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The Chemical Compositions of the Type II Cepheids-The BL Herculis and W Virginis Variables
Abundance analyses from high-resolution optical spectra are presentedfor 19 type II Cepheids in the Galactic field. The sample includes bothshort-period (BL Her) and long-period (W Vir) stars. This is the firstextensive abundance analysis of these variables. The C, N, and Oabundances with similar spreads for the BL Her and W Vir show evidencefor an atmosphere contaminated with 3α process and CN-cyclingproducts. A notable anomaly of the BL Her stars is an overabundance ofNa by a factor of about 5 relative to their presumed initial abundances.This overabundance is not seen in the W Vir stars. The abundanceanomalies running from mild to extreme in W Vir stars but not seen inthe BL Her stars are attributed to dust-gas separation that provides anatmosphere deficient in elements of high condensation temperature,notably, Al, Ca, Sc, Ti, and s-process elements. Such anomalies havepreviously been seen among RV Tau stars which represent a long-periodextension of the variability enjoyed by the type II Cepheids. Commentsare offered on how the contrasting abundance anomalies of BL Her and WVir stars may be explained in terms of the stars' evolution from theblue horizontal branch.
| Fourier Analysis of Hipparcos Photometry of Cepheid Variables
Fourier parameters have been computed for 240 field Cepheids observed bythe Hipparcos satellite. We have identified three new PopulationIovertone Cepheids: V411Lac, V898 Cen and V572 Aql. We have comparedFourier progressions of Population I and Population II Cepheids. Thepossibility of using Fourier parameters to distinguish between the twotypes is discussed.
| Stroemgren photometry of F- and G-type stars brighter than V = 9.6. I. UVBY photometry
Within the framework of a large photometric observing program, designedto investigate the Galaxy's structure and evolution, Hβ photometryis being made for about 9000 stars. As a by-product, supplementary uvbyphotometry has been made. The results are presented in a cataloguecontaining 6924 uvby observations of 6190 stars, all south ofδ=+38deg. The overall internal rms errors of one observation(transformed to the standard system) of a program star in the interval6.5
| The 71st Name-List of Variable Stars
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| BV 690, a new bright type II Cepheid
B and V observations of the suspected variable BV 690 = NSV 04298 arereported. The star shows light variations with a period of 1.2400 d andwith amplitudes of 0.27, 0.36, and 0.11 m in V, B, and B-V respectively.The light curves show steeper rise than decline, and there is evidencefor the presence of a bump in the descending branch around the phase of0.35. From considerations of the period, spectral type, presence of thebump, and high tangential velocity is concluded that BV 690 belongs tothe BL Herculis class of type II Cepheids.
| Estimation of spectral classifications for bright southern stars with interesting Stromgren indices
This paper investigates the degree of success with which uvby photometrycan be applied to predict spectral classifications for 947 A, F, and Gstars brighter than an apparent magnitude of 8.3 and with four-colorindices indicating some kind of interesting, unusual, or peculiarspectrum. One or several possible spectral classifications are estimatedfor each star from photometry alone, double stars are distinguished, andthe estimates are compared with published classifications. The resultsshow that the framework provided by uvby photometry can be extended toinclude most G and K stars, reddened stars, peculiar stars, and certaintypes of double star.
| Bright Southern BV-Stars
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