All our evidence of duplicity lies in four measurements of an hardly perceptible
spectral feature. Maybe the answer to all our problems will be contained in the
above mentioned paper announced by
Pavlovski et al. (1994). Anyway,
awaiting further pieces of information, we can suggest (to ourselves as well as
to the readers) that the observation of some select spectral regions would be in
principle a conclusive test. In particular, the presence of a secondary star
like the one hypothesized in Sect. 4 (click here) would be betrayed by the CaII K and H
doublet: the CaII K equivalent width in the combined spectrum would range
between 
0.07 Å (M0 type companion) and 0.4 Å (G0). If
the secondary body was a late type giant, also the observation of the MgI
and 
doublet would allow us to detect easily
its presence.
Do to the non-standard variability pattern shown by this star, both a possible refutation and a confirmation of the binary hypothesis would hold the greatest interest for us.
We are observing a light curve which differs from the ones exhibited by many Be
stars, according to Balona and co-workers (see e.g.
Balona et al.
1987, or van Vuuren et al. 1988), only in its
atypical period. We meet, as these authors do, almost the same frequency in
different years, whereas shape and amplitude of the signal show considerable
variations. Also the double-wave pattern observed in this star would fit
their scenario. If 14 Lac belongs to a close binary system, these
similarities may represent the fortuitous outcome of two distinct
mechanisms: orbital and rotational modulation respectively. Otherwise, if we
consider this star as a normal Be object, we have to look for other models
accounting for the same peculiar kind of variability in all the observed
time scales: in 14 Lac it cannot be ascribed, as in the above quoted papers,
to systems of spots carried around the star by its rotation (the entailed
equatorial radius of not less than 44 
would not be
credible).
In the binary hypothesis, we got indications of a strongly eccentric orbit which
hold our attention to the probable youth of the system: the evolutionary
status of the Be stars is still unknown. On the other hand, the observation of
an orbital period which is really increasing would puzzle us very much: neither
tidal frictions nor realistic mass transfer phenomena seem to be able to account
for our estimate of the increase rate (more than 1% in 20 years). Obviously,
also this scenario would need some checks: a spectroscopic monitoring of the
whole 10 d period would give us useful bits of information about the
orbital parameters, whereas an extended photometric baseline would reduce the
error in our period determinations, allowing us to verify reality and rate of
the observed secular frequency trend.
For these reasons we included 14 Lac in a list of few selected Be stars to be observed in the next seasons. Proposals of collaboration would be welcome.
spectral line.