Photometric system

For other uses, see Photometry (disambiguation).

In astronomy, a photometric system is a set of well-defined passbands (or optical filters), with a known sensitivity to incident radiation. The sensitivity usually depends on the optical system, detectors and filters used. For each photometric system a set of primary standard stars is provided.

A commonly adopted standardized photometric system is the Johnson-Morgan or UBV photometric system (1953). At present, there are more than 200 photometric systems.^[1]

Photometric systems are usually characterized according to the widths of their passbands:

• broadband (passbands wider than 30 nm, of which the most widely used is Johnson-Morgan UBV system)
• intermediate band (passbands between 10 and 30 nm wide)
• narrow band (passbands less than 10 nm wide)

Photometric letters

Each letter designates a section of light of the electromagnetic spectrum; these cover well the consecutive major groups, near-ultraviolet (NUV), visible light (centered on the V band), near-infrared (NIR) and part of mid-infrared (MIR).^[a] The letters are not standards, but are recognized by common agreement among astronomers and astrophysicists.

The use of U,B,V,R,I bands dates from the 1950s, being single-letter abbreviations.^[b]

With the advent of infrared detectors in the next decade, the J to N bands were labelled following on from near-infrared's closest-to-red band, I.

Later the H band was inserted, then Z in the 1990s and finally Y, without changing earlier definitions. Hence, H is out of alphabetical order from its neighbours, while Z,Y are reversed from the alphabetical – higher-wavelength – sub-series which dominates current photometric bands.

Filter Letter	Effective Wavelength Midpoint λeff for Standard Filter[3]	Full width at half maximum[3] [c] (archetypal Bandwidth) (Δλ)[d]	Variant(s)	Description
Ultraviolet
U	365 nm	66 nm	u, u', u*	"U" stands for ultraviolet.
Visible
B	445 nm	94 nm	b	"B" stands for blue.
G[4]	464 nm	128 nm	g, g'	"G" stands for green.
V	551 nm	88 nm	v, v'	"V" stands for visual.
R	658 nm	138 nm	r, r', R', Rc, Re, Rj	"R" stands for red.
Near-Infrared
I	806 nm	149 nm	i, i', Ic, Ie, Ij	"I" stands for infrared.
z-s'	893.2 nm	100 nm	z-s'
Z	900 nm[5]	152 nm	z, z'
Y	1020 nm	120 nm	y
J	1220 nm	213 nm	J', Js
H	1630 nm	307 nm
K	2190 nm	390 nm	K Continuum, K', Ks, Klong, K8, nbK
L	3450 nm	472 nm	L', nbL'
Mid-Infrared
M	4750 nm	460 nm	M', nbM
N	10500 nm	2500 nm
Q	21000 nm[6]	5800 nm[6]	Q'

Note: colors are only approximate and based on wavelength to sRGB representation (when possible).^[7]

Combinations of these letters are frequently used; for example the combination JHK has been used more or less as a synonym of "near-infrared", and appears in the title of many papers.^[8]

Filters used

The filters currently being used by other telescopes or organizations.

Units of measurements:

• Å = Ångström
• nm = nanometre
• μm = micrometre

Name	Filters									Link
2.2 m telescope at La Silla, ESO	J = 1.24 μm	H = 1.63 μm	K = 2.19 μm	L' = 3.78 μm	M = 4.66 μm	N1 = 8.36 μm	N2 = 9.67 μm	N3 = 12.89 μm		2.2 m telescope at La Silla, ESO[9]
2MASS/PAIRITEL	J = 1.25 μm	H = 1.65 μm	Ks = 2.15 μm							Two Micron All-Sky Survey, Peters Automated InfraRed Imaging TELescope
CFHTLS (Megacam)	u* = 374 nm	g' = 487 nm	r' = 625 nm	i' = 770 nm	z' = 890 nm					Canada-France-Hawaii Telescope
Chandra X-ray Observatory	LETG = 0.08-0.2 keV	HETG = 0.4-10 keV								Chandra X-ray Observatory
CTIO	J = 1.20 μm	H = 1.60 μm	K = 2.20 μm	L = 3.50 μm						Cerro Tololo Inter-American Observatory, a division of NOAO
Cousins RI photometry	Rc = 647 nm	Ic = 786.5 nm								Cousins RI photometry, 1976[10]
the Dark Energy Camera	g = 472.0 nm	r = 641.5 nm	i = 783.5 nm	z = 926.0 nm	Y = 1009.5 nm					Central wavelengths for bands in the Dark Energy Survey[11]
DENIS	I = 0.79 μm	J = 1.24 μm	K = 2.16 μm							Deep Near Infrared Survey
Eggen RI photometry	Re = 635 nm	Ie = 790 nm								Eggen RI photometry, 1965[12]
FIS	N60 = 65.00 μm	WIDE-S = 90.00 μm	WIDE-L = 145.00 μm	N160 = 160.00 μm						Far-Infrared Surveyor on board, AKARI space telescope
Gaia	G = 673 nm	GBP = 532 nm	GRP = 797 nm	GRVS = 860 nm						Gaia (spacecraft)[13]
GALEX[14]	NUV = 175–280 nm	FUV = 135–175 nm								GALaxy Evolution Explorer
GOODS (Hubble ACS)	B = 435 nm	V = 606 nm	i = 775 nm	z = 850 nm						Advanced Camera for Surveys on the Hubble Space Telescope
HAWC+	Band 1 = 53 μm	Band 2 = 89 μm	Band 3 = 154 μm	Band 4 = 214 μm						High-resolution Airborne Wideband Camera+ for SOFIA[15]
HDF	450 nm	606 nm	814 nm							Hubble Deep Field from the Hubble Space Telescope
IRTF NSFCAM	J = 1.26 μm	H = 1.62 μm	K' = 2.12 μm	Ks = 2.15 μm	K = 2.21 μm	L = 3.50 μm	L' = 3.78 μm	M' = 4.78 μm	M = 4.85 μm	NASA Infrared Telescope Facility NSFCAM[16]
ISAAC UTI/VLT[17]	Js = 1.2 μm	H = 1.6 μm	Ks = 2.2 μm	L = 3.78 μm	Brα = 4.07 μm					Infrared Spectrometer And Array Camera at Very Large Telescope
Johnson system (UBV)	U = 364 nm	B = 442 nm	V = 540 nm							UBV photometric system
Vera C. Rubin Observatory (LSST)[18]	u = 320.5–393.5 nm	g = 401.5–551.9 nm	r = 552.0–691.0 nm	i = 691.0–818.0 nm	z = 818.0–923.5 nm	y = 923.8–1084.5 nm				Vera C. Rubin Observatory
OMC	Johnson V-filter = 500-580 nm									Optical Monitor Camera[19] on INTEGRAL
Pan-STARRS	g = 481 nm	r = 617 nm	i = 752 nm	z = 866 nm	y = 962 nm					Panoramic Survey Telescope And Rapid Response System[20]
ProNaOS/SPM	Band 1 = 180-240 μm	Band 2 = 240-340 μm	Band 3 = 340-540 μm	Band 4 = 540-1200 μm						PROgramme NAtional d'Observations Submillerètrique/Systéme Photométrique Multibande, balloon-borne experiment[21]
Sloan, SDSS	u' = 354 nm	g' = 475 nm	r' = 622 nm	i' = 763 nm	z' = 905 nm					Sloan Digital Sky Survey
SPIRIT III	Band B1 = 4.29 μm	Band B2 = 4.35 μm	Band A = 8.28 μm	Band C = 12.13 μm	Band D = 14.65 μm	Band E = 21.34 μm				Infrared camera on Midcourse Space Experiment[22]
Spitzer IRAC	ch1 = 3.6 μm	ch2 = 4.5 μm	ch3 = 5.8 μm	ch4 = 8.0 μm						Infrared Array Camera on Spitzer Space Telescope
Spitzer MIPS	24 μm	70 μm	160 μm							Multiband Imaging Photometer for Spitzer on Spitzer
Stromvil filters	U = 345 nm	P = 374 nm	S = 405 nm	Y = 466 nm	Z = 516 nm	V = 544 nm	S = 656 nm			Stromvil photometry
Strömgren filters	u = 350 nm	v = 411 nm	b = 467 nm	y = 547 nm	β narrow = 485.8 nm	β wide = 485 nm				Strömgren photometric system
UKIDSS (WFCAM)	Z = 882 nm	Y = 1031 nm	J = 1248 nm	H = 1631 nm	K = 2201 nm					UKIRT Infrared Deep Sky Survey
Vilnius photometric system	U = 345 nm	P = 374 nm	S = 405 nm	Y = 466 nm	Z = 516 nm	V = 544 nm	S = 656 nm			Vilnius photometric system
VISTA IRC	Z = 0.88 μm	Y = 1.02 μm	J = 1.25 μm	H = 1.65 μm	Ks = 2.20 μm	NB1.18 = 1.18 μm				Visible & Infrared Survey Telescope for Astronomy
WISE	W1 = 3.4 μm	W2 = 4.6 μm	W3 = 12 μm	W4 = 22 μm						Wide-field Infrared Survey Explorer
XMM-Newton OM	UVW2 = 212 nm	UVM2 = 231 nm	UVW1 = 291 nm	U = 344 nm	B = 450 nm	V = 543 nm				XMM-Newton Optical/UV Monitor[23]
XEST Survey	UVW2 = 212 nm	UVM2 = 231 nm	UVW1 = 291 nm	U = 344 nm	B = 450 nm	V = 543 nm	J = 1.25 μm	H = 1.65 μm	Ks = 2.15 μm	Survey includes the point source of 2MASS with XMM-Newton OM[24]

Note: colors are only approximate and based on wavelength to sRGB representation (when possible).^[25]

See also

• Photometry
• AB magnitude