galaxy main sequence
rešte-ye farist-e kahkešânhâ
Fr.: séquence principale des galaxies
A scaling relation between the → star formation rate (SFR) in galaxies and the total stellar mass (M*) of the galaxies. This relation, colloquially called the "galaxy main sequence," extends over several orders of magnitudes in M* and out to → high redshifts, with a modest scatter of ~ 0.3 dex which includes both intrinsic scatter and measurement uncertainties. The existence of such tight scatter at all observed epochs suggests that most galaxies assembled their stellar mass fairly steadily rather than predominantly in → starburst episodes, implying that → mergers have a sub-dominant contribution to the global star formation history (Wuyts et al., 2011 ApJ 742, 96).
lower main sequence
rešte-ye farist-e zirin
Fr.: séquence principale inférieure
A → main sequence star whose mass is less than 1.5 Msun. Lower main sequence stars generate their energy chiefly through the → proton-proton chain. The core is surrounded by a → radiative zone above which lies a → convective envelope. In such stars the → opacity at the surface is high because of the low → surface temperature. Therefore, radiation cannot carry all the radiation because of high opacity. Thus, energy transfer takes place by → convection to the outer layer.
Fr.: séquence principale
An evolutionary stage in the life of a star when it generates its energy by the conversion of hydrogen to helium via → nuclear fusion in its core. Stars spend 90% of their life on the main sequence. On the → Hertzsprung-Russell diagram it appears as a track running from top left (high temperature, high luminosity, high mass) to lower right (low temperature, low luminosity, low mass). See also → zero age main sequence (ZAMS), → terminal age main sequence (TAMS).
post-main sequence star
setâre-ye pasâ-rešte-ye farist
Fr.: étoile post séquence principale
A star that has evolved off the → main sequence.
pre-main sequence binary
dorin-e piš-rešte-ye farist
Fr.: binaire pré-séquence principale Markarian's Chain
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
terminal age main sequence (TAMS)
rešte-ye farist bâ senn-e pâyâni
Fr.: séquence principale d'âge terminal
The locus of stars on the → Hertzsprung-Russell diagram that are at the point of exhausting hydrogen in their cores. TAMS forms the upper luminosity boundary of the → main sequence strip. See also → zero age main sequence (ZAMS).
upper main sequence
rešte-ye farist-e zabarin
Fr.: séquence principale supérieure
A → main sequence star with a mass above 1.5 Msun. Upper main sequence stars have high central temperatures so that they produce their energy through the → CNO cycle. The outward energy flux is very high and therefore this flux cannot be maintained by → radiative transfer. Thus, upper main sequence stars have → convective cores. Outside the core, there is a → radiative zone. The mass of the convective core gradually diminishes as the hydrogen is consumed. The surface hydrogen is fully ionized and the → opacity is due to → electron scattering The opacity due to electron scattering.
zero age main sequence (ZAMS)
rešte-ye farist bâ senn-e sefr
Fr.: séquence principale d'âge zéro
The position on the → Hertzsprung-Russell diagram for newborn stars which have just started → hydrogen burning in their cores. The ZAMS forms the lower luminosity boundary of of the → main sequence strip. See also → terminal age main sequence (TAMS).