Issue |
A&A
Volume 430, Number 1, January IV 2005
|
|
---|---|---|
Page(s) | 165 - 186 | |
Section | Galactic structure, stellar clusters, and populations | |
DOI | https://doi.org/10.1051/0004-6361:20041272 | |
Published online | 12 January 2005 |
Local kinematics of K and M giants from CORAVEL/Hipparcos/Tycho-2 data *,**
Revisiting the concept of superclusters
1
Institut d'Astronomie et d'Astrophysique, Université Libre de Bruxelles, CP 226, Boulevard du Triomphe, 1050 Bruxelles, Belgium e-mail: [bfamaey;ajorisse]@astro.ulb.ac.be
2
Departament d'Astronomia i Meteorologia, Universitat de Barcelona, Avda. Diagonal 647, 08028 Barcelona, Spain
3
Observatoire de Genève, Chemin des Maillettes 51, 1290 Sauverny, Switzerland
4
Sterrenkundig Observatorium, Universiteit Gent, Krijgslaan 281, 9000 Gent, Belgium
5
Observatoire de Paris, section de Meudon, GEPI/CNRS UMR 8111, 92195 Meudon CEDEX, France
Received:
11
May
2004
Accepted:
21
September
2004
The availability of the Hipparcos Catalogue has triggered many kinematic and
dynamical studies of the solar neighbourhood. Nevertheless, those
studies generally lacked the third component of the space velocities, i.e., the
radial velocities. This work presents the kinematic analysis of 5952 K and 739 M giants in the solar neighbourhood which includes for the
first time radial
velocity data from a large survey performed with the CORAVEL
spectrovelocimeter. It also uses proper motions from the Tycho-2 catalogue,
which are expected to be more accurate than the Hipparcos ones. An
important by-product of this study is the observed fraction of only 5.7%
of spectroscopic binaries among M giants as compared to 13.7% for K giants. After excluding the binaries for which no center-of-mass velocity
could be estimated, 5311 K and 719 M giants remain in the final sample.
The UV-plane constructed from these data for the stars with precise
parallaxes (%) reveals a rich small-scale
structure, with several clumps corresponding to the Hercules stream, the
Sirius moving group, and the Hyades and Pleiades superclusters.
A maximum-likelihood method, based on a Bayesian approach, has been applied
to the data, in order to make full use of all the available stars (not only
those with precise parallaxes) and to derive the kinematic properties of
these subgroups. Isochrones in the Hertzsprung-Russell diagram
reveal a very wide range of ages for stars belonging to these groups.
These groups are most probably related to the dynamical perturbation by
transient spiral waves (as recently modelled by De Simone et al. [CITE]) rather than to cluster remnants. A possible explanation for the presence of young group/clusters in the same
area of the UV-plane is that they have been put there by the spiral wave
associated with their formation, while the kinematics of the older
stars of our sample has also been disturbed by the same wave. The emerging
picture is thus one of dynamical streams pervading the solar neighbourhood and
travelling in the Galaxy with similar space velocities. The term dynamical stream is more appropriate than the traditional term supercluster since it
involves stars of different ages, not born at the same place nor at the
same time. The position of those streams in the UV-plane is responsible
for the vertex deviation of
for the whole
sample. Our study suggests that the vertex deviation for younger
populations could have the same dynamical origin.
The underlying velocity ellipsoid, extracted by the maximum-likelihood
method after removal of the streams, is not centered on the value commonly
accepted for the radial antisolar motion: it is centered on
km s-1. However,
the full data set (including the various streams) does yield the
usual value for the radial solar motion, when properly accounting for the
biases inherent to this kind of analysis (namely,
km s-1). This discrepancy clearly raises the essential question
of how to derive the solar motion in the presence of dynamical
perturbations altering the kinematics of the solar neighbourhood: does
there exist in the solar neighbourhood a subset of stars having no net
radial motion which can be used as a reference against which to measure the
solar motion?
Key words: Galaxy: kinematics and dynamics / Galaxy: disk / Galaxy: solar neighbourhood / Galaxy: evolution / Galaxy: structure / stars: kinematics
© ESO, 2005
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