8 research outputs found
Rate of Period Change as a Diagnostic of Cepheid Properties
Rate of period change for a Cepheid is shown to be a parameter that
is capable of indicating the instability strip crossing mode for individual
objects, and, in conjunction with light amplitude, likely location within the
instability strip. Observed rates of period change in over 200 Milky Way
Cepheids are demonstrated to be in general agreement with predictions from
stellar evolutionary models, although the sample also displays features that
are inconsistent with some published models and indicative of the importance of
additional factors not fully incorporated in models to date.Comment: Published in PASP (March 2006); TeX source & figures now provide
Galactic clusters with associated Cepheid variables. VII. Berkeley 58 and CG Cassiopeiae
Photoelectric, photographic, and CCD UBV photometry, spectroscopic
observations, and star counts are presented for the open cluster Berkeley 58 to
examine a possible association with the 4.37d Cepheid CG Cas. The cluster is
difficult to separate from the early-type stars belonging to the Perseus spiral
arm, in which it is located, but has reasonably well-defined parameters: an
evolutionary age of ~10^8 years, a mean reddening of E(B-V)_(B0)=0.70+-0.03
s.e., and a distance of 3.03+-0.17 kpc (V_0-M_V=12.40+-0.12 s.d.). CG Cas is a
likely cluster coronal member on the basis of radial velocity, and its period
increase of +0.170+-0.014 s yr^(-1) and large light amplitude describe a
Cepheid in the third crossing of the instability strip lying slightly blueward
of strip centre. Its inferred reddening and luminosity are E(B-V)=0.64+-0.02
s.e. and =-3.06+-0.12. A possible K supergiant may also be a cluster
member.Comment: Accepted for Publication (MNRAS