Distance to Alpha/Beta:  pi = 0.7468 +/- 0.0012 arcsec
     G2V + K1V, masses 1.105, 0.934 solar
     orbit: semimajor axis a = 17.57 arcsec = 23.4 +/- 0.03 AU
            eccentricity e = 0.518

 
  Distance to Proxima:     pi = 0.7681 +/- 0.0010 arcsec
     M5.5Ve , mass 0.123 solar
     radius 0.141 solar
     luminosity 0.00155 solar
     eff temp T = 3050 K


  from https://arxiv.org/abs/1611.03495,
     Proxima bound to AB with period 550,000 yr, eccen 0.50,
            periastron 4,300 AU  apastron 13,000 AU
            currently close to apastron


  Proxima b: 
     see Nature http://www.nature.com/nature/journal/v536/n7617/full/nature19106.html
     mass >= 1.3 Earth
     period 11.2 days
     semimajor axis a = 0.05 AU
     


  Good papers:
     MOST sees no transits: https://arxiv.org/abs/1609.08718
     MOST does see flares: https://arxiv.org/abs/1608.06672
     X-ray flares: https://arxiv.org/abs/astro-ph/0312297
        (very large solar flare = 2 x 10^(28) erg/s -- see 
            https://heasarc.gsfc.nasa.gov/docs/heasarc/headates/brightest.html)
        (which is 7 erg/s/cm^2, vs. 2 erg/s/cm^2 for ordinary sun
            at solar maximum -- so flare increases flux by factor 3 or so)

     Ion Escape: http://iopscience.iop.org/article/10.3847/2041-8213/836/1/L3
            
     best limits from imaging: https://arxiv.org/abs/1611.10362


     Another paper on atmosphere escape
         https://arxiv.org/abs/1702.03386