Entry content

Creation date: ,   Archive date:

Discovery of a new group of double-periodic RR Lyrae stars

In a paper Discovery of a new group of double-periodic RR Lyrae stars in the OGLE-IV photometry (accepted for publication in MNRAS Letters), Henryka Netzel (student at Wroclaw University), Radoslaw Smolec and Wojciech Dziembowski (CAMK) report the discovery of a new group of very interesting RR Lyrae stars. 11 stars were detected in the OGLE photometry of the Galactic bulge, one additional star was identified in the Kepler space telescope photometry. In all these stars pulsation in the radial first overtone mode dominates. In addition, variability with a longer period was detected, the period ratios tightly cluster around 0.686. In the Petersen diagram plotted above, i.e. in a diagram of period ratio (shorter to longer) versus the logarithm of the longer period, these stars are plotted with red symbols. In the diagram other known groupsof double-periodic RR Lyrae stars are also plotted, in particular RRd stars, that pulsate simultaneously in the radial fundamental and radial first overtone modes (small blue symbols). Comparison of the new group with RRd stars indicates, that period of the additional mode must be longer than period of the radial fundamental mode. Thus, additional mode must be nonradial and of gravity or of mixed character.

Many other stars plotted in the diagram were discovered or analysed in detail by the team led by CAMK scientists, including majority of the 0.61 double-periodic stars  (magenta symbols: Double-mode radial-non-radial RR Lyrae stars in the OGLE photometry of the Galactic bulge, Netzel, Smolec and Moskalik (2015), Kepler photometry of RRc stars: peculiar double-mode pulsations and period doubling, Moskalik et al. (2015) and encircled are modulated (Blazhko) RRd stars Blazhko-type modulation in the double-mode RR Lyrae stars of the OGLE Galactic bulge collection, Smolec et al., 2015).