{it Kepler} satellite photometry and phase-resolved spectroscopy of the ultracompact AM CVn type binary SDSS J190817.07+394036.4 are presented. The average spectra reveal a variety of weak metal lines of different species, including silicon, sulphur
and magnesium as well as many lines of nitrogen, beside the strong absorption lines of neutral helium. The phase-folded spectra and the Doppler tomograms reveal an S-wave in emission in the core of the He I 4471 AA,absorption line at a period of $P_{rm orb}=1085.7pm2.8$,sec identifying this as the orbital period of the system. The Si II, Mg II and the core of some He I lines show an S-wave in absorption with a phase offset of $170pm15^circ$ compared to the S-wave in emission. The N II, Si III and some helium lines do not show any phase variability at all. The spectroscopic orbital period is in excellent agreement with a period at $P_{rm orb}=1085.108(9)$,sec detected in the three year {it Kepler} lightcurve. A Fourier analysis of the Q6 to Q17 short cadence data obtained by {it Kepler} revealed a large number of frequencies above the noise level where the majority shows a large variability in frequency and amplitude. In an O-C analysis we measured a $vertdot{P}vertsim1.0,$x$,10^{-8},$s,s$^{-1}$ for some of the strongest variations and set a limit for the orbital period to be $vertdot{P}vert<10^{-10}$s,s$^{-1}$. The shape of the phase folded lightcurve on the orbital period indicates the motion of the bright spot. Models of the system were constructed to see whether the phases of the radial velocity curves and the lightcurve variation can be combined to a coherent picture. However, from the measured phases neither the absorption nor the emission can be explained to originate in the bright spot.
Phase-resolved spectroscopy of four AM CVn systems obtained with the William Herschel Telescope and the Gran Telescopio de Canarias (GTC) is presented. SDSS,J120841.96+355025.2 was found to have an orbital period of 52.96$pm$0.40,min and shows the pr
esence of a second bright spot in the accretion disc. The average spectrum contains strong Mg,{sc i} and Si,{sc i/ii} absorption lines most likely originating in the atmosphere of the accreting white dwarf. SDSS,J012940.05+384210.4 has an orbital period of 37.555$pm$0.003 min. The average spectrum shows the Stark broadened absorption lines of the DB white dwarf accretor. The orbital period is close to the previously reported superhump period of 37.9,min. Combined, this results in a period excess $epsilon$=0.0092$pm$0.0054 and a mass ratio $q=0.031pm$0.018. SDSS,J164228.06+193410.0 displays an orbital period of 54.20$pm$1.60,min with an alias at 56.35,min. The average spectrum also shows strong Mg,{sc i} absorption lines, similar to SDSS,J120841.96+355025.2. SDSS,J152509.57+360054.50 displays an period of 44.32$pm$0.18,min. The overall shape of the average spectrum is more indicative of shorter period systems in the 20-35 minute range. The accretor is still clearly visible in the pressure broadened absorption lines most likely indicating a hot donor star and/or a high mass accretor. Flux ratios for several helium lines were extracted from the Doppler tomograms for the disc and bright spot region, and compared with single-slab LTE models with variable electron densities and path lengths to estimate the disc and bright spot temperature. A good agreement between data and the model in three out of four systems was found for the disc region. All three systems show similar disc temperatures of $sim$10,500 K. In contrast, only weak agreement between observation and models was found for the bright spot region.
