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We present a new insight on NGC 6034 and UGC 842, two groups of galaxiespreviously reported in the literature as being fossil groups. The study isbased on optical photometry and spectroscopy obtained with the CTIO Blancotelescope and Sloan Digital Sky Survey archival data. We find that NGC 6034 isembedded in a large structure, dominated by three rich clusters and other smallgroups. Its first and next four ranked galaxies have magnitude differences inthe r band and projected distances which violate the optical criteria toclassify it as a fossil group. We confirm that the UGC 842 group is a fossilgroup, but with about half the velocity dispersion that is reported in previousworks. The velocity distribution of its galaxies reveals the existence of twostructures in its line of sight, one with sigmaV ~ 223 km/s and another withsigmaV ~ 235 km/s, with a difference in velocity of ~820 km/s. The mainstructure is dominated by passive galaxies, while these represent ~60% of thesecond structure. The X-ray temperature for the intragroup medium of a groupwith such a velocity dispersion is expected to be kT ~0.5-1 keV, against theobserved value of kT ~1.9 keV reported in the literature. This result makes UGC842 a special case among fossil groups because (1) it represents more likelythe interaction between two small groups, which warms the intragroup mediumand/or (2) it could constitute evidence that member galaxies lost energy in theprocess of spiraling toward the group center, and decreased the velocitydispersion of the system. As far as we know, UGC 842 is the first low-massfossil group studied in detail.

Revisiting the fossil group candidates UGC 842 and NGC 6034