Hr 7308: A unique Cepheid

Abstract

We have obtained photometric observations and radial velocities of the F6I-IIb star HR 7308. The spectral type, the period ($\underset{\raise0.3em\hbox{$\smash{\scriptscriptstyle\cdot}$}}{d}$), the relative range and phase of light, colour and velocity variations all suggest that the star is a small-amplitude Cepheid. The metal abundance appears to be normal. However, the light amplitude decreased slowly during 1978 from 0$\underset{\raise0.3em\hbox{$\smash{\scriptscriptstyle\cdot}$}}{m}$3 to 0$\underset{\raise0.3em\hbox{$\smash{\scriptscriptstyle\cdot}$}}{m}$1, and increased during 1979 and 1980 from 0$\underset{\raise0.3em\hbox{$\smash{\scriptscriptstyle\cdot}$}}{m}$05 to 0$\underset{\raise0.3em\hbox{$\smash{\scriptscriptstyle\cdot}$}}{m}$15. Such behaviour is unprecedented in a population I Cepheid.