1) Relating to or having a constant temperature.
Isothermal, from → iso- + therm, from Gk. therme "heat" thermos "warm;" cognate with Pers. garm "warm" (garmâ "heat, warmth," from Mid.Pers. garmâg; O.Pers./Av. garəma- "hot, warm;" cf. Skt. gharmah "heat;" L. formus "warm," fornax "oven;" P.Gmc. *warmaz; O.E. wearm; E. warm; O.H.G., Ger. warm; PIE *ghworm-/*ghwerm- "warm") + → -al; → process.
Fr.: processus isotherme
A → thermodynamic process that takes place at → constant → temperature. For the temperature of a system to remain strictly constant, the changes in other coordinates (pressure and volume) must be carried out slowly, and → heat must enter or leave the system to maintain a constant temperature. → polytropic process. Astrophysical examples include the → collapse of a → protostar down the → Hayashi track, and the collapse of a star at the end of its life to become a → white dwarf.
Fr.: vent isotherme
A → stellar wind in which the gas is subject to only two forces: the inward directed gravity and the outward directed gradient of the gas pressure.
singular isothermal sphere
kore-ye izodamâ-ye takin
Fr.: sphère isotherme singulère
In models of star formation, an isothermal sphere in which the density distribution in the static or nearly static outer envelope obeys an r-2 power law. In the limit of infinite central concentration, the unstable equilibrium approaches the singular isothermal sphere which has the density and mass distributions ρ(r) = (a2/2πG)r-2 and M(r) = (2a2/G)r, where a is the isothermal → sound speed inside the cloud, G is the → gravitational constant, and r the distance from the center (F. H. Shu, 1977, ApJ 214, 488).