horizontal branch star
setâre-ye šâxe-ye ofoqi
Fr.: étoile de la branche horizontale
A star lying on the → horizontal branch.
setâre-ye dâq (#)
Fr.: étoile chaude
A member of a class of stars having high → effective temperatures (above some 15,000 K); mainly → massive stars, but also including → exciting stars of → planetary nebulae, → white dwarfs, and → symbiotic stars.
Fr.: étoile hybride
A high luminosity star with absolute visual magnitude around -10, about 106 times as luminous as the Sun. Hypergiant stars are evolved → massive stars belonging to the luminosity class Ia+ or Ia0. Their spectra show very broadened emission and absorption lines resulting from the high luminosity and low surface gravity which favor strong → stellar wind. See also → Humphreys-Davidson limit; → yellow hypergiant.
hypervelocity star (HVS)
Fr.: étoile hypervéloce
A star whose velocity is so great that it will escape the
→ gravitational potential of our
→ Galaxy. Depending on the location and direction of
motion, this criterion typically corresponds to a stellar velocity in
the Galactic → rest frame larger than
400 km s-1, and up to about 1200 km s-1.
The nature of the HVSs spans a wide range of types from
→ OB stars, to metal-poor
→ F-type stars and G/K dwarfs. While there is evidence from many
late-type B HVSs in the → halo
to originate from the Galactic
→ supermassive black hole (SMBH),
other HVSs seem to originate from the → galactic disk.
HVSs can obtain their large velocities from a number of different processes:
Fr.: protoétoile de masse intermédiare
A protostar that evolves into an → intermediate-mass star.
Fr.: étoile de masse intermédiare
A star whose mass lies in the range about 2 to 8 → solar masses approximately.
internal structure of stars
sâxtâr-e daruni-ye setâregân (#)
Fr.: structure interne des étoiles
The physical characteristics of that part of a star lying below the → photosphere. More specifically, the study of its various zones (→ core, → convective zone, → radiative zone) and the transfer of energy through them.
isolated massive star formation
diseš-e vâyutide-ye setâre-ye porjerm
Fr.: formation isolée d'étoile massive
Massive star formation outside → OB associations. Recent observational findings suggest that → massive star formation is a collective process. In other words, massive stars form in → cluster environments and the mass of the most massive star in a cluster is correlated with the mass of the cluster itself. Nevertheless, other observational results give grounds for supposing that massive stars do not necessarily form in clusters but that they can be formed as isolated stars or in very small groups. According to statistical studies nearly 95% of Galactic → O star population is located in clusters or OB associations. This means that a small percentage, about 5%, of high mass stars may form in isolation. Isolation is meant not traceable to an origin in an OB association. This definition therefore excludes → runaway massive stars, which are thought to result from either dynamical interaction in massive dense clusters, or via a kick from a → supernova explosion in a → binary system. Alternatively, isolated massive star has been defined as follows: An O-type star belonging to a cluster whose total mass is < 100 Msun and moreover is devoid of → B stars (Selier et al. 2011, A&A 529, A40 and references therein).
isolated neutron star (INS)
setâre-ye notroni-ye vâyutidé
Fr.: étoile à neutron isolée
A → neutron star which does not belong to a → binary system, does not have radio emission, and is not surrounded by a progenitor → supernova remnant. INSs appear to be thermally cooling with no emission outside the → soft X-ray band, except for faint optical/UV counterparts. Although these properties are similar to those of → compact central object (CCO)s, they are a distinct class because they lack any observable associated supernova remnant or nebula. There are presently seven confirmed INSs (sometimes referred to as The Magnificent Seven), six of which have measured weakly modulated X-ray pulsations with periods between 3 s and 11 s, much longer than those of CCOs (A. K. Harding, 2013, Front. Phys. 8, 679).
setâre-ye K (#)
Fr.: étoile de type K
An orange-red star of → spectral type K with a surface temperature of about 3600-5000 K. The spectra of K stars are dominated by the H and K lines of calcium and lines of neutral iron and titanium, with molecular bands due to cyanogen (CN) and titanium dioxide (TiO). Examples are → Arcturus and → Aldebaran.
K the letter of alphabet; → star.
setâre-ye Kepler (#)
Fr.: étoile de Kepler
A → supernova in → Ophiuchus, first observed on 1604 October 9, and described by Johannes Kepler in his book De stella nova (1606). It reached a maximum → apparent magnitude of -3 in late October. The star remained visible for almost a year. The → light curve is that of a → Type Ia supernova. The → supernova remnant consists of a few filaments and brighter knots at a distance of about 30,000 → light-years. It is the radio source 3C 358. Also known as SN 1604 and Kepler's supernova.
Lambda Bootis star
setâre-ye lâmbda Gâvrân
Fr.: étoile lambda du Bouvier
The prototype of a small class of stars (A-F types) which have weak metallic lines (indicating that they are depleted in metals heavier than Si, but with solar abundances of C, N, O, and S). Moreover, they have moderately large rotational velocities and small space velocities. Lambda Boo stars may be pre-main-sequence objects, or they may be main sequence stars that formed from gas whose metal atoms had been absorbed by interstellar dust.
setâre-ye gune-ye farjâmin
Fr.: étoile de type tardif
setâre-ye litiomi (#)
Fr.: étoile à lithium
A peculiar evolved star of spectral type G or M whose spectrum displays a high abundance of lithium.
setâre-ye kamjerm (#)
Fr.: étoile de faible masse
setâre-ye M (#)
Fr.: étoile de type M
A cool, red star of spectral type M with a surface temperatures of less than 3600 K. The spectra of M stars are dominated by molecular bands, especially those of TiO. Naked-eye examples are Betelgeuse and Antares.
M, letter of alphabet, → star.
setâre-ye meqnâtisi (#)
Fr.: étoile magnétique
A star (usually of spectral type A) with strong integrated magnetic field ranging up to 30,000 gauss.
setâre-ye porjerm (#)
Fr.: étoile massive
A star whose mass is larger than approximately 10 → solar masses. The → spectral types of massive stars range from about B3 (→ B star) to O2 (→ O star) and include → Wolf-Rayet stars as well as → Luminous Blue Variables. Massive stars are very rare; for each star of 20 solar masses there are some 100,000 stars of 1 solar mass. Despite this rarity, they play a key role in astrophysics. They are major sites of → nucleosynthesis beyond oxygen and, therefore, are mainly responsible for the → chemical evolution of galaxies. Due to their high ultraviolet flux and powerful → stellar winds, they bring about interesting phenomena in the → interstellar medium, like → H II regions, → turbulence, → shocks, → bubbles, and so on. Massive stars are progenitors of → supernovae (→ type Ia, → type Ic and → type II), → neutron stars, and → black holes. The formation processes of massive stars is still an unresolved problem. For massive stars the → accretion time scale is larger than the → Kelvin-Helmholtz time scale. This means that massive stars reach the → main sequence while → accretion is still going on.
rujâ (#), setâre-ye bâmdâd (#)
Fr.: étoile du matin
Not actually a star, but the planet Venus shining brightly in the east just before or at sunrise. Opposed to → evening star.
Rujâ "morning star" in Tabari, "star" in Gilaki. This word is a variant of official Pers. ruz "day," since in Tabari and Gilaki the phoneme z is sometimes changed into j, as in rujin = rowzan "window" and jir or jer = zir "under." Therefore it is related to rowšan "bright, clear," rowzan "window, aperture;" foruq "light," afruxtan "to light, kindle;" Mid.Pers. rôšn "light; bright, luminous," rôc "day;" O.Pers. raucah-rocânak "window;" O.Pers. raocah- "light, luminous; daylight;" Av. raocana- "bright, shining, radiant;" akin to Skt. rocaná- "bright, shining," roka- "brightness, light;" Gk. leukos "white, clear;" L. lumen (gen. luminis) "light," from lucere "to shine," related to lux "light," lucidus "clear," luna, "moon;" Fr. lumière "light;" O.E. leoht, leht, from W.Gmc. *leukhtam (cf. O.Fris. liacht, M.Du. lucht, Ger. Licht), from PIE *leuk- "light, brightness;" → morning; → star.