  A thorough multiwavelength, multiheight study of the vector magnetic field in
a compact active region (AR) filament (NOAA10781) is presented. We suggest an
evolutionary scenario for this filament. Full Stokes vectors were acquired with
TIP-II in a spectral range which comprises the chromospheric He I 10830 A
multiplet and the photospheric Si I 10827 A line. An AR filament (that was
formed before our observing run) was detected in the He I absorption images on
2005 July 3rd. The chromospheric vector magnetic field in this portion of the
filament was strongly sheared whereas the photospheric field lines underneath
had an inverse polarity configuration. From July 3rd to July 5th, an opening
and closing of the polarities at either side of the polarity inversion line
(PIL) was recorded, resembling the recently discovered process of the sliding
door effect seen by Hinode. During this time, a newly created region that
contained pores and orphan penumbrae at the PIL was observed.On July 5th, a
normal polarity configuration was inferred from the chromospheric spectra,
while strongly sheared field lines aligned with the PIL were found in the
photosphere. In this same data set, the spine of the filament is also observed
in a different portion of the FOV and is clearly mapped by the Silicon line
core. The inferred vector magnetic fields of the filament suggest a flux rope
topology. Furthermore, the observations indicate that the filament is divided
in two parts, one which lies in the chromosphere and another one that stays
trapped in the photosphere. Therefore, only the top of the helical structure is
seen by the Helium lines. The pores and orphan penumbrae at the PIL appear to
be the photospheric counterpart of the extremely low-lying filament. We suggest
that orphan penumbrae are formed in very narrow PILs of compact ARs and are the
photospheric manifestation of flux ropes in the photosphere.
