Population II star
setâre-ye porineš-e II
Fr.: étoiles de population II
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.
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-main sequence star
setâre-ye pasâ-rešte-ye farist
Fr.: étoile post séquence principale
A star that has evolved off the → main sequence.
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.
pre-main sequence B[e] star (HAeB[e])
setâre-ye B[e]-ye piš-rešte-ye farist
Fr.: étoile B[e] pré-séquence principale
pre-main sequence star
setâre-ye piš-rešte-ye farist
Fr.: étoile pré-séquence principale
setâre-ye piš-kutule-ye sefid
Fr.: étoile pré-naine blanche
Fr.: étoile principale
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.
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.
Fr.: étoile de quarks
A hypothetical star so dense that it is composed of degenerate quarks, a matter denser than that of a neutron star.
râdio setâré, setâre-ye râdioyi
Fr.: étoile radio
A star which is a source of emission at radio frequencies. Radio stars include pulsars, flare stars, binary star systems in which mass is transferred from one component to the other, and some X-ray stars.
rapidly oscillating Ap star
Fr.: étoile Ap à oscillation rapide
A chemically peculiar star characterized by the presence of high-frequency non-radial oscillations, with periods that range between about 4 and 16 min. These variations have periods from about 5 to 20 minutes and low amplitudes (B < 10 mmag). They are consistent with acoustic (→ p mode) pulsations of low degree and high radial overtone.
red clump star
setâre-ye gude-ye sorx
Fr.: étoile du grumeau rouge