SIMBAD references

The evidence for positive cosmological constant Λ from Type Ia supernovae is re-examined.

Both high redshift supernova teams are found to underestimate the effects of host galaxy extinction. The evidence for an absolute magnitude-decay time relation is much weakened if supernovae not observed before maximum light are excluded. Inclusion of such objects artificially suppresses the scatter about the mean relation.

With a consistent treatment of host galaxy extinction and elimination of supernovae not observed before maximum, the evidence for a positive lambda is not very significant (3-4σ). A factor which may contribute to apparent faintness of high-z supernovae is evolution of the host galaxy extinction with z

The Hubble diagram using all high-z distance estimates, including SZ clusters and gravitational lens time-delay estimates, does not appear inconsistent with an Ω_o =1 model.

Although a positive Λ can provide an (albeit physically unmotivated) resolution of the low curvature implied by cosmic microwave background (CMB) experiments and evidence that Ω_o <1 from large-scale structure, the direct evidence from Type Ia supernovae seems at present to be inconclusive.