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.
magnetic massive star
setâre-ye porjerm-e meqnâtisi
Fr.: étoile massive magnétique
A → stellar magnetic field associated with
a → massive star.
Magnetic fields are detected only for seven to ten percent of all
studied massive → OB stars, and the
magnetic field occurrence does not depend on the
→ spectral type. Because
these magnetic fields seem to be stable over long time-scales and their
strength does not seem to correlate with known stellar properties, it
is assumed that they are of fossil origin
(→ fossil magnetic field)
and are frozen into the → radiative envelope
of the stars.
The fields are those of the birth
→ molecular clouds, partly trapped inside
the → pre-main sequence star
during the cloud → collapse
phase, possibly further enhanced by a
→ dynamo effect in the early fully convective
Typically, the polar field strength ranges from about a
hundred → Gauss up to several kiloGauss.
However, some weaker fields,
below 100 G, have recently been detected.
setâre-ye meqnâtisi (#)
Fr.: étoile magnétique
Magnetism in Massive Stars (MiMeS)
An international collaboration devoted to the study of the origin and physics of → magnetic fields in → massive stars. The project uses several observatories and a large number of telescopes equipped with → spectropolarimetric and → asteroseismologic instruments, including → HARPS, → HARPSpol, and → ESPaDOnS (Wade et al., 2016, MNRAS 456, 2).
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.
Fr.: étoile multiple
multiple star system
Fr.: système multiple
A stellar system composed of several stars bound together by gravitational attraction and revolving around a common center of mass.
setâre-ye cašm-e berehné
Fr.: étoile visible à l'œil nu
A star visible without a telescope. In principle, stars down to about sixth magnitude are visible to the naked eye under ideal conditions, but this depends on the individual, the location, and the conditions of the observation.
setâre-ye notroni, notron setâré (#)
Fr.: étoile à neutrons
An extremely compact ball of matter created from the central core of a star that has collapsed under gravity to such an extent that it consists almost entirely of → neutrons. Neutron stars result from two possible evolutionary scenarios: 1) The → collapse of a → massive star during a → supernova explosion; and 2) The accumulation of mass by a → white dwarf in a → binary system. The mass of a neutron star is the same as or larger than the → Chandrasekhar limit (1.4 → solar masses). Neutron stars are only about 10 km across and have a density of 1014 g cm-3, representing the densest objects having a visible surface. The structure of neutron stars consists of a thin outer crust of about 1 km thickness composed of → degenerate electrons and nuclei, which becomes progressively neutron rich with increasing depth and pressure due to → inverse beta decays. In the main body the matter consists of → superfluid neutrons in equilibrium with their decay products, a few percent protons and electrons. Neutron stars have extremely strong magnetic fields, from 3 x 1010 to 1015 gauss. As of 2010 more than 2000 neutron stars have been catalogued, which show a large variety of manifestations, mainly → pulsars.
neutron star binary system
râžmân-e dorin-e setârehâ-ye noroni
Fr.: système binaire d'étoiles à neutron
setâre-ye hamiše penhân (#)
A star that is never seen above the horizon from a given position. These stars are located between the celestial pole and a diurnal circle with an angular distance larger than the altitude of the pole.
Setâré, → star; hamiše penhân, literally "always hidden," coined by Biruni (A.D. 973-1050) in his at-Tafhim, from hamišé "always" (Mid.Pers. hamêšag "always") + penhân "hidden."
setâre-ye hamiše peydâ (#)
A star that is always seen above the horizon from a given position. These stars are located between the celestial pole and a diurnal circle with an angular distance smaller than the altitude of the pole. Same as → circumpolar star.
setâre-ye O (#)
Fr.: étoile de type O
A luminous, hot, blue star whose spectrum is dominated by the lines of hydrogen, atomic helium, and ionized helium; also known as O-type star. This is the earliest → spectral type and the only → main sequence star in which ionized helium is present. The → effective temperatures of these stars range from about 30,000 K to 50,000 K, their luminosities from 50,000 to 1,000,000 times that of → solar luminosity, and their masses from about 20 to 100 → solar masses. The hottest O-type stars display high ionization emission features such as N III and He II, → Of star. They are divided into subtypes O2, the hottest, to O9.7, the coldest. O-type stars are relatively rare, for each star of 100 solar masses there are 106 stars of solar mass. They are relatively short-lived since they spend only a few million years on the main sequence. The brightest O-type star in the sky visible with naked eye is → Alnitak. For prominent Galactic O stars see → HD 93129.
O, letter of alphabet used in the Harvard spectral classification; → star.
setâre-ye gune-ye O
Fr.: étoile de type O
Same as → O star.
Fr.: étoile OB
A collective designation for massive O and B stars.