An Etymological Dictionary of Astronomy and Astrophysics

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory



Number of Results: 18 Search : spectral
early spectral class star
  ستاره با رده‌ی ِ بینابی ِ آغازین   
setâré bâ rade-ye binâbi-ye âqâzin

Fr.: étoile de type spectral précoce   

A star near the beginning of the → spectral classification sequence. A star of → spectral type O, B, A, or F0 to F5. Same as → early-type star.

early; → spectral; → class; → star.

power spectral density
  چگالی ِ بینابی ِ توان   
cagâli-ye binâbi-ye tavân

Fr.: densité spectrale de puissance   

Same as → spectral density.

power; → spectral; → density.

binâbi (#)

Fr.: spectral   

Of or pertaining to a → spectrum.

spectrum; → -al.

spectral classification
  رده‌بندی ِ بینابی   
radebandi-ye binâbi (#)

Fr.: classification spectrale   

A system that assigns a → spectral type to a star according to characteristics of its spectrum. The earliest attempt to divide stars on the basis of their spectra was the → Secchi classification in the 1860s. This scheme paved the way for the → Harvard classification that led to the current → Morgan-Keenan classification of spectral types. In the Harvard system stars were originally thought to follow an evolutionary sequence from the "early" O and B types to the "late" K and M types. Although this is now known to be wrong, the terms → early-type star and → late-type star are still in use. In the Morgan-Keenan system stars are classified as type O, B, A, F, G, K, or M in order of decreasing → effective temperature, and each type further subdivided into subclasses from 0 (hottest, except for → O-type stars) to 9 (coolest). They are also accompanied by a → luminosity class. In the late 1990s, spectral types L and T were added to the sequence to accommodate the coolest stars and → brown dwarfs (with class Y reserved for the coolest brown dwarfs of all, as yet unobserved).

spectral; → classification.

spectral coverage
  پوشش ِ بینابی   
pušeš-e binâbi

Fr.: couverture spectrale   

The → range of → wavelengths or frequencies (→ frequency) at which a → detector is sensitive. Same as → bandwidth.

spectral; → coverage.

spectral density
  چگالی ِ بینابی   
cagâli-ye binâbi

Fr.: densité spectrale   

For a specified → bandwidth of radiation consisting of a continuous → frequency spectrum, the total → power in the bandwidth divided by the bandwidth. Spectral density describes how the power (or variance) of a time series is distributed with frequency. Also called power spectral density.

spectral; → density.

spectral energy distribution (SED)
  واباژش ِ کاروژ ِ بینابی   
vâbâžeš-e kâruž-e binâbi

Fr.: distribution de l'énergie spectrale   

A plot showing the energy emitted by a source as a function of the radiation wavelength or frequency. It is used in many branches of astronomy to characterize astronomical sources, in particular mainly in → near infrared and → middle infrared to study → protostars or → young stellar objects. The SED of these objects is divided in four classes.
Class 0 in which the SED represents a very embedded protostar, where the mass of the central core is small in comparison to the mass of the → accreting envelope. The SED is characterized by the → blackbody radiation of the envelope and peaks at → submillimeter wavelengths.
Class I objects possess a SED that peaks in the → far infrared and is characterized by a weak contribution of the blackbody of the central protostar (detected in near infrared) and the emission of a thick disk and dense envelope. These objects have less mass in the envelope and more massive central cores with respect to Class 0.
Class II objects are the → classical T Tauri stars with a SED due to the emission of a thin disk and the central star. They have accumulated most of their final mass and have dispersed almost completely their circumstellar envelope.
Finally, Class III objects have pure photospheric spectra. Their SED is peaked in the optical and is well approximated by a blackbody emission with a faint → infrared excess due to the presence of a residual optically thin disk that may be the origin of → planetesimals.
This classification scheme can be made more quantitative by defining a → spectral index.

spectral; → energy; → distribution.

spectral feature
  آرنگ ِ بیناب، ~ بینابی   
ârang-e binâb, ~ binâbi

Fr.: motif spectral   

An emission or absorption mark in the spectrum of an astronomical object, of known or unknown origin, usually with complex structure.

spectral; → feature.

spectral index
  دیشن ِ بینابی   
dišan-e binâbi

Fr.: indice spectral   

1) The → exponent of the → frequency on which depends the intensity of the → continuum emission, that is: Fν∝ να. The exponent (α) typically takes positive values from 0 to 2 for → thermal emission, while → non-thermal emission, such as → synchrotron radiation, leads to negative values of the spectral index ranging from about -0.5 to -1.5.
2) The ratio αIR = dlog(λFλ)/dlogλ, where F represents the flux and λ the wavelength, in the range 2.2 μm ≤ λ ≤ 25 μm, particularly used in the classification of → protostars (→ Class I, → Class II, and → Class III).

spectral; → index.

spectral line
  خطّ ِ بینابی   
xatt-e binâbi

Fr.: raie spectrale   

A dark or bright line in an otherwise uniform and continuous spectrum, resulting from an excess or deficiency of photons in a narrow wavelength range, compared with the nearby wavelengths.

spectral; → line.

spectral range
  گستره‌ی ِ بینابی   
gostare-ye binâbi

Fr.: domain spectral   

The observable spectral range provided by a spectroscope, as determined by the grating dispersion, camera focal length, and detector size.

spectral; → range.

spectral region
  ناحیه‌ی ِ بینابی   
nâhiye-ye binâbi

Fr.: région spectrale   

An extent of wavelengths into which the electromagnetic spectrum is divided; e.g. infrared or ultraviolet region.

spectral; → region.

spectral resolution
  واگشود ِ بیناب، ~ بینابی   
vâgošud-e binâb, ~ binâbi

Fr.: résolution spectrale   

The capacity of a spectrograph to separate two adjacent spectral lines. The theoretical spectral resolution depends on the grating dispersion, grating position, pixel size, collimator and camera focal length, and the entrance slit-width.

spectral; → resolution.

spectral response
  پاسخ ِ بینابی   
pâsox-e binâbi

Fr.: réponse spectrale   

Domain of the electromagnetic spectrum over which a detector is sensitive. Same as spectral sensitivity.

spectral; → response.

spectral series
  سری ِ بینابی   
seri-ye binâbi

Fr.: série spectrale   

Spectral lines or group of lines occurring in sequence.

spectral; → series.

spectral synthesis
  هندایش ِ بینابی   
handâyeš-e binâbi

Fr.: synthèse spectrale   

The process of computing line strengths in stellar spectra using an appropriate stellar atmosphere model, atomic and molecular data, and the numerical solution of the → radiative transfer equation at each point in the spectrum.

spectral; → synthesis.

spectral type
  گونه‌ی ِ بینابی   
gune-ye binâbi

Fr.: type spectral   

A group into which stars may be classified according to the characteristics of their spectra. Spectral type correlates with the star's → effective temperature and → color. There are seven main spectral types. From hot and blue to cool and red, they are O, B, A, F, G, K, and M. Each spectral type is divided into several subtypes. For example, from warmest to coolest, spectral type G is G0, G1, G2, G3, and so on to G9. A precise → spectral classification requires determining the → luminosity class. The Sun is spectral type G2 V.

spectral; → type.

spectral variability
  ورتندگی ِ بینابی   
vartandegi-ye binâbi

Fr.: variabilité spectrale   

The state of a spectrum from an astronomical object in which the lines change with time as far as their intensity, profile, and wavelength are concerned.

spectral; → variability.