Stellar parameters for the First Release of the MaStar Library: An
  Empirical Approach
  We report the stellar atmospheric parameters for 7503 spectra contained in
the first release of the MaNGA stellar library (MaStar) in SDSS DR15. The first
release of MaStar contains 8646 spectra measured from 3321 unique stars, each
covering the wavelength range 3622 \AA\ to 10354 \AA\ with a resolving power of
$R \sim$ 1800. In this work, we first determined the basic stellar parameters:
effective temperature ($\rm T_{eff}$), surface gravity ($\log g$), and
metallicity ($\rm[Fe/H]$), which best fit the data using an empirical
interpolator based on the Medium-resolution Isaac Newton Telescope library of
empirical spectra (MILES), as implemented by the University of Lyon
Spectroscopic analysis Software (Koleva et al. 2008, ULySS) package. While we
analyzed all 8646 spectra from the first release of MaStar, since MaStar has a
wider parameter-space coverage than MILES, not all of these fits are robust. In
addition, not all parameter regions covered by MILES yield robust results,
likely due to the non-uniform coverage of the parameter space by MILES. We
tested the robustness of the method using the MILES spectra itself and
identified a proxy based on the local density of the training set. With this
proxy, we identified 7503 MaStar spectra with robust fitting results. They
cover the range from 3179K to 20,517K in effective temperature ($\rm T_{eff}$),
from 0.40 to 5.0 in surface gravity ($\log g$), and from $-$2.49 to $+$0.73 in
metallicity ($\rm[Fe/H]$).
