SIMBAD references

Spectra of high-metallicity [12+log(O/H) ≳ 8.2] Hii regions, where oxygen auroral lines are measurable in both the O⁺ and O⁺⁺ zones, have been extracted from the Data Release 6 of the Sloan Digital Sky Survey (SDSS). Our final sample consists of 181 SDSS spectra of Hii regions in galaxies in the redshift range from ∼0.025 to ∼0.17. The t_2,O-t_3,O diagram is examined. In the SDSS Hii regions, the electron temperature t_2,O is found to have a large scatter at a given value of the electron temperature t_3,O. The majority of the SDSS Hii regions lie below the t_2,O-t_3,O relation derived for Hii regions in nearby galaxies, i.e. the positions of the SDSS Hii regions show a systematic shift towards lower t_2,O temperatures or/and towards higher t_3,O temperatures. The scatter and shift of the SDSS Hii regions in the t_2,O-t_3,O diagram can be understood if they are composite nebulae excited by two or more ionizing sources of different temperatures.