Why Do Low-Mass Stars Become Red Giants?
Richard J. Stancliffe A C, Alessandro Chieffi A B, John C. Lattanzio A and Ross P. Church A A Centre for Stellar and Planetary Astrophysics, Monash University, PO Box 28M, Victoria 3800, Australia B INAF–Istituto di Astrofisica, Spaziale e Fisica Cosmica, Via Fosso del Cavaliere, Rome, Italy C Corresponding author. Email: richard.stancliffe@sci.monash.edu.au Abstract We revisit the problem of why stars become red giants. We modify the physics of a standard stellar evolution code in order to determine what does and what does not contribute to a star becoming a red giant. In particular, we have run tests to try to separate the effects of changes in the mean molecular weight and in the energy generation. The implications for why stars become red giants are discussed. We find that while a change in the mean molecular weight is necessary (but not sufficient) for a 1-M⊙ star to become a red giant, this is not the case in a star of 5 M⊙. It therefore seems that there may be more than one way
