(Proposal ID) S15B-160

(PI) Kotani, Takayuki

(Proposal Title)
Probing the Cepheid mass discrepancy with SCExAO

(Abstract)
This proposal will employ SCExAO observations to target the long-standing 
problem of the Cepheid mass discrepancy. Despite their importance to 
contemporary astrophysics, Cepheids have poorly constrained masses. There are 
two widely employed approaches to obtain the mass, one based on analysis of 
the pulsational dynamics of the star, and the other on evolutionary stellar 
models. Unfortunately, these two methods do not agree: the finding that 
pulsation masses are systematically lower than the evolutionary masses is 
known as the Cepheid Mass Discrepancy. One promising avenue postulates mass 
loss in the He-burning phase. Prior findings by our group lend support to the 
idea that mass-loss may play an important role in the mass-discrepancy, with 
the discovery of circumstellar envelopes surrounding Cepheids. The unique 
capabilities of SCExAO will allow us to address this problem from two separate 
aspects. Firstly, this proposal will directly constrain Cepheid masses using a 
method independent of theoretical models: by detection of binary companions to 
refine the orbital parameters for dynamical mass determination. Secondly we 
will study the process of mass-loss from Cepheids by imaging faint nebulosity 
in relatively unexplored regions (<100s of AU) in the near-circumstellar 
environment.