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R Coronae Borealis Variables
An R Coronae Borealis variable (abbreviated RCB, R CrB) is an eruptive variable star that varies in luminosity in two modes, one low amplitude pulsation (a few tenths of a magnitude), and one irregular, unpredictably-sudden fading by 1 to 9 magnitudes. The prototype star R Coronae Borealis was discovered by the English amateur astronomer Edward Pigott in 1795, who first observed the enigmatic fadings of the star. Only about 150 RCB stars are currently known in our Galaxy while up to 1000 were expected, making this class a very rare kind of star. It is increasingly suspected that R Coronae Borealis (RCB) stars – rare hydrogen-deficient and carbon-rich supergiant stars – are the product of mergers of white-dwarfs in the intermediary mass regime (total mass between 0.6 and 1.2 ). The fading is caused by condensation of carbon to soot, making the star fade in visible light while measurements in infrared light exhibit no real luminosity decrease. R Coronae Borealis variables are ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
R Coronae Borealis Light Curve
R, or r, is the eighteenth letter of the Latin alphabet, used in the modern English alphabet, the alphabets of other western European languages and others worldwide. Its name in English is ''ar'' (pronounced ), plural ''ars'', or in Ireland ''or'' . The letter is the eighth most common letter in English and the fourth-most common consonant (after , , and ). The letter is used to form the ending "-re", which is used in certain words such as ''centre'' in some varieties of English spelling, such as British English. Canadian English also uses the "-re" ending, unlike American English, where the ending is usually replaced by "-er" (''center''). This does not affect pronunciation. Name The name of the letter in Latin was (), following the pattern of other letters representing continuants, such as F, L, M, N and S. This name is preserved in French and many other languages. In Middle English, the name of the letter changed from to , following a pattern exhibited in many o ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Antlia
Antlia (; from Ancient Greek ''ἀντλία'') is a constellation in the Southern Celestial Hemisphere. Its name means " pump" in Latin and Greek; it represents an air pump. Originally Antlia Pneumatica, the constellation was established by Nicolas-Louis de Lacaille in the 18th century. Its non-specific (single-word) name, already in limited use, was preferred by John Herschel then welcomed by the astronomic community which officially accepted this. North of stars forming some of the sails of the ship Argo Navis (the constellation Vela), Antlia is completely visible from latitudes south of 49 degrees north. Antlia is a faint constellation; its brightest star is Alpha Antliae, an orange giant that is a suspected variable star, ranging between apparent magnitudes 4.22 and 4.29. S Antliae is an eclipsing binary star system, changing in brightness as one star passes in front of the other. Sharing a common envelope, the stars are so close they will one day merge to form a singl ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
UX Antliae
UX Antliae is a post-AGB and R Coronae Borealis variable star that has a base apparent magnitude of around 11.85, with irregular dimmings down to below magnitude 18.0. Researchers David Kilkenny and J.E. Westerhuys of the South African Astronomical Observatory confirmed that UX Antliae was an R Coronae Borealis variable in 1990 after noting the similarity of its spectrum to the RCB star W Mensae W Mensae (W Men) is an unusual yellow supergiant star in the Large Magellanic Cloud in the southern constellation Mensa. It is an R Coronae Borealis variable and periodically decreases in brightness by several magnitudes. W Men is very .... It had been suspected of being one since 1940, but had been little-studied and exhibited no characteristic declines between 1975 and 1990. Assuming that its absolute magnitude is around -5, it has been estimated as lying 25000 parsecs distant from Earth. Kilkenny and Westerhuys noted that its spectrum fit with that of a star of ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Apparent Magnitude
Apparent magnitude () is a measure of the brightness of a star or other astronomical object observed from Earth. An object's apparent magnitude depends on its intrinsic luminosity, its distance from Earth, and any extinction of the object's light caused by interstellar dust along the line of sight to the observer. The word ''magnitude'' in astronomy, unless stated otherwise, usually refers to a celestial object's apparent magnitude. The magnitude scale dates back to the ancient Roman astronomer Claudius Ptolemy, whose star catalog listed stars from 1st magnitude (brightest) to 6th magnitude (dimmest). The modern scale was mathematically defined in a way to closely match this historical system. The scale is reverse logarithmic: the brighter an object is, the lower its magnitude number. A difference of 1.0 in magnitude corresponds to a brightness ratio of \sqrt /math>, or about 2.512. For example, a star of magnitude 2.0 is 2.512 times as bright as a star of magnitude 3.0, 6. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Extreme Helium Star
An extreme helium star (abbreviated EHe) is a low-mass supergiant that is almost devoid of hydrogen, the most common chemical element of the Universe. Since there are no known conditions where stars devoid of hydrogen can be formed from molecular clouds, it is theorized that they are the product of the mergers of helium-core and carbon-oxygen core white dwarfs. Properties Extreme helium stars form a sub-group within the broader category of hydrogen-deficient stars. The latter includes cool carbon stars like R Coronae Borealis variables, helium-rich spectral class O or B stars, population I Wolf–Rayet stars, AM CVn stars, white dwarfs of spectral type WC, and transition stars like PG 1159. The first known extreme helium star, HD 124448, was discovered in 1942 by Daniel M. Popper at the McDonald Observatory near Fort Davis, Texas, United States. This star displayed no lines of hydrogen in its spectrum, but strong helium lines as well as the presence of carbon and oxygen. The se ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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 from the emission of residual thermal energy; no fusion takes place in a white dwarf. The nearest known white dwarf is 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. White dwarfs are thought to be the final evolutionary state of stars whose mass is not high enough to become a neutron star or black hole. This includes over 97% of the other stars in the Milky Way. After the hydrogen- fusing period of a main-sequence star of low or medium mass ends, such a star will expand to a red giant ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
RY Sagittarii
RY Sagittarii is a yellow supergiant and an R Coronae Borealis type variable star in the constellation Sagittarius. Although it ostensibly has the spectrum of a G-type star, it differs markedly from most in that it has almost no hydrogen and much carbon. Discovery Colonel Ernest Elliott Markwick first came across what became known as RY Sagittarii during searches for variable stars while posted in Gibraltar. He recorded it dimming from magnitude 7 in July 1893 to fainter than 11 by 23 October that year, and brightening to magnitude 6.4 by November 1894. Edward Charles Pickering wrote that it was a "remarkable object", and "nearly got away". The spectrum was first noted to be peculiar at the time, and by 1953 it was classified as a R Coronae Borealis variable, along with a handful of other stars. Mystified by its origins, Danziger postulated possible explanations as forming from a helium cloud, an aged star that had exhausted its hydrogen, or a star that had somehow th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Light Curve
In astronomy, a light curve is a graph of light intensity of a celestial object or region as a function of time, typically with the magnitude of light received on the y axis and with time on the x axis. The light is usually in a particular frequency interval or band. Light curves can be periodic, as in the case of eclipsing binaries, Cepheid variables, other periodic variables, and transiting extrasolar planets, or aperiodic, like the light curve of a nova, a cataclysmic variable star, a supernova or a microlensing event or binary as observed during occultation events. The study of the light curve, together with other observations, can yield considerable information about the physical process that produces it or constrain the physical theories about it. Variable stars Graphs of the apparent magnitude of a variable star over time are commonly used to visualise and analyse their behaviour. Although the categorisation of variable star types is increasingly done from their s ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
DY Persei Variable
DY Persei variables are a subclass of R Coronae Borealis (R CrB) variables. They are carbon-rich asymptotic giant branch (AGB) stars that exhibit pulsational variability of AGB stars and irregular fades similar to R CrB stars. The star DY Persei DY Persei is a variable star and carbon star in the Perseus constellation. At maximum it is 11th magnitude and at its faintest it drops to 16th magnitude. DY Persei is the prototype of the very rare DY Persei class of variables that p ... is the prototype of this tiny class of variable stars. Only DY Persei itself was known in our galaxy until 2008 when systematic catalogue searches for R CrB variables discovered a 17th magnitude (at maximum) example. Since then automated searches have confirmed another four, including one of magnitude 5.9 at maximum. There are also several candidates that have not yet been observed to fade, and several DY Per stars in the Large Magellanic Cloud. Although DY Persei variables have bee ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Fraunhofer Line
In physics and optics, the Fraunhofer lines are a set of spectral absorption lines named after the German physicist Joseph von Fraunhofer (1787–1826). The lines were originally observed as dark features (absorption lines) in the optical spectrum of the Sun (white light) . Discovery In 1802, the English chemist William Hyde WollastonMelvyn C. UsselmanWilliam Hyde WollastonEncyclopædia Britannica, retrieved 31 March 2013 was the first person to note the appearance of a number of dark features in the solar spectrum. In 1814, Fraunhofer independently rediscovered the lines and began to systematically study and measure the wavelengths where these features are observed. He mapped over 570 lines, designating the principal features (lines) with the letters A through K and weaker lines with other letters. Modern observations of sunlight can detect many thousands of lines. About 45 years later, Kirchhoff and Bunsen noticed that several Fraunhofer lines coincide with characteristic em ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Iron
Iron () is a chemical element with symbol Fe (from la, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, right in front of oxygen (32.1% and 30.1%, respectively), forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust. In its metallic state, iron is rare in the Earth's crust, limited mainly to deposition by meteorites. Iron ores, by contrast, are among the most abundant in the Earth's crust, although extracting usable metal from them requires kilns or furnaces capable of reaching or higher, about higher than that required to smelt copper. Humans started to master that process in Eurasia during the 2nd millennium BCE and the use of iron tools and weapons began to displace copper alloys, in some regions, only around 1200 BCE. That event is considered the transition from the Bronze Age to the Iron A ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
