Calibration of stellar convection
with Sarbani Basu and Joel Tanner
Part of energy created in all stars is transported to the surface through convection. However, until recently we had little direct insight into convective properties of stars other than the Sun. The major advance came with asteroseismic observations from the Kepler spacecraft. They provide precise measurements of stellar masses and sizes, which can be used to better constrain stellar models and get a handle on stellar convection. Most stellar models use mixing length theory to describe convective transfer, which is entirely characterized by the mixing length parameter (MLP). Our goal was to measure the MLP in a sample of ∼ 90 solar-type stars.
Stars were modeled using the Yale Stellar Evolution Code. Using the measured values of mass, size, temperature and metallicity for each star, and assuming its initial helium abundance, we solved for the MLP. A range of parameter values was obtained across the sample, while models with solar value of MLP converged to unphysically low values of initial helium abundance. Furthermore, MLP is correlated with metallicity, but shows weak mass dependence, and no dependence on temperature or surface gravity. Stellar models have up till now been constructed using the solar value of the mixing length parameter. Given the metallicity dependence of MLP, such models are likely to have large systematic errors.
More information:
Calibrating Convective properties of Solar-like Stars in the Kepler Field of View
(ADS | Arxiv)
Bonaca, A., Tanner, J., Basu, S., Chaplin, W., Metcalfe, T., Monteiro, M. J. P. F. G.,
Ballot, J., Bedding, T. R., Bonanno, A., Broomhall, A.-M., Bruntt, H., Campante, T., Christensen-Dalsgaard, J.,
Corsaro, E., Elsworth, Y., Garcia, R. A., Hekker, S., Karoff, C., Kjeldsen, H., Mathur, S., Regulo, C.,
Roxburgh, I. W., Stello, D., Trampedach, R., Barclay, T., Barclay, C. J., and Caldwell, C., 2012, ApJ, 755, L12