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Exocomet
An exocomet, or extrasolar comet, is a comet outside the Solar System, which includes rogue comets and comets that orbit stars other than the Sun. The first exocomets were detected in 1987 around Beta Pictoris, a very young A-type main-sequence star. There are now (as of February 2019) a total of 27 stars around which exocomets have been observed or suspected. The majority of discovered exocometary systems (Beta Pictoris, HR 10, 51 Ophiuchi, HR 2174, HD 85905, 49 Ceti, 5 Vulpeculae, 2 Andromedae, HD 21620, Rho Virginis, HD 145964, HD 172555, Lambda Geminorum, HD 58647, Phi Geminorum, Delta Corvi, HD 109573, Phi Leonis, 35 Aquilae, HD 24966, HD 38056, HD 79469 and HD 225200) are around very young A-type stars. The relatively old shell star Phi Leonis shows evidence of exocomets in the spectrum and comet-like activity was detected around the old F2V-type star Eta Corvi. In 2018 transiting exocomets were discovered around F-type stars, using data from the Kepler space te ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Comet
A comet is an icy, small Solar System body that, when passing close to the Sun, warms and begins to release gases, a process that is called outgassing. This produces a visible atmosphere or coma, and sometimes also a tail. These phenomena are due to the effects of solar radiation and the solar wind acting upon the nucleus of the comet. Comet nuclei range from a few hundred meters to tens of kilometers across and are composed of loose collections of ice, dust, and small rocky particles. The coma may be up to 15 times Earth's diameter, while the tail may stretch beyond one astronomical unit. If sufficiently bright, a comet may be seen from Earth without the aid of a telescope and may subtend an arc of 30° (60 Moons) across the sky. Comets have been observed and recorded since ancient times by many cultures and religions. Comets usually have highly eccentric elliptical orbits, and they have a wide range of orbital periods, ranging from several years to potentially several mill ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
5 Vulpeculae
5 Vulpeculae is a single, white-hued star in the northern constellation of Vulpecula. It is situated amidst a random concentration of bright stars designated Collinder 399, or Brocchi's Cluster. This is a faint star that is just visible to the naked eye with an apparent visual magnitude of 5.60. Based upon an annual parallax shift of , it is located around 235 light years from the Sun. It is moving closer with a heliocentric radial velocity of −21 km/s, and will make its closest approach in 2.5 million years at a separation of around . This is a young A-type main-sequence star with a stellar classification of A0 V. It is a rapidly rotating star with a projected rotational velocity of 154 km/s. The star has an estimated 2.33 times the mass of the Sun and about 2.7 times the Sun's radius. It is radiating 34 times the Sun's luminosity from its photosphere at an effective temperature of 8,940 K. A warm debris disk was detected by the Spit ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Phi Leonis
Phi Leonis (φ Leo) is a single star in the constellation Leo. It is bright enough to be seen with the naked eye, having an apparent visual magnitude of 4.46. Based upon parallax measurements, the distance to Phi Leo is around 184 light years. The spectrum of this star fits a stellar classification of A7IVn, which suggests it is an A-type subgiant star that has left the main sequence and is evolving into a giant star. It is being viewed with the plane of the star's equator lying close the line of sight from the Earth, and shows a high rotation rate with a projected rotational velocity of 254 km/s. This rapid spin is giving the star an oblate shape with an equatorial bulge that is 29% larger than the polar radius. Phi Leonis has been mentioned as a shell star—indicating that there is a circumstellar disk of gas around the star's equator—and may display a slight variability. Sporadic variation of the spectra on the time scale of minutes up to months i ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Beta Pictoris
Beta Pictoris (abbreviated β Pictoris or β Pic) is the second brightest star in the constellation Pictor. It is located from the Solar System, and is 1.75 times as massive and 8.7 times as luminous as the Sun. The Beta Pictoris system is very young, only 20 to 26 million years old, although it is already in the main sequence stage of its evolution. Beta Pictoris is the title member of the Beta Pictoris moving group, an association of young stars which share the same motion through space and have the same age. The European Southern Observatory (ESO) has confirmed the presence of two planets, Beta Pictoris b, and Beta Pictoris c, through the use of direct imagery. Both planets are orbiting in the plane of the debris disk surrounding the star. Beta Pictoris c is currently the closest extrasolar planet to its star ever photographed: the observed separation is roughly the same as the distance between the asteroid belt and the Sun. Beta Pictoris shows an excess of in ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Publications Of The Astronomical Society Of The Pacific
''Publications of the Astronomical Society of the Pacific'' (often abbreviated as ''PASP'' in references and literature) is a monthly peer-reviewed scientific journal managed by the Astronomical Society of the Pacific. It publishes research and review papers, instrumentation papers and dissertation summaries in the fields of astronomy and astrophysics. Between 1999 and 2016 it was published by the University of Chicago Press and since 2016, it has been published by IOP Publishing. The current editor-in-chief is Jeff Mangum of the National Radio Astronomy Observatory. ''PASP'' has been published monthly since 1899, and along with ''The Astrophysical Journal'', ''The Astronomical Journal'', ''Astronomy and Astrophysics'', and the ''Monthly Notices of the Royal Astronomical Society'', is one of the primary journals for the publication of astronomical research. See also * ''List of astronomy journals This is a list of scientific journals publishing articles in astronomy, astroph ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Space
Space is the boundless three-dimensional extent in which objects and events have relative position and direction. In classical physics, physical space is often conceived in three linear dimensions, although modern physicists usually consider it, with time, to be part of a boundless four-dimensional continuum known as spacetime. The concept of space is considered to be of fundamental importance to an understanding of the physical universe. However, disagreement continues between philosophers over whether it is itself an entity, a relationship between entities, or part of a conceptual framework. Debates concerning the nature, essence and the mode of existence of space date back to antiquity; namely, to treatises like the ''Timaeus'' of Plato, or Socrates in his reflections on what the Greeks called ''khôra'' (i.e. "space"), or in the ''Physics'' of Aristotle (Book IV, Delta) in the definition of ''topos'' (i.e. place), or in the later "geometrical conception of place" as "spac ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
HD 172555
HD 172555 is a white-hot A7V star located relatively close by, 95 light years from Earth in the direction of the constellation Pavo. Spectrographic evidence indicates a relatively recent collision between two planet-sized bodies that destroyed the smaller of the two, which had been at least the size of Earth's moon, and severely damaged the larger one, which was at least the size of Mercury. Evidence of the collision was detected by NASA's Spitzer Space Telescope. Giant hypervelocity impact debris HD172555 was first recognized in the 1980s as being unusually bright in the mid-infrared by the IRAS sky survey. Follow-up, ground-based observations by Schütz et al. and the Spitzer Space Telescope, also in 2004, confirmed the unusually strong nature of the infrared spectral emission from this system, much brighter than what would be emitted normally from the star's surface. As part of the Beta Pictoris moving group, HD172555 is coeval with that more famous system ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Lambda Geminorum
Lambda Geminorum, Latinized from λ Geminorum, is a candidate multiple star system in the constellation Gemini. It is visible to the naked eye at night with a combined apparent visual magnitude of 3.57. The distance to this system is 101 light years based on parallax, and it is drifting closer with a radial velocity of –7.4 km/s. It is a member of what is suspected to be a trailing tidal tail of the Hyades Stream. Components A and B of this system form a wide binary. The secondary, component B, is a magnitude 10.7 stellar companion at an angular separation of from the primary along a position angle of 35.72°, as of 2009. The primary was identified as a spectroscopic binary by E. B. Frost in 1924. This companion was confirmed during a lunar occultation with a separation of and magnitude 6.8. The primary, designated component A, typically has been assigned a stellar classification of A3V, which indicates this is an A-type main-sequence star that ge ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Phi Geminorum
Phi Geminorum, Latinized from φ Geminorum, is a binary star in the constellation Gemini, to the southwest of Pollux. It is visible to the naked eye with an apparent visual magnitude of 4.95. Based upon an annual parallax shift of 14.66 mas, this system is located around 220 light years from the Sun. The two components of this system have a circular orbit with a period of 582 days. The primary component is an A-type main sequence star with a stellar classification of A3 V. It is around 600 million years old and spinning relatively rapidly with a projected rotational velocity of 165 km/s. This rate of spin is giving the star an oblate shape with an equatorial bulge that is 6% larger than the polar radius. The star has nearly double the mass of the Sun and radiates 36.5 times the solar luminosity The solar luminosity (), is a unit of radiant flux ( power emitted in the form of photons) conventionally used by astronomers to measure the lumi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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