Cepheids provide insight into both star formation and stellar evolution.
Multiwavelength studies supply binary/multiple properties for
these reasonably massive stars, which allows the exploration of differences
between between high and low mass stars formation. A 3 part
program to derive binary parameters is underway. We are
conducting a survey of Cepheids with the Hubble Space Telescope Wide
Field Camera 3 (WFC3) to identify possible resolved companions, for
example Eta Aql. X-ray observations (Chandra and XMM-Newton) can
confirm whether possible low mass companions are young enough to be physical
companions of Cepheids, hence providing constraints on star formation.
In a related study of intermediate mass stars, Chandra X-ray
observations of late B stars in Tr 16 have been used to
determine the fraction which have low mass companions (which are
X-ray active in contrast to the late B stars which are X-ray quiet).
Finally, velocity data from the Groynya, et al. is being combined with
CORAVEL data develop statistics on long period orbits.
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