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Yellow Supergiants
A yellow supergiant (YSG) is a star, generally of spectral type F or G, having a supergiant luminosity class (e.g. Ia or Ib). They are stars that have evolved away from the main sequence, expanding and becoming more luminous. Yellow supergiants are hotter and smaller than red supergiants; naked eye examples include Polaris, Alpha Leporis, Alpha Persei, Delta Canis Majoris and Iota1 Scorpii, Iota¹ Scorpii. Many of them are variable stars, mostly pulsating Cepheid variable, Cepheids such as Delta Cephei, δ Cephei itself. Spectrum Yellow supergiants generally have spectral types of F and G, although sometimes late A or early K stars are included. These spectral types are characterised by hydrogen lines that are very strong in class A, weakening through F and G until they are very weak or absent in class K. Calcium H and K lines are present in late A spectra, but stronger in class F, and strongest in class G, before weakening again in cooler stars. Lines of ionised metals are st ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Star
A star is a luminous spheroid of plasma (physics), plasma held together by Self-gravitation, self-gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked eye at night sky, night; their immense distances from Earth make them appear as fixed stars, fixed points of light. The most prominent stars have been categorised into constellations and asterism (astronomy), asterisms, and many of the brightest stars have proper names. Astronomers have assembled star catalogues that identify the known stars and provide standardized stellar designations. The observable universe contains an estimated to stars. Only about 4,000 of these stars are visible to the naked eye—all within the Milky Way galaxy. A star's life star formation, begins with the gravitational collapse of a gaseous nebula of material largely comprising hydrogen, helium, and traces of heavier elements. Its stellar mass, total mass mainly determines it ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Alpha Aquarii
Alpha Aquarii is a yellow supergiant star in the constellation of Aquarius. Its identifier is a Bayer designation that is Latinized from α Aquarii, and is abbreviated Alf Aqr or α Aqr, respectively. This star has the official name Sadalmelik, pronounced . At an apparent visual magnitude of 2.94, it is the second-brightest star in Aquarius, just marginally fainter than Beta Aquarii. Based upon parallax measurements made by the ''Gaia'' spacecraft, it is located at a distance of roughly . It is drifting further away from the Sun with a radial velocity of 7.5 km/s. Nomenclature ''α Aquarii'' ( Latinised to ''Alpha Aquarii'') is the star's Bayer designation. WDS J22058-0019 A is its designation in the Washington Double Star Catalog. It bore the traditional name ''Sadalmelik'', which derived from an Arabic expression سعد الملك (''sa‘d al-malik''), meaning "Luck of the king" or “arm/support of God”. The name ''Rucbah'' had also b ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Classical Cepheid Variable
Classical Cepheids are a type of Cepheid variable star. They are young, population I variable stars that exhibit regular radial pulsations with periods of a few days to a few weeks and visual amplitudes ranging from a few tenths of a magnitude up to about 2 magnitudes. Classical Cepheids are also known as Population I Cepheids, Type I Cepheids, and Delta Cepheid variables. There exists a well-defined relationship between a classical Cepheid variable's luminosity and pulsation period, securing Cepheids as viable standard candles for establishing the galactic and extragalactic distance scales. Hubble Space Telescope (HST) observations of classical Cepheid variables have enabled firmer constraints on Hubble's law, which describes the expansion rate of the observable Universe. Classical Cepheids have also been used to clarify many characteristics of our galaxy, such as the local spiral arm structure and the Sun's distance from the galactic plane. Around 3,600 classical Cepheids ar ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Period-luminosity Relationship
In astronomy, a period-luminosity relation is a relationship linking the bolometric luminosity, luminosity of pulsating variable stars with their pulsation period. The best-known relation is the direct proportionality law holding for Classical Cepheid variables, sometimes called the Leavitt Law. Discovered in 1908 by Henrietta Swan Leavitt, the relation established Cepheids as foundational Cosmic distance ladder#Galactic distance indicators, indicators of cosmic benchmarks for scaling cosmic distance ladder, galactic and extragalactic distances. The physical model explaining the Leavitt's law for classical cepheids is called ''kappa mechanism''. History Leavitt, a graduate of Radcliffe College, worked at the Harvard College Observatory as a "Human computer, computer", tasked with examining photographic plates in order to measure and catalog the brightness of stars. Observatory Director Edward Charles Pickering assigned Leavitt to the study of variable stars of the Small Magella ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Standard Candle
The cosmic distance ladder (also known as the extragalactic distance scale) is the succession of methods by which astronomers determine the distances to celestial objects. A ''direct'' distance measurement of an astronomical object is possible only for those objects that are "close enough" (within about a thousand parsecs or 3e16 km) to Earth. The techniques for determining distances to more distant objects are all based on various measured correlations between methods that work at close distances and methods that work at larger distances. Several methods rely on a ''standard candle'', which is an astronomical object that has a known luminosity. The ladder analogy arises because no single technique can measure distances at all ranges encountered in astronomy. Instead, one method can be used to measure nearby distances, a second can be used to measure nearby to intermediate distances, and so on. Each rung of the ladder provides information that can be used to determine the distan ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cepheid Variables
A Cepheid variable () is a type of variable star that pulsates radially, varying in both diameter and temperature. It changes in brightness, with a well-defined stable period (typically 1–100 days) and amplitude. Cepheids are important cosmic benchmarks for scaling galactic and extragalactic distances; a strong direct relationship exists between a Cepheid variable's luminosity and its pulsation period. This characteristic of classical Cepheids was discovered in 1908 by Henrietta Swan Leavitt after studying thousands of variable stars in the Magellanic Clouds. The discovery establishes the ''true luminosity'' of a Cepheid by observing its pulsation period. This in turn gives the distance to the star by comparing its known luminosity to its observed brightness, calibrated by directly observing the parallax distance to the closest Cepheids such as RS Puppis and Polaris. Cepheids change brightness due to the κ–mechanism, which occurs when opacity in a star increases with ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Instability Strip
The unqualified term instability strip usually refers to a region of the Hertzsprung–Russell diagram largely occupied by several related classes of pulsating variable stars: Delta Scuti variables, SX Phoenicis variables, and rapidly oscillating Ap stars (roAps) near the main sequence; RR Lyrae variables where it intersects the horizontal branch; and the Cepheid variables where it crosses the supergiants. RV Tauri variables are also often considered to lie on the instability strip, occupying the area to the right of the brighter Cepheids (at lower temperatures), since their stellar pulsations are attributed to the same mechanism. Position on the HR diagram The Hertzsprung–Russell diagram plots the real luminosity of stars against their effective temperature (their color, given by the temperature of their photosphere). The instability strip intersects the main sequence, (the prominent diagonal band that runs from the upper left to the lower right) in the region of A an ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Delta Cephei Lightcurve
Delta commonly refers to: * Delta (letter) (Δ or δ), the fourth letter of the Greek alphabet * D (NATO phonetic alphabet: "Delta"), the fourth letter in the Latin alphabet * River delta, at a river mouth * Delta Air Lines, a major US carrier Delta may also refer to: Places Canada * Delta, British Columbia ** Delta (federal electoral district), a federal electoral district ** Delta (provincial electoral district) * Delta, Ontario United States * Mississippi Delta * Arkansas Delta * Delta, Alabama * Delta Junction, Alaska * Delta, Colorado * Delta, Illinois * Delta, Iowa * Delta, Kentucky * Delta, Louisiana * Delta, Missouri * Delta, North Carolina * Delta, Ohio * Delta, Pennsylvania * Sacramento–San Joaquin River Delta, California * Delta, Utah * Delta, Wisconsin, a town and an unincorporated community * Delta County (other) Elsewhere * Delta Island, Antarctica * Delta Stream, Antarctica * Delta, Minas Gerais, Brazil * Nile Delta, Egypt * Delta, Thessaloniki, Gree ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Andromeda Galaxy
The Andromeda Galaxy is a barred spiral galaxy and is the nearest major galaxy to the Milky Way. It was originally named the Andromeda Nebula and is cataloged as Messier 31, M31, and NGC 224. Andromeda has a Galaxy#Isophotal diameter, D25 isophotal diameter of about and is approximately from Earth. The galaxy's name stems from the area of Earth's sky in which it appears, the constellation of Andromeda, which itself is named after Andromeda (mythology), the princess who was the wife of Perseus in Greek mythology. The virial mass of the Andromeda Galaxy is of the same order of magnitude as that of the Milky Way, at . The mass of either galaxy is difficult to estimate with any accuracy, but it was long thought that the Andromeda Galaxy was more massive than the Milky Way by a margin of some 25% to 50%. However, this has been called into question by early-21st-century studies indicating a possibly lower mass for the Andromeda Galaxy and a higher mass for the Milky Way. The Androm ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
V810 Centauri
V810 Centauri is a double star consisting of a yellow hypergiant primary (V810 Cen A) and blue giant secondary (V810 Cen B). It is a small amplitude variable star, entirely due to the supergiant primary which is visually over three magnitudes (about 12x) brighter than the secondary. It is the MK spectral standard for class G0 0-Ia. A 5th magnitude star, it is visible to the naked eye under good observing conditions. Maurice Pim FitzGerald announced that the star's brightness varies, in 1973. It was given its variable star designation, V810 Centauri, in 1979. V810 Cen A shows semi-regular variations with several component periods. The dominant mode is around 156 days and corresponds to Cepheid fundamental mode radial pulsation. Without the other stellar pulsation modes it would be considered a Classical Cepheid variable. Other pulsation modes have been detected at 89 to 234 days, with the strongest being a possible non-radial p-mode at 107 days and a possible non-radia ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
W Virginis
W Virginis is the prototype W Virginis variable, a subclass of the Cepheid variable stars. It is located in the constellation Virgo (constellation), Virgo, and varies between magnitudes 9.46 and 10.75 over a period of approximately 17 days. There are variations in the light curve apparently due to multiple pulsation periods rather than inherent instabilities in the pulsation. The dominant pulsation mode has a period of 17.27134 days with a period decrease detected over a 75-year period. The pulsations cause changes in both temperature and size, leading to large changes in the luminosity and brightness. The maximum temperature occurs when the star is at its brightest visually, when the star is also at its smallest. The minimum temperature and maximum radius occur at around phase 0.5 when the brightness is decreasing and nearly at minimum. Because relatively more infrared radiation is produced when the star is cooler, the maximum brightness in the infrared occurs when th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
