667 research outputs found
A catalogue of velocities in the cluster of galaxies Abell 85
We present a catalogue of velocities for 551 galaxies (and give the
coordinates of 39 stars misclassified as galaxies in our photometric plate
catalogue) in a region covering about 100'100' (0.940.94 Mpc
for an average redshift of 0.0555, assuming H=50 km s
Mpc) in the direction of the rich cluster Abell 85. This catalogue
includes previously published redshifts by Beers et al. (1991) and Malumuth et
al. (1992), together with our 367 new measurements. A total of 305 galaxies
have velocities in the interval 13350-20000 km s, and will be considered
as members of the cluster. Abell 85 therefore becomes one of the clusters with
the highest number of measured redshifts; its optical properties are being
investigated in a companion paper.Comment: Accepted for publication in A&AS, Table 4 available in electronic
form onl
Unveiling hidden structures in the Coma cluster
We have assembled a large data-set of 613 galaxy redshifts in the Coma
cluster, the largest presently available for a cluster of galaxies. We have
defined a sample of cluster members complete to b, using a
membership criterion based on the galaxy velocity, when available, or on the
galaxy magnitude and colour, otherwise. Such a data set allows us to define
nearly complete samples within a region of 1~\Mpc\ radius, with a sufficient
number of galaxies per sample to make statistical analyses possible. Using this
sample and the {\em ROSAT} PSPC X--ray image of the cluster, we have
re-analyzed the structure and kinematics of Coma, by applying the wavelet and
adaptive kernel techniques. A striking coincidence of features is found in the
distributions of galaxies and hot intracluster gas. The two central dominant
galaxies, NGC4874 and NGC4889, are surrounded by two galaxy groups, mostly
populated with galaxies brighter than b and well separated in
velocity space. On the contrary, the fainter galaxies tend to form a single
smooth structure with a central peak coinciding in position with a secondary
peak detected in X--rays, and located between the two dominant galaxies; we
suggest to identify this structure with the main body of the Coma cluster. A
continuous velocity gradient is found in the central distribution of these
faint galaxies, a probable signature of tidal interactions rather than
rotation. There is evidence for a bound population of bright galaxies around
other brightest cluster members. Altogether, the Coma cluster structure seems
to be better traced by the faint galaxy population, the bright galaxies being
located in subclusters. We discuss this evidence in terms of an ongoing
accretion of groups onto the cluster.Comment: to appear in A&A, 19 pages, uuencoded gzipped postscript fil
On the galaxy luminosity function in the central regions of the Coma cluster
We have obtained new redshifts for 265 objects in the central
48~~25~arcmin region of the Coma cluster. When supplemented with
literature data, our redshift sample is 95~\% complete up to a magnitude
b=18.0 (the magnitudes are taken from the photometric sample of Godwin
et al. 1983). Using redshift-confirmed membership for 205 galaxies, and the
location in the colour-magnitude diagram for another 91 galaxies, we have built
a sample of cluster members which is complete up to b=20.0. We show
that the Coma cluster luminosity function cannot be adequately fitted by a
single Schechter (1976) function, because of a dip in the magnitude
distribution at b17. The superposition of an Erlang (or a Gauss)
and a Schechter function provides a significantly better fit. We compare the
luminosity function of Coma to those of other clusters, and of the field.
Luminosity functions for rich clusters look similar, with a maximum at , while the Virgo and the field luminosity
functions show a nearly monotonic behaviour. These differences may be produced
by physical processes related to the environment which affect the luminosities
of a certain class of cluster galaxies.Comment: 7 pages, uuencoded postscript file (figures included) Accepted for
publication on A&
A photometric catalogue of galaxies in the cluster Abell 85
We present two catalogues of galaxies in the direction of the rich cluster
\a85. The first one includes 4,232 galaxies located in a region
from the cluster centre. It has been obtained from a list of more than 25,000
galaxy candidates detected by scanning a Schmidt photographic plate taken in
the \bj band. Positions are very accurate in this catalogue but magnitudes are
not. This led us to perform CCD imaging observations in the V and R bands to
calibrate these photographic magnitudes. A second catalogue (805 galaxies)
gives a list of galaxies with CCD magnitudes in the V and R bands for a much
smaller region in the centre of the cluster. These two catalogues will be
combined with a redshift catalogue of 509 galaxies (Durret et al. 1997;
astro-ph/9709298) to investigate the cluster properties at optical wavelengths
(Durret et al. in preparation), as a complement to our previous X-ray studies
(Pislar et al. 1997, Lima-Neto et al. 1997).Comment: accepted for publication in A&AS; 7 pages, including 8 figures,
Tables are only available in electronic form at the CDS via anonymous ftp to
cdsarc.u-strasbg.fr (130.79.128.5
Investigating the Effectiveness of the Tutorials in Introductory Physics in Multiple Instructional Settings
This paper examines the educational impact of the implementation of "Changes
in Energy and Momentum" from the Tutorials in Introductory Physics in five
different instructional settings. These settings include (1) a completely
computer-based learning environment and (2) use of cooperative learning groups
with varying levels of instructor support. Pre- and post-tests provide evidence
that a computer-based implementation falls significantly short of classroom
implementations which involve both collaborative learning groups and
interactions with a teaching assistance. Other findings provide insight into
the importance of certain elements of instructor training and the appropriate
use of the tutorial as an initial introduction to a new concept.Comment: 8 Pages, 3 figures, 4 table
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