Summary: 4 S. Vennes et al.: Discovery of a white dwarf companion (EUVE J0254053) to the K0 IV star HD18131
Fig. 3. A solution to the ROSAT WFC is found in the range
26; 000 ź T eff ź 36; 000 K and a solution to the EUVE count
rates is found near 27; 000 ź T eff ź 31; 000 K assuming pure
ant branch, and eventually the asymptotic giant branch.
Because of the large orbital separation, evolution occurs
without any significant interaction with the companion.
The second component, following its companion after pos
sibly a few 100 Myr, is now evolving through the subgiants
with a spectral classification K0 IV. It is unlikely that the
K0 IV companion will fill its Roche lobe and, thus, lead to
the formation of a short period degenerate pair (see Bra
gaglia et al. 1990), however a more comprehensive search
for orbital variations may answer this question.
The sample of binaries comprising one or two evolved
components offers important insights on the formation
and evolution of stars. In particular we find evidence that,
in cases like HR 1608 and HD 18131, the mass distribu
tion in binaries tends to favor components with similar