Symbiotic novae are slow irregular eruptive

variable star A variable star is a star whose brightness as seen from Earth (its apparent magnitude) changes with time. This variation may be caused by a change in emitted light or by something partly blocking the light, so variable stars are classified as e ...

s with very slow

nova A nova (plural novae or novas) is a transient astronomical event that causes the sudden appearance of a bright, apparently "new" star (hence the name "nova", which is Latin for "new") that slowly fades over weeks or months. Causes of the dramat ...

-like outbursts with an amplitude of between 9 and 11 magnitudes. The symbiotic nova remains at maximum for one or a few decades, and then declines towards its original

luminosity Luminosity is an absolute measure of radiated electromagnetic power (light), the radiant power emitted by a light-emitting object over time. In astronomy, luminosity is the total amount of electromagnetic energy emitted per unit of time by a st ...

. Variables of this type are

double star In observational astronomy, a double star or visual double is a pair of stars that appear close to each other as viewed from Earth, especially with the aid of optical telescopes. This occurs because the pair either forms a binary star (i.e. a bi ...

systems with one

red giant A red giant is a luminous giant star of low or intermediate mass (roughly 0.3–8 solar masses ()) in a late phase of stellar evolution. The outer atmosphere is inflated and tenuous, making the radius large and the surface temperature around o ...

, which probably is a

Mira variable Mira variables (named for the prototype star Mira) are a class of pulsating stars characterized by very red colours, pulsation periods longer than 100 days, and amplitudes greater than one magnitude in infrared and 2.5 magnitude at visual wavele ...

, and one a hot

compact object In astronomy, the term compact star (or compact object) refers collectively to white dwarfs, neutron stars, and black holes. It would grow to include exotic stars if such hypothetical, dense bodies are confirmed to exist. All compact objects ha ...

(usually a

white dwarf A white dwarf is a stellar core remnant composed mostly of electron-degenerate matter. A white dwarf is very dense: its mass is comparable to the Sun's, while its volume is comparable to the Earth's. A white dwarf's faint luminosity comes ...

), with markedly contrasting spectra and whose proximity and mass characteristics indicate it as a symbiotic star. They are divided into D-type (dusty) or S-type (stellar), depending on whether the giant is a Mira variable or not. The red giant fills its

Roche lobe In astronomy, the Roche lobe is the region around a star in a binary system within which orbiting material is gravitationally bound to that star. It is an approximately teardrop-shaped region bounded by a critical gravitational equipotential, ...

so that matter is transferred to the white dwarf and accumulates until a nova-like outburst occurs, caused by ignition of

thermonuclear fusion Thermonuclear fusion is the process of atomic nuclei combining or “fusing” using high temperatures to drive them close enough together for this to become possible. There are two forms of thermonuclear fusion: ''uncontrolled'', in which the re ...

. The temperature at maximum is estimated to rise up to 200,000 K, similar to the energy source of novae, but dissimilar to the

dwarf nova A U Geminorum-type variable star, or dwarf nova (pl. novae) is one of several types of cataclysmic variable star, consisting of a close binary star system in which one of the components is a white dwarf that accretes matter from its companion. Dw ...

e. The slow luminosity increase would then be simply due to time needed for growth of the ionization front in the outburst. It is believed that the white dwarf component of a symbiotic nova remains below the

Chandrasekhar limit The Chandrasekhar limit () is the maximum mass of a stable white dwarf star. The currently accepted value of the Chandrasekhar limit is about (). White dwarfs resist gravitational collapse primarily through electron degeneracy pressure, compar ...

, so that it remains a white dwarf after its outburst. One example of a symbiotic nova is V1016 Cygni, whose outburst in 1971–2007 clearly indicated a thermonuclear explosion.Photometric and Spectroscopic Evolution of the Symbiotic Nova ...
Other examples are

HM Sagittae HM Sagittae is a dusty-type symbiotic nova in the northern constellation of Sagitta. It was discovered by O. D. Dokuchaeva and colleagues in 1975 when it increased in brightness by six magnitudes (a factor of around 250 brighter). The ...

and

RR Telescopii RR Telescopii is a symbiotic nova in the southern constellation Telescopium. It was recorded on photographic survey plates as a faint variable star between photographic magnitude (mpg) 9 to 16.6 from 1889 to 1944. In late 1944 the sta ...

References

External links

* * {{DEFAULTSORT:Symbiotic Nova

See also

References

External links