Observations of the Sagittarius dwarf spheroidal (Sgr dSph) galaxy were carried out with the H.E.S.S. array of four imaging air Cherenkov telescopes in June 2006. A total of 11 hours of high quality data are available after data selection. There is no evidence for a very high energy γ-ray signal above the energy threshold at the target position. A 95% C.L. flux limit of 3.6 × 10 −12 cm −2 s −1 above 250 GeV has been derived. Constraints on the velocity-weighted cross section σv are calculated in the framework of Dark Matter particle annihilation using realistic models for the Dark Matter halo profile of Sagittarius dwarf galaxy. Two different models have been investigated encompassing a large class of halo types. A 95% C.L. exclusion limit on σv of the order of 2 × 10 −25 cm 3 s −1 is obtained for a core profile in the 100 GeV -1 TeV neutralino mass range.

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Abstract. -CCD B and V observations of 16 low-surface-brightness galaxies and HI data for a subsample of 4 of them are presented. Both paired and isolated dwarf galaxies are observed to study possible environmental effects on their characteristics. Most of the observed galaxies are true dwarfs with −8.

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