62 research outputs found
Spectroscopic orbits of nearby stars
We observed stars with variable radial velocities to determine their
spectroscopic orbits. Velocities of 132 targets taken over a time span reaching
30 years are presented. They were measured with the correlation radial velocity
spectrometers (1913 velocities) and the new VUES echelle spectrograph (632
velocities), with typical accuracy of 0.5 and 0.2 km/s, respectively. We
derived spectroscopic orbits of 57 stars (including 53 first-time orbits),
mostly nearby dwarfs of spectral types K and M. Their periods range from 2.2
days to 14 years, some of those are Hipparcos astrometric binaries. Comments on
individual objects are provided. Many stars belong to hierarchical systems
containing three or more components, including 20 new hierarchies resulting
from this project. The preliminary orbit of the young star HIP~47110B has a
large eccentricity e=0.47 despite short period of 4.4 d; it could be still
circularizing. Our results enrich the data on nearby stars and contribute to a
better definition of the multiplicity statistics.Comment: Accepted by Astronomy & Astrophysics; 17 pages, 5 figures, 3 table
The lower main sequence of stars in the solar neighborhood: Model predictions versus observation
We have used the Simbad database and VizieR catalogue access tools to
construct the observational color-absolute magnitude diagrams of nearby K-M
dwarfs with precise Hipparcos parallaxes (\sigma_\pi/\pi < 0.05). Particular
attention has been paid to removing unresolved double/multiple and variable
stars. In addition to archival data, we have made use of nearly 2000 new
radial-velocity measurements of K-M dwarfs to identify spectroscopic binary
candidates. The main sequences, cleaned from unresolved binaries, variable
stars, and old population stars which can also widen the sequence due to their
presumably lower metallicity, were compared to available solar-metallicity
models. Significant ofsets of most of the model main-sequence lines are seen
with respect to observational data, especially for the lower-mass stars. Only
the location and slope of the Victoria-Regina and, partly, BaSTI isochrones
match the data quite well.Comment: Submitted to JENAM-2011 SpS3 (Saint Petersburg, July 4-8, 2011)
Proceeding
Studies of Variability in Proto-Planetary Nebulae: II. Light and Velocity Curve Analyses of Iras 22272+5435 and 22223+4327
We have carried out a detailed observational study of the light, color, and
velocity variations of two bright, carbon-rich proto-planetary nebulae, IRAS
22223+4327 and 22272+5435. The light curves are based upon our observations
from 1994 to 2011, together with published data by Arkhipova and collaborators.
They each display four significant periods, with primary periods for IRAS
22223+4327 and 22272+5435 being 90 and 132 days, respectively. For each of
them, the ratio of secondary to primary period is 0.95, a value much different
from that found in Cepheids, but which may be characteristic of post-AGB stars.
Fewer significant periods are found in the smaller radial velocity data sets,
but they agree with those of the light curves. The color curves generally mimic
the light curves, with the objects reddest when faintest. A comparison in
seasons when there exist contemporaneous light, color, and velocity curves
reveals that the light and color curves are in phase, while the radial velocity
curves are 0.25 out of phase with the light curves. Thus they differ from what
is seen in Cepheids, in which the radial velocity curve is 0.50 P out of phase
with the light curve. Comparison of the observed periods and amplitudes with
those of post-AGB pulsation models shows poor agreement, especially for the
periods, which are much longer than predicted. These observational data,
particularly the contemporaneous light, color, and velocity curves, provide an
excellent benchmark for new pulsation models of cool stars in the post-AGB,
proto-planetary nebula phase.Comment: 15 Figures plus Erratu
Spectroscopic Variability of IRAS 22272+5435
A time series of high-resolution spectra was observed in the optical wavelength region for the bright proto-planetary nebula IRAS 22272+5435 (HD 235858), along with a simultaneous monitoring of its radial velocity and BV R C magnitudes. The object is known to vary in light, color, and velocity owing to pulsation with a period of 132 days. The light and color variations are accompanied by significant changes in spectral features, most of which are identified as lines of carbon-bearing molecules. According to the observations, the C 2 Swan system and CN Red system lines are stronger near the light minimum. A photospheric spectrum of the central star was calculated using new self-consistent atmospheric models. The observed intensity variations in the C 2 Swan system and CN Red system lines were found to be much larger than expected if due solely to the temperature variation in the atmosphere of the pulsating star. In addition, the molecular lines are blueshifted relative to the photospheric velocity. The site of formation of the strong molecular features appears to be a cool outflow triggered by the pulsation. The variability in atomic lines seems to be mostly due variations of the effective temperature during the pulsation cycle. The profiles of strong atomic lines are split, and some of them are variable in a timescale of a week or so, probably because of shock waves in the outer atmosphere
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