RV Tauri (''RV Tau'') is a

star A star is an astronomical object comprising a luminous spheroid of plasma (physics), plasma held together by its gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked ...

in the

constellation A constellation is an area on the celestial sphere in which a group of visible stars forms Asterism (astronomy), a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object. The origins of the e ...

Taurus Taurus is Latin for 'bull' and may refer to: * Taurus (astrology), the astrological sign * Taurus (constellation), one of the constellations of the zodiac * Taurus (mythology), one of two Greek mythological characters named Taurus * '' Bos tauru ...

. It is a yellow

supergiant Supergiants are among the most massive and most luminous stars. Supergiant stars occupy the top region of the Hertzsprung–Russell diagram with absolute visual magnitudes between about −3 and −8. The temperature range of supergiant stars spa ...

and is the prototype of a class of

pulsating variable 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 ...

s known as

RV Tauri variable RV Tauri variables are luminous variable stars that have distinctive light variations with alternating deep and shallow minima. History and discovery German astronomer Friedrich Wilhelm Argelander monitored the distinctive variations in brightne ...

s. It is a post-AGB star and a

spectroscopic binary A binary star is a system of two star, stars that are gravity, gravitationally bound to and in orbit around each other. Binary stars in the night sky that are seen as a single object to the naked eye are often resolved using a telescope as separa ...

about away.

Variability

RV Tau was discovered to be variable in 1905 by

Lydia Ceraski Lydia (Lydian language, Lydian: ‎𐤮𐤱𐤠𐤭𐤣𐤠, ''Śfarda''; Aramaic: ''Lydia''; el, Λυδία, ''Lȳdíā''; tr, Lidya) was an Iron Age Monarchy, kingdom of western Asia Minor located generally east of ancient Ionia in the mod ...

, and by 1907 it was clear that it had minima of alternating brightness. Over a period of 78.5 days it shows two maxima at around magnitude 9.5, a minimum around magnitude 10.0, and another minimum about 0.5 magnitudes fainter. This change in brightness is caused by pulsations: the temperature and radius vary, causing some variation in luminosity but mostly a shift of the emitted radiation from visual to infrared. The

spectral type In astronomy, stellar classification is the classification of stars based on their stellar spectrum, spectral characteristics. Electromagnetic radiation from the star is analyzed by splitting it with a Prism (optics), prism or diffraction grati ...

varies in line with the temperature, being classified as G2 at its brightest and M2 at its dimmest. In addition to the fundamental period given, RV Tauri also shows variations in its mean brightness over a period of about 1,200 days, a characteristic which defines the subclass RVb. The maxima and minima in each period vary by several tenths of a magnitude with no obvious regularity.

Binary system

RV Tauri is a single-lined

. The period of 1,198 days corresponds to the long-term variations in the mean brightness of the system. These are caused by changing obscuration of the primary star by a

circumstellar disc A circumstellar disc (or circumstellar disk) is a torus, pancake or ring-shaped accretion disk of matter composed of gas, dust, planetesimals, asteroids, or collision fragments in orbit around a star. Around the youngest stars, they are the re ...

. The companion is thought to be more massive than the variable primary star, but it cannot be detected in the spectrum and it is likely to be a

red dwarf ''Red Dwarf'' is a British science fiction comedy franchise created by Rob Grant and Doug Naylor, which primarily consists of a television sitcom that aired on BBC Two between 1988 and 1999, and on Dave since 2009, gaining a cult following. T ...

. The disc surrounds both stars at a distance of about five

astronomical unit The astronomical unit (symbol: au, or or AU) is a unit of length, roughly the distance from Earth to the Sun and approximately equal to or 8.3 light-minutes. The actual distance from Earth to the Sun varies by about 3% as Earth orbits t ...

s (AU). The stars themselves have an eccentric orbit and their separation varies between about 0.75 and .

Visibility

RV Tau is well placed for northern hemisphere observers during the winter months, and observations can be made from August to April. However it is faint, located in a nondescript patch of sky between The Pleiades and

Beta Aurigae Beta Aurigae (Latinized from β Aurigae, abbreviated Beta Aur, β Aur), officially named Menkalinan , is a binary star system in the northern constellation of Auriga. The combined apparent visual magnitude of the system is 1.9, making ...

Properties

The distance to RV Tau has been calculated by various methods, including modelling the atmosphere. RV Tauri stars have been shown to follow a period-luminosity relationship, and this can be used to confirm the luminosity and distance. They have low masses, but are extended cool stars of high luminosity undergoing strong mass loss. RV Tau has a luminosity of but a spectral luminosity class of

bright supergiant In astronomy, stellar classification is the classification of stars based on their spectral characteristics. Electromagnetic radiation from the star is analyzed by splitting it with a prism or diffraction grating into a spectrum exhibiting the ...

(Ia), indicating the rarified nature of its atmosphere. Its temperature varies as it pulsates, between about and . Surface abundances show enhancement of some heavy elements, fusion products thought to have been dredged up during an earlier AGB phase. Carbon in particular is strongly in excess in RV Tau. However, its overall

metallicity In astronomy, metallicity is the abundance of elements present in an object that are heavier than hydrogen and helium. Most of the normal physical matter in the Universe is either hydrogen or helium, and astronomers use the word ''"metals"'' as a ...

is lower than the Sun's.

Evolution

RV Tau is likely a post-

asymptotic giant branch The asymptotic giant branch (AGB) is a region of the Hertzsprung–Russell diagram populated by evolved cool luminous stars. This is a period of stellar evolution undertaken by all low- to intermediate-mass stars (about 0.5 to 8 solar masses) lat ...

(AGB) star, an originally sun-like star which is in the end stages of its life just prior to the expulsion of a

planetary nebula A planetary nebula (PN, plural PNe) is a type of emission nebula consisting of an expanding, glowing shell of ionized gas ejected from red giant stars late in their lives. The term "planetary nebula" is a misnomer because they are unrelated to ...

and contraction to 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 fro ...

. RV Tau gives an insight into the lives and deaths of stars like the

Sun The Sun is the star at the center of the Solar System. It is a nearly perfect ball of hot plasma, heated to incandescence by nuclear fusion reactions in its core. The Sun radiates this energy mainly as light, ultraviolet, and infrared radi ...

. Evolution models show it takes about 10 billion years for a 1 solar mass () star to reach the Asymptotic Giant Branch.

References

External links

*
AAVSO observations of RV Tauri

RV Tauri — The strange prototype of a strange class
{{DEFAULTSORT:RV Tauri Taurus (constellation) RV Tauri variables G-type supergiants K-type supergiants M-type supergiants Tauri, RV 283868 BD+25 732 IRAS catalogue objects J04470673+2610455