scholarly journals Classical Novae – Before and After Outburst

1988 ◽  
Vol 108 ◽  
pp. 226-231
Author(s):  
Mario Livio
Keyword(s):  
White Dwarf ◽  
Main Sequence ◽  
Orbital Parameters ◽  
Classical Novae ◽  
Classical Nova ◽  
Before And After ◽  
Low Mass ◽  
Orbital Periods ◽  
Thermonuclear Runaway ◽  
Nova Outburst

Classical nova (CN) and dwarf nova (DN) systems have the same binary components (a low-mass main sequence star and a white dwarf) and the same orbital periods. An important question that therefore arises is: are these systems really different ? (and if so, what is the fundamental difference ?) or, are these the same systems, metamorphosing from one class to the other ?The first thing to note in this respect is that the white dwarfs in DN systems are believed to accrete continuously (both at quiescence and during eruptions). At the same time, both analytic (e.g. Fujimoto 1982) and numerical calculations show, that when sufficient mass accumulates on the white dwarf, a thermonuclear runaway (TNR) is obtained and a nova outburst ensues (see e.g. reviews by Gallagher and Starrfield 1978, Truran 1982). It is thus only natural, to ask the question, is the fact that we have not seen a DN undergo a CN outburst (in about 50 years of almost complete coverage) consistent with observations of DN systems ? In an attempt to answer this question, we have calculated the probability for a nova outburst not to occur (in 50 years) in 86 DN systems (for which at least some of the orbital parameters are known).

scholarly journals Two-dimensional simulations of mixing in classical novae: The effect of white dwarf composition and mass

2018 ◽  
Vol 619 ◽  
pp. A121 ◽  
Author(s):  
Jordi Casanova ◽  
Jordi José ◽  
Steven N. Shore
Keyword(s):  
White Dwarf ◽  
Binary Systems ◽  
Main Sequence ◽  
Chemical Species ◽  
Two Dimensions ◽  
Classical Novae ◽  
Nova Shells ◽  
Solar Abundances ◽  
Low Mass ◽  
Thermonuclear Runaway

Context. Classical novae are explosive phenomena that take place in stellar binary systems. They are powered by mass transfer from a low-mass main sequence star onto either a CO or ONe white dwarf. The material accumulates for 104–105 yr until ignition under degenerate conditions, resulting in a thermonuclear runaway. The nuclear energy released produces peak temperatures of ∼0.1–0.4 GK. During these events, 10−7−10−3 M⊙ enriched in intermediate-mass elements, with respect to solar abundances, are ejected into the interstellar medium. However, the origin of the large metallicity enhancements and the inhomogeneous distribution of chemical species observed in high-resolution spectra of ejected nova shells is not fully understood. Aims. Recent multidimensional simulations have demonstrated that Kelvin-Helmholtz instabilities that operate at the core-envelope interface can naturally produce self-enrichment of the accreted envelope with material from the underlying white dwarf at levels that agree with observations. However, such multidimensional simulations have been performed for a small number of cases and much of the parameter space remains unexplored. Methods. We investigated the dredge-up, driven by Kelvin-Helmholtz instabilities, for white dwarf masses in the range 0.8–1.25 M⊙ and different core compositions, that is, CO-rich and ONe-rich substrates. We present a set of five numerical simulations performed in two dimensions aimed at analyzing the possible impact of the white dwarf mass, and composition, on the metallicity enhancement and explosion characteristics. Results. At the time we stop the simulations, we observe greater mixing (∼30% higher when measured in the same conditions) and more energetic outbursts for ONe-rich substrates than for CO-rich substrates and more massive white dwarfs.

scholarly journals Nova Outburst Due to Accretion of H-Rich Matter onto White Dwarfs

1979 ◽  
Vol 53 ◽  
pp. 290-293
Author(s):  
G. Siegfried Kutter ◽  
Warren M. Sparks
Keyword(s):  
White Dwarf ◽  
White Dwarfs ◽  
Classical Novae ◽  
Secondary Star ◽  
Rich Material ◽  
Thermonuclear Runaway ◽  
Nova Outburst ◽  
Physical Realism ◽  
Degenerate Base

We assume that the outburst of classical novae is the result of transfer of H-rich material from a red secondary star to a He or C/O white dwarf and the development of a thermonuclear runaway in the e-degenerate “base of the accreted H-rich envelope. Based on these assumptions, we have investigated this problem in several stages of increasing theoretical complexity and physical realism.

scholarly journals Classical and Recurrent Nova Models

2011 ◽  
Vol 7 (S281) ◽  
pp. 80-87 ◽  
Author(s):  
Jordi José ◽  
Jordi Casanova ◽  
Enrique García–Berro ◽  
Margarita Hernanz ◽  
Steven N. Shore ◽  
...  
Keyword(s):  
Numerical Simulations ◽  
Classical Novae ◽  
Physical Mechanisms ◽  
Classical Nova ◽  
Solar Abundances ◽  
Low Mass ◽  
Thermonuclear Runaway ◽  
Nuclear Processing ◽  
Nova Outbursts ◽  
The Impact

AbstractRemarkable progress in the understanding of nova outbursts has been achieved through combined efforts in photometry, spectroscopy and numerical simulations. According to the thermonuclear runaway model, novae are powered by thermonuclear explosions in the hydrogen-rich envelopes transferred from a low-mass stellar companion onto a close white dwarf star. Extensive numerical simulations in 1-D have shown that the accreted envelopes attain peak temperatures ranging between 108 and 4 × 108 K, for about several hundred seconds, hence allowing extensive nuclear processing which eventually shows up in the form of nucleosynthetic fingerprints in the ejecta. Indeed, it has been claimed that novae can play a certain role in the enrichment of the interstellar medium through a number of intermediate-mass elements. This includes 17O, 15N, and 13C, systematically overproduced with respect to solar abundances, plus a lower contribution in a number of other species (A < 40), such as 7Li, 19F, or 26Al. At the turn of the XXI Century, classical novae have entered the era of multidimensional models, which provide a new insight into the physical mechanisms that drive mixing at the core-envelope interface.In this review, we will present hydrodynamic models of classical novae, from the onset of accretion up to the explosion and ejection stages, both for classical and recurrent novae, with special emphasis on their gross observational properties and their associated nucleosynthesis. The impact of nuclear uncertainties on the final yields will be discussed. Recent results from 2-D models of mixing during classical nova outbursts will also be presented.

scholarly journals The sustained post-outburst brightness of Nova Per 2018, the evolved companion, and the long orbital period

2020 ◽  
Vol 639 ◽  
pp. L10 ◽  
Author(s):  
U. Munari ◽  
S. Moretti ◽  
A. Maitan
Keyword(s):  
Optical Spectroscopy ◽  
Orbital Period ◽  
White Dwarf ◽  
Interstellar Space ◽  
Plateau Phase ◽  
Classical Novae ◽  
Classical Nova ◽  
Fast Decline ◽  
Symbiotic Binaries ◽  
Nova Outburst

Nova Per 2018 (= V392 Per) halted the decline from maximum when it was 2 mag brighter than quiescence and since 2019 has been stable at such a plateau. The ejecta have already fully diluted into the interstellar space. We obtained BVRIgrizY photometry and optical spectroscopy of V392 Per during the plateau phase and compared it with equivalent data gathered prior to the nova outburst. We find the companion star (CS) to be a G9 IV/III and the orbital period to be 3.4118 days, making V392 Per the longest known period for a classical nova. The location of V392 Per on the theoretical isochrones is intermediate between that of classical novae and novae erupting within symbiotic binaries, in a sense bridging the gap. The reddening is derived to be EB − V = 0.72 and the fitting to isochrones returns a 3.6 Gyr age for the system and 1.35 M⊙, 5.3 R⊙, and 15 L⊙ for the companion. The huge Ne overabundance in the ejecta and the very fast decline from nova maximum both point to a massive white dwarf (WD) (MWD ≥ 1.1−1.2 M⊙). The system is viewed close to pole-on conditions and the current plateau phase is caused by irradiation of the CS by the WD still burning at the surface.

scholarly journals The White Dwarf Mass and Orbital Period Distribution in Zero-Age Cataclysmic Binaries

1989 ◽  
Vol 114 ◽  
pp. 440-442
Author(s):  
M. Politano ◽  
R. F. Webbink
Keyword(s):  
Star Formation ◽  
White Dwarf ◽  
Galactic Disk ◽  
Orbital Energy ◽  
Orbital Parameter ◽  
Orbital Parameters ◽  
Cataclysmic Binaries ◽  
Magnetic Braking ◽  
Orbital Periods ◽  
The Individual

A zero-age cataclysmic binary (ZACB) we define as a binary system at the onset of interaction as a cataclysmic variable. We present here the results of calculations of the distributions of white dwarf masses and of orbital periods in ZACBs, due to binaries present in a stellar population which has undergone continuous, constant star formation for 1010 years.Distributions of ZACBs were calculated for binaries formed t years ago, for log t = 7.4 (the youngest age at which viable ZACBs can form) to log t = 10.0 (the assumed age of the Galactic disk), in intervals of log t = 0.1. These distributions were then integrated over time to obtain the ZACB distribution for a constant rate of star formation. To compute the individual distributions for a given t, we require the density of systems forming (number of pre-cataclysmics forming per unit volume of orbital parameter space), n£(t), and the rates at which the radii of the secondary and of its Roche lobe are changing in time, s (t) and L, s (t), respectively. In calculating nf(t), we assume that the distribution of the orbital parameters in primordial (ZAMS) binaries may be written as the product of the distribution of masses of ZAMS stars (Miller and Scalo 1979), the distribution of mass ratios in ZAMS binaries (cf. Popova, et al., 1982), and the distribution of orbital periods in ZAMS binaries (Abt 1983). In transforming the the orbital parameters from progenitor (ZAMS) to offspring (ZACB) binaries, we assume that all of the orbital energy deposited into the envelope during the common envelope phase leading to ZACB formation goes into unbinding that envelope. R.L, s (t) is determined from orbital angular momentum loss rates due to gravitational radiation (Landau and Lifshitz 1951) and magnetic braking (γ = 2 in Rappaport, Verbunt, and Joss 1983). We turn off magnetic braking if the secondary is completely convective.

scholarly journals VLT/SPHERE astrometric confirmation and orbital analysis of the brown dwarf companion HR 2562 B

2018 ◽  
Vol 615 ◽  
pp. A177 ◽  
Author(s):  
A.-L. Maire ◽  
L. Rodet ◽  
C. Lazzoni ◽  
A. Boccaletti ◽  
W. Brandner ◽  
...  
Keyword(s):  
Orbital Motion ◽  
Orbital Plane ◽  
Real Data ◽  
Far Infrared ◽  
Brown Dwarf ◽  
Orbital Parameters ◽  
System A ◽  
Low Mass ◽  
Debris Disk ◽  
Orbital Periods

Context. A low-mass brown dwarf has recently been imaged around HR 2562 (HD 50571), a star hosting a debris disk resolved in the far infrared. Interestingly, the companion location is compatible with an orbit coplanar with the disk and interior to the debris belt. This feature makes the system a valuable laboratory to analyze the formation of substellar companions in a circumstellar disk and potential disk-companion dynamical interactions. Aims. We aim to further characterize the orbital motion of HR 2562 B and its interactions with the host star debris disk. Methods. We performed a monitoring of the system over ~10 months in 2016 and 2017 with the VLT/SPHERE exoplanet imager. Results. We confirm that the companion is comoving with the star and detect for the first time an orbital motion at high significance, with a current orbital motion projected in the plane of the sky of 25 mas (~0.85 au) per year. No orbital curvature is seen in the measurements. An orbital fit of the SPHERE and literature astrometry of the companion without priors on the orbital plane clearly indicates that its orbit is (quasi-)coplanar with the disk. To further constrain the other orbital parameters, we used empirical laws for a companion chaotic zone validated by N-body simulations to test the orbital solutions that are compatible with the estimated disk cavity size. Non-zero eccentricities (>0.15) are allowed for orbital periods shorter than 100 yr, while only moderate eccentricities up to ~0.3 for orbital periods longer than 200 yr are compatible with the disk observations. A comparison of synthetic Herschel images to the real data does not allow us to constrain the upper eccentricity of the companion.

scholarly journals Asteroseismological Probing of the Thermal Evolution of White Dwarf Stars

1992 ◽  
Vol 9 ◽  
pp. 643-645
Author(s):  
G. Fontaine ◽  
F. Wesemael
Keyword(s):  
White Dwarf ◽  
White Dwarfs ◽  
Main Sequence ◽  
Thermal Evolution ◽  
Sequence Evolution ◽  
Helium Burning ◽  
Dwarf Stars ◽  
White Dwarf Stars ◽  
The Galaxy ◽  
Low Mass

AbstractIt is generally believed that the immediate progenitors of most white dwarfs are nuclei of planetary nebulae, themselves the products of intermediate- and low-mass main sequence evolution. Stars that begin their lifes with masses less than about 7-8 M⊙ (i.e., the vast majority of them) are expected to become white dwarfs. Among those which have already had the time to become white dwarfs since the formation of the Galaxy, a majority have burnt hydrogen and helium in their interiors. Consequently, most of the mass of a typical white dwarf is contained in a core made of the products of helium burning, mostly carbon and oxygen. The exact proportions of C and 0 are unknown because of uncertainties in the nuclear rates of helium burning.

scholarly journals The 1987 Outburst of the Recurrent Nova U SCO

1988 ◽  
Vol 103 ◽  
pp. 337-338
Author(s):  
K. Sekiguchi ◽  
M.W. Feast ◽  
P.A. Whitelock ◽  
M.D. Overbeek ◽  
W. Wargau ◽  
...  
Keyword(s):  
White Dwarf ◽  
High Velocity ◽  
Accretion Disc ◽  
Low Mass ◽  
Recurrent Nova ◽  
Thermonuclear Runaway

AbstractSpectral observations obtained soon after the 1987 brightening of U Sco support a thermonuclear runaway model for outbursts of this object. Spectra later in the decline are, however, more characteristic of a hot accretion disc. These observations are reconciled in a model where the low-mass high-velocity shell ejected from the surface of the white dwarf collides with the accretion disc causing it to brighten.

scholarly journals The Evolutionary Status of the Secondaries of Cataclysmic Binaries

1983 ◽  
Vol 72 ◽  
pp. 257-262
Author(s):  
H. Ritter
Keyword(s):  
Probability Distribution ◽  
Main Sequence ◽  
The Other ◽  
Initial Mass ◽  
Evolutionary Status ◽  
Mass Ratio ◽  
Main Sequence Stars ◽  
Cataclysmic Binaries ◽  
Low Mass ◽  
Orbital Periods

ABSTRACTIt is shown that the secondary components of cataclysmic binaries with orbital periods of less than ~10 hours are indistinguishable from ordinary low-mass main-sequence stars and that, therefore, they are essentially unevolved. On the other hand, it is shown that, depending on the mass ratio of the progenitor system, the secondary of a cataclysmic binary could be significantly evolved. The fact that nevertheless most of the observed secondaries are essentially unevolved can be accounted for by assuming that the probability distribution for the initial mass ratio is not strongly peaked towards unity mass ratio.

scholarly journals Photometry of AM Her Stars – Line and Continuum Emission

1979 ◽  
Vol 53 ◽  
pp. 324-328
Author(s):  
Paula Szkody
Keyword(s):  
Emission Line ◽  
White Dwarf ◽  
Main Sequence ◽  
Close Binary ◽  
Line Spectrum ◽  
Continuum Emission ◽  
Late Type ◽  
Emission Line Spectrum ◽  
Orbital Periods

The 4 known AM Her stars or polars (AM Her, ANUMa, W Pup, and 2A0311-227) are characterized by large circular polarizations of 10-35%, (Tapia 1977a, b, Krzeminski and Serkowski 1977), an emission line spectrum with strong H and He lines (Crampton and Cowley 1977, Greenstein et al. 1977), complex photometric variations (Szkody 1978, Priedhorsky and Krzeminski 1978, Warner & Nather 1972), long term high and low states and short orbital periods (80-180 min.). Models of these systems envision a close binary containing a magnetic white dwarf primary (B ~ 108G) and late type main sequence secondary transferring material into an accretion funnel over one or both poles of the white dwarf (Stockman et al. 1977, Lamb & Masters 1979, Liebert et al. 1978).

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