SIMBAD references

We present the results of the optical spectroscopy follow up of a sample of 28 unclassified blazars from the Third Fermi-LAT Catalog of High-Energy Sources (3FHL). All the spectra were taken with the 4 m Mayall telescope at Kitt Peak. With this follow-up program, we are able to classify 27 out of 28 objects as BL Lacs, while the remaining one is a flat spectrum radio quasar. We determine a redshift (z) for three of these objects and a lower limit on z for other four sources: the farthest object for which we obtain a redshift has z > 0.836. These results are part of a more extended campaign of optical spectroscopy follow up of 3FHL blazars, aimed to obtain a complete sample of blazars at >10 GeV, which will then be used to extend our knowledge on blazar emission mechanisms and on the extragalactic background light.