A Photometric Study of XX Virginis and V716 Ophiuchi
Abstract
We present Stromgren photometry of the two Population II variables XX Vir and V716 Oph. Our analysis of the photometry yields the following physical parameters of the variables: for XX Vir < Teff >= 6410 K, [Fe/H]=2.0, and <log g>=1.95 for V716 Oph <Teff>=6450 K, [Fe/H]=2.1, and <log g>=1.67. The <log g> values of these two metal-poor variables are considerably smaller than the metal-strong variable BL Herculis (<log g>=2.37). The big surprise in this investigation is that the surface gravity of V716 Oph (P=1.12), the shorter-period variable, is smaller than the surface gravity of XX Vir (P=1.35), the longer period variable. With the aid of P square root of rho = Q relation we derive a semi-theoretical P-L relation for the Type II Cepheids of the form M_V=-1.88 log P+0.13. This expression is in rough agreement (within the uncertainties of many quantities used in deriving the expression) with the observational data. The relatively gentle slope of the P-L relation (compared with the slope of the P-L relations of other pulsating stars) is probably a consequence of the fact that the masses of the Type II Cepheids are constant or nearly constant, independent of period, and a large variations of the M/R values with period. (SECTION: Stars)
- Publication:
-
Publications of the Astronomical Society of the Pacific
- Pub Date:
- May 1994
- DOI:
- 10.1086/133402
- Bibcode:
- 1994PASP..106..472M
- Keywords:
-
- Hydrogen;
- Iron;
- Metallicity;
- Stellar Gravitation;
- Stellar Magnitude;
- Stellar Temperature;
- Variable Stars;
- Astronomical Photometry;
- Periodic Variations;
- Stellar Color;
- Stellar Luminosity;
- Temperature Distribution;
- Ubv Spectra;
- Astronomy;
- STARS: INDIVIDUAL: XX VIRGINIS;
- STARS: INDIVIDUAL: V716 OPHIUCHI;
- CEPHEIDS;
- STARS: POPULATION II