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[abridged]  Context: Very few examples of luminous blue variable (LBV) stars or LBVcandidates (LBVc) are known, particularly at metallicities below the SMC. TheLBV phase is crucial for the evolution of massive stars, and its behavior withmetallicity is poorly known. V39 in IC 1613 is a well-known photometricvariable, with B-band changes larger than 1mag. over its period. The star,previously proposed to be a projection of a Galactic W Virginis and an IC 1613red supergiant, shows features that render it a possible LBVc.  Method: We investigate mid-resolution blue and red VLT-VIMOS spectra of V39,covering a time span of 40 days, and perform a quantitative analysis of thecombined spectrum using the model atmosphere code CMFGEN.  Results: We identify strong Balmer and FeII P-Cygni profiles, and a hybridspectrum resembling a B-A supergiant in the blue and a G-star in the red. Nosignificant Vrad variations are detected, and the spectral changes are smallover the photometric period. Our analysis places V39 in the low-luminosity partof the LBV and LBVc region, but it is also consistent with a sgB[e] star.  Conclusions: The radial velocity indicates that V39 belongs to IC 1613. Thelack of Vrad changes and spectroscopic variations excludes binary scenarios.The features observed are not consistent with a W Virginis star, and thispossibility is also discarded. We propose that the star is a B-A LBVc or sgB[e]star surrounded by a thick disk precessing around it.  If confirmed, V39 would be the lowest metallicity resolved LBV candidateknown to date. Alternatively, it could represent a new transient phase ofmassive star evolution, an LBV impostor.

The nature of V39: an LBV candidate or LBV impostor in the very low metallicity galaxy IC 1613?