3,083 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
Anchors for the Cosmic Distance Scale: the Cepheids U Sgr, CF Cas and CEab Cas
New and existing X-ray, UBVJHKsW(1-4), and spectroscopic observations were
analyzed to constrain fundamental parameters for M25, NGC 7790, and dust along
their sight-lines. The star clusters are of particular importance given they
host the classical Cepheids U Sgr, CF Cas, and the visual binary Cepheids CEa
and CEb Cas. Precise results from the multiband analysis, in tandem with a
comprehensive determination of the Cepheids' period evolution (dP/dt) from ~140
years of observations, helped resolve concerns raised regarding the clusters
and their key Cepheid constituents. Specifically, distances derived for members
of M25 and NGC 7790 are 630+-25 pc and 3.40+-0.15 kpc, respectively.Comment: To appear in Astronomy and Astrophysic
Reactions of dichlorocarbene and arenesulfenyl chlorides with 3,4-epoxy-1-butene and vinylethylene carbonate
Reaction of 3,4-epoxy-1-butene with dichlorocarbene is accompanied by deoxygenation and yields a mixture of 1,1-dichloro-2-vinylcyclopropane, 2,2,2',2'-tetrachlorobicyclopropyl, and 2,2-dichlorocyclopropyloxirane. Arenesulfenyl chlorides react with 3,4-epoxy-1-butene to afford both Markownikoff and anti-Markownikoff addition products, whereas vinylethylene carbonate gives rise exclusively to the anti-Markownikoff adducts
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