Two-Component Variability of the Semi-Regular Pulsating Star U Delphini
  Photometric analysis of photometric variability of the semi-regular pulsating
variable U Del is analyzed. From the international AFOEV database, 6231
brightness values in the time interval JD 2451602-55378 were chosen. For the
periodogram analysis, we have used a trigonometric polynomial fit. Using the
criterion of minimal variance of the approximation at arguments of
observations, the optimal degree is s=1. Initial epoch for maximum is
T0=JD2453340(3), the period P=1198(4)d. Mean brightness at maximum is 6.624(5),
at minimum 7.124(5), i.e. the amplitude is 0.499(5)m. Besides this slow
variability, there is a faster oscillation of a period of 119.45(6)d, amplitude
0.303(5)m and an initial epoch for maximum 2453215.1(5). These results are mean
during the time interval after that analyzed in the catalogue of Chinarova and
Andronov (2000). Also the method of "running sines" with a filter half-width
Delta t=0.5P. The local mean (averaged over a short period) brightness varies
in a range 6.58-7.41m, the semi-amplitude exhibits very strong variations from
0.01 to 0.46m. The phase is also variable - typically of a full amplitude of
0.5. Close to JD 2452589, occurred a phase jump by a complete period during a
descending branch of a slow wave. This effect was not observed during other
cycles. No significant correlation between mean brightness and amplitude of
short-period oscillation was found. Despite significant variability of
amplitude, the periodic contribution is not statistically significant. Also
characteristics of individual brightness extrema were found. The study was made
in a course of the international project "Inter-Longitude Astronomy" (Andronov
et al., 2010) and national project "Ukrainian Virtual Observatory (Vavilova et
al., 2012).
