The light curves of luminous stars often
show spectacular secular changes which can be
connected to stellar evolution. Such events are,
e.g. the outbursts of P Cygni in the 17th century
and 77 Carinae in the last century. Both stars
belong to the Luminous Blue Variables, but these
changes are not restricted to blue stars. The
light curve of HR 8752 (V509 Cassiopeiae) shows a
certain similarity to that of the former two
stars. When it was first catalogued in the middle
of the 19th century, it had been a
6m star. During 100 years the
star showed a secular brightening of
lm. A similar yellow
hypergiant, p
Cassiopeiae produced at least two outbursts this
century, though both have smaller amplitudes than
it is in the case of the LBVs. Moreover, these
yellow variables also have an apparently secular
colour change: the B −
V colour of HR 8752 is
decreasing while that of ρ Cassiopeiae is
increasing. In both cases evolutionary changes are
possible but one cannot exclude other
causes.
Besides these well studied stars there are
several other yellow hypergiants with promising
light curves. One of the most interesting cases
seems to be R Puppis, which was discovered to be
variable in the last century, but then did not
show any appreciable change in the following 70-80
years. In the late 1970s, however, it began to
vary once more.
An extensive photometric study of the Blazhko RR Lyrae star RZ Lyr*