Spectroscopic and photometric studies on four solar-type short-period contact binaries in the triple stellar systems

We reported new spectroscopy and photometry for four short-period binaries, which were acquired by several small telescopes in China from 2020 to 2022. From new spectrum and Large Sky Area Multiobject Fiber Spectroscopic Telescope data, we determined their spectral types of G8V for PZ UMa, G7 for MM Com, and V0685 Peg and G3 for V1055 Her. When compared to the Transiting Exoplanet Survey Satellite (TESS) light curve (LC) with a 2-min cadence, the difference between two light maxima for V1055 Her displays a 29.7-d oscillation. Utilizing the Wilson-Devinney program, we deduced 10 photometric solutions from our new and TESS data. Four binaries are W-type ones with variable O'Connell effects. For LC2022.1 (MM Com) and LC2022.9 (V1055 Her),?m(max)=Max.I-Max.II is as large as 15 per cent of variable light amplitude, which may be attributed to the spot's migration and evolution. From the mass-luminosity diagram, the more massive components aref somewhat evolved main-sequence stars, whereas the less massive ones are overluminous as a result of energy exchange. Based on all eclipse timing residuals, the orbital period variations are preferably described by the light-travel time effects via the presence of additional companions. Their modulation periods range from 10 to 20 yr for four binaries, corresponding the companion's mass ranging from M-3 = 0.11 to 0.34 M-?. Therefore, four solar-type short-period contact binaries (i.e. MM Com, PZ UMa, V0685 Peg, and V1055 Her) may be triple stellar systems.