Browsing by Autor "W. Gieren"

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    Increased evidence for overtone pulsation in galactic cepheids - SU Cassiopeiae
    (Institute of Physics, 1982) W. Gieren
    The status and the pulsation mode of the classical cepheid SU Cas are discussed in light of a radius value which has been determined on the basis of a homogeneous and accurate data set and two independent methods. It is hypothesized that (1) the radius within its error limits is not compatible with currently accepted period-radius relations, assuming fundamental mode pulsations, (2) the anomalously large Wesselink radius mass can only be explained if first- or second-order pulsation is assumed, (3) the location of the star in the H-R diagram with respect to the fundamental mode blue edge indicates the likelihood of first overtone pulsation, (4) the relative radius variation and effective temperature show the star to belong to a very small group of cepheids which are probably overtone pulsators, and (5) the peculiar properties of the light curve Fourier components can probably be understood in terms of a nonfundamental mode pulsation.
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    Surface Brightness Radii and Distances of Cepheids and the Period-Radius Relationship
    (Cambridge University Press, 1985) W. Gieren
    Recently Gieren (1984) has derived accurate radii and distances of a sample of short-period classical Cepheids using the surface brightness (SB) method introduced by Barnes & Evans (1976). The results indicated that the period-radius (P-R) relationship obtained from SB radii might possess a slope close to the value of 0.82 defined by the Cepheids in clusters and associations (Fernie, 1983) and in conflict with the values obtained from Baade-Wesselink radii and from theoretical models (see Fernie, 1983). Since this finding would lend considerable support to the presently accepted absolute magnitudes of the cluster Cepheids, it was decided to obtain SB radii and distances of well-observed long-period Cepheids in order to strengthen the P-R relationship obtained from the SB technique.