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The nature of shock waves in non-fundamental mode RR Lyrae stars remains amystery because of limited spectroscopic observations. We apply a patternrecognition algorithm on spectroscopic data from SDSS and LAMOST and report thefirst evidence of hydrogen emission in first-overtone and multi-mode RR Lyraestars showing the "first apparition", which is the most prominent observationalcharacteristic of shock in RR Lyrae variables. We find ten RRc stars in SDSS,ten RRc stars in LAMOST, and three RRd stars in LAMOST that show blueshiftedBalmer emissions. The emission features possibly indicate the existence ofshock waves. We calculate the radial velocities of the emission lines, whichare related to the physical conditions occurring in the radiative zone of shockwaves. Using photometric observations from ZTF, we present a detailed lightcurve analysis for the frequency components in one of our RRd stars withhydrogen emission, RRdl3, for possible modulations. With the enormous volume ofupcoming spectral observations of variable stars, our study raises thepossibility of connecting the unexplained Blazhko effect to shock waves innon-fundamental mode RR Lyrae stars.

Possible evidence of hydrogen emission in the first-overtone and multi-mode RR Lyrae variables