Hayashi forbidden zone
zonâr-e baſkam-e Hayashi
Fr.: zone interdite de Hayashi
The region to the right the → Hayashi track, representing objects that cannot be in → hydrostatic equilibrium. Energy transport in these objects would take place with a → superadiabatic temperature gradient.
Fr.: phase de Hayashi
A period in the → pre-main sequence evolution of a low mass star during which the star has negligible nuclear energy production and low internal temperature. Hence energy transport inside the star takes place dominantly through → convection. The star contracts homologously and evolves in the → H-R diagram along the → hayashi track with decreasing → luminosity and nearly constant → effective temperature. The time taken by a star of mass M* to contract to radius R* along a Hayashi track is of the order of the → Kelvin-Helmholtz time: tKH = 107(M*/Msun)2/(R*/Rsun)3 yr.
Fr.: température de Hayashi
The minimum → effective temperature required for a → pre-main sequence star of given mass and radius to be in → hydrostatic equilibrium. This temperature delimits the boundary of the → Hayashi forbidden zone.
Fr.: trajet de Hayashi
The path on the → Hertzsprung-Russell diagram that is followed by a fully → convective → pre-main sequence star to reach the → zero-age main sequence. Hayashi tracks for → low-mass stars are near vertical. At higher masses, stars become increasingly radiative as they contract and the Hayashi tracks are almost horizontal.
Named after the Japanese astrophysicist Chushiro Hayashi (1920-2010), who published his paper in 1961 (PASJ 13, 450); → track.
Fr.: hasard, risque, danger
1) A danger that one can foresee but cannot avoid.
M.E. hasard, from O.Fr. hasard, hasart "game of chance played with dice," possibly from Sp. azar "an unfortunate card or throw at dice," postulated to derive from Ar. az-zahr "the die," but this etymology is controversial.
Âpé, from Av. au-pat-, "to fall down, off," from pat- "to fall, fly;" Proto-Ir. *pat- "to fall; fly; rise;" related to Pers. oftâdan "to fall; to befall; to happen," → fall. Pers. âfat "blight, pest, curse," may belong to this family.
1) Full of risk; perilous; risky.
Adj. from → hazard.
Fr.: brume sèche
Maybe from M.E. *hase, O.E. hasu, variant of haswa "ashen, dusky."
Nezm "mist, fog, vapor."
Fr.: HD 5980
A remarkable → binary star system composed of → massive stars that is associated with NGC 346, the largest → H II region + OB star cluster in the → Small Magellanic Cloud. HD 5980 is a rather complex system because it consists of at least three stars: two stars form an → eclipsing binary with a period of 19.266 days, while the third component, an → O star, is detected by means of a set of absorption lines. Whether or not the third star is physically bound to the eclipsing binary remains currently unclear. HD 5980 underwent an → LBV-type event in August 1994. Before the LBV eruption, both components of the eclipsing binary already showed emission lines in their spectra and were thus classified as → Wolf-Rayet stars. However, as shown by the analysis of the spectra taken during and after the LBV event, at least the star that underwent the eruption was not a classical, helium-burning, Wolf-Rayet object, but rather a WNha star. This means a rather massive star with substantial amounts of hydrogen present in its outer layers. These WNha stars have → stellar wind properties that are intermediate between those of extreme → Of stars and classical → WN Wolf-Rayet stars.
Fr.: HD 93129
A multiple → O-type star in the → Trumpler 14 cluster, which consists of at least three components. The main component, HD 93129A, is of spectral type O2 If*, a very rare hot star and the closest known O2 star (Walborn et al. 2002). It is one of the most luminous stars known. HD 93129B, lying 2.7 arcsec apart, is an O3.5 V((f+)) type. Recent → HST observations have shown that component A is itself probably a double or → binary star with a separation of 0.055 arcsec.
→ HD number.
Fr.: HD 97950
→ HD number.
adad-e HD (#)
Fr.: numéro HD
An identifying number assigned to the stars in the Henry Draper catalog. For example, the star Vega is HD 172167.
Head, from O.E. heafod "top of the body," also "chief person" (cf. O.S. hobid; Goth. haubiþ Ger. Haupt "head"), from PIE *kauput- "head;" cf. Skt. kaput-, kapala- "skull;" L. caput "head;" Pers. dialect Lori: kapu "head," kapulek "skull, middle of the head;" Kurd. kapol "skull;" Pashto kaparay "skull."
Sar "head," soru, sorun "horn" (karnâ "a trumpet-like wind instrument," variant sornâ "a wind instrument"); Mid.Pers. sar "head," sru "horn;" Av. sarah- "head," srū- "horn, nail;" cf. Skt. śiras- "head, chief;" Gk. kara "head," karena "head, top," keras "horn;" L. cornu "horn," cerebrum "brain;" P.Gmc. *khurnaz (Ger. Horn, Du. horen; cognate with E. horn, as above, from PIE *ker- "head, horn;" O.E. horn "horn of an animal," also "wind instrument;" E. horn); PIE base *ker- "head, horn, top, summit."
Fr.: galaxie tête-queue, ~ têtard
A member of the class of radio galaxies (→ radio galaxy) that have a strong radio emission coming from a bright "head" and a more diffuse emission from a "tail." They are often found in clusters.
Energy possessed by a substance in the form of kinetic energy of atomic or molecular translation, rotation, or vibration.
Heat, from O.E. hætu, hæto, from P.Gmc. *khaitin- "heat," from *khaitaz "hot" (cf. O.N. hiti, Ger. hitze "heat," Goth. heito "fever").
Garmâ "heat, warmth," from Mid.Pers. garmâg; O.Pers./Av. garəma- "hot, warm;" cf. Skt. gharmah "heat;" Gk. thermos "warm;" L. formus "warm," fornax "oven;" P.Gmc. *warmaz; O.E. wearm; E. warm; O.H.G., Ger. warm; PIE *ghworm-/*ghwerm- "warm."
gonjâyeš-e garmâyi (#)
Fr.: capacité thermique, ~ calorifique
The ratio of an amount of heat, dQ, transferred to a body in some process to the corresponding change in the temperature of the body: C = dQ/dT. The heat capacity depends upon the mass of the body, its chemical composition, thermodynamic state, and the kind of process employed to transfer the heat. The word "capacity" may be misleading because it suggests the essentially meaningless statement "the amount of heat a body can hold," whereas what is meant is the heat added per unit temperature rise. → specific heat.
Fr.: conduction de chaleur
A type of → heat transfer by means of molecular agitation within a material without any motion of the material as a whole.
hambaz-e garmâ (#)
Fr.: convection de chaleur
A type of → heat transfer involving mass motion of a fluid such as air or water when the heated fluid is caused to move away from the source of heat, carrying energy with it.
heat death of the Universe
marg-e garmâyi-ye giti (#)
Fr.: mort thermique de l'Univers
Assuming that the Universe is a thermodynamically → isolated system, a state of absolute uniformity in the Universe in which all temperature differences would reduce to zero and no energy will be available for use, according to the → second law of thermodynamics. In that condition of maximum → entropy, the Universe would be in a state of unchanging death. First introduced by the German physicist Hermann von Helmholtz (1821-1894) in 1854, on the basis of William Thomson's (1824-1907) idea.
heat of vaporization
Fr.: chaleur de vaporisation
The amount of heat energy required to transform an amount of a substance from the liquid phase to the gas phase. → molar heat of vaporization.
separ-e garmâyi (#), garmâ-separ
Fr.: bouclier thermique
A structure that protects against excessive heat, especially that which covers the vulnerable surfaces of a → spacecraft and protects it when re-entering the Earth's atmosphere.