2,051 research outputs found
Palomar 13: a velocity dispersion inflated by binaries ?
Recently, combining radial velocities from Keck/HIRES echelle spectra with
published proper motion membership probabilities, Cote et al (2002) observed a
sample of 21 stars, probable members of Palomar 13, a globular cluster in the
Galactic halo. Their projected velocity dispersion sigma_p = 2.2 +/-0.4 km/s
gives a mass-to-light ratio M/L_V = 40 +24/-17, about one order of magnitude
larger than the usual estimate for globular clusters. We present here radial
velocities measured from three different CCD frames of commissioning
observations obtained with the new ESO/VLT instrument FLAMES (Fibre Large Array
Multi Element Spectrograph). From these data, now publicly available, we
measure the homogeneous radial velocities of eight probable members of this
globular cluster. A new projected velocity dispersion sigma_p = 0.6-0.9 +/-0.3
km/s implies Palomar 13 mass-to-light ratio M/L_V = 3-7, similar to the usual
value for globular clusters. We discuss briefly the two most obvious reasons
for the previous unusual mass-to-light ratio finding: binaries, now clearly
detected, and more homogeneous data from the multi-fibre FLAMES spectrograph.Comment: 9 pages, 2 Postscript figure
Régionalisation de données entachées d'erreurs de mesure par krigeage : application à la pluviométrie
Le krigeage est largement utilisé pour l'interpolation d'une variable régionalisée. On montre cependant que si les points connus sont entachés d'une erreur de mesure non stationnaire, il convient de modifier la méthode classique en introduisant la notion de variogramme structural. Dès lors le krigeage peut être abordé de façon rigoureuse. On compare cette formulation à celle de Delhomme, dont on corrige l'expression de la variance. Un exemple d'application concernant la pluviométrie est présenté. (Résumé d'auteur
Exploring the gravitationally lensed system HE 1104-1805: Near-IR Spectroscopy
(Abridged) A new technique for the spatial deconvolution of spectra is
applied to near-IR (0.95 - 2.50 micron) NTT/SOFI spectra of the lensed,
radio-quiet quasar HE 1104-1805. The continuum of the lensing galaxy is
revealed between 1.5 and 2.5 micron. It is used in combination with previous
optical and IR photometry to infer a plausible redshift in the range 0.8 < z <
1.2. Modeling of the system shows that the lens is probably composed of the red
galaxy seen between the quasar images and a more extended component associated
with a galaxy cluster with fairly low velocity dispersion (~ 575 km/s). The
spectra of the two lensed images of the source show no trace of reddening at
the redshift of the lens nor at the redshift of the source. Additionally, the
difference between the spectrum of the brightest component a nd that of a
scaled version of the faintest component is a featureless continuum. Broad and
narrow emission lines, including the FeII features, are perfectly subtracted.
The very good quality of our spectrum makes it possible to fit precisely the
optical Fe II feature, taking into account the underlying continuum over a wide
wavelength range. HE 1104-1805 can be classified as a weak Fe II emitter.
Finally, the slope of the continuum in the brightest image is steeper than the
continuum in the faintest image and supports the finding by Wisotzki et al.
(1993) that the brightest image is microlensed. This is particularly
interesting in view of the new source reconstruction methods from
multiwavelength photometric monitoring.Comment: to be published in A&A, 8 pages, 9 postscript figure
Firedec: a two-channel finite-resolution image deconvolution algorithm
We present a two-channel deconvolution method that decomposes images into a
parametric point-source channel and a pixelized extended-source channel. Based
on the central idea of the deconvolution algorithm proposed by Magain, Courbin
& Sohy (1998), the method aims at improving the resolution of the data rather
than at completely removing the point spread function (PSF). Improvements over
the original method include a better regularization of the pixel channel of the
image, based on wavelet filtering and multiscale analysis, and a better
controlled separation of the point source vs. the extended source. In addition,
the method is able to simultaneously deconvolve many individual frames of the
same object taken with different instruments under different PSF conditions.
For this purpose, we introduce a general geometric transformation between
individual images. This transformation allows the combination of the images
without having to interpolate them. We illustrate the capability of our
algorithm using real and simulated images with complex diffraction-limited PSF.Comment: Accepted in A&A. An application of the technique to real data is
available in Cantale et al. http://arxiv.org/abs/1601.05192v
COSMOGRAIL: the COSmological MOnitoring of GRAvItational Lenses X. Modeling based on high-precision astrometry of a sample of 25 lensed quasars: consequences for ellipticity, shear, and astrometric anomalies
(abridged) Gravitationally lensed quasars can be used as powerful
cosmological and astrophysical probes. We can (i) infer the Hubble constant
based on the time-delay technique, (ii) unveil substructures along the l.o.s.
toward distant galaxies, and (iii) compare the shape and the slope of baryons
and dark matter distributions in galaxies. To reach these goals, we need
high-accuracy astrometry and morphology measurements of the lens. In this work,
we first present new astrometry for 11 lenses with measured time delays. Using
MCS deconvolution on NIC2 HST images, we reached an astrometric accuracy of
about 1-2.5 mas and an accurate shape measurement of the lens galaxy. Second,
we combined these measurements with those of 14 other systems to present new
mass models of these lenses. This led to the following results: 1) In 4
double-image quasars, we show that the influence of the lens environment on the
time delay can easily be quantified and modeled, hence putting these lenses
with high priority for time-delay determination. 2) For quadruple-image
quasars, the difficulty often encountered in reproducing the image positions to
milli-arcsec accuracy (astrometric anomaly) is overcome by explicitly including
the nearest visible galaxy in the model. However, one anomalous system
(J1131-1231) does not show any luminous perturber in its vicinity, and three
others (WFI2026-4536, WFI2033-4723, and B2045+265) have problematic modeling.
These 4 systems are the best candidates for a pertubation by a dark matter
substructure. 3) We find a significant correlation between the PA of the light
and of the mass distributions in lensing galaxies. In contrast with other
studies, we find that the ellipticity of the light and of the mass also
correlate well, suggesting that the overall spatial distribution of matter is
not very different from the baryon distribution in the inner \sim 5 kpc of
lensing galaxies.Comment: Accepted for publication in Astronomy and Astrophysics abridged
abstrac
Resolved Stellar Populations of Super-Metal-Rich Star Clusters in the Bulge of M31
We have applied the MCS image deconvolution algorithm (Magain, Courbin & Sohy
1998) to HST/WFPC2 V, I data of three M31 bulge globular clusters (G170, G177,
and G198) and control fields near each cluster. All three clusters are clearly
detected, with an increase in stellar density with decreasing radius from the
cluster centers; this is the first time that stars have been resolved in bulge
clusters in the inner regions of another galaxy. From the RGB slopes of the
clusters and the difference in I magnitude between the HB and the top of the
RGB, we conclude that these three clusters all have roughly solar metallicity,
in agreement with earlier integrated-light spectroscopic measurements. Our data
support a picture whereby the M31 bulge clusters and field stars were born from
the same metal-rich gas, early in the galaxy formation.Comment: 7 pages, 4 Postscript figures, accepted for publication in A&
On-axis spectroscopy of the host galaxies of 20 optically luminous quasars at z~0.3
We present the analysis of a sample of 20 bright low-redshift quasars
(M_B<-23 and z < 0.35) observed spectroscopically with the VLT. The FORS1
spectra, obtained in Multi Object Spectroscopy (MOS) mode, allow to observe
simultaneously the quasars and several reference stars used to spatially
deconvolve the data. Applying the MCS deconvolution method, we are able to
separate the individual spectra of the quasar and of the underlying host
galaxy. Contrary to some previous claims, we find that luminous quasars are not
exclusively hosted by massive ellipticals. Most quasar host galaxies harbour
large amounts of gas, irrespective of their morphological type. Moreover, the
stellar content of half of the hosts is a young Sc-like population, associated
with a rather low metallicity interstellar medium. A significant fraction of
the galaxies contain gas ionized at large distances by the quasar radiation.
This large distance ionization is always associated with signs of gravitational
interactions (as detected from images or disturbed rotation curves). The
spectra of the quasars themselves provide evidence that gravitational
interactions bring dust and gas in the immediate surrounding of the super
massive black hole, allowing to feed it. The quasar activity might thus be
triggered (1) in young gas-rich spiral galaxies by local events and (2) in more
evolved galaxies by gravitational interactions or collisions. The latter
mechanism gives rises to the most powerful quasars. Finally, we derive mass
models for the isolated spiral host galaxies and we show that the most reliable
estimators of the systemic redshift in the quasar spectrum are the tips of the
Ha and Hb lines.Comment: 30 pages, 19 figures, 9 tables, accepted for publication in MNRAS,
major revisio
Sub-arcsecond imaging and spectroscopy of the radio-loud highly polarized quasar PKS 1610-771
We report on imaging and spectroscopic observations of the radio-loud, highly
polarized quasar PKS 1610-771 (z = 1.71). Our long-slit spectroscopy of the
companion 4.55 arcseconds NW of the quasar confirms the stellar nature of this
object, so ruling out the previously suspected gravitationally lensed nature of
this system. PKS 1610-771 looks fuzzy on our sub-arcsecond R and I images and
appears located in a rich environment of faint galaxies. Possible
magnification, without image splitting of the quasar itself, by some of these
maybe foreground galaxies cannot be excluded. The continuum fuzz (made of the
closest two objects, viz. A and D) is elongated in a direction orthogonal to
the E vector of the optical polarization, as in high-redshift radio-galaxies.
The spectrum of PKS 1610-771 appears strongly curved, in a convex way, with a
maximum of intensity at ~ 7,600 A (2,800 A rest frame), possibly indicating a
strong ultraviolet absorption by dust.Comment: 6 pages, uuencoded gziped tar file including TeX file + postscript
figures. Accepted for publication in A&A main journa
Mayall II = G1 in M31: Giant Globular Cluster or Core of a Dwarf Elliptical Galaxy ?
(Abridged version) Mayall II = G1 is one of the brightest globular clusters
belonging to M31, the Andromeda galaxy. Our observations with HST/WFPC2 provide
data for the (I vs. V-I) and (V vs. V-I) color-magnitude diagrams. From model
fitting, we determine a rather high mean metallicity of [Fe/H] = --0.95 +-
0.09, somewhat similar to 47 Tucanae. We find a larger spread in V-I than can
be explained by the measurement errors, and we attribute this to an intrinsic
metallicity dispersion amongst the stars of G1. So far, only omega Centauri,
the giant Galactic globular cluster, has been known to exhibit such an
intrinsic metallicity dispersion.
Three estimates of the total mass of this globular cluster can be obtained:
King mass = 15 x 10^6 with M/Lv ~ 7.5, Virial mass = 7.3 x 10^6 with M/Lv ~
3.6, and King-Michie mass range from 14 to 17 x 10^6. Although uncertain, all
of these mass estimates make G1 more than twice as massive as omega Centauri.
Such large masses relate to the metallicity spread whose origin is still
unknown (either self-enrichment, an inhomogeneous proto-cluster cloud, or
remaining core of a dwarf galaxy). When considering the positions of G1 in the
different diagrams defined by Kormendy (1985), G1 always appears on the
sequence defined by globular clusters, and definitely away from the other
sequences defined by elliptical galaxies, bulges, and dwarf spheroidal
galaxies. The same is true for omega Centauri and for the nucleus of the dwarf
elliptical NGC 205. This does not prove that all (massive) globular clusters
are the remnant cores of nucleated dwarf galaxies.Comment: 24 pages, 5 figures, accepted for publication in AJ (August 2001
Role of Complement-Derived and Bacterial Formylpeptide Chemotactic Factors in the In Vivo Migration of Neutrophils in Experimental Escherichia coli Pyelonephritis in Rats
In experimental Escherichia coli pyelonephritis, the bacterial multiplication in the kidney parenchyma triggers a burst of neutrophil extravascular migration, as measured by the myeloperoxidase (MPO) activity in the kidney, a marker for tissue neutrophil infiltration. To test the mechanisms of in vivo neutrophil migration, pyelonephritis was surgically induced in rats that were then either complement-depleted with cobra venom factor (CVF), resulting in a profound hypocomplementemia for 72 h after inoculation, or treated with phenylbutazone (PB), a competitive antagonist of bacterial chemotactic formylpeptides. Compared to controls, CVF-and PB-treated animals killed when the neutrophil infiltration started (32 h) had a significantly reduced neutrophil infiltration, as measured by kidney MPO activity. This effect disappeared in animals killed 72 h after surgery, when neutrophil infiltration peaked. These data suggest that redundant chemotactic mechanisms triggered neutrophil migration. Inhibiting one of these mechanisms only transiently delayed neutrophil migration but did not affect the peak infiltratio
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