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We have studied the spectral time variations of candidate luminous bluevariable stars (cLBV) in two low-metallicity blue compact dwarf galaxies, DDO68 and PHL 293B. The LBV in DDO 68, located in HII region #3, shows anoutburst, with an increase of more than 1000 times in Halpha luminosity duringthe period 2008-2010. The broad emission of the HI and HeI lines display a PCygni profile, with a relatively constant terminal velocity of ~800 km/s,reaching a maximum luminosity L(Halpha) of ~2x10^38 erg/s, with a FWHM of~1000-1200 km/s. On the other hand, since the discovery of a cLBV in 2001 inPHL 293B, the fluxes of the broad components and the broad-to-narrow fluxratios of the HI and HeI emission lines in this galaxy have remained nearlyconstant over 16 years, with small variations. The luminosity of the broadHalpha component varies between ~2x10^38 erg/s and ~10^39 erg/s, with the FWHMvarying in the range ~500-1500 km/s. Unusually persistent P Cygni features areclearly visible until the end of 2020 despite a decrease of the broad-to-narrowflux ratio in the most recent years. A terminal velocity of ~800 km/s ismeasured from the P Cygni profile, similar to the one in DDO 68, although thelatter is 3.7 more metal-deficient than PHL 293B. The relative constancy of thebroad Halpha luminosity in PHL 293B suggests that it is due to a long-livedstellar transient of type LBV/SN IIn.

Decade-long time-monitoring of candidate Luminous Blue Variable Stars in the two very metal-deficient compact dwarf galaxies DDO 68 and PHL 293B