Four New Observational $H(z)$ Data From Luminous Red Galaxies of Sloan Digital Sky Survey Data Release Seven

By adopting the differential age method, we utilize selected 17832 luminous red galaxies (LRGs) from Sloan Digital Sky Survey Data Release Seven (SDSS DR7) covering redshift $0<z<0.4$ to measure Hubble parameters. Using a full spectrum fitting package UlySS, these spectra are reduced with single stellar population (SSP) models and optimal age information of our selected sample are derived. With the decreasing age-redshift relation, four new observational $H(z)$ data (OHD) points are obtained, which are $H(z)=69.0\pm 19.6$ km s${}^{-1}$ Mpc${}^{-1}$ at $z=0.07$, $H(z)=68.6\pm 26.2$ km s${}^{-1}$ Mpc${}^{-1}$ at $z=0.12$, $H(z)$=$72.9\pm 29.6$ km s${}^{-1}$ Mpc${}^{-1}$ at $z=0.2$ and $H(z)$=$88.8\pm 36.6$ km s${}^{-1}$ Mpc${}^{-1}$ at $z=0.28$, respectively. Combined with other 21 available OHD data points, a performance of constraint on both flat and non-flat $\mathrm{\Lambda }$CDM model is presented.