  We obtained the first long, homogenous time-series of V2104Cyg, consisting of
679 datapoints, with the uvbybeta photometers of Sierra Nevada and San Pedro
Martir Observatories with the aim to detect and subsequently interpret the
intrinsic frequencies of this previously unstudied variable star, which turned
out to be a Be star. We try to figure out its place among the variable B stars
on the upper Main Sequence. In order to obtain additional information on
physical parameters we collected a few spectra with the ELODIE and FIES
instruments. We searched for frequencies in the uvby passbands using 2
different frequency analysis methods and used the S/N>4 criterion to select the
significant periodicities. We obtained an estimate of the physical parameters
of the underlying B star of spectral type between B5 and B7, by correcting for
the presence of a circumstellar disk, using a formalism based on the strenght
of the Halpha line emission. We detected 3 independent frequencies with
amplitudes below 0.01mag, f1 = 4.7126 c/d, f2 = 2.2342 c/d and f3 = 4.671 c/d,
and discovered that V2104Cyg is a Be star. The fast rotation (vsini=290+/-10
km/s, and 27<i<45) hampered the investigation of the associated pulsational
parameters l. Nevertheless, the most plausible explanation for the observed
variability of this mid-late type Be star is a non-radial pulsation model. This
paper is based on observations obtained at the Observatorio Astronomico
Nacional San Pedro Martir (Mexico), Observatorio de Sierra Nevada (Spain),
Observatoire de Haute Provence (France), and on observations made with the
Nordic Optical Telescope, Observatorio Roque de los Muchachos, La Palma, Spain.
