Issue |
Astron. Astrophys. Suppl. Ser.
Volume 135, Number 1, February II 1999
|
|
---|---|---|
Page(s) | 5 - 28 | |
DOI | https://doi.org/10.1051/aas:1999160 | |
Published online | 15 February 1999 |
The distribution of nearby stars in phase space mapped by Hipparcos*
III. Clustering and streaming among A-F type stars
1
Centre de Données de Strasbourg, Observatoire Astronomique de Strasbourg, 11 rue de l'Université, F-67000 Strasbourg, France
2
I.U.P de Vannes, Tohannic, rue Yves Mainguy, F-56000 Vannes, France
Received:
21
April
1998
Accepted:
21
September
1998
This paper presents the detailed results obtained in the search of density-velocity
inhomogeneities in a volume limited and absolute magnitude limited sample of A-F type
dwarfs within 125 parsecs of the Sun. A 3-D wavelet analysis is used to extract
inhomogeneities, both in the density and velocity distributions. Thus, a real picture
of the phase space is produced. Not only are some clusters and streams detected, but
the fraction of clumped stars can be measured. By estimating individual stellar ages
one can relate the streams and clusters to the state of the interstellar medium (ISM)
at star formation time and provide a quantitative view of cluster evaporation and
stream mixing.
Having established this picture without assumption we come back to previously known
observational facts regarding clusters and associations, moving groups or so-called
superclusters.
In the 3-D position space, well known open clusters (Hyades, Coma Berenices and Ursa
Major), associations (parts of the Scorpio-Centaurus association) as well as the
Hyades evaporation track are retrieved. Three new probably loose clusters are
identified (Bootes, Pegasus 1 and 2). The sample is relatively well mixed in the
position space since less than 7 per cent of the stars belong to structures with
coherent kinematics, most likely gravitationally bound.
The wavelet analysis exhibits strong velocity structuring at typical scales of velocity
dispersion ~ 6.3, 3.8 and 2.4 km s-1.
The majority of large scale velocity structures (
~ 6.3 km s-1) are Eggen's superclusters (Pleiades SCl, Hyades SCl
and Sirius SCl) with the whole Centaurus association. A new supercluster-like
structure is found with a mean velocity between the Sun and Sirius SCl velocities.
These structures are all characterized by a large age range which reflects the overall
sample age distribution. Moreover, a few old streams of ~ 2 Gyr are also extracted at this scale with high U components. We show that
all these large velocity dispersion structures represent 63% of the sample. This
percentage drops to 46% if we remove the velocity background created by a smooth
velocity ellipsoid in each structure. Smaller scales
(
3.8 and 2.4 km s-1) reveal that
superclusters are always substructured by 2 or more streams which generally exhibit a
coherent age distribution. At these scales, background stars are negligible and
percentages of stars in streams are 38% and 18% respectively.
Key words: methods: data analysis, Galaxy: solar neighbourhood / galaxies open clusters and associations / galaxies: kinematics and dynamics
© European Southern Observatory (ESO), 1999