71 research outputs found
The orbit of the Cepheid AW Per
An orbit for the classical Cepheid AW Per was derived. Phase residuals from the light curve are consistent with the light-time effect from the orbit. The companion was studied using IUE spectra. The flux distribution from 1300 to 1700 A is unusual, probably an extreme PbSi star, comparable to a B7V or B8V star. The flux of the composite spectrum from 1200 A through V is well matched by F7Ib and B8V standard stars with Delta M(sub upsilon) = 3(m) multiplied by 1. The mass function from the orbit indicates that the mass of the Cepheid must be greater that 4.7 solar mass if it is the more massive component. A B7V to B8V companion is compatible with the 1 sigma lower limit (3.5 solar mass) from the mass function. This implies that the Cepheid has the same mass, but the large magnitude difference rules this out. It is likely that the companion is itself a binary
Cepheid binaries with large mass ratios (M1/M2)
The IUE observations of 3 Cepheid systems (Polaris, FF Aql, and S Sge) are used to derive, or set limits on, the temperatures and masses of the companions. Light from the companions of FF Aql and S Sge from 1700 to 2000 A is consistent with an A5 to A7 main sequence companion for both Cepheids, with a mass of 1.8 solar mass. This mass for the companion of S Sge is smaller than required by the orbital mass function and an evolutionary mass of the Cepheid, suggesting that the companion may itself be a binary. For Polaris, the mass of the companion must be less than 1.8 solar mass
Fundamental Parameters of Cepheids: Masses and Multiplicity
Masses determined from classical Cepheids in binary systems are a primary
test of both pulsation and evolutionary calculations. The first step is to
determine the orbit from ground-based radial velocities. Complementary
satellite data from Hubble, FUSE, IUE, and Chandra provide full information
about the system. A summary of recent results on masses is given. Cepheids have
also provided copious information about the multiplicity of massive stars, as
well as the distribution of mass ratios and separations. This provides some
important constraints for star formation scenarios including differences
between high and low mass results and differences between close and wide
binaries
Asteroseismology, standard candles and the Hubble Constant: what is the role of asteroseismology in the era of precision cosmology?
Classical Cepheids form one of the foundations of modern cosmology and the
extragalactic distance scale, however, cosmic microwave background observations
measure cosmological parameters and indirectly the Hubble Constant, H0, to
unparalleled precision. The coming decade will provide opportunities to measure
H0 to 2% uncertainty thanks to the GAIA satellite, JWST, ELTs and other
telescopes using Cepheids and other standard candles. In this work, we discuss
the upcoming role for variable stars and asteroseismology in calibrating the
distance scale and measuring H0 and what problems exist in understanding these
stars that will feedback on these measurements.Comment: 8 pages, summary of splinter session at IAU Symposium 301, Precision
Asteroseismology, August 2013, Wroclaw, Polan
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