Vilnius photometric system


The Vilnius photometric system is a medium-band seven-colour photometric system, 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. To measure it one must have two bandpasses placed in the ultraviolet, one beyond the Balmer jump and another after the jump. The Y bandpass is near the breakpoint of the interstellar extinction law. The P magnitude is placed exactly on the Balmer jump in order to provide separation for luminosity classes of B-A-F stars.
The Z magnitude is placed on the Mg I triplet and the MgH molecular band. It is sensitive to the luminosity classes of G-K-M stars. Finally, the V magnitude is chosen to coincide with a similar bandpass in the UBV system. It provides the possibility to relate these two photometric systems. S bandpass coincides with H alpha line position and provides information about emission or absorption phenomena in that line.

Normalization

of the system were normalized to satisfy the condition:
U-P = P-X = X-Y = Y-Z = Z-V = V-S = 0
for unreddened O-type stars.

Mean wavelength and half-widths of response functions