Decade-long time-monitoring of candidate Luminous Blue Variable Stars in
  the two very metal-deficient compact dwarf galaxies DDO 68 and PHL 293B
  We have studied the spectral time variations of candidate luminous blue
variable stars (cLBV) in two low-metallicity blue compact dwarf galaxies, DDO
68 and PHL 293B. The LBV in DDO 68, located in HII region #3, shows an
outburst, with an increase of more than 1000 times in Halpha luminosity during
the period 2008-2010. The broad emission of the HI and HeI lines display a P
Cygni 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 in
PHL 293B, the fluxes of the broad components and the broad-to-narrow flux
ratios of the HI and HeI emission lines in this galaxy have remained nearly
constant over 16 years, with small variations. The luminosity of the broad
Halpha component varies between ~2x10^38 erg/s and ~10^39 erg/s, with the FWHM
varying in the range ~500-1500 km/s. Unusually persistent P Cygni features are
clearly visible until the end of 2020 despite a decrease of the broad-to-narrow
flux ratio in the most recent years. A terminal velocity of ~800 km/s is
measured from the P Cygni profile, similar to the one in DDO 68, although the
latter is 3.7 more metal-deficient than PHL 293B. The relative constancy of the
broad Halpha luminosity in PHL 293B suggests that it is due to a long-lived
stellar transient of type LBV/SN IIn.
