On the spectral resolution of the MILES stellar library
  Empirical stellar libraries are extensively used to extract stellar
kinematics in galaxies and to build stellar population models. An accurate
knowledge of the spectral resolution of these libraries is critical to avoid
propagation errors and uncertain estimates of the intrinsic stellar velocity
dispersion of galaxies. In this research note we re-assess the spectral
resolution of the MILES stellar library and of the stellar population models
based on it. This exercise was performed, because of a recent controversy over
the exact MILES resolution. We perform our test through the comparison of MILES
stellar spectra with three different sets of higher-resolution templates, one
fully theoretical - the MARCS library - and two empirical ones, namely the
Indo-U.S. and ELODIE v3.1 libraries. The theoretical template has a
well-defined very high (R=20000) resolution. Hence errors on this theoretical
value do not affect our conclusions. Our approach based on the MARCS library
was crucial to constrain the values of the resolution also for the other two
empirical templates. We find that the MILES resolution has previously been
slightly overestimated. We derive a new spectral resolution of 2.54 A FWHM,
instead of the nominal 2.3 A. The reason for this difference is due to an
overestimation of the resolution for the Indo-U.S. library that was previously
used for estimates of the MILES resolution. For the Indo-U.S. we obtain a new
value of 1.35 A FWHM. Most importantly, the results derived from the MARCS and
ELODIE libraries are in very good agreement. These results are important for
users of the MILES spectra library and for further development of stellar
population models aimed to obtain accurate stellar kinematics in galaxies.
