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As part of a wider investigation of evolved massive stars in Galactic openclusters, we have spectroscopically identified three candidate classicalCepheids 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 arebona fide Cepheids, with pulsation periods of 9.83+/-0.01 d and 5.850+/-0.005 drespectively, while NGC 6603 star W2249 does not show significant photometricvariability. Using the period-luminosity relationship for Cepheid variables, wedetermine 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, wefind a distance of 2.2+/-0.3 kpc and age of 63(+12,-11) Myr, locating thecluster in the Local arm. Taken together with our recent discovery of along-period Cepheid in the starburst cluster VdBH222, these represent animportant increase in the number of young, massive Cepheids known in Galacticopen clusters. We also consider new Gaia (data release 2) parallaxes and propermotions for members of Be 51 and Be 55; the uncertainties on the parallaxes donot allow us to refine our distance estimates to these clusters, but thewell-constrained proper motion measurements furnish further confirmation ofcluster membership. However, future final Gaia parallaxes for such objectsshould provide valuable independent distance measurements, improving thecalibration of the period-luminosity relationship, with implications for thedistance ladder out to cosmological scales.

New Cepheid variables in the young open clusters Berkeley 51 and Berkeley 55