  We consider a pair of parallel ${\rm D}_{p-1}$ and anti-${\rm D}_{p-1}$
branes in flat space, with a finite separation $d$ along some perpendicular
spatial direction and at finite temperature. If this spatial direction is
compactified on a circle then by T-duality, the system is equivalent to a ${\rm
D}_{p}$-anti ${\rm D}_{p} $ pair wrapped around the dual circle with a constant
Wilson line $A \approx d $ on one of the branes. We focus in particular on the
$p=9$ case and compute the free energy of this system and study the occurrence
of second order phase transitions as both the temperature and Wilson line
(brane-antibrane separation) are varied. In the limit of vanishing Wilson line
we recover the previous results obtained in the literature, whereby the open
string vacuum at the origin of the tachyon field T=0 is stabilized at
sufficiently high temperature at which a second order phase transition occurs.
For sufficiently large Wilson line, we find new second order phase transitions
corresponding to the existence of two minima in the tachyon effective potential
at finite temperature and tachyon field value. Entropic arguments suggest that
as the system cools, the tachyon is likely to find itself in the minimum that
approaches infinity as the temperature vanishes (i.e. the one corresponding to
the closed string vacuum), rather than the minimum at T=0 (corresponding to the
open string vacuum).
