BUZZ-Henderson: best day in 7.5 yrs on Janus merger
** Henderson Group (Frankfurt: HDJ.F - news) rises 16 pct in volume after agreeing a merger with Janus Capital (NYSE: JNS - news)
** Brokers point to accretiveness of the deal - $110 mln of synergies p.a. or 16 pct of the combined group's EBITDA - for share price reaction
** Best day for the stock since January 2009
** Easily top riser on Stoxx 600 (as well as UK's FTSE 250 ); peers Aberdeen and Jupiter fourth and fifth top risers (second and third top on FTSE 250); Schroders (Frankfurt: 929969 - news) third top riser on FTSE 100