Please answer the following question: Information:  - A symbiotic star is a type of binary star. They are usually a white dwarf with a companion late sequence red giant. They are indicated by the exhibition of spectral lines of the highly contrasting temperatures of the red giant (~3000 K) and the white dwarf (~20 000 K). The white dwarf gains mass from stellar wind from the red giant or gravitational streaming.  - In mathematics, the logarithm is the inverse operation to exponentiation. That means the logarithm of a number is the exponent to which another fixed number, the base, must be raised to produce that number. In simple cases the logarithm counts factors in multiplication. For example, the base logarithm of is , as to the power is; 10 is used as a factor three times. More generally, exponentiation allows any positive real number to be raised to any real power, always producing a positive result, so the logarithm can be calculated for any two positive real numbers and where is not equal to . The logarithm of to "base" , denoted , is the unique real number such that For example, as , then:  - A white dwarf, also called a degenerate dwarf, is a stellar core remnant composed mostly of electron-degenerate matter. A white dwarf is very dense: its mass is comparable to that of the Sun, while its volume is comparable to that of Earth. A white dwarf's faint luminosity comes from the emission of stored thermal energy; no fusion takes place in a white dwarf wherein mass is converted to energy. The nearest known white dwarf is Sirius B, at 8.6 light years, the smaller component of the Sirius binary star. There are currently thought to be eight white dwarfs among the hundred star systems nearest the Sun. The unusual faintness of white dwarfs was first recognized in 1910. The name "white dwarf" was coined by Willem Luyten in 1922. The universe has not existed long enough to experience a white dwarf releasing all of its energy as it will take many billions of years.  - Brightness is an attribute of visual perception in which a source appears to be radiating or reflecting light. In other words, brightness is the perception elicited by the luminance of a visual target. This is a subjective attribute/property of an object being observed and one of the color appearance parameters of color appearance models. Brightness refers to an absolute term and should not be confused with Lightness.  - A red giant is a luminous giant star of low or intermediate mass (roughly 0.38 solar masses) in a late phase of stellar evolution. The outer atmosphere is inflated and tenuous, making the radius large and the surface temperature as low as 5,000 K and lower. The appearance of the red giant is from yellow-orange to red, including the spectral types K and M, but also class S stars and most carbon stars.  - A binary star is a star system consisting of two stars orbiting around their common barycenter. Systems of two or more stars are called "multiple star systems". These systems, especially when more distant, often appear to the unaided eye as a single point of light, and are then revealed as multiple by other means. Research over the last two centuries suggests that half or more of visible stars are part of multiple star systems.  - The Sun is the star at the center of the Solar System. It is a nearly perfect sphere of hot plasma, with internal convective motion that generates a magnetic field via a dynamo process.<ref name="doi10.1146/annurev-astro-081913-040012"></ref> It is by far the most important source of energy for life on Earth. Its diameter is about 109 times that of Earth, and its mass is about 330,000 times that of Earth, accounting for about 99.86% of the total mass of the Solar System. About three quarters of the Sun's mass consists of hydrogen (~73%); the rest is mostly helium (~25%), with much smaller quantities of heavier elements, including oxygen, carbon, neon, and iron.  - A stellar wind is a flow of gas ejected from the upper atmosphere of a star. It is distinguished from the bipolar outflows characteristic of young stars by being less collimated, although stellar winds are not generally spherically symmetric.  - AG Draconis is a binary system consisting of an orange - red giant star and a white dwarf star that revolve around each other every 550 days . It has a baseline apparent magnitude of around 9.8 and flares up to around magnitude 7.3 and is one of the most - studied of symbiotic star systems and its variations in brightness have been observed for 124 years . The outbursts occur every 15 years and last for 3 -- 6 years . The larger star is thought to be an orange giant around 1.5 times as massive as the Sun that has swollen to around 35 times the diameter of the Sun with a spectral type measured at K3IIIep . The smaller star is a compact hot white dwarf around 0.4 times as massive as the Sun , with a surface temperature of around 80,000 K. The star is located in a spherical halo around the Milky Way , and is a nova variable , erupting every 10 -- 15 years .  - The apparent magnitude of a celestial object is a number that is a measure of its brightness as seen by an observer on Earth. The brighter an object appears, the lower its magnitude value (i.e. inverse relation). The Sun, at apparent magnitude of 27, is the brightest object in the sky. It is adjusted to the value it would have in the absence of the atmosphere. Furthermore, the magnitude scale is logarithmic; a difference of one in magnitude corresponds to a change in brightness by a factor of , or about 2.512.    Given the paragraphs above, decide what entity has the relation 'instance of' with 'binary star'.
A:
ag draconis