Astrophysics (Index)About

passband

(band, filter)
(range of electromagnetic wavelengths that a filter allows)

A passband (or just band) is a specification of the range and strength of wavelengths (and in effect, frequencies) allowed through a filter that cuts off both high and low wavelengths, i.e., a specification of the wavelengths allowed to pass through the filter, i.e., the filter's specified sensitivity function. The term is also sometimes used to indicate the physical filter. Filter and passband are common terms in optical telescopes (infrared through ultraviolet) while the word band is also used in radio astronomy to refer to the wavelength-sensitivity of a radio receiver and as a general term for a wavelength or frequency range.

The term is used in engineering disciplines such as communications engineering as well as astronomy. In the latter, a photometric system, e.g., the UBV photometric system, is a conventional set of such filter specifications.

Passbands and their associated filters are generally indicated by letters, but the same letter may have differing specifications under different photometric systems or different portions of the electromagnetic spectrum. Within visible light, sometimes the letters are chosen that correspond with their associated color, e.g., B for blue, R for red, etc. Some common passband letters in astronomy:

Infrared observations from the ground are confined to atmospheric windows, the commonly-used infrared bands match a window, and the relevant band letters are also used to label the window itself. Near infrared includes bands lettered Y, J, H, K, and midinfrared, M, N, and Q. The letter Z is also used for infrared bands, but some systems use it for a near-infrared band and some for a far-infrared band.

The above passbands are commonly used, and considered basic to photometry, but for particular uses, narrower bands are used. Among the descriptive terms based upon bandwidth:

The term wide band also means a large width, but its exact usage varies.

The passbands of filters are sufficiently consistent to produce scientifically-useful observation data, such as filtered magnitudes consistent within a tenth of a magnitude. However, their characterization by a mid-frequency (or wavelength) and a FWHM only loosely describes a sensitivity function, and furthermore, actual filters only loosely match either of these: it is a challenge to manufacture filters consistently: they (slightly) vary according to manufacturing process, and even by manufacturing run. Furthermore, specifications of the passbands themselves evolve with time: an improved manufacturing process that produces more consistent filters certainly produces some differences in the sensitivity function and may even affect the mid-frequency and the FWHM. There can be scientific reasons to adjust particular values as well. The letter names generally give an overfall idea of where the passband falls, but these may vary according to particular photometric systems, and also according to the actual filter used. (The response of sensors, such as CCDs, now also affects the resulting observation data, as has the response of photographic film or plates.) In some cases, differences associated with observations using (slightly) differing filters can be accommodated through application of methods to calculate magnitudes of one passband from those of another; SDSS has used such conversions to enhance consistency of its data products.


(EMR,color,magnitude,photometry)
Further reading:
https://en.wikipedia.org/wiki/Passband
https://en.wikipedia.org/wiki/Photometric_system
https://en.wikipedia.org/wiki/Infrared_astronomy#Modern_infrared_astronomy
https://en.wiktionary.org/wiki/passband
https://dictionary.obspm.fr/index.php/index.php?showAll=1&formSearchTextfield=passband
https://www.oxfordreference.com/display/10.1093/oi/authority.20110803100309242
https://astronomy.swin.edu.au/cosmos/b/Bandpass
http://spiff.rit.edu/classes/phys445/lectures/colors/colors.html
https://sites.astro.caltech.edu/~george/ay122/Bessel2005ARAA43p293.pdf

Referenced by pages:
AB system
aperture photometry
Archeops
Arecibo Observatory (NAIC)
astronomical survey
Atacama Cosmology Telescope (ACT)
Australian Square Kilometre Array Pathfinder (ASKAP)
B
band shifting
bandwidth
BATC
bolometer
bolometric magnitude (Mbol)
brightness temperature (TB)
CCAT
Cherenkov Telescope Array (CTA)
color index
color temperature (TC)
Deep Lens Survey (DLS)
Deep Multicolor Survey (DMS)
DENIS
downconverter
dropout
effective temperature (Teff)
European Southern Observatory Very Large Telescope (ESO VLT)
exposure time calculator (ETC)
extended source
filter
filter bank
filter designator
full width at half maximum (FWHM)
G band (G)
galaxy SED
gas fraction estimation
Gemini Observatory
GISMO
globular cluster luminosity function (GCLF)
Gran Telescopio Canarias (GTC)
Green Bank Telescope (GBT)
griz photometric system
GUPPI
Hawaii K-band Galaxy Survey
HERMES
Hubble Ultra-Deep Field (HUDF)
I band
imaging Fourier transform spectroscopy (IFTS)
infrared (IR)
infrared excess (IRX)
IPHAS
J band
J-region asymptotic giant branch (JAGB)
JHK photometric system (JHK)
K band
K correction
Large Binocular Telescope (LBT)
Large Millimeter Telescope (LMT)
light curve
linearly variable filter (LVF)
Lowell Discovery Telescope (LDT)
luminosity (L)
luminosity function (LF)
Magellan Telescopes
magnitude
mid infrared (MIR)
Millennium Galaxy Catalogue (MGC)
Mimir
MKO photometric system
multichroic feedhorn array
NOAO Deep Wide-field Survey (NDWFS)
Ooty Radio Telescope (ORT)
PAPER
Parkes Observatory
photometric system
photometry
Plateau de Bure Interferometer (PdBI)
Psyche
PUPPI
Q band
R band
radiometer
secondary eclipse
sensitivity function (S)
SIMSTACK
Sloan Digital Sky Survey (SDSS)
spectral correlator
spectroscopy
SPHEREx
Spitzer Space Telescope (SST)
Strömgren photometric system
Subaru PFS
Subaru Telescope
Subaru XMM-Newton Deep Survey (SXDS)
survey depth
synthetic photometry
telluric star
temperature
TolTEC
Two Micron All-sky Survey (2MASS)
U
UBV photometric system
ugriz photometric system
UVJ diagram
V
Vega system
Very Long Baseline Array (VLBA)
Very Small Array (VSA)
Wesenheit function
Wide Field Infrared Explorer (WIRE)
Wide-field Infrared Survey Explorer (WISE)
WISE 1506+7027
Yohkoh

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