CW W Virginis6 stars

- These are pulsating variables of the galactic spherical component (old disk) population with periods of approximately ft'8 to 35d and amplitudes of 0".'3 to l".'2 in V. They obey a period-luminosity relation different from that for S Cep variables (DCEP). For an equal period value, the W Vir variables are fainter than the S Cep stars by 0"!7-2"'. The light curves of W Vir variables for some period intervals differ from those of S Cep variables for corresponding periods either by amplitudes or by the presence of humps on their

Observation Key

Bright stars Jo/H Mixed ampli tudes

'Virgo, the Virgin. In the earliest records, she appears as a mother goddess, sometimes a wife to a creator or major god.

descending branches, sometimes turning in broad flat maxima. W Vir variables are present in globular clusters and at high galactic latitudes. They may be separated into the following subtypes: CWA (subtype) - IV Vir variables with periods longer than 8 days. CWB (subtype) - W Vir variables with periods shorter than 8 days. GCVS

These pulsating stars are sometimes called Type II Cepheids. Care must be taken to differentiate these Cepheids from the S Cep variables. The key is their periods of approximately 0^8 to 35i*0 and amplitudes from 0".'3 to 1™2 in V. Comparison of their light curves with S Cep variables is interesting and with a little care taken during analysis, the difference can be detected.

When analysing light curves of W Vir variables, also look for the presence of humps on their descending branches, sometimes turning into broad, flat maxima. Since W Vir variables are present within globular clusters and at high galactic latitudes, you may be able to use this information to help further discriminate, or possibly, support your suspicion regarding these variables.

Observation Key

Bright stars sS* Mixed amplitudes

Mixed periods <S> CCD or PEP

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