrence of even one could ameliorate the effects of global warming. Poisson probability distributions reveal that the probability of one or more VEI equal to 4 or larger events occurring within the next ten years is >99%, while it is about 49% for VEI equal to 5 or larger events and 18% for VEI equal to 6 or larger events. Hence, the likelihood that a, climatically significant volcanic eruption will occur within the next 10 years appears reasonably high.
Wilson, Robert M.↗
An Estimation of the Likelihood of Significant Eruptions During 2000-2009 Using Poisson Statistics on Two-Point Moving Averages of the Volcanic Time Series
Since 1750, the number of cataclysmic volcanic eruptions (volcanic explosivity index (VEI)>=4) per decade spans 2-11, with 96 percent located in the tropics and extra-tropical Northern Hemisphere. A two-point moving average of the volcanic time series has higher values since the 1860's than before, being 8.00 in the 1910's (the highest value) and 6.50 in the 1980's, the highest since the 1910's peak. Because of the usual behavior of the first difference of the two-point moving averages, one infers that its value for the 1990's will measure approximately 6.50 +/- 1, implying that approximately 7 +/- 4 cataclysmic volcanic eruptions should be expected during the present decade (2000-2009). Because cataclysmic volcanic eruptions (especially those having VEI>=5) nearly always have been associated with short-term episodes of global cooling, the occurrence of even one might confuse our ability to assess the effects of global warming. Poisson probability distributions reveal that the probability of one or more events with a VEI>=4 within the next ten years is >99 percent. It is approximately 49 percent for an event with a VEI>=5, and 18 percent for an event with a VEI>=6. Hence, the likelihood that a climatically significant volcanic eruption will occur within the next ten years appears reasonably high.
Wilson, Robert M.↗
Mass Flux in the Ancient Earth-Moon System and Benign Implications for the Origin of Life on Earth
The origin of life on Earth is commonly considered to have been negatively affected by intense impacting in the Hadean, with the potential for the repeated evaporation and sterilization of any ocean. The impact flux is based on scaling from the lunar crater density record, but that record has no tie to any absolute age determination for any identified stratigraphic unit older than approx. 3.9 Ga (Nectaris basin). The flux can be described in terms of mass accretion, and various independent means can be used to estimate the mass flux in different intervals. The critical interval is that between the end of essential crustal formation (approx. 4.4 Ga) and the oldest mare times (approx. 3.8 Ga). The masses of the basin-forming projectiles during Nectarian and early Imbrian times, when the last 15 of the approx.45 identified impact basins formed, can be reasonably estimated as minima. These in sum provide a minimum of 2 x 10(exp 21)g for the mass flux to the Moon during those times. If the interval was 80 million years (Nectaris 3.90 Ga, Orientale 3.82 Ga), then the flux was approx. 2 x 10(exp 13) g/yr over this period. This is higher by more than an order of magnitude than a flux curve that declines continuously and uniformly from lunar accretion to the rate inferred for the older mare plains. This rate cannot be extrapolated back increasingly into pre-Nectarian times, because the Moon would have added masses far in excess of itself in post-crust-formation time. Thus this episode was a distinct and cataclysmic set of events. There are approx. 30 pre-Nectarian basins, and they were probably part of the same cataclysm (starting at approx. 4.0 Ga?) because the crust is fairly intact, the meteoritic contamination of the pre-Nectarian crust is very low, impact melt rocks older than 3.92 Ga are virtually unknown, and ancient volcanic and plutonic rocks have survived this interval. The accretionary flux from approx. 4.4 to approx. 4.0 Ga was comparatively benign. When scaled to Earth, even the late cataclysm does not produce oceane vaporating, globally sterilizing events. The rooted concept that such events took place is based on the extrapolation of a nonexistent lunar record to the Hadean. The Earth from approx. 4.4 to approx. 3.8 Ga was comparatively peaceful, and the impacting itself could have been thermally and hydrothermally beneficial. The origin of life could have taken place at any time between 4.4 and 3.85 Ga, given the current impact constraints, and there is no justification for the claim that life originated (or re-originated) as late as 3.85 Ga in response to the end of hostile impact conditions.
Ryder, Graham↗
The Impact History Of The Moon
The bombardment history of the Earth-Moon system has been debated since the first recognition that the circular features on the Moon may be impact craters. Because the lunar impact record is the only planetary impact record to be calibrated with absolute ages, it underpins our understanding of geologic ages on every other terrestrial planet. One of the more remarkable results to come out of lunar sample analyses is the hypothesis that a large number of impact events occurred on the Moon during a narrow window in time approximately 3.8 to 4.1 billion years ago (the lunar cataclysm ). Subsequent work on the lunar and martian meteorite suites; remote sensing of the Moon, Mars, asteroids, and icy satellites; improved dynamical modeling; and investigation of terrestrial zircons extend the cataclysm hypothesis to the Earth, other terrestrial planets, and possibly the entire solar system. Renewed US and international interest in exploring the Moon offers new potential to constrain the Earth-Moon bombardment history. This paper will review the lunar bombardment record, timing and mechanisms for cataclysmic bombardment, and questions that may be answered in a new age of exploration.
Cohen, B. A.↗
Theories of white dwarf oscillations
The current status of theoretical understanding of the oscillations observed in the ZZ Ceti stars and cataclysmic variables is briefly reviewed. Nonradial g-mode oscillations appear to provide a satisfactory explanation for the low amplitude variables such as R548, with periods in the range of approximately 200 to 300 seconds, but for the longer period (800 to 1000 seconds) oscillators, the situation is still unclear. Rotation may play an important role in this problem, and the effects of both slow and fast rotation upon the mode structure are discussed. In the cataclysmic variables, both accretion and thermonuclear burning may act to excite oscillations of the white dwarf.
Vanhorn, H. M.↗
Dropping stones in magma oceans - Effects of early lunar cratering
A new methodology is used to calculate the accumulation rate of megaregolith materials for two models of early lunar cratering, both with and without episodes of late cataclysmic cratering. Results show that the pulverization of early rock layers was an important process competing with the formation of a coherent rock lithosphere at the surface of the hypothetical lunar magma ocean. If a magma ocean existed, then its initial cooling was marked by a period of pre-lithospheric chaos in which impacts punched through the initially thin rocky skin, mixing rock fragments with splashed magma. Furthermore, the results show that intense brecciation and pulverization of rock materials must have occurred to a depth of at least tens of kilometers in the first few hundred years of lunar history regardless of whether a 'terminal lunar cataclysm' occurred around 4.0 G.y. ago. The predicted pattern of brecciation and the ages of surviving rock fragments is similar to that actually observed among lunar samples. More reliable dating of basin-forming events and models of rock exhumation and survival are needed in order to understand better the relation between the early intense bombardment of the moon and the samples collected on the moon today.
Hartmann, W. K.↗
The evolution of highly compact binary stellar systems
A new theoretical treatment of the evolution of highly compact binary systems is presented. The evolution is calculated until almost the entire mass of the secondary has been transferred to the primary or lost from the system. It is assumed that gravitational radiation from the system is the cause of mass transfer. It is found that the structure of the mass-losing star can be approximated by an n = 3/2 polytrope, and as a result a relatively large number of different cases can be explored and some general conclusions drawn. An explanation is found for the existence of a cutoff in the orbital period distribution among the cataclysmic variables and light is shed upon the possible generic relationships among cataclysmic variables, the low-mass X-ray binaries, and the spectrally soft transient X-ray sources.
Rappaport, S.↗
Radio emission from AM Herculis-type binaries
A VLA search for 4.9 GHz radiation from the magnetic cataclysmic variable AM Her, along with the similar EF Eri binary, has led to the discovery of AM Her radio emission having a flux density of 0.67 + or - 0.052 mJy, where 1 mJy is equal to 10 to the -29th W/sq m per Hz. Neither AM Her circular polarization nor EF Eri were detected. The AM Her data are shown to be consistent with a model in which radiation is due to geosynchrotron emission from electrons of energies of a few hundred keV, which are trapped in the magnetosphere of the white dwarf element of the cataclysmic variable.
Chanmugam, G.↗
Mass loss from interacting close binary systems
The three well-defined classes of evolved binary systems that show evidence of present and/or past mass loss are the cataclysmic variables, the Algols, and Wolf-Rayet stars. It is thought that the transformation of supergiant binary systems into the very short-period cataclysmic variables must have been a complex process. The new evidence that has recently been obtained from the far ultraviolet spectra that a certain subclass of the Algols (the Serpentids) are undergoing fairly rapid evolution is discussed. It is thought probable that the remarkable mass outflow observed in them is connected with a strong wind powered by accretion. The origin of the circumbinary clouds or flat disks that probably surround many strongly interacting binaries is not clear. Attention is also given to binary systems with hot white dwarf or subdwarf components, such as the symbiotic objects and the BQ stars; it is noted that in them both components may be prone to an enhanced stellar wind.
Plavec, M. J.↗