Angle-dependent radiative grain alignment; Confirmation of a magnetic
  field - radiation anisotropy angle dependence on the efficiency of
  interstellar grain alignment
  Interstellar grain alignment studies are currently experiencing a renaissance
due to the development of a new quantitative theory based on Radiative
Alignment Torques (RAT). One of the distinguishing predictions of this theory
is a dependence of the grain alignment efficiency on the relative angle
($\Psi$) between the magnetic field and the anisotropy direction of the
radiation field. In an earlier study we found observational evidence for such
an effect from observations of the polarization around the star HD 97300 in the
Chamaeleon I cloud. However, due to the large uncertainties in the measured
visual extinctions, the result was uncertain.
  By acquiring explicit spectral classification of the polarization targets, we
have sought to perform a more precise reanalysis of the existing polarimetry
data.
  We have obtained new spectral types for the stars in our for our polarization
sample, which we combine with photometric data from the literature to derive
accurate visual extinctions for our sample of background field stars. This
allows a high accuracy test of the grain alignment efficiency as a function of
$\Psi$.
  We confirm and improve the measured accuracy of the variability of the grain
alignment efficiency with $\Psi$, seen in the earlier study. We note that the
grain temperature (heating) also shows a dependence on $\Psi$ which we
interpret as a natural effect of the projection of the grain surface to the
illuminating radiation source. This dependence also allows us to derive an
estimate of the fraction of aligned grains in the cloud.
