SMALLER. An O star is bluer than the sun, so the luminosity in the B (blue) band relative to the luminosity in the V (green) band will be larger than it is in the case of the sun. A larger luminosity means a smaller (more negative) magnitude, so B will be smaller relative to V for the O star, making the color index (B-V) SMALLER.
O and B stars have surface temperatures pushing as high as 60,000 K. At such high temperatures, H and He will be fully ionized, leaving no bound electrons to jump atomic levels producing absorption lines. Those atoms that do have bound electrons have line transitions predominantly in the UV spectrum, leaving the visible spectrum rather dull.
The Hubble Space Telescope promised a clearer, deeper look into the Universe, allowing astronomers to explore nearby objects in greater detail, and to explore the far reaches of the Universe. Since the "fix", the results obtained from HST appear well worth the investment of the US taxpayers.
The primary effects of a solar flare felt here on earth (for example, the disruption in telecommunications) are due to a large flux of charged particles advected out with the solar wind. Given that it takes these particles a few days to arrive at earth, while the photons from the flare take only 8 minutes for the same journey, we can foretell the coming of the disruptive particles by watching for the photons produced in a solar flare.
It would shrink. If there were no source of energy to replace the thermal energy leaking out of the center of the sun, the interior temperature, and hence the interior pressure of the sun would drop. This would upset the hydrostatic equilibrium of the sun in the favor of gravity, which would begin to pull the sun in on itself.
Because of their very low temperature, the lowest mass stars have a peak wavelength in the infrared band of the EM spectrum, making them "invisible" to optical telescopes.
The presence of X-ray emission suggests that the emitting gas is very hot, since X-rays are high energy photons. The presence of emission lines implies that the corona is at least hotter than the photosphere of the sun. The presence of highly ionized atoms, like FeXIIV, suggests very high temperatures required to collisionally ionize the gas.
The wavelength dependence of the resolution of a telescope (lambda/Diameter) means that a telescope will have better resolving power at shorter (bluer) wavelengths. A close binary system might be resolved in blue light, but when viewed in red light the same telescope may not be able to resolve the binary into two stars.
Use the Stefan-Boltzmann law to compute the ratio of fluxes
Although it is very hot, the solar corona is very low density. The photons are NOT in local thermodynamic equilibrium with the diffuse coronal plasma.
Equate the thermal energy, kT, to the ionization potential for OIII
The observed doppler shift implies that the component of the gas velocity along
the line of sight is directed toward the observer at a velocity of