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Type II Cepheids
Type II Cepheids are variable stars which pulsate with periods typically between 1 and 50 days. They are population II stars: old, typically metal-poor, low mass objects. Like all Cepheid variables, Type IIs exhibit a relationship between the star's luminosity and pulsation period, making them useful as standard candles for establishing distances where little other data is available Longer period Type II Cepheids, which are more luminous, have been detected beyond the Local Group in the galaxies NGC 5128 and NGC 4258. Classification Historically Type II Cepheids were called W Virginis variables, but are now divided into three subclasses based on the length of their period. Stars with periods between 1 and 4 days are of the BL Herculis subclass and 10–20 days belong to the W Virginis subclass. Stars with periods greater than 20 days, and usually alternating deep and shallow minima, belong to the RV Tauri subclass. RV Tauri variables are usually classified by a formal ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Blue Loop
In the field of stellar evolution, a blue loop is a stage in the life of an evolved star where it changes from a cool star to a hotter one before cooling again. The name derives from the shape of the evolutionary track on a Hertzsprung–Russell diagram which forms a loop towards the blue (i.e. hotter) side of the diagram. Blue loops can occur for red supergiants, red-giant branch stars, or asymptotic giant branch stars. Some stars may undergo more than one blue loop. Many pulsating variable stars such as Cepheids are blue loop stars. Stars on the horizontal branch are not generally referred to as on a blue loop even though they are temporarily hotter than on the red giant or asymptotic giant branches. Loops occur far too slowly to be observed for individual stars, but are inferred from theory and from the properties and distribution of stars in the H–R diagram. Red giants Most stars on the red-giant branch (RGB) have an inert helium core and remain on the RGB until a h ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Scutum (constellation)
Scutum is a small constellation. Its name is Latin for shield, and it was originally named Scutum Sobiescianum by Johannes Hevelius in 1684. Located just south of the celestial equator, its four brightest stars form a narrow diamond shape. It is one of the 88 IAU designated constellations defined in 1922. History Scutum was named in 1684 by Polish astronomer Johannes Hevelius (Jan Heweliusz), who originally named it ''Scutum Sobiescianum'' (Shield of Sobieski) to commemorate the victory of the Christian forces led by Polish King John III Sobieski (Jan III Sobieski) in the Battle of Vienna in 1683. Later, the name was shortened to Scutum. Five bright stars of Scutum ( α Sct, β Sct, δ Sct, ε Sct and η Sct) were previously known as 1, 6, 2, 3, and 9 Aquilae respectively. The constellation of Scutum was adopted by the International Astronomical Union in 1922 as one of the 88 constellations covering the entire sky, with the official abbreviation of "Sct". The constella ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pavo (constellation)
Pavo is a constellation in the Southern Celestial Hemisphere, southern sky whose name is Latin for "peafowl, peacock". Pavo first appeared on a 35-cm (14 in) diameter celestial globe published in 1598 in Amsterdam by Plancius and Jodocus Hondius and was depicted in Johann Bayer's star atlas ''Uranometria'' of 1603, and was likely conceived by Petrus Plancius from the observations of Pieter Dirkszoon Keyser and Frederick de Houtman. French explorer and astronomer Nicolas-Louis de Lacaille gave its stars Bayer designations in 1756. The constellations Pavo, Grus (constellation), Grus, Phoenix (constellation), Phoenix and Tucana are collectively known as the "Southern Birds". The constellation's brightest member, Alpha Pavonis, is also known as Peacock and appears as a 1.91-Apparent magnitude, magnitude blue-white star, but is actually a spectroscopic binary. Delta Pavonis is a nearby Sun-like star some 19.9 light-years distant. Six of the star systems in Pavo have been found ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Kappa Pavonis
Kappa Pavonis (κ Pav) is a variable star in the constellation Pavo. It is the brightest W Virginis variable in the sky. Discovery In 1901, κ Pavonis was reported to be a variable star with a magnitude range of 3.8 to 5.2 with a period of 9.0908 days. Further observations revealed radial velocity variations in time with the brightness variations, but this was assumed to indicate a spectroscopic binary system. The brightness variations were then interpreted as eclipses. Less than 10 years later, was κ Pav was listed as a likely Cepheid variable. In 1937 it was used as part of the effort to calibrate the Cepheid distance scale. Only years later were the separate period luminosity relationships for population I and II Cepheid variables identified, and κ Pav was assigned to the type II group. Variability κ Pavonis ranges between apparent magnitudes 3.91 and 4.78, and spectral types F5 to G5, over a period of 9.1 days. It is a W Virginis variable, a type II C ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Carbon Star
A carbon star (C-type star) is typically an asymptotic giant branch star, a luminous red giant, whose atmosphere contains more carbon than oxygen. The two elements combine in the upper layers of the star, forming carbon monoxide, which consumes most of the oxygen in the atmosphere, leaving carbon atoms free to form other carbon compounds, giving the star a "sooty" atmosphere and a strikingly ruby red appearance. There are also some dwarf and supergiant carbon stars, with the more common giant stars sometimes being called classical carbon stars to distinguish them. In most stars (such as the Sun), the atmosphere is richer in oxygen than carbon. Ordinary stars not exhibiting the characteristics of carbon stars but cool enough to form carbon monoxide are therefore called oxygen-rich stars. Carbon stars have quite distinctive spectral characteristics, and they were first recognized by their spectra by Angelo Secchi in the 1860s, a pioneering time in astronomical spectroscopy. Spectra ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Camelopardalis
Camelopardalis is a large but faint constellation of the northern sky representing a giraffe. The constellation was introduced in 1612 or 1613 by Petrus Plancius. Some older astronomy books give Camelopardalus or Camelopardus as alternative forms of the name, but the version recognized by the International Astronomical Union matches the genitive form, seen suffixed to most of its key stars. Etymology First attested in English in 1785, the word ''camelopardalis'' comes from Latin, and it is the romanization of the Greek "καμηλοπάρδαλις" meaning "giraffe", from "κάμηλος" (''kamēlos''), "camel" + "πάρδαλις" (''pardalis''), " spotted", because it has a long neck like a camel and spots. Features Stars Although Camelopardalis is the 18th largest constellation, it is not a particularly bright constellation, as the brightest stars are only of fourth magnitude. In fact, it only contains four stars brighter than magnitude 5.0. * α Cam is a blue-hued su ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
RU Camelopardalis
RU Camelopardalis, or RU Cam, is a W Virginis variable (type II Cepheid) in the constellation of Camelopardalis. It is also a Carbon star, which is very unusual for a Cepheid variable. History RU Cam was reported as a new variable star in 1907. It was quickly recognised as one of the Cepheid class of variable stars. The first detailed study of the spectrum of RU Cam showed that it changed during the brightness variations. From partway down the descending branch of the light curve to just after minimum brightness, the spectrum is class R with hydrogen absorption lines. The spectrum then develops hydrogen emission lines. For several days either side of maximum brightness, the spectrum becomes a relatively normal class K. RU Cam remained a somewhat unusual W Virginis variable until 1964, when the relatively regular pulsation of about 1 magnitude almost entirely stopped. Since then the pulsations have varied from cycle to cycle, with amplitudes changing from severa ... [...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] |
Monthly Notices Of The Royal Astronomical Society
''Monthly Notices of the Royal Astronomical Society'' (MNRAS) is a peer-reviewed scientific journal covering research in astronomy and astrophysics. It has been in continuous existence since 1827 and publishes letters and papers reporting original research in relevant fields. Despite the name, the journal is no longer monthly, nor does it carry the notices of the Royal Astronomical Society. History The first issue of MNRAS was published on 9 February 1827 as ''Monthly Notices of the Astronomical Society of London'' and it has been in continuous publication ever since. It took its current name from the second volume, after the Astronomical Society of London became the Royal Astronomical Society (RAS). Until 1960 it carried the monthly notices of the RAS, at which time these were transferred to the newly established ''Quarterly Journal of the Royal Astronomical Society'' (1960–1996) and then to its successor journal ''Astronomy & Geophysics'' (since 1997). Until 1965, MNRAS ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Galaxies
A galaxy is a system of stars, stellar remnants, interstellar gas, dust, dark matter, bound together by gravity. The word is derived from the Greek ' (), literally 'milky', a reference to the Milky Way galaxy that contains the Solar System. Galaxies, averaging an estimated 100 million stars, range in size from dwarfs with less than a hundred million stars, to the largest galaxies known – supergiants with one hundred trillion stars, each orbiting its galaxy's center of mass. Most of the mass in a typical galaxy is in the form of dark matter, with only a few percent of that mass visible in the form of stars and nebulae. Supermassive black holes are a common feature at the centres of galaxies. Galaxies are categorized according to their visual morphology as elliptical, spiral, or irregular. Many are thought to have supermassive black holes at their centers. The Milky Way's central black hole, known as Sagittarius A*, has a mass four million times greater than the Sun. As of ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Globular Clusters
A globular cluster is a spheroidal conglomeration of stars. Globular clusters are bound together by gravity, with a higher concentration of stars towards their centers. They can contain anywhere from tens of thousands to many millions of member stars. Their name is derived from Latin (small sphere). Globular clusters are occasionally known simply as "globulars". Although one globular cluster, Omega Centauri, was observed in antiquity and long thought to be a star, recognition of the clusters' true nature came with the advent of telescopes in the 17th century. In early telescopic observations globular clusters appeared as fuzzy blobs, leading French astronomer Charles Messier to include many of them in his catalog of astronomical objects that he thought could be mistaken for comets. Using larger telescopes, 18th-century astronomers recognized that globular clusters are groups of many individual stars. Early in the 20th century the distribution of globular clusters in the sky wa ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
