====== Challenge 4: Build test data with realistic HR diagram ====== 

===== Objectives =====

  * GSP-Phot draws its training data from a synthetic HR diagram. This synthetic HR diagram currently lacks giants. In particular, it lacks significant numbers of red-clump stars, BHB stars, RR Lyraes and other important stars. Consequently, GSP-Phot cannot perform very well on such stars.
  * Add red-clump stars, BHB stars, RR Lyraes and other important stars to the synthetic HR diagram used by GSP-Phot.

===== Red clump =====

  * Adopt definition of red-clump stars from [[http://adsabs.harvard.edu/abs/2014ApJ...790..127B|Bovy et al. (2014)]] ([Fe/H]>-1, 4600K<Teff<4850K, 1.8<logg<2.5 + 0.0018*(Teff - TeffRef) where TeffRef = -382.5*FeH + 4607).
  * Selecting all available BP/RP spectra in that regime adds a significant number of red-clump stars.
  * Caveat: The ratio of red-clump stars relative to other types of stars is not realistic (before and after this procedure).

{{:tests:adding-red-clump-stars.png|}}

===== Blue horizontal branch =====

  * Adopt definition of BHB stars from [[http://adsabs.harvard.edu/abs/2004AJ....127..899S|Sirko et al. (2004)]] ([Fe/H]< -1, 7000K<Teff<13000K, 2.9<logg<4).
  * Synthetic Gaia libraries contain no BHB stars that we could include.

{{:tests:adding-BHB-stars.png|}}

===== RR Lyrae =====

  * Adopt definition of RR Lyrae stars from [[http://adsabs.harvard.edu/abs/2010A&A...519A..64K|Kolenberg et al. (2010)]] (6250K<Teff<8000K, 2.5<logg<3.8).

{{:adding-rr-lyrae-stars.png|}}

===== Cepheids =====

===== Red giant branch =====