[Show abstract][Hide abstract] ABSTRACT: We analyzed the space distribution of 117 galaxies in an area of 0.9 deg
radius centered on NGC 6045 in the Hercules cluster in the velocity
range 9000 to 14,000 km/s. By taking advantage of 74 morphologies based
on CCD images, we succeed in isolating a cluster of galaxies with an
average velocity of 11,467 km/s located to the NE of the assumed
centroid of A2151, where early and late type galaxies share the same
dynamical properties. The implications of this result for the nature and
identification of the x-ray source is briefly discussed.
The Astronomical Journal 01/1995; 109:465-472. · 4.97 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: 216 redshifts have been obtained in a region of 981 sq deg south of the
Hercules supercluster. 172 of these redshifts are of galaxies with
mpg less than or equal to 15.1, 110 of which had no previous
velocity measurement. 44 new redshifts are of galaxies fainter than
mpg = 15.1. With these new data we have been able to define a
sample in a vast region (approximately 1700 sq deg) around Hercules
limited to mpg less than or equal to 15.1 with a velocity
completeness of 81.5%. 189 galaxies have been morphologically classified
so that all galaxies in the sample with known velocity now also have
known morphology. The magnitude limited sample, including 556 galaxies,
is then used to identify and describe galaxy structures in the region.
We find that the overdense volume is small, that its overall appearance
is that of a coral branch floating in a sea of nothing and that early
and late type galaxies defined different structures.
The Astronomical Journal 04/1994; 107:1629-1636. · 4.97 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A search of unpublished observations yielded data for eight clusters of galaxies in the southern hemisphere. Presented are finding charts, positions, and radial velocities for 80 galaxies in these clusters, together with morphological classification of the galaxies and estimates of cluster velocity dispersions in cases when more than seven velocities of member galaxies were available.
[Show abstract][Hide abstract] ABSTRACT: Attention has been drawn to the importance of environmental effects,
given a strong morphological segregation of the dwarf galaxies. A simple
quantitative test for segregation between dwarfs and giants is
suggested. The dwarf elliptical (dE) galaxies are considered to be
confined to the clouds and to strongly prefer dense environments on all
scales. Their abundance (per giant) is observed to be much lower in the
field than in the clusters and the few dE systems outside of the
clusters (i.e., in the clouds) look like companions to the giant
galaxies. Thus, the dwarf galaxies are shown to obey a
morphology-density relation in the same way as the giants do, and not
only in the restricted environment of the Virgo cluster.
Astronomy and Astrophysics 01/1990; 228:42-60. · 5.08 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: New X-ray and optical observations of the BL Lac object 3C 66A show
small amplitude (≡30%) variability occurring probably
contemporaneously in both ranges. The time scale is of the order of a
week. This indicates that small intensity variations engage the whole
electromagnetic spectrum of the source between visible and X-ray
wavelengths, while large outbursts are mainly confined in the X-ray
band. No evidence is found for a steep X-ray spectrum at times of low
intensity levels, as had been previously found, hinting to a different
physical process in the source at times of large X-ray outbursts.
Astronomy and Astrophysics 04/1987; 178:21-24. · 5.08 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Images and spectra of Comet IRAS-Araki-Alcock obtained on May 13, 1983
at ESO are analyzed. The distributions of the dust and of gaseous
species (C2, CN, C3, NH2, and O I) in a region surrounding the nucleus
are derived. The data reveal that the nucleus is surrounded by a cloud
of solid particles whose continuum emission distribution is represented
by a Gaussian function of about 20 km. The structure of the continuum
emission indicates that this central region is embedded in an asymmetric
cloud of solid particles of smaller size, and the structure of the
gaseous emission distribution reveals that the neutral coma cannot be
described in terms of steady activity of the nucleus. The structures of
the sunward and antisunward profiles of the continuum emission are
compared, and it is determined that the unlit side of the nucleus
outgases at a rate one third less than that of the lit side. The
lifetimes of the discrete emissions are evaluated.
Astronomy and Astrophysics 02/1987; 174:299-305. · 5.08 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: On 1979 June 3 - 6, a number of spectra of SS433 were obtained using the
UCL Image Photon Counting System on the 3.6-m telescope of the European
Southern Observatory, La Silla, Chile. The stationary Hα and He I
λλ5875, 6678 and 7065 lines have a complex structure which
on June 4 - 5 exhibited a central feature accompanied by two equally
displaced (±1000 km s-1) side components. Variability
of the line profile and equivalent width is observed on time-scales as
short as a quarter of an hour.
Monthly Notices of the Royal Astronomical Society 12/1986; 224:323-334. · 5.52 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A sequence of several images of the recently proposed optical
counterpart of the X-ray source 1E 0630+178, possibly associated with
the bright γ-ray source Geminga, is presented and discussed. From
these data covering 410 days, an upper limit of 0arcsec.1 on its
parallax can be derived, which places the object definitely further than
10 pc from the solar system. No evidence of proper motion has been
detected up to 0arcsec.2/yr, which again places it further than 10 pc
for a tangential velocity of 10 km s-1 relatively to the Sun.
UBV photometry is compatible with the object being a G star, without
measurable long-term variability. Another possible identification
involves a very faint (B ≅ 24.3) object.
Astronomy and Astrophysics 02/1985; 144:109-114. · 5.08 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: NGC 4151 was observed four times in Nov. 83. The results indicate that: a) there exists a correlation between the X-ray and UV fluxes on the long term; b) the soft X-ray excess between 0.1 and 1 keV is probably steeper than expected from the leaky absorber model by Holt et al (1980); c)the spectral fit to the ME data, after correction for a soft component, yields =1,730.27, NH=(15.22.2)1022 cm–2, E.W.(Fe line)=0.2080.084 keV, and does not require a strong overabundance of Fe in the absorber. The relationship between NH and the strength of the broad emission lines is commented.
Space Science Reviews 01/1985; 40(3):593-596. · 5.52 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Preliminary results obtained with IUE and the ME and LE EXOSAT instruments indicate the existence of a long term correlation between the UV and the X-ray continuum intensities, and confirm the presence of the soft X-ray excess discovered by Holt et al. (1980).
[Show abstract][Hide abstract] ABSTRACT: The Seyfert nucleus of NGC 4151 was monitored for six years, including
periods of intensive study of the complex variations in the ultraviolet
spectra with IUE. Important IUE results relating to the broad line
region (BLR) and its physical conditions are reviewed herein. Active
galactic nuclei like NGC 4151 are studied to derive detailed constraints
on radiation mechanisms and physical conditions in the emission region,
and hence also constraints on possible central power sources. The
ultraviolet spectrum of NGC 4151 comprises continuum, strong emission
lines with different widths along with a rich absorption line spectrum.
Variations in the broad absorption lines seem to derive principally from
changes in column densities of absorbing species rather than in velocity
dispersions or line profiles.
[Show abstract][Hide abstract] ABSTRACT: Radio maps of the irregular galaxy UGC 6697 in A1367, obtained at 0.6,
1.4, and 5 GHz with the WSRT and at 1.4 GHz with the VLA, are presented
and combined with multicolor 4-m KPNO observations to establish that the
marked asymmetry of the radio source (resembling a head-tail source)
reflects an intrinsic asymmetry of the parent galaxy. Narrow-band
H-alpha observations reveal a ringlike structure in this object, which
indicates that the galaxy is not seen edge-on. The peculiar rotation
curve of UGC 6697, as derived from IPCS spectra, can be interpreted as
due to a rotating ring with strong non-circular motions. The many pieces
of data collected on this interesting object are discussed in the
context of a possible interaction between UGC 6697 and the IGM or with
its companion galaxy.
Astronomy and Astrophysics 07/1984; 137:235-244. · 5.08 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The authors present observations, spectroscopic and photometric, of a
subsample of the Shapley catalogue in Horologium. The clumpy
distribution of objects is dominated by a structure at = 13436
Astronomy and Astrophysics Supplement Series 06/1984; 57:1-21.
[Show abstract][Hide abstract] ABSTRACT: Long et al. (1981) detected 97 soft X-ray sources by means of the
imaging X-ray telescopes aboard the Einstein Observatory during a study
of the Large Magellanic Cloud. Further spectroscopic observations have
revealed a typical Seyfert 1 galaxy. The presence of a correlation in
this galaxy between a Seyfert nucleus and an external ring could have
important implications for attempts to explain the origin of the
Seyferts in terms of dynamical perturbations, collisions, or explosions.
Astronomy and Astrophysics 02/1984; 132:351-353. · 5.08 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: An analysis of NGC 4151's absorption line behavior has been conducted on
the basis of 90 of the ESA data base's low dispersion, high resolution
and large aperture UV spectra for the April 1978-February 1982 period.
Attention is also given to features of the visible and X-ray spectra of
this source. It is found that the continuum source is double, with one
constant component and the other variable. The absorbing clouds cover
the variable continuum source, as well as the broad emission line
[Show abstract][Hide abstract] ABSTRACT: Attention is given to the technical aspects of photometric measurements of 109 galaxies near the center of the Virgo Cluster, noting various types of radii and surface brightness for about 50 E and dE galaxies in the sample that range in absolute magnitude from -20 to -12. These data are combined with data from the literature for giant E and dwarf E galaxies in the Local Group to study the systematic properties of E galaxies over a range of one million luminosities. The radial intensity profiles derived are fitted to the manifold of King (1978) models to derive model-dependent central surface brightness, core radii, and cutoff radii.
The Astronomical Journal 02/1984; · 4.97 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Observations of the variability of the three strong ultraviolet emission
lines in the Seyfert galaxy NGC 4151 (C IV, C III] and Mg II) are used
to study the structure of the broad line region and the nuclear energy
source of this active galaxy. Data on the line profile variations
further permit the kinematic mapping of the broad line region through
the response of the line profiles to the sudden continuum increase
during 1979 May. From the widths and variability time-scales of the
three emission lines the authors deduce values of the quantity
v2r, which is proportional to a mass. The three independent
estimates converge on 0.5 - 1×108 M_sun;. It is shown
that the behaviour is compatible with the black hole/accretion disc
model of Lynden-Bell (1969).
Monthly Notices of the Royal Astronomical Society 12/1983; 206:221-237. · 5.52 Impact Factor