|Posted: 2012-March-13 at 11:17pm | IP Logged
The Sun does produce gamma rays, especially from solar flares. Even on the bigger stars the gamma and X-rays aren't much of a threat to atmospheres. The biggest problem there is solar wind, and a magnetic field blocks that.
Where flares become a problem is on the red dwarfs. Their flares can be as big as Sol's, and on such a small star, can easily be several times as bright as the normal stellar luminosity. With any habitable planets huddled close to the star, the radiation may be a threat to life, and the extra heating and CME's will erode the atmosphere. Even there, though, some scientists believe that quieter red dwarfs won't destroy a planet's atmosphere if it has a magnetic field, and a dense atmosphere will block the radiation, so life may still be possible. If so, the flares may actually be a benefit to the plants. Shorter wavelengths are more energetic, which makes photosynthesis easier, and the plants may evolve to use infrared and red for survival, and the yellows and blues for extra energy when available.
Some stars do produce "super flares", which can strip a planet's atmosphere. Some of them are powerful enough to remove Earth's atmosphere completely, and to melt ice on Jupiter's moons. If the Sun had ever had one we'd know it, even if it missed Earth, unless it missed all of the other planets as well. Venus or Mars wouldn't have air and Mercury and the outer icy moons would show clear signs of melting. However, such flares seem to be the result of a close orbiting Jovian tangling the star's magnetic field, so a system like ours wouldn't have them.
With technology being overcautious is better than being unprepared!