We report the discovery and characterization of a deeply eclipsingAMCVn-system, Gaia14aae
(=ASSASN-14cn). Gaia14aae was identified independently by the All-Sky Automated
Survey for Supernovae (ASAS-SN; Shappee et al.) and by the Gaia Science Alerts project,
during two separate outbursts. A third outburst is seen in archival Pan-STARRS-1 (PS1;
Schlafly et al.; Tonry et al.; Magnier et al.) and ASAS-SN data. Spectroscopy reveals a hot,
hydrogen-deficient spectrum with clear double-peaked emission lines, consistent with an accreting
double-degenerate classification.We use follow-up photometry to constrain the orbital
parameters of the system. We find an orbital period of 49.71 min, which places Gaia14aae
at the long period extremum of the outbursting AM CVn period distribution. Gaia14aae is
dominated by the light from its accreting white dwarf (WD). Assuming an orbital inclination
of 90◦ for the binary system, the contact phases of the WD lead to lower limits of 0.78 and
0.015M on the masses of the accretor and donor, respectively, and a lower limit on the mass
ratio of 0.019. Gaia14aae is only the third eclipsingAMCVn star known, and the first in which
the WD is totally eclipsed. Using a helium WD model, we estimate the accretor’s effective
temperature to be 12 900 ± 200 K. The three outburst events occurred within four months of
each other, while no other outburst activity is seen in the previous 8 yr of Catalina Real-time
Transient Survey (CRTS; Drake et al.), Pan-STARRS-1 and ASAS-SN data. This suggests
that these events might be rebrightenings of the first outburst rather than individual events.
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