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HD 166191
HD 166191 is a young F-type main-sequence star, late-F or early G-type main-sequence star, G-type star in the constellation Sagittarius (constellation), Sagittarius. It is surrounded by a large amount of dust. In 2019 it was reported in the The Astronomer's Telegram, Astronomer's Telegram that the star had brightened in the Infrared astronomy, infrared, as was seen from Spitzer Space Telescope, Spitzer observations. A study was published in 2022, reporting on the result of a follow-up campaign. This study showed that a dust cloud as large as the star did Astronomical transit, transit in front of it. This cloud was produced from a giant collision between two planetesimals. In early works the age of the system was not certain and ranged between 10-100 Myrs. The large amount of dust was interpreted as being produced by a recent collision of planetary embryos or by massive ongoing collisional grinding. A later work did determine a younger age. The star was observed with ground- ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Planetesimal Collison Around Star HD 166191 (Illustration)
Planetesimals () are solid objects thought to exist in protoplanetary disks and debris disks. Believed to have formed in the Solar System about 4.6 billion years ago, they aid study of Formation and evolution of the Solar System, its formation. Formation A widely accepted theory of planet formation, the planetesimal hypothesis of Viktor Safronov, states that planets form from cosmic dust grains that collide and Adhesion, stick to form ever-larger bodies. Once a body reaches around a kilometer in size, its constituent grains can attract each other directly through mutual gravity, enormously aiding further growth into moon-sized protoplanets. Smaller bodies must instead rely on Brownian motion or turbulence to cause the collisions leading to sticking. The mechanics of collisions and mechanisms of sticking are intricate. Alternatively, planetesimals may form in a very dense layer of dust grains that undergoes a collective gravitational instability in the mid-plane of a protoplan ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Astronomical Transit
In astronomy, a transit (or astronomical transit) is the passage of a astronomical object, celestial body directly between a larger body and the observer. As viewed from a particular vantage point, the transiting body appears to move across the face of the larger body, eclipse, covering a small portion of it. The word "transit" refers to cases where the nearer object apparent size, appears smaller than the more distant object. Cases where the nearer object appears larger and completely hides the more distant object are known as occultation, ''occultations''. However, the probability of seeing a transiting planet is low because it is dependent on the alignment of the three objects in a nearly perfectly straight line. Many parameters of a planet and its parent star can be determined based on the transit. In the Solar System One type of transit involves the motion of a planet between a Earth, terrestrial observer and the Sun. This can happen only with inferior and superior pla ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Optical Depth (astrophysics)
Optical depth in astrophysics refers to a specific level of transparency. Optical depth and actual depth, \tau and z respectively, can vary widely depending on the absorptivity of the astrophysical environment. Indeed, \tau is able to show the relationship between these two quantities and can lead to a greater understanding of the structure inside a star. Optical depth is a measure of the extinction coefficient or absorptivity up to a specific 'depth' of a star's makeup. :\tau \equiv \int_0^z \alpha dz = \sigma N. The assumption here is that either the extinction coefficient \alpha or the column number density N is known. These can generally be calculated from other equations if a fair amount of information is known about the chemical makeup of the star. From the definition, it is also clear that large optical depths correspond to higher rate of obscuration. Optical depth can therefore be thought of as the opacity of a medium. The extinction coefficient \alpha can be calc ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hereford Arizona Observatory
Hereford Arizona Observatory (HAO), IAU-code G95, is an astronomical observatory, owned and operated by amateur astronomer Bruce L. Gary. Observational studies of unusual starlight fluctuations in Tabby's Star (KIC 8462852) and WD 1145+017 are recent interests. HAO consists of two telescopes, in two separate observatory installations: HAO#1 (contains a Celestron CPC 1100, 11-inch Schmidt-Cassegrain telescope on an equatorial mount) and HAO#2 (contains an Astro-Tech Ritchey–Chrétien, 16-inch telescope on an equatorial mount). The observatory is located in Arizona about southeast of Tucson and about north of the Mexican border. Coordinates are at the following: North Latitude +31:27:08 and West Longitude 110:14:16, at an altitude of . Gallery File:HerefordArizonaObservatory-HAO-1-C11-BruceGary-20091201.jpg, HAO#1 − Celestron 11-inch CPC-1100 telescope File:HerefordArizonaObservatory-HAO-SouthernHorizonNotated-BruceGary.jpg, HAO view of the southern horizon − mo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
All Sky Automated Survey For SuperNovae
The All Sky Automated Survey for SuperNovae (ASAS-SN) is an automated program to search for new supernovae and other astronomical transients, headed by astronomers from the Ohio State University, including Christopher Kochanek and Krzysztof Stanek. It has 20 robotic telescopes in both the northern and southern hemispheres. It can survey the entire sky approximately once every day. Initially, there were four ASAS-SN telescopes at Haleakala and another four at Cerro Tololo, a Las Cumbres Observatory site. Twelve more telescopes were deployed in 2017 in Chile, South Africa and Texas, with funds from the Gordon and Betty Moore Foundation, the Ohio State University, the Mount Cuba Astronomical Foundation, China, Chile, Denmark, and Germany. All the telescopes (Nikon telephoto 400mm/F2.8 lenses) have a diameter of 14 cm and ProLine PL230 CCD cameras. The pixel resolution in the cameras is 7.8 arc seconds, so follow-up observations on other telescopes are usually required to get a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
HD 163296
HD 163296 is a young Herbig Ae/Be star, Herbig Ae star surrounded by a protoplanetary disk. The disk is a popular target to study disk composition, and several works suggested the presence of Protoplanet, protoplanets inside the gaps of the disk. The star HD 163296 was first identified in the Henry Draper Catalogue. The star was first identified to have peculiar hydrogen emission lines in 1925, based on observations with the Mount Wilson Observatory by Paul W. Merrill, Milton L. Humason and Cora G. Burwell. The star was classified as having a spectral type of A2e. In 1984, it was first considered that HD 163296 is a Herbig Ae star due to the H-alpha and NaD lines having a P Cygni profile. The status as a Herbig Ae star was questioned at the time. It was, however concluded that it is surrounded by a dust shell from near-infrared excess. Later in 1989, it was found that magnesium and calcium lines have short-term variability from observations with the International Ultravi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Kelvin
The kelvin (symbol: K) is the base unit for temperature in the International System of Units (SI). The Kelvin scale is an absolute temperature scale that starts at the lowest possible temperature (absolute zero), taken to be 0 K. By definition, the Celsius scale (symbol °C) and the Kelvin scale have the exact same magnitude; that is, a rise of 1 K is equal to a rise of 1 °C and vice versa, and any temperature in degrees Celsius can be converted to kelvin by adding 273.15. The 19th century British scientist Lord Kelvin first developed and proposed the scale. It was often called the "absolute Celsius" scale in the early 20th century. The kelvin was formally added to the International System of Units in 1954, defining 273.16 K to be the triple point of water. The Celsius, Fahrenheit, and Rankine scales were redefined in terms of the Kelvin scale using this definition. The 2019 revision of the SI now defines the kelvin in terms of energy by setting the Bo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Astronomical Unit
The astronomical unit (symbol: au or AU) is a unit of length defined to be exactly equal to . Historically, the astronomical unit was conceived as the average Earth-Sun distance (the average of Earth's aphelion and perihelion), before its modern redefinition in 2012. The astronomical unit is used primarily for measuring distances within the Solar System or around other stars. It is also a fundamental component in the definition of another unit of astronomical length, the parsec. One au is approximately equivalent to 499 light-seconds. History of symbol usage A variety of unit symbols and abbreviations have been in use for the astronomical unit. In a 1976 resolution, the International Astronomical Union (IAU) had used the symbol ''A'' to denote a length equal to the astronomical unit. In the astronomical literature, the symbol AU is common. In 2006, the International Bureau of Weights and Measures (BIPM) had recommended ua as the symbol for the unit, from the French ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Submillimeter Array
The Submillimeter Array (SMA) consists of eight diameter radio telescopes arranged as an interferometer for submillimetre astronomy, submillimeter wavelength observations. It is the first purpose-built submillimeter interferometer, constructed after successful interferometry experiments using the pre-existing James Clerk Maxwell Telescope and Caltech Submillimeter Observatory (now decommissioned) as an interferometer. All three of these observatories are located at Mauna Kea Observatory on Mauna Kea, Hawaii, and have been operated together as a ten element interferometer in the 230 and 345 GHz bands (eSMA, for extended Submillimeter Array). The baseline lengths presently in use range from . The radio frequencies accessible to this telescope range from which includes rotational transitions of dozens of molecular species as well as continuum emission from interstellar dust grains. Although the array is capable of operating both day and night, most of the observations take pl ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Debris Disk
A debris disk (American English), or debris disc ( Commonwealth English), is a circumstellar disk of dust and debris in orbit around a star. Sometimes these disks contain prominent rings, as seen in the image of Fomalhaut on the right. Debris disks are found around stars with mature planetary systems, including at least one debris disk in orbit around an evolved neutron star. Debris disks can also be produced and maintained as the remnants of collisions between planetesimals, otherwise known as asteroids and comets. As of 2001, more than 900 candidate stars had been found to possess a debris disk. They are usually discovered by examining the star system in infrared light and looking for an excess of radiation beyond that emitted by the star. This excess is inferred to be radiation from the star that has been absorbed by the dust in the disk, then re-radiated away as infrared energy. Debris disks are often described as massive analogs to the debris in the Solar System. Most kn ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Silicate Mineral
Silicate minerals are rock-forming minerals made up of silicate groups. They are the largest and most important class of minerals and make up approximately 90 percent of Earth's crust. In mineralogy, the crystalline forms of silica (silicon dioxide, ) are usually considered to be Silicate mineral#Tectosilicates, tectosilicates, and they are classified as such in the Dana system (75.1). However, the Nickel-Strunz system classifies them as oxide minerals (4.DA). Silica is found in nature as the mineral quartz, and its polymorphism (materials science), polymorphs. On Earth, a wide variety of silicate minerals occur in an even wider range of combinations as a result of the processes that have been forming and re-working the crust for billions of years. These processes include partial melting, crystallization, fractionation, metamorphism, weathering, and diagenesis. Living organisms also contribute to this carbonate–silicate cycle, geologic cycle. For example, a type of plankton ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Protoplanetary Disk
A protoplanetary disk is a rotating circumstellar disc of dense gas and dust surrounding a young newly formed star, a T Tauri star, or Herbig Ae/Be star. The protoplanetary disk may not be considered an accretion disk; while the two are similar, an accretion disk is hotter and spins much faster; it is also found on black holes, not stars. This process should not be confused with the accretion process thought to build up the planets themselves. Externally illuminated photo-evaporating protoplanetary disks are called proplyds. Formation Protostars form from molecular clouds consisting primarily of molecular hydrogen. When a portion of a molecular cloud reaches a critical size, mass, or density, it begins to collapse under its own gravity. As this collapsing cloud, called a solar nebula, becomes denser, random gas motions originally present in the cloud average out in favor of the direction of the nebula's net angular momentum. Conservation of angular momentum causes the r ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
