  We derive improved stellar luminosity limits on a generic light CP-even
scalar field $S$ mixing with the Standard Model (SM) Higgs boson from the
supernova SN1987A, the Sun, red giants (RGs) and white dwarfs (WDs). For the
first time, we include the geometric effects for the decay and absorption of
$S$ particles in the stellar interior. For SN1987A and the Sun, we also take
into account the detailed stellar profiles. We find that a broad range of the
scalar mass and mixing angle can be excluded by our updated astrophysical
constraints. For instance, SN1987A excludes $1.0\times10^{-7} \lesssim
\sin\theta \lesssim 3.0\times 10^{-5}$ and scalar mass up to 219 MeV, which
covers the cosmological blind spot with a high reheating temperature. The
updated solar limit excludes the mixing angle in the range of $1.5\times
10^{-12} < \sin\theta < 1$, with scalar mass up to 45 keV. The RG and WD limits
are updated to $5.3\times 10^{-13} < \sin \theta < 0.39$ and $2.8\times
10^{-18} < \sin \theta < 1.8\times 10^{-4}$, with scalar mass up to 392 keV and
290 keV, respectively.
