Photoelectric UBV photometry and star counts are presented for the previously-unstudied open cluster Collinder 236 , supplemented by observations for stars near the Cepheid WZ Car .
Collinder 236 is typical of groups associated with Cepheids , with an evolutionary age of ( 3.4 \pm 1.1 ) \times 10 ^ { 7 } years , but it is 1944 \pm 71 pc distant , only half the predicted distance to WZ Car .
The cluster is reddened by { E } _ { B - V } \simeq 0.26 , and has nuclear and coronal radii of r _ { n } \simeq 2 \arcmin ( 1.1 pc ) and R _ { c } \simeq 8 \arcmin ( 4.5 pc ) , respectively .
The Cepheid is not a member of Collinder 236 on the basis of location beyond the cluster tidal radius and implied distance , but its space reddening can be established as E _ { B - V } = 0.268 \pm 0.006 s.e .
from 5 adjacent stars .
Period changes in WZ Car studied with the aid of archival data are revised .
The period of WZ Car is increasing , its rate of +8.27 \pm 0.19 s yr ^ { -1 } being consistent with a third crossing of the instability strip .