Study of Neglected Variable Stars Classified as Type II Cepheids Four variable stars classified as Type II Cepheids have been studiedpartly based on new photometry and the Hipparcos photometric data. Thecorrect period is derived for V341 Ara and NW Pav and it is pointed outthat RR Mic and V1711 Sgr do not belong to Type II Cepheids, insteadthey may be semi-regular variables. The cycle length of theirvariability is also determined.
Secondary UVBY standards in the Harvard E-regions Photoelectric uvby photometry for 201 stars which are already UBV (RI)cstandards is presented. The photoelectric data are closely tied to theCousins uvby standards and the stars should be suitable for use asfainter (7-11 mag) secondary standards.
UBV photometry of E region standard stars of intermediate brightness Photometry data are given for 335 stars in the nine E regions.Observations were made using a photometer and filters on the 47 cmreflector at Cape Town. The stellar dispersions are summarized. Data arepresented in tabular form.
Atmospheric extinction in the /U-B/ color index Various methods for obtaining the atmospheric extinction in the (U-B)color index taking into account the dependence of extinction coefficienton the intrinsic color index of the star are examined. Numericalintegrations are performed to determine synthetic color indices for 32stars of spectral classes O9 to M0 and luminosity classes I, III and Vthrough 0, 1 and 2 air masses, resulting in three (u-b) color indicesfor each star. Photometric reduction of the color indices to the (U-B)color index was then performed by the classical method, by the methodproposed by Gutierrez-Moreno et al. (1966) and various modifications ofit, and by the method proposed by Moffat and Vogt (1977). Comparisonwith observations of 71 stars in the standard region E5, nine extinctionstandard stars and 25 Johnson standard stars in the UBV reveals that thereduction of (U-B) by the classical method gives internal errors betweentwo and three times larger than those obtained for (B-V) and V, whilethe methods of Gutierrez-Moreno et al. and Moffat and Vogt providegreatly improved accuracy.
