xts objects containing adjusted close prices of the
  constituents of the respective stock indices. These are
  the S&P 500 constituents (SP500_const with corresponding
  Global Industry Classification Standard (GICS) information
  SP500_const_info; see
  https://en.wikipedia.org/wiki/List_of_S%26P_500_companies;
  given these tickers, the data was obtained from Yahoo! Finance)
  as of 2015-10-12, the Dow Jones constituents (DJ_const;
  information about the constituents not available anymore)
  as of 2016-01-03, the FTSE 100 constituents (FTSE_const; see
  https://uk.finance.yahoo.com/quote/%5EFTSE/components?ltr=1/) as of
  2016-01-03 (the data was only available for 98 constituents),
  the Euro Stoxx 50 constituents (EURSTX_const; see
  https://uk.finance.yahoo.com/quote/%5ESTOXX50E/components?ltr=1/)
  as of 2016-01-03 (the data was only available for 98 constituents) and
  the Hang Seng Index constituents (HSI_const;
  see https://uk.finance.yahoo.com/quote/%5EHSI/components?ltr=1/)
  as of 2016-01-03.
The constituents data ranges from the first date at least
  one of the constituents is available (with missing
  data if not available) to 2015-12-31.