vice.solar_z.epsilon_to_z_conversion
====================================

Convert an element's abundance in the sun according to the definition

.. math:: \epsilon_x = \log_{10}(N_x / N_H) + 12

to a metallicity by mass :math:`Z_x = M_x / M_\odot`.

**Signature**: vice.solar_z.epsilon_to_z_conversion(epsilon, mu,
Xsun = 0.73)

.. versionadded:: 1.2.0

Parameters
----------
epsilon : float
	The log-scaled number density relative to hydrogen defined above
	for a particular element.
mu : float
	The mean molecular weight of the element.
Xsun : float [default : 0.73]
	The hydrogren mass fraction of the solar photosphere.

Returns
-------
Zsun : float
	The abundance by mass of the element :math:`x` in the sun,
	:math:`M_x / M_\odot`.

Notes
-----
The values returned by this function are calculated according to the
following conversion, which can be derived from the definition of
:math:`\epsilon_x` and :math:`Z_x` above:

.. math:: Z_x = X_\odot \mu_x 10^{\epsilon_x - 12}

VICE uses this function to compute the default solar composition based
on internal data storing the Asplund et al. (2009) [1]_ photospheric
measurements.

.. [1] Asplund et al. (2009), ARA&A, 47, 481