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Intrinsically luminous stars that are the best targets for BRITE Constellation fall into two groups:
1. Hot luminous stars: O and B stars which make up about half of the stars brighter than V <= 4.0 mag (see figure below). A study of the variability in O and B stars has the potential to lead to the solution of two of the outstanding problems of stellar structure and evolution: the size of convective cores in massive stars and the influence of rotation.
The figure above is an all-sky map of brightest stars V<= 4mag). The spectral type is color-coded. The luminosity class is indicated with symbols.
2. Cool luminous stars: Giants, Asymptotic Giant Branch (AGB) Stars, Red Giants and Red Supergiants. High precision, long-time monitoring of these stars will help to measure the typical time scales involved in surface fluctuations and thus to constrain convection models in AGB stars and red supergiants.
There are 534 stars brighter than V <= 4.0 mag in the sky and observable at the mmag level with BRITE Constellation. Considering the typical time scales for their variability ranging from a few hours to several days or even weeks and aiming for a frequency resolution sufficient for asteroseismology, these stars need to be continuously observed for at least three months and at least at two different epochs. BRITE Constellation expects to observe simultaneously ~2 to 16 bright targets in the 24-degree field of view.
The figure above shows the 534 stars brighter than V <= 4 mag in the Hertzsprung-Russell Diagram colour-coded with the object types taken from the VISAT database. Apart from the main targets for BRITE-Constellation, numerous other stars observable with the miniature BRITE space telescopes are of scientific interest.
The target stars for BRITE Constellation cannot be observed photometrically from the ground with the precision required: atmospheric scintillation, weather, day-night cycle of the Earth all perturb such observations. Furthermore, the necessary differential high -precision photometry of at least two similarly bright stars is very difficult to achieve from the ground, since atmospheric conditions are normally not sufficiently homogenous across the usually large angular distances between such bright objects in the sky.
The BRITE nano-satellites will be launched into a Low Earth Orbit (LEO) from India (see Orbit and Launcher) to achieve the scientific goals of the mission.
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