Nova Herculis 1991: Thermonuclear Runaway on a Massive ONeMg White Dwarf

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.

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Classical Novae – Before and After Outburst

International Astronomical Union Colloquium ◽

10.1017/s0252921100093908 ◽

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).

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The 1987 Outburst of the Recurrent Nova U SCO

International Astronomical Union Colloquium ◽

10.1017/s025292110010380x ◽

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.

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The Ejecta of Classical Novae

Symposium - International Astronomical Union ◽

10.1017/s007418090022113x ◽

2001 ◽

Vol 205 ◽

pp. 260-263

Author(s):

T.J. O'Brien ◽

R.J. Davis ◽

M.F. Bode ◽

S. P. S. Eyres ◽

J.M. Porter

Keyword(s):

Coherent Structures ◽

White Dwarf ◽

Binary Stars ◽

Hubble Space Telescope ◽

Classical Novae ◽

Common Envelope ◽

Physical Mechanisms ◽

The Common ◽

Thermonuclear Runaway ◽

Prolate Ellipsoidal

Classical novae are interacting binary stars in which a thermonuclear runaway in material accreted onto a white dwarf from a companion red dwarf results in the ejection of around 10−4M⊙ at hundreds to thousands of kilometres per second. Recent Hubble Space Telescope and MERLIN imaging of the expanding ejecta from several classical novae are presented. In general the ejecta are clumpy but often display coherent structures, most notably equatorial rings of enhanced emission encircling prolate ellipsoidal shells. Physical mechanisms (including the common envelope phase and anisotropic irradiation of the shell) which may result in the generation of these structures are discussed.

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

International Astronomical Union Colloquium ◽

10.1017/s0252921100076077 ◽

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.

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Thermonuclear Runaway Models for Symbiotic Novae

International Astronomical Union Colloquium ◽

10.1017/s0252921100103318 ◽

1988 ◽

Vol 103 ◽

pp. 161-168

Author(s):

Scott J. Kenyon

Keyword(s):

White Dwarf ◽

Dwarf Stars ◽

White Dwarf Stars ◽

Basic Physics ◽

Thermonuclear Runaway

AbstractThis paper reviews the basic physics of thermonuclear runaways on the surfaces of accreting white dwarf stars, with a special emphasis on understanding the evolution of symbiotic novae.

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On the Time-Scale for Turn-Off of a Nova After the Outburst

International Astronomical Union Colloquium ◽

10.1017/s0252921100076041 ◽

1979 ◽

Vol 53 ◽

pp. 274-279

Author(s):

Sumner Starrfield

Keyword(s):

Chemical Composition ◽

White Dwarf ◽

Time Scale ◽

Light Curves ◽

Substantial Agreement ◽

The Past ◽

Thermonuclear Runaway ◽

Mass Ejection ◽

Nova Outburst

It is now generally accepted that a nova outburst is caused by a thermonuclear runaway (TR) in the accreted hydrogen rich envelope of a carbon white dwarf. Over the past few years we have studied the evolution of such runaways and have shown that the calculated evolutionary sequences are in substantial agreement with the observations (Starrfield, et. al. 1978; Sparks, et. al. 1978). In the published work we have varied the white dwarf mass, the envelope mass, the accreted envelope mass, and the chemical composition in the envelope (Starrfield, et. al. 1976; Gallagher and Starrfield 1978). In all cases we find that a TR results in mass ejection and the luminosity variations of this ejected material can reproduce the observed light curves of the fast and slow novae.

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Recurrent Novae

International Astronomical Union Colloquium ◽

10.1017/s0252921100068949 ◽

1990 ◽

Vol 122 ◽

pp. 405-415 ◽

Cited By ~ 1

Author(s):

Ronald F. Webbink

Keyword(s):

Orbital Period ◽

White Dwarf ◽

White Dwarfs ◽

Heavy Element ◽

Structural Parameters ◽

Space Distribution ◽

True Absorption ◽

Thermonuclear Runaway

AbstractThermonuclear models of recurrent novae demand white dwarf accretors near the Chandrasekhar mass. In this case, the known recurrent novae should possess classical counterparts bearing the same structural parameters and space distribution, save for having only marginally less massive white dwarfs. Furthermore, recurrent novae should occur exclusively on ONeMg white dwarfs, and display in their ejecta either neon-group overabundances (if the white dwarfs are eroded through an outburst cycle) or no heavy element enhancements whatever (if the white dwarfs increase in mass).The known recurrent novae are reviewed in the light of these and other characteristics of thermonuclear runaway models, and also in terms of accretion-powered events, with special attention to the difficulties encountered by both models. Pivotal tests to distinguish between between thermonuclear and accretion models rely on the fact that the latter require far more mass transferred than the former to produce the same outburst energetics. Thus, photospheric opacities in thermonuclear recurrent novae are dominated by scattering; those in recurrent accretion events by true absorption. Orbital period changes through outburst are 103 times greater in accretion models than in thermonuclear models.

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123–321 models of classical novae

Astronomy and Astrophysics ◽

10.1051/0004-6361/201936893 ◽

2020 ◽

Vol 634 ◽

pp. A5 ◽

Cited By ~ 2

Author(s):

Jordi José ◽

Steven N. Shore ◽

Jordi Casanova

Keyword(s):

White Dwarf ◽

Time Dependent ◽

High Resolution Spectroscopy ◽

Composition Material ◽

3D Simulations ◽

Inverse Energy Cascade ◽

Solar Composition ◽

Thermonuclear Runaway ◽

Hydrodynamic Code ◽

Nova Outbursts

Context. High-resolution spectroscopy has revealed large concentrations of CNO and sometimes other intermediate-mass elements (e.g., Ne, Na, Mg, or Al, for ONe novae) in the shells ejected during nova outbursts, suggesting that the solar composition material transferred from the secondary mixes with the outermost layers of the underlying white dwarf during thermonuclear runaway. Aims. Multidimensional simulations have shown that Kelvin-Helmholtz instabilities provide self-enrichment of the accreted envelope with material from the outermost layers of the white dwarf, at levels that agree with observations. However, the Eulerian and time-explicit nature of most multidimensional codes used to date and the overwhelming computational load have limited their applicability, and no multidimensional simulation has been conducted for a full nova cycle. Methods. This paper explores a new methodology that combines 1D and 3D simulations. The early stages of the explosion (i.e., mass-accretion and initiation of the runaway) were computed with the 1D hydrodynamic code SHIVA. When convection extended throughout the entire envelope, the structures for each model were mapped into 3D Cartesian grids and were subsequently followed with the multidimensional code FLASH. Two key physical quantities were extracted from the 3D simulations and were subsequently implemented into SHIVA, which was used to complete the simulation through the late expansion and ejection stages: the time-dependent amount of mass dredged-up from the outer white dwarf layers, and the time-dependent convective velocity profile throughout the envelope. Results. This work explores for the first time the effect of the inverse energy cascade that characterizes turbulent convection in nova outbursts. More massive envelopes have been found that are those reported from previous models with pre-enrichment. These result in more violent outbursts, characterized by higher peak temperatures and greater ejected masses, with metallicity enhancements in agreement with observations.

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Element Abundances of Nova PW Vulpeculae

International Astronomical Union Colloquium ◽

10.1017/s0252921100068627 ◽

1990 ◽

Vol 122 ◽

pp. 204-205

Author(s):

J. Andreae ◽

H. Drechsel

Keyword(s):

White Dwarf ◽

Element Abundances ◽

Classical Nova ◽

Thermonuclear Runaway

AbstractElement abundances, electron temperatures and densities of the shell ejected during the outburst of the classical nova PW Vulpeculae were determined using ultraviolet (IUE) and optical (ESO 1.52m + B&C + IDS) spectra obtained during the nebular phase (April - July 1985). The C, N, O abundances are enhanced by factor 10 - 100 relative to solar values according to the predictions of the TNR (thermonuclear runaway) theory. The overabundances of Ne, Si, Mg are comparatively small compared with other novae indicating that the outburst of this slow nova occurred on a CO white dwarf.

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