Stellar differential rotation with depth: the case of the pulsating pre-white dwarf PG 0122+200

A. H. CÓRSICO; L. G. ALTHAUS; S. KAWALER; M. M. MILLER BERTOLAMI

Hakone

Seminario; The 61st Fujihara seminar: Progress in solar/stellar physics with helio- and asteroseismology; 2011

Fujihara Foundation of Science

Stellar rotation breaks  the spherical symmetry of a  star, and in the case of a pulsating star,  it removes the intrinsic mode degeneracy of a nonradial $g$-mode characterized by  an harmonic degree $\ell$ and a radial order $k$.  As a result, each pulsation frequency is split into multiplets of  $2\ell+1$ frequencies specified by  different values of the azimuthal  index $m$, with  $m= 0, \pm  1, \ldots, \pm  \ell$.  In this  work, we  explore  the potential  of  asteroseismology to  place constraints  on the internal  rotation of  PG 0122$+$200,  the coolest known GW Vir variable star.  We employ a dedicated seismological model for  this pulsating  star in  order to  assess the  expected frequencysplittings  induced by rotation,  and compare  them with  the observed ones. To  this end,  we assume different  types of  plausible internal rotation profiles. This is the so called ``forward approach'' employed in previous studies. We also  employ an inversion method amply used in helioseismology  for  the inversion  of  the  rotation  profile of  PG0122$+$200.   We found  strong evidence  for differential  rotation in this star,  being the observed frequency splittings  of the rotational multiplets  compatible with a  rotation profile  in which  the central regions are spinning more than  twice faster than the stellar surface.