  Over the past decade, the Secret Lives of Cepheids (SLiC) program has been
carried out at Villanova University to study aspects and behaviors of classical
Cepheids that are still not well-understood. In this, the first of several
planned papers on program Cepheids, we report the current results for delta
Cep, the Cepheid prototype. Ongoing photometry has been obtained to search for
changes in the pulsation period, light curve morphology and amplitude.
Combining our photometry with the times of maximum light compilation by
Berdnikov 2000 returns a small period change of dP/dt ~ -0.1006 +/- 0.0002 sec
yr^-1. There is also evidence for a gradual light amplitude increase of
~0.011-mag (V-band) and ~0.012-mag (B-band) per decade over the last ~50 years.
In addition, HST-COS UV spectrophotometry and XMM-Newton X-ray data were
carried out to investigate the high-temperature plasmas present above the
Cepheid photospheres. In total, from the five visits (eight exposures) with
XMM-Newton, delta Cep is found to be a soft X-ray source (Lx [0.3--2 keV] ~
4.5-13x10^28 erg sec^-1) with peak flux at kT = 0.6-0.9 keV. The X-ray activity
is found to vary, possibly in phase with the stellar pulsations. From
2010-2013, nine observations of delta Cep were carried out with HST-COS. The UV
emissions are also variable, and well-phased with the stellar pulsations.
Maximum UV line emissions occur near, or slightly before, maximum optical
light, varying by as much as twenty times. This variability shows that
pulsation-induced shock-heating plays a significant role in Cepheid
atmospheres, possibly in addition to a quiescent, magnetic heating. The results
of this study show Cepheid atmospheres to be rather complex and dynamic.
