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Stellar flares sometimes show red/blue asymmetries of H$\alpha$ line, whichcan indicate chromospheric dynamics and prominence activations. However, theorigin of asymmetries is not completely understood. For a deeper understandingof stellar data, we performed a Sun-as-a-star analysis of H$\alpha$ lineprofiles of an M4.2-class solar flare showing dominant emissions from flareribbons by using the data of the Solar Dynamics Doppler Imager onboard theSolar Magnetic Activity Research Telescope at Hida Observatory. TheSun-as-a-star H$\alpha$ spectra of the flare show red asymmetry of up to$\sim$95 km s$^{-1}$ and line broadening of up to $\sim$7.5 {\AA}. TheSun-as-a-star H$\alpha$ profiles are consistent with spectra from flare regionswith weak intensity, but they take smaller redshift velocities and line widthsby a factor of $\sim$2 than those with strong intensity. The redshiftvelocities, as well as line widths, peak out and decay more rapidly than theH$\alpha$ equivalent widths, which is consistent with chromosphericcondensation model and spatially-resolved flare spectra. This suggests that asa result of superposition, the nature of chromospheric condensation isobservable even from stellar flare spectra. The time evolution of redshiftvelocities is found to be similar to that of luminosities of near-ultravioletrays (1600 {\AA}), while the time evolution of line broadening is similar tothat of optical white lights. These H$\alpha$ spectral behaviors inSun-as-a-star view could be helpful to distinguish whether the origin ofH$\alpha$ red asymmetry of stellar flares is a flare ribbon or other phenomena.

Sun-as-a-star Analysis of H$\alpha$ Spectra of a Solar Flare Observed by SMART/SDDI: Time Evolution of Red Asymmetry and Line Broadening