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PLAnetary Transits and Oscillations of stars (PLATO)
A space observatory under development by the → European Space Agency for launch around 2024. Its objective is to detect and characterize → exoplanets by means of their → transit signature in front of a very large sample of → bright stars, and measure the seismic oscillations (→ asteroseismology) of the parent stars orbited by these planets in order to understand the properties of the exoplanetary systems.
→ planetary; → transit; → oscillation; → star.
setâre-ye Plaskett (#)
Fr.: étoile de Plaskett
A → binary system consisting of two → massive stars, which are → supergiants of → spectral types O7.5 and O6. The two components are so close together that they orbit each other with a period of 14.4 days only. The Plaskett's star is a → double-line binary. The estimated masses of the components are 43 (Plaskett A) and 51 (Plaskett B) → solar masses. The lower mass component is optically brighter than the other star. Also known as HR 2422 and HD 47129 (See, e.g., Bagnuolo et al. 1992, ApJ 385, 708).
Named after the Canadian astronomer John S. Plaskett (1865-1941), who made a detailed spectroscopic study of this star in 1922.
setâre-ye qotbi (#)
Fr.: étoile polaire
A star that lies along the Earth's → rotation axis. The term usually refers to the star → Polaris, which is the current → North Celestial Pole star. The → South Celestial Pole is not currently associated with any bright star. See also: → North Pole Star, → South Pole Star.
Population I star
setÃ¢re-ye-e porineš-e I
Fr.: étoiles de population I
A member of a class of relatively young stars, containing a large fraction of → metals, found mainly in the disk of the Galaxy.
→ population; I, Roman number 1; → star.
Population II star
setÃ¢re-ye porineš-e II
Fr.: étoiles de population II
A member of a population of relatively old stars, containing a small fraction of → metals, found mainly in the → halo of the Galaxy and in → globular clusters.
→ population; II, Roman number 2; → star.
Population III star
setâre-ye porineš-e III
Fr.: étoile de population III
A member of the first generation of stars, formed out of pristine gas, enriched by → primordial nucleosynthesis alone. The material from which these stars formed consisted mostly of hydrogen and helium. Because neutral hydrogen clouds were free of dust, their cooling mechanism was drastically ineffective. As a result, these star forming clouds had a much higher temperature than in the present epoch, and their → Jeans mass was much higher. Therefore, these first generation of stars were principally massive, with a typical mass scale of order of about 100 Msun. Population III stars started forming about 300 million years after the → Big Bang at → redshifts between 50 and 6, when the Universe had between 1 and 5% of its present age. These stars were probably responsible for the → reionization of the Universe. Given their high mass, they lived only a few million years ending with either a → pair-instability supernova phase or a direct collapse to a → black hole. Population III stars thus initiated the chemical enrichment of the Universe and opened the way to more normal modes of star formation, namely → Population II. Some models predict a bimodal → initial mass function for the first stars, allowing also for solar mass stars. See also → extremely metal-poor star.
→ population; III, Roman number 3; → star.
post-asymptotic giant branch star (post-AGB)
setâre-ye pasâ-šâxe-ye qulân-e nâhamsâvi
Fr.: étoile post-asymptotique
A star in a short-lived evolutionary stage evolving from the → asymptotic giant branch toward higher → effective temperatures. The majority of low and intermediate mass stars (1 to 8 → solar masses) are believed to pass through this stage on their way to becoming → planetary nebulae.
→ post-; → asymptotic giant branch.
post-main sequence star
setâre-ye pasâ-rešte-ye farist
Fr.: étoile post séquence principale
A star that has evolved off the → main sequence.
→ post-; → main sequence; → star.
post-planetary nebula star
setâre-ye pasâ-miq-e sayyâre-yi
Fr.: étoile post-nébuleuse planétaire
An evolved star whose → planetary nebula has dissipated.
Fr.: étoile pré-dégénérée
Same as → PG 1159 star.
→ post-; → degenerate; → star.
pre-main sequence B[e] star (HAeB[e])
setâre-ye B[e]-ye piš-rešte-ye farist
Fr.: étoile B[e] pré-séquence principale
A → Herbig AeBe star displaying → forbidden emission lines in its spectrum.
pre-main sequence star
setâre-ye piš-rešte-ye farist
Fr.: étoile pré-séquence principale
A star that evolves in the → Hayashi phase and has not yet reached the → zero-age main sequence.
→ pre-; → main sequence, → star.
setâre-ye piš-kutule-ye sefid
Fr.: étoile pré-naine blanche
A → post-planetary nebula star that is approaching the top of the → white dwarf sequence. These stars have exhausted the capacity of → nuclear burning in their cores.
Fr.: Ã©toile principale
In a → multiple star system, the most massive → component. In other words, the star nearest to the system's → center of garvity.
Fr.: étoile mère
A star which is supposed to be at the origin of phenomenon, for example a progenitor neutron star which has given rise to a black hole.
→ progenitor; → star.
Fr.: étoiles du programme
Stars for the observation of which telescope time has been awarded.
Fr.: proto-étoile à neutrons
A compact, hot, and → neutrino-rich object that results from a → supernova explosion and is a transition between an → iron core and a → neutron star or → black hole. The life span of a protoneutron star is less than one minute.
A stage in the process of → star formation, after the → gravitational collapse of the dense → pre-stellar core and before the initiation of → nuclear fusion in the central object which will eventually become a star. Protostars are classified into four groups: → Class 0, → Class I, → Class II, and → Class III.
Fr.: étoile de Przybylski
A blue star, named HD 101065 or V816 Cen, with an extremely peculiar chemical composition and spectral features. Although the star has a surface temperature very close to that of stars with solar chemical composition, it displays some abundance anomalies typical of much hotter → Ap stars. The spectrum is dominated by a group of lines of → lanthanides, while in the spectra of normal stars with similar temperature the absorption lines of neutral elements from the iron group are predominant. The lanthanides may have abundances 103-104 times solar. The spectrum of Przybylski's star also shows the presence of radioactive → rare earth elements, such as → promethium and → technetium. Moreover, there are numerous strong absorption lines which defy identification. In some spectrum regions unidentified lines are more numerous than known lines. It is also a → roAp star (see, e.g., Gopka et al. 2008, Kinematics and Physics of Celestial Bodies Vol. 24, No. 2, 89).
Named after its discoverer, Antoni Przybylski (1961, Nature 189, 739).
setâre-ye tapandé (#)
Fr.: étoile pulsante
A type of → variable star that changes its brightness by changing its volume through expansion and contraction. Classical pulsating stars, including → Cepheids, → RR Lyrae, and → Delta Scuti variables, are located in a quite narrow almost vertical region in the → H-R diagram, known as → instability strip. See also → kappa mechanism.
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