59 research outputs found
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
Type II and anomalous Cepheids in the Kepler K2 mission
We present the results of the analysis of Type II and anomalous Cepheids
using the data from the Kepler K2 mission. The precise light curves of these
pulsating variable stars are the key to study the details of their pulsation,
such as the period-doubling effect or the presence of additional modes. We
applied the Automated Extended Aperture Photometry (autoEAP) to obtain the
light curves of the targeted variable stars which were observed. The light
curves were Fourier analyzed. We investigated twelve stars observed by the K2
mission, seven Type II and five anomalous Cepheids. Among the Type II Cepheids
EPIC 210622262 shows period-doubling, and four stars have modulation present in
their light curves which are different from the period-doubling effect. We
calculated the high-order Fourier parameters for the short-period Cepheids. We
also determined physical parameters by fitting model atmospheres to the
spectral energy distributions. The determined distances using the parallaxes
measured by the Gaia space telescope have limited precision below 16 mag for
these types of pulsating stars, regardless if the inverse method is used or the
statistical method to calculate the distances. The BaSTI evolutionary models
were compared to the luminosities and effective temperatures. Most of the Type
II Cepheids are modeled with low metallicity models, but for a few of them
solar-like metallicity ([Fe/H]=0.06) model is required. The anomalous Cepheids
are compared to low-metallicity single stellar models. We do not see signs of
binarity among our sample stars.Comment: 21 pages, 13 figures, accepted for publication in MNRA
Metal Abundances, Radial Velocities, and Other Physical Characteristics for the RR Lyrae Stars in The Kepler Field
Spectroscopic iron-to-hydrogen ratios, radial velocities, atmospheric parameters, and new photometric analyses are presented for 41 RR Lyrae stars (and one probable high-amplitude δ Sct star) located in the field-of-view of the Kepler space telescope. Thirty-seven of the RR Lyrae stars are fundamental-mode pulsators (i.e., RRab stars) of which sixteen exhibit the Blazhko effect. Four of the stars are multiperiodic RRc pulsators oscillating primarily in the first-overtone mode. Spectroscopic [Fe/H] values for the 34 stars for which we were able to derive estimates range from –2.54 ± 0.13 (NR Lyr) to –0.05 ± 0.13 dex (V784 Cyg), and for the 19 Kepler-field non-Blazhko stars studied by Nemec et al. the abundances agree will with their photometric [Fe/H] values. Four non-Blazhko RR Lyrae stars that they identified as metal-rich (KIC 6100702, V2470 Cyg, V782 Cyg and V784 Cyg) are confirmed as such, and four additional stars (V839 Cyg, KIC 5520878, KIC 8832417, KIC 3868420) are also shown here to be metal-rich. Five of the non-Blazhko RRab stars are found to be more metal-rich than [Fe/H] ~–0.9 dex while all of the 16 Blazhko stars are more metal-poor than this value. New P-Ø_(31)^s-[Fe/H] relationships are derived based on ~970 days of quasi-continuous high-precision Q0-Q11 long- and short-cadence Kepler photometry. With the exception of some Blazhko stars, the spectroscopic and photometric [Fe/H] values are in good agreement. Several stars with unique photometric characteristics are identified, including a Blazhko variable with the smallest known amplitude and frequency modulations (V838 Cyg)
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