73 research outputs found
New homogeneous iron abundances of double-mode Cepheids from high-resolution echelle spectroscopy
Aims: We define the relationship between the double-mode pulsation of
Cepheids and metallicity in a more accurate way, determine the empirical
metallicities of double-mode Cepheids from homogeneous, high-resolution
spectroscopic data, and study of the period-ratio -- metallicity dependence.
Methods: The high S/N echelle spectra obtained with the FEROS spectrograph were
analyzed using a self-developed IRAF script, and the iron abundances were
determined by comparing with synthetic spectra assuming LTE. Results: Accurate
[Fe/H] values of 17 galactic beat Cepheids were determined. All these stars
have solar or slightly subsolar metallicity. Their period ratio P1/P0 shows
strong correlation with their derived [Fe/H] values. The corresponding period
ratio -- metallicity relation has been evaluated.Comment: 10 pages, 7 figures, accepted in A&
Classical Cepheids: Yet another version of the Baade-Becker-Wesselink method
We propose a new version of the Baade--Becker--Wesselink technique, which
allows one to independently determine the colour excess and the intrinsic
colour of a radially pulsating star, in addition to its radius, luminosity, and
distance. It is considered to be a generalization of the Balona approach. The
method also allows the function F(CI) = BC + 10 log (Teff) for the class of
pulsating stars considered to be calibrated. We apply this technique to a
number of classical Cepheids with very accurate light and radial-velocity
curves and with bona fide membership in open clusters (SZ Tau, CF Cas, U Sgr,
DL Cas, GY Sge), and find the results to agree well with the reddening
estimates of the host open clusters. The new technique can also be applied to
other pulsating variables, e.g. RR Lyrae and RV Tauri.Comment: 6 pages, 2 figures, 1 table; Submitted to Astrophysical Bulletin,
201
Binary Properties from Cepheid Radial Velocities (CRaV)
We have examined high accuracy radial velocities of Cepheids to determine the
binary frequency. The data are largely from the CORAVEL spectrophotometer and
the Moscow version, with a typical uncertainty of ~km~s, and a
time span from 1 to 20 years. A systemic velocity was obtained by removing the
pulsation component using a high order Fourier series. From this data we have
developed a list of stars showing no orbital velocity larger than
~km~s. The binary fraction was analyzed as a function of
magnitude, and yields an apparent decrease in this fraction for fainter stars.
We interpret this as incompleteness at fainter magnitudes, and derive the
preferred binary fraction of \% ( \% per decade of orbital
period) from the brightest 40 stars. Comparison of this fraction in this period
range (1-20 years) implies a large fraction for the full period range. This is
reasonable in that the high accuracy velocities are sensitive to the longer
periods and smaller orbital velocity amplitudes in the period range sampled
here. Thus the Cepheid velocity sample provides a sensitive detection in the
period range between short period spectroscopic binaries and resolved
companions. The recent identification of Cep as a binary with very low
amplitude and high eccentricity underscores the fact that the binary fractions
we derive are lower limits, to which other low amplitude systems will probably
be added. The mass ratio (q) distribution derived from ultraviolet observations
of the secondary is consistent with a flat distribution for the applicable
period range (1 to 20 years).Comment: accepted for publication in A
- …