Microphysics Modules
These modules calculate various functions based on local properties of the stellar matter such as temperature, density, and composition. There are modules for equation of state, opacity, nuclear reactions, and neutrino losses.
mesa/eos
mesa/kap
mesa/net
mesa/neu
mesa/micro
mesa/eos
The mesa/eos module provides a smooth blending of three widely used equations of state: HELM, OPAL, and SCVH.
References
F.X. Timmes and F.D. Swesty, “The Accuracy, Consistency, and Speed of an Electron-Positron Equation of State Based on Table Interpolation of the Helmholtz Free Energy”, Astro. J. Supplement Series, 126, 501-516 (2000). pdf
F. J. Rogers and A. Nayfonov, “Updated and Expanded Opal Equation-Of-State Tables: Implications for Helioseismology”, Astrophys. J., 576, 1064-1074 (2002). pdf
D. Saumon, G. Chabrier, and H. M. Van Horn, “An Equation of State for Low-Mass Stars and Giant Planets”, Astrophysical Journal Supplement Series, 99:713-741 (1995) pdf
mesa/kap
The mesa/kap module smoothly blends the results from two widely used sources of opacity tables and also includes the effects of electron conduction. For typical stellar temperatures, we use the OPAL “Type 2 Tables” that include options for enhanced carbon and oxygen abundances. For low temperatures, we use a special set of tables kindly provided by Jason Ferguson that give extended coverage in the higher density regions needed for low mass objects.
The implementation of electron conduction uses tables from Potekhin available at http://www.ioffe.rssi.ru/astro/conduct/. For values of T-Rho not covered by Potkhin’s tables, the electron conduction is calculated following Timmes. Non-degenerate cases use Iben’s (ApJ 196 525 1975) fits to Hubbard & Lampe’s low density thermal opacity (ApJ s18,279,1969). Degenerate cases use the Yakovlev and Urpin (Soviet Astro 24 303 1980) fits for high density thermal conductivity.
References
C. A. Iglesias and F. J. Rogers, Astrophys. J. 464, 943 (1996). pdf
C. A. Iglesias and F. J. Rogers,”Radiative Opacities for Carbon- and Oxygen-Rich Mixtures,” Astrophys. J. 412, 752 (1993). pdf
Ferguson et al. “Low Temperature Opacities”, ApJ, 623, 585-596 (2005). pdf
S. Cassisi, A. Y. Potekhin, A. Pietrinferni, M. Catelan, M. Salaris (2007). Updated electron-conduction opacities: the impact on low-mass stellar models. Astrophys. J., 661, 1094 [astro-ph/0703011].
mesa/net
The mesa/net module implements the nuclear reaction networks. It is based on Frank Timmes’ code and includes a basic net for standard stellar evolution and a set of extensions that can be used in any combination.
the ‘basic net’
This is for standard hydrogen, helium, and carbon/oxygen burning. It includes 3 PP chains, 4 CNO cycles, triple alpha, alpha chains up to mg24, and carbon/oxygen burning. The isotopes explicitly followed are h1, he4, c12, n14, o16, ne20, and mg24. The n14 alpha chain is “short circuited” into the c12 chain by the pseudo-reaction n14 + he4 -> 0.5 * (o16 + ne20).
The triple-alpha reaction in the pyconuclear regime is supported according to the analytic expressions in Fushiki and Lamb, 1987.
the ‘Alpha chain’ extension
This adds an alpha chain linking mg24, si28, s32, ar36, ca40, ti44, fe52, and ni56.
the ‘full PP’ extension
This fills out the set of isotopes involved in the PP chains by adding h2, he3, li7, and be7.
the ‘full CNO’ extension
This adds hot cno reactions and some early rp process reactions. The added isotopes are c13, n13, n15, o14, o15, f17, f18, ne18, and ne19. In addition, we include the initial part of the rp process by adding mg22 and the reactions leading to it. Any significant build up of mg22 indicates the need for a more complete rp network.
References
F.X. Timmes, “Integration of Nuclear Reaction Networks for Stellar Hydrodynamics”, The Astrophysical Journal Supplement Series, 124, 241-263 (1999). pdf
Fushiki and Lamb, “S-Matrix Calculation of the Triple-Alpha Reaction”, Apj, 317, 368-388, 1987. pdf
mesa/neu
The mesa/neu module is for calculating energy loss rates for neutrinos from sources other than nuclear burning. It is based on Frank Timmes implementation of the analytic fitting formulas given in the following reference.
Reference
Itoh, N., Hayashi, H., Nishikawa, A., & Kohyama, Y. “Neutino Energy Loss in Stellar Interiors. VII. Pair, Photo-, Plasma, Bremstrahlung, and Recombination Neutrino Processes”, ApJS, 102, 411-424 (1996). pdf
mesa/micro
The mesa/micro module is a small convenience package that simplifies the common case of loading all of the microphysics modules.
website design by
Andreas Viklund