Astrophysics (index)about

spectral line

(dark or light line in a spectrum)

A spectral line (or just line) is a dark or light line within a continuous spectrum. For example, a SED representing the spectrum of some object's light may generally be described curve, i.e., nearby wavelengths have nearly the same brightness. A "spike" in the SED indicates wavelength at which light has a much higher magnitude than nearby wavelengths, or a dip where a wavelength has a much lower magnitude than nearby wavelengths. If the spectrum is displayed as a rectangular area with the source's wavelengths spread across a dimension (per a photographic plate produced a spectrograph), each of these shows as a line, lighter or darker than its surroundings.

In a source's spectrum, light lines are generally caused by emissions at specific wavelengths (emission lines), and dark lines are caused by absorption at specific wavelengths (absorption lines). Lines are related to chemical makeup of the light source or absorber, indicating changes of energy level of electrons, which have characteristic values based upon chemistry. Characteristics of the details of lines can show other characteristics of the light source or intervening absorber such as velocity, turbulence, etc. The term line broadening refers to the mechanisms that create the shape of a line, e.g., in electromagnetic radiation from a star.

Among the widely used spectral lines are the hydrogen series of lines, e.g.,

Atomic spectral lines are sometimes classified by element and ionization, specified by the chemical symbol followed by a Roman numeral, I meaning neutral, II meaning singly ionized positive, III meaning doubly ionized, etc.

Spectral-line mapping refers to imaging or surveying a portion of the sky for the presence of particular spectral lines, often noting their redshift, to determine their radial velocity. Its uses include investigations of accretion disks, jets, molecular clouds, the entire Milky Way, and other galaxies.


Referenced by:
absorption line
Am star
Balmer jump
Balmer series
broad emission line region
broad-line region (BLR)
blue horizontal branch (BHB)
Bohr model
Brackett series
calcium (Ca)
calcium-rich gap transient
carbon (C)
ionized carbon fine structure line ([CII])
carbon monoxide (CO)
cold gas
continuous absorption
continuous spectrum
continuum emission
core collapse supernova
cosmological time dilation
velocity dispersion (σ)
Doppler broadening
double-line spectroscopic binary
electron orbital
electron shell
emission line galaxy (ELG)
emission line
Faber-Jackson relation (FJR)
falling evaporating body (FEB)
fine structure
forbidden line
full width at half maximum (FWHM)
gravitational redshift
Gunn-Peterson trough
H-alpha (Ha)
Hydrogen Accretion in Local Galaxies Survey (HALOGAS)
helium 1083nm line
neutral atomic hydrogen (HI)
HI region (HI)
hydrogen (H)
hydroxyl (OH)
hyperfine structure
ionization correction factor (ICF)
intensity mapping
K correction
Kepler radius
kinematic distance
Kirchhoff's laws
Lyman-alpha emitter (LAE)
line blanketing
line broadening
line shape function
Lick Observatory Calcium Line Survey (LkCl)
Lyman alpha (Ly-α)
Lyman-alpha forest
Lyman series
Millimeter-wave Intensity Mapping Experiment (mmIME)
molecular cloud
Molecular Deep Field
nitrogen (N)
oxygen lines
Paschen series
P Cygni profile
planetary nebula luminosity function (PNLF)
position-position-velocity space (PPV)
radial velocity (RV)
radioactive decay
redshift (z)
silicon (Si)
spectral line energy distribution (SLED)
supernova (SN)
Sobolev approximation
sodium (Na)
spectral band
spectral class
spectral signature
spectroscopic binary
state of excitation
state of ionization
stellar model atmosphere
stellar rotation
stellar temperature determination
S-type star
sulfur (S)
surface abundance
surface gravity
surface temperature
telluric star
Tully-Fisher relation (TFR)
Tomographic Ionized-carbon Mapping Experiment (TIME)
21cm line
Type Ia supernova
virial theorem
Voigt profile
water lines
weak-line star
white dwarf
Wilson-Bappu effect
CO to H2 factor (Xco)
Zeeman-Doppler imaging (ZDI)