Humps and bumps: the effects of shocks on the optical light curves of fundamental-mode RR Lyrae stars

Abstract

We present the most extended and homogeneous study carried out so far of the main and early shocks in 1485 RR Lyrae stars in the Galactic bulge observed by the Optical Gravitational Lensing Experiment (OGLE). We selected non-modulated fundamental-mode RR Lyrae stars with good-quality photometry. Using a self-developed method, we determined the centers and strengths of main and early shock features in the phased light curves. We found that the position of both humps and bumps are highly correlated with the pulsation properties of the studied variables. Pulsators with a pronounced main shock are concentrated in the low-amplitude regime of the period-amplitude diagram, while stars with a strong early shock have average and above-average pulsation amplitudes. A connection between the main and early shocks and the Fourier coefficients is also observed. In the color-magnitude diagram (CMD), we see a separation between stars with strong and weak shocks. Variables with a pronounced main shock cluster close to the fundamental red edge of the instability strip (IS), while stars with a strong early shock tend to clump in the center and near the fundamental blue edge of the IS. The appearance of shocks and their properties seem independent of the direction of evolution estimated from the period change rate of the studied stars. In addition, the differences in the period change rate between the two main Oosterhoff groups found in the Galactic bulge suggest that stars of Oosterhoff type I are located close to the zero-age horizontal branch while Oosterhoff type II variables are on their way toward the fundamental red edge of the instability strip, thus having already left the zero-age horizontal branch.

Asteroseismology of RRab variable star EZ Cnc from K2 photometry and LAMOST spectroscopy

“…Then the light curves of the EPIC 212182292 folded through the is shown in the top panel of Figure 1 where the morphology of the light curve confirms no Blazhko modulation happened. We note the features of the RRab light curves (Prudil et al 2020), which are a significant bump at = 0.50 and a slight hump at = 0.95. Note that the zero phases ( = 0) is defined at the moment when the light curve maximum bright for the first time.…”

Hydrogen and Helium Shock Phenomena during Rising Light in RR Lyrae Fundamental Mode Pulsators

“…They identified new light curve properties 1 induced by five shock waves, with different amplitudes and origins. Recently Prudil et al (2020) have used broad band photometry to identify (hump) shock phenomena in a large sample of field RRab. Metallic-line absorption phenomena, particularly shock-induced increases in macroturbulence during rising in stable RRab, were reviewed by Preston (2009), and studied in great detail more recently by Preston et al (2019).…”