SIMBAD references

We present the results of 297 nights of observations of four dwarf novae – DX And, U Gem, VW Vul, and CH Her – made in 2017, 2019, 2020, and 2021 for a total of 897 photometric data points. Observations were made in the U, B, V, RC, and IC Johnson-Cousins photometric bands. U Gem was observed for 75 nights, DX And 147 nights, and VW Vul 38 nights. All these observations were made at Gianni Rocchi's private observatory. CH Her was observed for 36 nights only in RC at Perugia Observatory in 2001 and for this faint dwarf nova we present archival data. The light curve of this dwarf nova at bright minimum with very deep depths suggests that it is perhaps an eclipsing dwarf nova with a short orbital period. In this paper we present an analysis of the light curves of these four dwarf novae, observed in the various photometric bands both in the outburst phase and in the luminous minimum phase, and an in-depth study of the color indices. In particular, U Gem was followed during a long outburst in 2019 in which it reached 9th magnitude in almost all photometric bands. We observed five small outbursts of VW Vul but our attempt to give a better classification to this variable failed. For DX And we present an analysis of the light minimum phase. The application of Fourier analysis, through the Peranso program, to the observational data taken in the RC band with the determination of a period P = 11.29 days, suggests that DX And may have a third orbiting body.