HD 106906 b
HD 106906 b is a directly imaged planetary-mass companion and candidate exoplanet orbiting the star HD 106906, in the constellation Crux at about 336 ± 13 light-years from Earth. It is estimated to be about eleven times the mass of Jupiter and is located about 738 AU away from its host star. HD 106906 b is rare in science. HD 106906 b is the only known companion orbiting HD 106906, a spectroscopic binary star composed of two F5V main-sequence stars with a combined mass of 2.71 M☉. Based on the star's luminosity and temperature, the system is estimated to be about 13±2 million years old; the system is a member of the Scorpius–Centaurus Association. The star is surrounded by a debris disk oriented 21 degrees away from HD 106906 b. Based on its near-infrared spectral-energy distribution, its age, relevant evolutionary models, HD 106906 b is estimated to be 11±2 MJup, with a surface temperature of 1,800 K; the high surface temperature, a relic of its recent formation, gives it a luminosity of about 0.02% of the Sun's.
While its mass and temperature are similar to other planetary-mass companions/exoplanets like beta Pictoris b or 1RXS J160929.1−210524 b, its projected separation from the star is much larger, about 738 AU, giving it one of the widest orbits of any known planetary-mass companions. The measurements obtained thus far are not adequate to evaluate its orbital properties. If its eccentricity is large enough, it might approach the outer edge of the primary's debris disk enough to interact with it at periastron. In such a case, the outer extent of the debris disk would be truncated at the inner edge of HD 106906 b's Hill sphere at periastron; the discovery team evaluated the possibility that HD 106906 b is not gravitationally bound to HD 106906, but is seen close to it along our line of sight and moving in the same direction by chance. The odds of such a coincidence were found to be less than 0.01%. Observation of star HD 106906 began in 2005, utilizing the Magellan Telescopes at the Las Campanas Observatory in the Atacama Desert of Chile, some eight years before the companion was discovered.
The initial interest in HD 106906 A was directed to the debris disk surrounding the star, a pre-main-sequence member of Lower Centaurus Crux. On December 4, 2013, University of Arizona graduate student Vanessa Bailey, leader of an international team of astronomers, detailed the discovery of HD 106906 b with a paper first published as a preprint on the arXiv and as a refereed article in The Astrophysical Journal Letters; the discovery team and astronomers worldwide were puzzled by HD 106906 b's extreme separation from its host star, because it is not considered possible that a star's protoplanetary disk could be extensive enough to permit formation of gas giants at such a distance. To account for the separation, it is theorized that the companion formed independently from its star as part of a binary system; this proposal is somewhat problematic in that the mass ratio of ~140:1 is not in the range expected from this process. This is still considered preferable, however, to the alternate theory that the companion formed closer to its primary and was scattered to its present distance by gravitational interaction with another orbital object.
This second companion would need to have a mass greater than that of HD 106906 b, the discovery team found no such object beyond 35 AU from the primary. Additionally, the scattering process would have disrupted the protoplanetary disk. Subsequently, astronomer Paul Kalas and colleagues discovered that Hubble Space Telescope images show a asymmetric shape to the debris disk beyond a radius of 200 AU, supporting the hypothesis of a dynamical upheaval that involved the planet and another perturber, such as a second planet in the system or a close encounter with a passing star. One theory modeled the planet as originating in a disk close to the central binary, migrating inward to an unstable resonance with the binary, evolving to a eccentric orbit; the planet would be ejected unless its periastron distance was increased away from the binary, such as by a gravitational encounter with a passing star during apastron. An analysis of the motions of 461 nearby stars using Gaia observations revealed two that passed within 1 pc of HD 106906 between 2 and 3 million years ago.
A petition had been launched asking the International Astronomical Union to name the companion Gallifrey, after the homeworld of The Doctor on the British science fiction series Doctor Who. The petition gathered over 139,000 signatures. In January 2014, however, it was agreed by the IAU not to accept the petition's goal to name it Gallifrey, as the petition did not follow the public policy of the IAU that a discussion between the public and IAU should be started before naming any spatial entity, that this policy was not respected. In 2009, IAU stated that it had no plans to assign names to extrasolar planets, considering it impractical. However, in August 2013 the IAU changed its stance, inviting members of the public to suggest names for exoplanets. DT Virginis, a binary star about which orbits a planet with the farthest orbit around such a system. GU Piscium b, an exoplanet orbiting G
Dragonfish Nebula
The Dragonfish Nebula, as it is known for its appearance on infrared images, is a massive emission nebula and star-forming region 30,000 light years from the Sun in the direction of the constellation Crux, the Southern Cross. The Dragonfish Nebula gets its name from a giant toothy fish known as the deep-sea dragonfish; the giant stars in this nebula blow a bubble in the surrounding gas. This bubble forms the mouth of the dragonfish; the two largest and luminous stars, which form its eyes, are said to be newly formed stars. The stars heat up the surrounding gas; the Dragonfish Nebula contains some of the most massive stars in the milky way galaxy. This nebula was first discovered in 2010 by Mubdi Rahman and Norman Murray from the University of Toronto, they discovered a cloud of ionized gas which led them to suspect that it was formed from the radiation of nearby stars. Since more than four hundred stars have been found and there is reason to believe that many smaller stars are hiding in the cluster.
The ionized gas around this cluster produces more microwaves than most clusters in our galaxy, making the Dragonfish Nebula the brightest and most massive cluster discovered so far. Due to its distance and location, it is invisible in visible light because the interstellar dust absorbs and reddens its light, hiding it. So in order to study it, wavelengths that are not affected, like infrared, are required. Research done with the help of the Spitzer Space Telescope has shown this object has a size of 450 light years, having a large cavity with a diameter of 100 light years, created by the strong stellar winds of the young and massive stars inside it; as of 2011 400 stars of spectral types O and B have been identified within the nebula. Subsequent studies have confirmed not only at least 15 O-type stars but 3 Luminous Blue Variable/Wolf-Rayet star candidates, they have calculated the total mass of the stars associated with the Dragonfish nebula as 105 solar masses, a mass only comparable with that of the super star cluster Westerlund 1, the most massive stellar association and the brightest nebula known in our galaxy
BU Crucis
BU Crucis is a variable star in the open cluster NGC 4755, known as the Kappa Crucis Cluster or Jewel Box Cluster. BU Cru is one of the brightest members of the NGC 4775 open cluster, better known as the Jewel Box Cluster, it forms the right end of the bar of the prominent letter "A" asterism at the centre of the cluster. The cluster is part of lies about 8,500 light years away; the cluster, BU Crucis itself, is just to the south-east of β Crucis, the lefthand star of the famous Southern Cross. BU Crucis is a B2 bright supergiant, it is 275,000 times the luminosity of the sun due to its higher temperature over 20,000 K, to being forty times larger than the sun. The κ Crucis cluster has a calculated age of 11.2 million years, BU Crucis itself around five million years. BU Crucis is a variable star with a brightness range of about 0.1 magnitudes. It is listed as a probable eclipsing binary in the General Catalogue of Variable Stars, but the International Variable Star Index classifies it as an α Cygni variable with a visual magnitude range of 6.82 - 7.01.
NASA Astronomy Picture of the Day: NGC 4755: A Jewel Box of Stars
Beta Crucis
Beta Crucis called Mimosa, is a binary star system. It forms part of the prominent asterism called the Southern Cross. Β Crucis is the system's Bayer designation. Although β Crucis is at −60° declination, therefore not visible north of 30° latitude, in the time of the ancient Greeks and Romans it was visible north of 40° due to the precession of equinoxes, these civilizations regarded it as part of the constellation of Centaurus, it bore the historical name Becrux. Mimosa, derived from the Latin for'actor', may come from the flower of the same name. Becrux is a modern contraction of the Bayer designation. In 2016, the International Astronomical Union organized a Working Group on Star Names to catalog and standardize proper names for stars; the WGSN's first bulletin of July 2016 included a table of the first two batches of names approved by the WGSN. In Chinese, 十字架, meaning Cross, refers to an asterism consisting of α Crucis, β Crucis, γ Crucis, δ Crucis. Β Crucis itself is known as 十字架三. Based on parallax measurements, β Crucis is located at a distance of 280 ly from the Earth.
In 1957, German astronomer Wulff-Dieter Heintz discovered that it is a spectroscopic binary with components that are too close together to resolve with a telescope. The pair orbit each other every 5 years with an estimated separation that varies from 5.4 to 12.0 Astronomical Units. The system is only 8 to 11 million years old; the primary, β Crucis A, is a massive star with about 16 times the Sun's mass. The projected rotational velocity of this star is about 35 km s−1. However, the orbital plane of the pair is only about 10°, which means the inclination of the star's pole is likely to be low; this suggests that the azimuthal rotational velocity is quite high, at about 120 km s−1. With a radius of about 8.4 times the radius of the Sun, this would mean the star has a rotational period of only about 3.6 days.β Crucis A is a known β Cephei variable, although with an effective temperature of about 27,000 K it is at the hot edge of the instability strip where such stars are found. It has three different pulsation modes.
The periods of all three modes are in the range of 4.03–4.59 hours. The star has a stellar classification of B0.5 III, with the luminosity class of'III' indicating that this is a giant star that has exhausted the supply of hydrogen at its core. The high temperature of the star's outer envelope is what gives the star the blue-white hue, characteristic of B-type stars, it is generating a strong stellar wind and is losing about 10−8 M☉ per year, or the equivalent of the mass of the Sun every 100 million years. The wind is leaving the system with a velocity of 2,000 km; the secondary, β Crucis B, may be a main sequence star with a stellar class of B2. In 2007, a third companion was announced, which may be a low pre-main sequence star; the X-ray emission from this star was detected using the Chandra X-ray Observatory. Two other stars, located at angular separations of 44 and 370 arcseconds, are optical companions that are not physically associated with the system; the β Crucis system may be a member of the Lower Centaurus-Crux sub-group of the Scorpius-Centaurus Association.
This is a stellar association of stars. Β Crucis is represented in the flags of Australia, New Zealand and Papua New Guinea as one of five stars making up the Southern Cross. It is featured in the flag of Brazil, along with 26 other stars, each of which represents a state. Mimosa represents the State of Rio de Janeiro. A vessel named. An episode dedicated to the vessel features in the television documentary series Mighty Ships. Http://jumk.de/astronomie/big-stars/becrux.shtml
Star
A star is type of astronomical object consisting of a luminous spheroid of plasma held together by its own gravity. The nearest star to Earth is the Sun. Many other stars are visible to the naked eye from Earth during the night, appearing as a multitude of fixed luminous points in the sky due to their immense distance from Earth; the most prominent stars were grouped into constellations and asterisms, the brightest of which gained proper names. Astronomers have assembled star catalogues that identify the known stars and provide standardized stellar designations. However, most of the estimated 300 sextillion stars in the Universe are invisible to the naked eye from Earth, including all stars outside our galaxy, the Milky Way. For at least a portion of its life, a star shines due to thermonuclear fusion of hydrogen into helium in its core, releasing energy that traverses the star's interior and radiates into outer space. All occurring elements heavier than helium are created by stellar nucleosynthesis during the star's lifetime, for some stars by supernova nucleosynthesis when it explodes.
Near the end of its life, a star can contain degenerate matter. Astronomers can determine the mass, age and many other properties of a star by observing its motion through space, its luminosity, spectrum respectively; the total mass of a star is the main factor. Other characteristics of a star, including diameter and temperature, change over its life, while the star's environment affects its rotation and movement. A plot of the temperature of many stars against their luminosities produces a plot known as a Hertzsprung–Russell diagram. Plotting a particular star on that diagram allows the age and evolutionary state of that star to be determined. A star's life begins with the gravitational collapse of a gaseous nebula of material composed of hydrogen, along with helium and trace amounts of heavier elements; when the stellar core is sufficiently dense, hydrogen becomes converted into helium through nuclear fusion, releasing energy in the process. The remainder of the star's interior carries energy away from the core through a combination of radiative and convective heat transfer processes.
The star's internal pressure prevents it from collapsing further under its own gravity. A star with mass greater than 0.4 times the Sun's will expand to become a red giant when the hydrogen fuel in its core is exhausted. In some cases, it will fuse heavier elements in shells around the core; as the star expands it throws a part of its mass, enriched with those heavier elements, into the interstellar environment, to be recycled as new stars. Meanwhile, the core becomes a stellar remnant: a white dwarf, a neutron star, or if it is sufficiently massive a black hole. Binary and multi-star systems consist of two or more stars that are gravitationally bound and move around each other in stable orbits; when two such stars have a close orbit, their gravitational interaction can have a significant impact on their evolution. Stars can form part of a much larger gravitationally bound structure, such as a star cluster or a galaxy. Stars have been important to civilizations throughout the world, they have used for celestial navigation and orientation.
Many ancient astronomers believed that stars were permanently affixed to a heavenly sphere and that they were immutable. By convention, astronomers grouped stars into constellations and used them to track the motions of the planets and the inferred position of the Sun; the motion of the Sun against the background stars was used to create calendars, which could be used to regulate agricultural practices. The Gregorian calendar used nearly everywhere in the world, is a solar calendar based on the angle of the Earth's rotational axis relative to its local star, the Sun; the oldest dated star chart was the result of ancient Egyptian astronomy in 1534 BC. The earliest known star catalogues were compiled by the ancient Babylonian astronomers of Mesopotamia in the late 2nd millennium BC, during the Kassite Period; the first star catalogue in Greek astronomy was created by Aristillus in 300 BC, with the help of Timocharis. The star catalog of Hipparchus included 1020 stars, was used to assemble Ptolemy's star catalogue.
Hipparchus is known for the discovery of the first recorded nova. Many of the constellations and star names in use today derive from Greek astronomy. In spite of the apparent immutability of the heavens, Chinese astronomers were aware that new stars could appear. In 185 AD, they were the first to observe and write about a supernova, now known as the SN 185; the brightest stellar event in recorded history was the SN 1006 supernova, observed in 1006 and written about by the Egyptian astronomer Ali ibn Ridwan and several Chinese astronomers. The SN 1054 supernova, which gave birth to the Crab Nebula, was observed by Chinese and Islamic astronomers. Medieval Islamic astronomers gave Arabic names to many stars that are still used today and they invented numerous astronomical instruments that could compute the positions of the stars, they built the first large observatory research institutes for the purpose of producing Zij star catalogues. Among these, the Book of Fixed Stars was written by the Persian astronomer Abd al-Rahman al-Sufi, who observed a number of stars, star clusters and galaxies.
According to A. Zahoor, in the 11th century, the Persian polymath scholar Abu Rayhan Biruni described the Milky
Stellar classification
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 rainbow of colors interspersed with spectral lines; each line indicates a particular chemical element or molecule, with the line strength indicating the abundance of that element. The strengths of the different spectral lines vary due to the temperature of the photosphere, although in some cases there are true abundance differences; the spectral class of a star is a short code summarizing the ionization state, giving an objective measure of the photosphere's temperature. Most stars are classified under the Morgan-Keenan system using the letters O, B, A, F, G, K, M, a sequence from the hottest to the coolest; each letter class is subdivided using a numeric digit with 0 being hottest and 9 being coolest. The sequence has been expanded with classes for other stars and star-like objects that do not fit in the classical system, such as class D for white dwarfs and classes S and C for carbon stars.
In the MK system, a luminosity class is added to the spectral class using Roman numerals. This is based on the width of certain absorption lines in the star's spectrum, which vary with the density of the atmosphere and so distinguish giant stars from dwarfs. Luminosity class 0 or Ia+ is used for hypergiants, class I for supergiants, class II for bright giants, class III for regular giants, class IV for sub-giants, class V for main-sequence stars, class sd for sub-dwarfs, class D for white dwarfs; the full spectral class for the Sun is G2V, indicating a main-sequence star with a temperature around 5,800 K. The conventional color description takes into account only the peak of the stellar spectrum. In actuality, stars radiate in all parts of the spectrum; because all spectral colors combined appear white, the actual apparent colors the human eye would observe are far lighter than the conventional color descriptions would suggest. This characteristic of'lightness' indicates that the simplified assignment of colors within the spectrum can be misleading.
Excluding color-contrast illusions in dim light, there are indigo, or violet stars. Red dwarfs are a deep shade of orange, brown dwarfs do not appear brown, but hypothetically would appear dim grey to a nearby observer; the modern classification system is known as the Morgan–Keenan classification. Each star is assigned a spectral class from the older Harvard spectral classification and a luminosity class using Roman numerals as explained below, forming the star's spectral type. Other modern stellar classification systems, such as the UBV system, are based on color indexes—the measured differences in three or more color magnitudes; those numbers are given labels such as "U-V" or "B-V", which represent the colors passed by two standard filters. The Harvard system is a one-dimensional classification scheme by astronomer Annie Jump Cannon, who re-ordered and simplified a prior alphabetical system. Stars are grouped according to their spectral characteristics by single letters of the alphabet, optionally with numeric subdivisions.
Main-sequence stars vary in surface temperature from 2,000 to 50,000 K, whereas more-evolved stars can have temperatures above 100,000 K. Physically, the classes indicate the temperature of the star's atmosphere and are listed from hottest to coldest; the spectral classes O through M, as well as other more specialized classes discussed are subdivided by Arabic numerals, where 0 denotes the hottest stars of a given class. For example, A0 denotes A9 denotes the coolest ones. Fractional numbers are allowed; the Sun is classified as G2. Conventional color descriptions are traditional in astronomy, represent colors relative to the mean color of an A class star, considered to be white; the apparent color descriptions are what the observer would see if trying to describe the stars under a dark sky without aid to the eye, or with binoculars. However, most stars in the sky, except the brightest ones, appear white or bluish white to the unaided eye because they are too dim for color vision to work. Red supergiants are cooler and redder than dwarfs of the same spectral type, stars with particular spectral features such as carbon stars may be far redder than any black body.
The fact that the Harvard classification of a star indicated its surface or photospheric temperature was not understood until after its development, though by the time the first Hertzsprung–Russell diagram was formulated, this was suspected to be true. In the 1920s, the Indian physicist Meghnad Saha derived a theory of ionization by extending well-known ideas in physical chemistry pertaining to the dissociation of molecules to the ionization of atoms. First he applied it to the solar chromosphere to stellar spectra. Harvard astronomer Cecilia Payne demonstrated that the O-B-A-F-G-K-M spectral sequence is a sequence in temperature; because the classification sequence predates our understanding that it is a temperature sequence, the placement of a spectrum into a given subtype, such as B3 or A7, depends upon estimates of the strengths of absorption features in stellar spectra. As a result, these subtypes are not evenly divided into any sort of mathematically representable intervals; the Yerkes spectral classification called the MKK system from the authors' initial
Constellation
A constellation is a group of stars that forms an imaginary outline or pattern on the celestial sphere representing an animal, mythological person or creature, a god, or an inanimate object. The origins of the earliest constellations go back to prehistory. People used them to relate stories of their beliefs, creation, or mythology. Different cultures and countries adopted their own constellations, some of which lasted into the early 20th century before today's constellations were internationally recognized. Adoption of constellations has changed over time. Many have changed in shape; some became popular. Others were limited to single nations; the 48 traditional Western constellations are Greek. They are given in Aratus' work Phenomena and Ptolemy's Almagest, though their origin predates these works by several centuries. Constellations in the far southern sky were added from the 15th century until the mid-18th century when European explorers began traveling to the Southern Hemisphere. Twelve ancient constellations belong to the zodiac.
The origins of the zodiac remain uncertain. In 1928, the International Astronomical Union formally accepted 88 modern constellations, with contiguous boundaries that together cover the entire celestial sphere. Any given point in a celestial coordinate system lies in one of the modern constellations; some astronomical naming systems include the constellation where a given celestial object is found to convey its approximate location in the sky. The Flamsteed designation of a star, for example, consists of a number and the genitive form of the constellation name. Other star patterns or groups called asterisms are not constellations per se but are used by observers to navigate the night sky. Examples of bright asterisms include the Pleiades and Hyades within the constellation Taurus or Venus' Mirror in the constellation of Orion.. Some asterisms, like the False Cross, are split between two constellations; the word "constellation" comes from the Late Latin term cōnstellātiō, which can be translated as "set of stars".
The Ancient Greek word for constellation is ἄστρον. A more modern astronomical sense of the term "constellation" is as a recognisable pattern of stars whose appearance is associated with mythological characters or creatures, or earthbound animals, or objects, it can specifically denote the recognized 88 named constellations used today. Colloquial usage does not draw a sharp distinction between "constellations" and smaller "asterisms", yet the modern accepted astronomical constellations employ such a distinction. E.g. the Pleiades and the Hyades are both asterisms, each lies within the boundaries of the constellation of Taurus. Another example is the northern asterism known as the Big Dipper or the Plough, composed of the seven brightest stars within the area of the IAU-defined constellation of Ursa Major; the southern False Cross asterism includes portions of the constellations Carina and Vela and the Summer Triangle.. A constellation, viewed from a particular latitude on Earth, that never sets below the horizon is termed circumpolar.
From the North Pole or South Pole, all constellations south or north of the celestial equator are circumpolar. Depending on the definition, equatorial constellations may include those that lie between declinations 45° north and 45° south, or those that pass through the declination range of the ecliptic or zodiac ranging between 23½° north, the celestial equator, 23½° south. Although stars in constellations appear near each other in the sky, they lie at a variety of distances away from the Earth. Since stars have their own independent motions, all constellations will change over time. After tens to hundreds of thousands of years, familiar outlines will become unrecognizable. Astronomers can predict the past or future constellation outlines by measuring individual stars' common proper motions or cpm by accurate astrometry and their radial velocities by astronomical spectroscopy; the earliest evidence for the humankind's identification of constellations comes from Mesopotamian inscribed stones and clay writing tablets that date back to 3000 BC.
It seems that the bulk of the Mesopotamian constellations were created within a short interval from around 1300 to 1000 BC. Mesopotamian constellations appeared in many of the classical Greek constellations; the oldest Babylonian star catalogues of stars and constellations date back to the beginning in the Middle Bronze Age, most notably the Three Stars Each texts and the MUL. APIN, an expanded and revised version based on more accurate observation from around 1000 BC. However, the numerous Sumerian names in these catalogues suggest that they built on older, but otherwise unattested, Sumerian traditions of the Early Bronze Age; the classical Zodiac is a revision of Neo-Babylonian constellations from the 6th century BC. The Greeks adopted the Babylonian constellations in the 4th century BC. Twenty Ptolemaic constellations are from the Ancient Near East. Another ten have the same stars but different names. Biblical scholar, E. W. Bullinger interpreted some of the creatures mentioned in the books of Ezekiel and Revelation as the middle signs of the four quarters of the Zodiac, with the Lion as Leo, the Bull as Taurus, the Man representing Aquarius and the Eagle standing in for Scorpio.
The biblical Book of Job also
