Comparative Study of TESS Photometry and Radial Velocities on Six Early K-type Contact Binaries with Similar Periods around 0.268 Day

High-precision light curves were extracted from TESScut images. Together with APOGEE and LAMOST medium resolution spectra, a joint study was made for six early K-type contact binary candidates selected unbiasedly orbital periods around 0.268 days. It is found that all of them (RV CVn, EK Com, V384 Ser, V1038 Her, EH CSS$\_$J125403.7+503945) are W-subtype shallow systems though different mass ratios ($1/q$ = 0.27--0.62). The effective temperature differences between components few hundred Kelvins. original definition A- W-subtypes compared the customarily used methods which rely on shape or photometric solutions curves. latter two not always reliable therefore radial velocity analysis strongly recommended. Through collection available binaries both spectroscopic measurements, it almost systems, except objects have nearly identical temperatures components. This phenomenon should be further checked more samples in future. Finally, physical parameters targets determined data multiplicity discussed these targets. Ser RV CVn confirmed very likely to triple comprehensive analysis, while Her candidate system based solutions.