We present results of a long-term spectroscopic monitoring program ( since mid 2009 ) of Luminous Blue Variables with the new HERMES echelle spectrograph on the 1.2m Mercator telescope at La Palma ( Spain ) .
We investigate high-resolution ( R =80,000 ) optical spectra of two LBVs , P Cyg and HD 168607 , the LBV candidates MWC 930 and HD 168625 , and the LBV binary MWC 314 .
In P Cyg we observe flux changes in the violet wings of the Balmer H \alpha , H \beta , and He i lines between May and Sep 2009 .
The changes around 200 to 300 km s ^ { -1 } are caused by variable opacity at the base of the supersonic wind from the blue supergiant . We observe in MWC 314 broad double-peaked metal emission lines with invariable radial velocities over time .
On the other hand , we measure in the photospheric S ii \lambda 5647 absorption line , with lower excitation energy of \sim 14 eV , an increase of the heliocentric radial velocity centroid from 37 km s ^ { -1 } to 70 km s ^ { -1 } between 5 and 10 Sep 2009 ( and 43 km s ^ { -1 } on 6 Apr 2010 ) .
The increase of radial velocity of \sim 33 km s ^ { -1 } in only 5 days can confirm the binary nature of this LBV close to the Eddington luminosity limit . A comparison with VLT-UVES and Keck-Hires spectra observed over the past 13 years reveals strong flux variability in the violet wing of the H \alpha emission line of HD 168625 and in the absorption portion of the H \beta line of HD 168607 .
In HD 168625 we observe H \alpha wind absorption at velocities exceeding 200 km s ^ { -1 } which develops between Apr and June 2010 .