New insight on the origin of the double red clump in the Milky Way bulge
  The double red clump (RC) observed in the Milky Way bulge is widely
interpreted as evidence for an X-shaped structure. We have recently suggested,
however, an alternative interpretation based on the multiple population
phenomenon, where the bright RC is from helium enhanced second-generation stars
(G2), while the faint RC is representing first-generation stars (G1) with
normal helium abundance. Here our RC models are constructed in a large
parameter space to see the effects of metallicity, age, and helium abundance on
the double RC feature. Our models show that the luminosity of RC stars is
mainly affected by helium abundance, while the RC color is primarily affected
by metallicity. The effect of age is relatively small, unless it is older than
12 Gyr or much younger than 6 Gyr. The observed double RC feature can therefore
be reproduced in a relatively large parameter space, once {\Delta}Y between G2
and G1 is assumed to be greater than $\sim$0.10. We further show that the
longitude dependence of the double RC feature at $b \approx -8.5 \deg$, which
was pointed out by Gonzalez et al. (2015) as a potential problem of our model,
is well explained in our scenario by a classical bulge embedded in a tilted
bar.
