The Monoperiodic Scuti Star UY Camelopardalis: An Analog to SX Phoenicis and RR Lyrae Variables

We present the results of a four-year photometric study of the high-amplitude$\delta$ Scuti star (HADS) UY Camelopardalis. Analyses on the available datafrom 1985 to 2003 show that UY Cam is monoperiodic. Fourier solutions forindividual data sets do not reveal period changes in the star. Although forcedparabolic fits to the $O-C$ residuals indicate measurable period change, thedistribution of the data points in $O-C$ diagram and the deviations betweenfits and observations suggest the period change is still not established. Weevidence the presence of cycle-to-cycle and longer time-scale amplitudevariations. The pulsation amplitude seemed to change from 1985 to 2000s, but itkept constant in 2000--2003. UY Cam locates in the upper portion of theinstability region of $\delta$ Sct variables. Photometric properties andestimated physical parameters reveal that UY Cam is an interesting objectconcerning its poorer metallicity, longer period, higher luminosity, lowersurface gravity and larger radius among the HADS. UY Cam could be a younger(age=0.7$\pm$0.1 Gyr) Population I HADS with poor metal abundances (Z=0.004)evolving on its post main sequence shell hydrogen-burning evolutionary phase.UY Cam intervenes among the Pop. I/II HADS and RRc Lyr variables. Thesecharacteristics suggest the star to be an analogue of HADS, SX Phe and RRcLyr-type variables.Comment: 16 pages, 6 figures, 8 tables, accepted for publication in AJ (Nov. 2003