A catalog of quasar properties from the Baryon Oscillation Spectroscopic
  Survey
  Using the quasars with z_em < 0.9 from the Baryon Oscillation Spectroscopic
Survey, we measure the spectral characteristics, including continuum and
emission lines, around the Hbeta and Halpha spectral regions, which are lacking
in Quasar Data Release 12 (DR12Q). We estimate the virial black hole mass from
broad Halpha and/or \hbeta, and infer quasar redshifts from O III5007 emission
lines. All the measurements and derived quantities are publicly available. The
comparison between O III5007 based redshifts and the visual inspection
redshifts included in DR12Q indicates that the visual inspection redshifts are
robust. We find that the FWHMs of the broad Halpha are consistent with those of
the broad Hbeta, while both the equivalent widths and line luminosities of the
broad Halpha are obviously larger than the corresponding quantities of the
broad Hbeta. We also find that there is an obviously systematic offset between
the Hbeta and Halpha based mass if they are inferred from the empirical
relationships in the literature. Using our large quasar sample, we have
improved the Hbeta and Halpha based mass estimators by minimizing the
difference between the Hbeta- and Halpha-based mass. For the black hole mass
estimator (Equation (1)), we find that the coefficients (a,b)=(7.00,0.50) for
the Halpha and (a,b)=(6.96,0.50) for the Hbeta are the best choices.
