 | This articledoes notcite anysources. Please helpimprove this article byadding citations to reliable sources. Unsourced material may be challenged andremoved. Find sources: "Vilnius photometric system" – news ·newspapers ·books ·scholar ·JSTOR(August 2021) (Learn how and when to remove this message) |
 | This article includes a list ofgeneral references, butit lacks sufficient correspondinginline citations. Please help toimprove this article byintroducing more precise citations.(August 2021) (Learn how and when to remove this message) |
Vilnius photometric system is a medium-band seven-colourphotometric system (UPXYZVS), created in 1963 byVytautas Straižys and his coworkers. This system was highly optimized forclassification of stars from ground-based observations. The system was chosen to be medium-band, to ensure the possibility to measure faint stars.
Thetemperature classification of early-type stars is based onBalmer jump (Balmer discontinuity). To measure it one must have twobandpasses placed in theultraviolet, one beyond the Balmer jump (U magnitude) and another after the jump (X magnitude).
The Y bandpass is near the breakpoint of theinterstellar extinction law (interstellar extinction in the 300–800 nm region can be approximated by twostraight lines, which intersect at ~435.5 nm).
The P magnitude is placed exactly on the Balmer jump in order to provide separation forluminosity classes ofB-A-F stars.
The Z magnitude is placed on theMg Itriplet and the MgHmolecular band. It is sensitive to theluminosity classes ofG-K-M stars.
The S bandpass coincides withH-alpha 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 theUBV system. It provides the possibility to relate these two photometric systems.
Colour indices of the system were normalized to satisfy the condition:
for un-reddenedO-type stars.
The following table shows the characteristics of each of the filters used (represented colors are only approximate):
| U | P | X | Y | Z | V | S | |
|---|---|---|---|---|---|---|---|
| Mean wavelength (nm) | 345 | 374 | 405 | 466 | 516 | 544 | 656 |
| Half-width (nm) | 40 | 26 | 22 | 26 | 21 | 26 | 20 |
