Astrophysics (Index)About

emission line

(narrow frequency-region of a spectrum with higher intensity)

An emission line is a spectral line due to emission of electromagnetic radiation from a (thin) cloud of gas with enough atomic excitation that the relaxation of atoms to lower energy levels is a primary source of the radiation it generates (as per Kirchhoff's laws). Such lines are used to identify such gas and analyze its properties: in addition indicating a component of its makeup, redshifted lines help estimate distance or radial velocity.

By contrast, absorption lines are produced when the continuous spectrum produced by a hot body passes through a (relatively) cooler gas. The gas's absorption of the EMR passing through tends to be at wavelengths matching the differences in energy from one atomic excitement level to another.

Further reading:

Referenced by pages:
absorption line
active galactic nucleus (AGN)
Atacama Pathfinder Experiment (APEX)
Balmer series (H)
broad emission line region
Be star
broad-line region (BLR)
Brackett series
brightness temperature (TB)
ionized carbon fine structure line ([CII])
carbon monoxide (CO)
Carbon Monoxide Mapping Array (COMA)
Compton reflection
core collapse supernova (CCSN)
diffuse emission
electron orbital
emission line galaxy (ELG)
emission nebula
star formation feedback
foreground subtraction
helium (He)
Herbig AeBe star (HAeBe)
HII region (HII)
hydrogen deuteride (HD)
iron (Fe)
Kirchhoff's laws
Lyman-alpha emitter (LAE)
spectral line shape
line tomography
Lyman series (L)
molecular cloud turbulence
Molecular Deep Field
non-thermal emission
Paschen series
Palomar Four-filter Survey (PC)
P Cygni profile
rare designator prefixes
redshift (z)
radio galaxy (RG)
Seyfert galaxy (Sy)
star formation rate (SFR)
shell star (sh)
submillimeter galaxy (SMG)
supernova (SN)
spectral feature
spectral line
spectral type
Tully-Fisher relation (TFR)
21-cm experiment
21-cm line
transit spectroscopy
T-Tauri star (TTS)
water lines
white dwarf (WD)
Wilson-Bappu effect
Wolf-Rayet star
Zeeman-Doppler imaging (ZDI)