As part of a wider investigation of evolved massive stars in Galactic open clusters , we have spectroscopically identified three candidate classical Cepheids in the little-studied clusters Berkeley 51 , Berkeley 55 and NGC 6603 .
Using new multi-epoch photometry , we confirm that Be 51 # 162 and Be 55 # 107 are bona fide Cepheids , with pulsation periods of 9.83 \pm 0.01 d and 5.850 \pm 0.005 d respectively , while NGC 6603 star W2249 does not show significant photometric variability .
Using the period-luminosity relationship for Cepheid variables , we determine a distance to Be 51 of 5.3 ^ { +1.0 } _ { -0.8 } kpc and an age of 44 ^ { +9 } _ { -8 } Myr , placing it in a sparsely-attested region of the Perseus arm .
For Be 55 , we find a distance of 2.2 \pm 0.3 kpc and age of 63 ^ { +12 } _ { -11 } Myr , locating the cluster in the Local arm .
Taken together with our recent discovery of a long-period Cepheid in the starburst cluster VdBH222 , these represent an important increase in the number of young , massive Cepheids known in Galactic open clusters .
We also consider new Gaia ( data release 2 ) parallaxes and proper motions for members of Be 51 and Be 55 ; the uncertainties on the parallaxes do not allow us to refine our distance estimates to these clusters , but the well-constrained proper motion measurements furnish further confirmation of cluster membership .
However , future final Gaia parallaxes for such objects should provide valuable independent distance measurements , improving the calibration of the period-luminosity relationship , with implications for the distance ladder out to cosmological scales .