The Strömgren photometric system, abbreviated also as
uvbyβ or simply
uvby, and sometimes referred as Strömgren - Crawford
photometric system
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 sy ...
, is a four-colour medium-
passband
A passband is the range of frequencies or wavelengths that can pass through a filter. For example, a radio receiver contains a bandpass filter to select the frequency of the desired radio signal out of all the radio waves picked up by its antenn ...
photometric system
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 sy ...
plus Hβ (H-beta) filters for determining magnitudes and obtaining
spectral classification
In astronomy, stellar classification is the classification of stars based on their spectral characteristics. Electromagnetic radiation from the star is analyzed by splitting it with a prism or diffraction grating into a spectrum exhibiting the ...
of stars. Its use was pioneered by the Danish astronomer
Bengt Strömgren
Bengt Georg Daniel Strömgren (21 January 1908 – 4 July 1987) was a Danish astronomer and astrophysicist.
Life and career
Bengt Strömgren was born in Gothenburg. His parents were Hedvig Strömgren (née Lidforss) and Elis Strömgren, wh ...
in 1956
and was extended by his colleague the American astronomer
David L. Crawford
David Livingston Crawford (March 7, 1889 – January 18, 1974) was an American Entomology, entomologist, coach of American football, football and basketball, and college professor and administrator. He served as the head football coach at the Uni ...
in 1958.
It is often considered to be a powerful tool and successful investigating the brightness and effective temperature of stars. This photometric system also has a general advantage as it can be used to measure the effects of reddening and
interstellar extinction
In astronomy, extinction is the absorption and scattering of electromagnetic radiation by dust and gas between an emitting astronomical object and the observer. Interstellar extinction was first documented as such in 1930 by Robert Julius Trumple ...
.
This system also allows calculation of parameters from the
b and
y filters (
b −
y) without the effects of reddening, termed m
1 and c
1.
Wavelength and half-width response functions
:
Indices
There are four main highly applied and technical indices: (b−y); m
1; c
1; and β.
m
1 = (v−b) − (b−y)
c
1 = (u−v) − (v−b)
β = β
narrow−β
wide
Where;
y magnitudes are well-correlated with
Johnson-Morgan V magnitude
Apparent magnitude () is a measure of the brightness of a star or other astronomical object observed from Earth. An object's apparent magnitude depends on its intrinsic luminosity, its distance from Earth, and any extinction of the object's ...
s (its V band).
(
b−
y) is sensitive to stellar
temperature
Temperature is a physical quantity that expresses quantitatively the perceptions of hotness and coldness. Temperature is measured with a thermometer.
Thermometers are calibrated in various temperature scales that historically have relied o ...
(measure of
Paschen continuum Paschen may refer to:
* Friedrich Paschen (1865–1947), German physicist
** Paschen (crater), a lunar crater on the far side of the Moon
** Paschen-Back effect, the splitting of atomic energy levels in the presence of a strong magnetic field
** ...
).
c
1 is sensitive to the
surface gravity
The surface gravity, ''g'', of an astronomical object is the gravitational acceleration experienced at its surface at the equator, including the effects of rotation. The surface gravity may be thought of as the acceleration due to gravity experien ...
(measures
Balmer discontinuity
The Balmer jump, Balmer discontinuity, or Balmer break is the difference of intensity of the stellar continuum spectrum on either side of the limit of the Balmer series of hydrogen, at approximately 364.5 nm. It is caused by electrons being com ...
strength).
m
1 is sensitive to the
metallicity
In astronomy, metallicity is the abundance of elements present in an object that are heavier than hydrogen and helium. Most of the normal physical matter in the Universe is either hydrogen or helium, and astronomers use the word ''"metals"'' as a ...
(measure of
line blanketing The blanketing effect (also referred to as line blanketing or the line-blanketing effect) is the enhancement of the red or infrared regions of a stellar spectrum at the expense of the other regions, with an overall diminishing effect on the whole s ...
).
See also
*
Photometric system
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 sy ...
s
*
Stellar classification
In astronomy, stellar classification is the classification of stars based on their stellar spectrum, spectral characteristics. Electromagnetic radiation from the star is analyzed by splitting it with a Prism (optics), prism or diffraction grati ...
References
External links
The Asiago Database on Photometric SystemsStromgren photometric system tutorialSAGA: Strömgren survey for Asteroseismology and Galactic Archaeology
{{DEFAULTSORT:Stromgren photometric system
Photometric systems