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Photometric and Spectroscopic Study of Flares on Ross 15

We conducted photometric and spectroscopic observations for Ross 15 in order to further study the flare properties of this less observed flare star. A total of 28 B-band flares are detected in 128 hours of photometric observations, leading to a total flare rate of 0.22(+-0.04) hour^-1, more accurate than that provided by previous work. We give the energy range of the B-band flare (10^29.5 - 10^31.5 erg) and the FFD for the star. Within the same energy range, the FFD are lower than that of GJ 1243 (M4) and YZ CMi (M4.5), roughly in the middle of those of three M5-type stars and higher than the average FFDs of spectral types >= M6. We performed, for the first time to Ross 15, simultaneous high-cadence spectroscopic and photometric observations, resulting in detection of the most energetic flare in our sample. The intensity enhancements of the continuum and Balmer lines with significant correlations between them are detected during the flare, which is same with that of the other deeply studied flare stars of the similar spectral type.