913 research outputs found
The Open Cluster NGC 7789: I. Radial Velocities for Giant Stars
A total of 597 radial-velocity observations for 112 stars in the ~1.6 Gyr old
open cluster NGC 7789 have been obtained since 1979 with the radial velocity
spectrometer at the Dominion Astrophysical Observatory. The mean cluster radial
velocity is -54.9 +/- 0.12 km/s and the dispersion is 0.86 km/s, from 50
constant-velocity stars selected as members from this radial-velocity study and
the proper motion study of McNamara and Solomon (1981). Twenty-five stars (32%)
among 78 members are possible radial-velocity variable stars, but no orbits are
determined because of the sparse sampling. Seventeen stars are radial-velocity
non-members, while membership estimates of six stars are uncertain.
There is a hint that the observed velocity dispersion falls off at large
radius. This may due to the inclusion of long-period binaries preferentially in
the central area of the cluster. The known radial-velocity variables also seem
to be more concentrated toward the center than members with constant velocity.
Although this is significant at only the 85% level, when combined with similar
result of Raboud and Mermilliod (1994) for three other clusters, the data
strongly support the conclusion that mass segregation is being detected.Comment: 16 pages (including 3 figures) and 3 table
Investigation of the Praesepe cluster. III. Radial velocity and binarity of the F5-K0 Klein-Wassink stars
Coravel observations of 103 F5-K0 stars in the Praesepe cluster yielded 24
spectroscopic binaries (3 are non-members), and 20 orbits were determined, with
periods from 4 to 7400 days. Based on a complete sample in the colour range
0.40 < B-V < 0.80 (80 stars, including KW 244 = TX Cnc), the companion star
fraction CSF = 0.45. The percentage of spectroscopic binaries with P < 1000d is
20% (16/80). The combined photometric and spectroscopic analysis showed that 12
among 18 single-lined spectroscopic binaries are located within the "single"
star sequence in the (V,B-V) diagram and cannot be detected by the photometric
analysis in the UBV system. In addition, seven photometrically analysed
binaries were not detected with the radial velocity observations, but are
confirmed members. The number of single:binary:triple stars is 47:30:3.Comment: 10 pages, 3 tables, 7 eps figures. Accepted for A&A. LaTe
Astrophysical supplements to the ASCC-2.5. Ia. Radial velocities of about 55000 stars and mean radial velocities of 516 Galactic open clusters and associations
We present the 2nd version of the Catalogue of Radial Velocities with
Astrometric Data (CRVAD-2). This is the result of the cross-identification of
stars from the All-Sky Compiled Catalogue of 2.5 Million Stars (ASCC-2.5) with
the General Catalogue of Radial Velocities and with other recently published
radial velocity lists and catalogues. The CRVAD-2 includes accurate J2000
equatorial coordinates, proper motions and trigonometric parallaxes in the
Hipparcos system, photometry in the Johnson system, spectral types,
radial velocities (RVs), multiplicity and variability flags for 54907 ASCC-2.5
stars. We have used the CRVAD-2 for a new determination of mean RVs of 363 open
clusters and stellar associations considering their established members from
proper motions and photometry in the ASCC-2.5. For 330 clusters and
associations we compiled previously published mean RVs from the literature,
critically reviewed and partly revised them. The resulting Catalogue of Radial
Velocities of Open Clusters and Associations (CRVOCA) contains about 460 open
clusters and about 60 stellar associations in the Solar neighbourhood. These
numbers still represent less than 30% of the total number of about 1820 objects
currently known in the Galaxy. The mean RVs of young clusters are generally
better known than those of older ones.Comment: 8 pages, 5 figures, accepted for publication in A
Open clusters with Hipparcos I. Mean astrometric parameters
New memberships, mean parallaxes and proper motions of all 9 open clusters
closer than 300 pc (except the Hyades) and 9 rich clusters between 300 and 500
pc have been computed using Hipparcos data. Precisions, ranging from 0.2 to 0.5
mas for parallaxes and 0.1 to 0.5 mas/yr for proper motions, are of great
interest for calibrating photometric parallaxes as well as for kinematical
studies. Careful investigations of possible biases have been performed and no
evidence of significant systematic errors on the mean cluster parallaxes has
been found. The distances and proper motions of 32 more distant clusters, which
may be used statistically, are also indicated.Comment: 15 pages, A&A in pres
Extragalactic Cepheid database
We present in this paper an exhaustive compilation of all published data of
extragalactic Cepheids. We have checked every light curve in order to
characterize the different types of Cepheid and detect potential overtone
pulsators, or to estimate the quality of the data. This compilation of about
3000 photometric measurements will constitute a very useful tool for
astronomers involved for instance in the extragalactic distance scale.Comment: Updated version of this database is now available through WWW at
http://www-obs.univ-lyon1.fr/~planoix/ECD/ . 1321 Cepheids located in 39
galaxies make up the base at the moment. One can also plot PL-relations and
compute distance moduli based on Hipparcos PL-relation
Constraining the fundamental parameters of the O-type binary CPD-41degr7733
Using a set of high-resolution spectra, we studied the physical and orbital
properties of the O-type binary CPD-41 7733, located in the core of \ngc. We
report the unambiguous detection of the secondary spectral signature and we
derive the first SB2 orbital solution of the system. The period is 5.6815 +/-
0.0015 d and the orbit has no significant eccentricity. CPD-41 7733 probably
consists of stars of spectral types O8.5 and B3. As for other objects in the
cluster, we observe discrepant luminosity classifications while using
spectroscopic or brightness criteria. Still, the present analysis suggests that
both components display physical parameters close to those of typical O8.5 and
B3 dwarfs. We also analyze the X-ray light curves and spectra obtained during
six 30 ks XMM-Newton pointings spread over the 5.7 d period. We find no
significant variability between the different pointings, nor within the
individual observations. The CPD-41 7733 X-ray spectrum is well reproduced by a
three-temperature thermal mekal model with temperatures of 0.3, 0.8 and 2.4
keV. No X-ray overluminosity, resulting e.g. from a possible wind interaction,
is observed. The emission of CPD-41 7733 is thus very representative of typical
O-type star X-ray emission.Comment: Accepted by ApJ, 15 pages, 9 figure
A Robust Measure of Tidal Circularization in Coeval Binary Populations: The solar-type spectroscopic Binary Population in The Open Cluster M35
We present a new homogeneous sample of 32 spectroscopic binary orbits in the
young (~ 150 Myr) main-sequence open cluster M35. The distribution of orbital
eccentricity vs. orbital period (e-log(P)) displays a distinct transition from
eccentric to circular orbits at an orbital period of ~ 10 days. The transition
is due to tidal circularization of the closest binaries. The population of
binary orbits in M35 provide a significantly improved constraint on the rate of
tidal circularization at an age of 150 Myr. We propose a new and more robust
diagnostic of the degree of tidal circularization in a binary population based
on a functional fit to the e-log(P) distribution. We call this new measure the
tidal circularization period. The tidal circularization period of a binary
population represents the orbital period at which a binary orbit with the most
frequent initial orbital eccentricity circularizes (defined as e = 0.01) at the
age of the population. We determine the tidal circularizationperiod for M35 as
well as for 7 additional binary populations spanning ages from the pre
main-sequence (~ 3 Myr) to late main-sequence (~ 10 Gyr), and use Monte Carlo
error analysis to determine the uncertainties on the derived circularization
periods. We conclude that current theories of tidal circularization cannot
account for the distribution of tidal circularization periods with population
age.Comment: 37 pages, 9 figures, to be published in The Astrophysical Journal,
February 200
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