Long-Term Light Curve of Highly-Variable Protostellar Star GM Cep
  We present data from the archival plates at Harvard College Observatory and
Sonneberg Observatory showing the field of the solar type pre-main sequence
star GM Cep. A total of 186 magnitudes of GM Cep have been measured on these
archival plates, with 176 in blue sensitivity, 6 in visible, and 4 in red. We
combine our data with data from the literature and from the American
Association of Variable Star Observers to depict the long-term light curves of
GM Cep in both B and V wavelengths. The light curves span from 1895 until now,
with two densely sampled regions (1935 to 1945 in B band, and 2006 until now in
V band). The long-term light curves do not show any fast rise behavior as
predicted by an accretion mechanism. Both the light curves and the magnitude
histograms confirm the conclusion that the light curves are dominated by dips
(possibly from extinction) superposed on some quiescence state, instead of
outbursts caused by accretion flares.Our result excludes the possibility of GM
Cep being a FUor, EXor, or McNeil's Nebula type star. Several special cases of
T Tauri stars were checked, but none of these light curves are compatible with
that of GM Cep. The lack of periodicity in the light curve excludes the
possibility of GM Cep being a KH 15D system.
