  There is wide observational evidence that electron velocity distribution
functions (eVDF) observed in the solar wind generally present enhanced tails
and field-aligned skewness. These properties may induce the excitation of
electromagnetic perturbations through the whistler heat-flux instability
(WHFI), that may contribute to a non-collisional regulation of the electron
heat-flux values observed in the solar wind via wave-particle interactions.
Recently, a new way to model the solar wind eVDF has been proposed: the
core-strahlo model. This representation consist in a bi-Maxwellian core plus a
Skew-Kappa distribution, representing the halo and strahl electrons as a single
skewed distribution. The core-strahlo model is able to reproduce the main
features of the eVDF in the solar wind (thermal core, enhanced tails, and
skewness), with the advantage that the asymmetry is controlled by only one
parameter. In this work we use linear kinetic theory to analyze the effect of
solar wind electrons described by the core-strahlo model, over the excitation
of the parallel propagating WHFI. We use parameters relevant to the solar wind
and focus our attention on the effect on the linear stability introduced by
different values of the core-to-strahlo density and temperature ratios, which
are known to vary throughout the Heliosphere. We also obtain the stability
threshold for this instability as a function of the electron beta and the
skewness parameter, which is a better indicator of instability than the
heat-flux macroscopic moment, and present a threshold conditions for the
instability that can be compared with observational data.
