This record contains the data of spectra, photometries and models used for the paper A seven-Earth-radius helium-burning star inside a 20.5-min detached binary. J0526_fchart.png - the finder chart of J0526; J0526_Keck_[0-5].spec (in Keck_ori_spectra.zip) - Keck I/LRIS spectra of J0526; J0526_GTC_[0-6].spec (in GTC_ori_spectra.zip) - GTC/OSIRIS spectra of J0526; J0526_GTC_syn_[0-6].spec (in GTC_spectra_models.zip) - GTC/OSIRIS spectra and their best-fit TLUSTY/Synspec spectra; J0526_RV_bary_corrected.dat - the barycenter-corrected radial velocities derived from LRIS and OSIRIS spectra; J0526_SED.dat - the photometric fluxes in the broad-band SED and corresponding synthetic fluxes from the best-fit model spectrum; ZTF_J0526_[r,g].dat (in light_curves.zip) - ZTF r-/g-band light cuvrs of J0526, the raw data were provided by NASA/IPAC Infrared Science Archive (https://irsa.ipac.caltech.edu ); Lijiang_J0526_[r,g].dat (in light_curves.zip) - LJT r-/g-band light cuvrs of J0526; TMTS_J0526_L.dat (in light_curves.zip) - LJT L-band light cuvrs of J0526; CHeB_c[0.32,0.33,0.34]+H1e-6.track (in MESA_models.zip) - the evolutionary tracks for core helium-burning stars with He-core mass of [0.32,0.33,0.34] Msun and H-envelope mass of 1e-6 Msun; ZAHeMS_H0_sequence.dat (in MESA_models.zip) - the zero-age He-star sequence (without H envelope); ZAHeMS_H1e-6_sequence.dat (in MESA_models.zip) - the zero-age He-star sequence (with H-envelope mass of 1e-6 M_sun ); binary_0.33+0.735.dat (in MESA_models.zip) - the binary evolutionary track for a core helium-burning star (Mcore=0.33 M_sun, Menv=1e-6 M_sun ) and a CO WD (M=0.735 M_sun); binary_0.36+0.735.dat (in MESA_models.zip) - the binary evolutionary track for a core helium-burning star (Mcore=0.36 M_sun, Menv=1e-6 M_sun ) and a CO WD (M=0.735 M_sun); J0526_[SED, RV, lc]_fit_corner.png - the corner plots for [SED, RV, light curve] MCMC fit.