Four new observational H(z) data from luminous red galaxies in the Sloan Digital Sky Survey data release seven

By adopting the differential age method, we select 17 832 luminous red galaxies from the Sloan Digital Sky Survey Data Release Seven covering redshift 0 < z < 0.4 to measure the Hubble parameter. Using the full spectrum fitting package UlySS, these spectra are reduced with single stellar population models and optimal age information from our selected sample is derived. With the decreasing age-redshift relation, four new observational H(z) data (OHD) points are obtained, which are H(z) = 69.0 ± 19.6 km s⁻¹ Mpc⁻¹ at z = 0.07, H(z) = 68.6 ± 26.2km s⁻¹ Mpc⁻¹ at z = 0.12, H(z) = 72.9 ± 29.6 km s⁻¹ Mpc⁻¹ at z = 0.2 and H(z)=88.8 ± 36.6 km s⁻¹ Mpc⁻¹ at z = 0.28, respectively. Combined with 21 other available OHD data points, the performance of the constraint on both flat and non-flat ΛCDM models is presented.