Carbon and nitrogen abundances in the carbon-rich Cepheid V553 Centauri.

A spectroscopic and photometric analysis of the carbon-rich Cepheid V553 Centauri has been undertaken, and the following results were obtained: [Fe/H] = 0.1, [C/Fe] = +0.8 and [N/Fe] = +0.5; all values relative to the Sun. This research also considered the nuclear processes and evolutionary status of a variable star having the above abundances. The near-solar composition means that V553 Cen must have an extremely small envelope to be evolving in the instability strip with its derived luminosity, log L/L_sun of ∼2. A possible interpretation of V553 Cen is as the progeny of the strong-lined RR Lyrae stars, where this object has evolved to a position above the horizontal branch and is currently either a supra-horizontal branch star of a loop Cepheid.