  We have observed 22 Lindroos stars with SCUBA on the JCMT to search for
evidence of dust discs. Stars in this sample are the less massive companions of
B-type primaries and have ages of 10-170Myr. Dust was detected around three of
these stars (HD74067, HD112412 and HD99803B). The emission around HD74067 is
centrally peaked and is approximately symmetrically distributed out to ~70".
This emission either arises from a two component disc, one circumstellar and
the other circumbinary with dust masses of 0.3 and >27Mearth respectively, or
an unrelated background object. The other two detections we attribute to
circumsecondary discs with masses of 0.04 and 0.3Mearth; a circumprimary disc
is also present around HD112413 with a similar mass to that around the
companion HD112412. Cross-correlation of our sample with the IRAS catalogs only
showed evidence for dust emission at 25um and 60um toward one star (HD1438);
none of the sub-mm detections were evident in the far-IR data implying that
these discs are cold (<40K assuming beta=1). Our sub-mm detections are some of
the first of dust discs surrounding evolved stars that were not detected by
IRAS or ISO and imply that 9-14% of stars could harbour previously undetected
dust discs that await discovery in unbiased sub-mm surveys. If these discs are
protoplanetary remnants, rather than secondary debris discs, dust lifetime
arguments show that they must be devoid of small <0.1mm grains. Thus it may be
possible to determine the origin of these discs from their spectral energy
distributions. The low dust masses for this sample support the picture that
protoplanetary dust discs are depleted to the levels of the brightest debris
discs (~1Mearth) within 10Myr.
