Vilnius photometric system is a medium-band seven-colour
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 ...
(UPXYZVS), created in 1963 by
Vytautas Straižys and his coworkers. This system was highly optimized for
classification of stars from ground-based observations. The system was chosen to be medium-band, to ensure the possibility to measure faint stars.
Selection of bandpasses
The
temperature classification of early-type stars is based on
Balmer jump
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 co ...
(Balmer discontinuity). To measure it one must have two
bandpass
A band-pass filter or bandpass filter (BPF) is a device that passes frequencies within a certain range and rejects (attenuates) frequencies outside that range.
Description
In electronics and signal processing, a filter is usually a two-po ...
es placed in the
ultraviolet
Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nm (with a corresponding frequency around 30 PHz) to 400 nm (750 THz), shorter than that of visible light, but longer than X-rays. UV radiation ...
, one beyond the Balmer jump (U magnitude) and another after the jump (X magnitude).
The Y bandpass is near the breakpoint of the
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 Trump ...
law (interstellar extinction in the 300–800
nm region can be approximated by two
straight lines, which intersect at ~435.5 nm).
The P magnitude is placed exactly on the Balmer jump in order to provide separation for
luminosity class
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 ...
es of
B-
A-
F stars
F, or f, is the sixth letter in the Latin alphabet, used in the modern English alphabet, the alphabets of other western European languages and others worldwide. Its name in English is ''ef'' (pronounced ), and the plural is ''efs''.
Hist ...
.
The Z magnitude is placed on the
Mg I
triplet and the MgH
molecular band. It is sensitive to the
luminosity class
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 ...
es of
G-
K-
M stars.
The S bandpass coincides with
H-alpha
H-alpha (Hα) is a specific deep-red visible spectral line
A spectral line is a dark or bright line in an otherwise uniform and continuous spectrum, resulting from emission or absorption of light in a narrow frequency range, compared wit ...
line position and provides information about emission or absorption phenomena in that line.
Finally, the V magnitude is chosen to coincide with a similar bandpass in the
UBV system
The UBV photometric system (from ''Ultraviolet, Blue, Visual''), also called the Johnson system (or Johnson-Morgan system), is a photometric system usually employed for classifying stars according to their colors.
It was the first standardized p ...
. It provides the possibility to relate these two photometric systems.
Normalization
Colour indices of the system were normalized to satisfy the condition:
for un-reddened
O-type stars
An O-type star is a hot, blue-white star of spectral type O in the Yerkes classification system employed by astronomers. They have temperatures in excess of 30,000 kelvin (K). Stars of this type have strong absorption lines of ionised helium, s ...
.
Mean wavelength and half-widths of response functions
The following table shows the characteristics of each of the filters used (represented colors are only approximate):
See also
UBV photometric system
The UBV photometric system (from ''Ultraviolet, Blue, Visual''), also called the Johnson system (or Johnson-Morgan system), is a photometric system usually employed for classifying stars according to their colors.
It was the first standardized ...
Sources
*
Straizys V., ''Multicolor Stellar Photometry'', Pachart Pub. House, 1992, 570 pages.
Photometric systems
Lithuanian inventions
Science and technology in the Soviet Union
Soviet inventions
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