18,409 research outputs found
The dark matter distribution in z~0.5 clusters of galaxies. I : Determining scaling relations with weak lensing masses
The total mass of clusters of galaxies is a key parameter to study massive
halos. It relates to numerous gravitational and baryonic processes at play in
the framework of large scale structure formation, thus rendering its
determination important but challenging. From a sample of the 11 X-ray bright
clusters selected from the excpres sample, we investigate the optical and X-ray
properties of clusters with respect to their total mass derived from weak
gravitational lensing. From multi-color wide field imaging obtained with
MegaCam at CFHT, we derive the shear profile of each individual cluster of
galaxies. We perform a careful investigation of all systematic sources related
to the weak lensing mass determination. The weak lensing masses are then
compared to the X-ray masses obtained from the analysis of XMM observations and
assuming hydrostatic equilibrium. We find a good agreement between the two mass
proxies although a few outliers with either perturbed morphology or poor
quality data prevent to derive robust mass estimates. The weak lensing mass is
also correlated with the optical richness and the total optical luminosity, as
well as with the X-ray luminosity, to provide scaling relations within the
redshift range 0.4<z<0.6. These relations are in good agreement with previous
works at lower redshifts. For the L_X-M relation we combine our sample with two
other cluster and group samples from the literature, thus covering two decades
in mass and X-ray luminosity, with a regular and coherent correlation between
the two physical quantities
Standard Cosmic Ray Energetics and Light Element Production
The recent observations of Be and B in metal poor stars has led to a
reassessment of the origin of the light elements in the early Galaxy. At low it
is metallicity ([O/H] < -1.75), it is necessary to introduce a production
mechanism which is independent of the interstellar metallicity (primary). At
higher metallicities, existing data might indicate that secondary production is
dominant. In this paper, we focus on the secondary process, related to the
standard Galactic cosmic rays, and we examine the cosmic ray energy
requirements for both present and past epochs. We find the power input to
maintain the present-day Galactic cosmic ray flux is about 1.5e41 erg/s = 5e50
erg/century. This implies that, if supernovae are the sites of cosmic ray
acceleration, the fraction of explosion energy going to accelerated particles
is about 30%, a value which we obtain consistently both from considering the
present cosmic ray flux and confinement and from the present 9Be and 6Li
abundances. Using the abundances of 9Be (and 6Li) in metal-poor halo stars, we
extend the analysis to show the effect of the interstellar gas mass on the
standard galactic cosmic ray energetic constraints on models of Li, Be, and B
evolution. The efficiency of the beryllium production per erg may be enhanced
in the past by a factor of about 10; thus the energetic requirement by itself
cannot be used to rule out a secondary origin of light elements. Only a clear
and undisputable observational determination of the O-Fe relation in the halo
will discriminate between the two processes. (abridged)Comment: 24 pages, LaTeX, uses aastex macro
Absolute-Magnitude Distributions and Light Curves of Stripped-Envelope Supernovae
The absolute visual magnitudes of three Type IIb, 11 Type Ib and 13 Type Ic
supernovae (collectively known as stripped-envelope supernovae) are studied by
collecting data on the apparent magnitude, distance, and interstellar
extinction of each event. Weighted and unweighted mean absolute magnitudes of
the combined sample as well as various subsets of the sample are reported. The
limited sample size and the considerable uncertainties, especially those
associated with extinction in the host galaxies, prevent firm conclusions
regarding differences between the absolute magnitudes of supernovae of Type Ib
and Ic, and regarding the existence of separate groups of overluminous and
normal-luminosity stripped-envelope supernovae. The spectroscopic
characteristics of the events of the sample are considered. Three of the four
overluminous events are known to have had unusual spectra. Most but not all of
the normal luminosity events had typical spectra. Light curves of
stripped-envelope supernovae are collected and compared. Because SN 1994I in
M51 was very well observed it often is regarded as the prototypical Type Ic
supernova, but it has the fastest light curve in the sample. Light curves are
modeled by means of a simple analytical technique that, combined with a
constraint on E/M from spectroscopy, yields internally consistent values of
ejected mass, kinetic energy, and nickel mass.Comment: 39 pages, 14 figures, 7 tables; Accepted to A
Polariton propagation in weak confinement quantum wells
Exciton-polariton propagation in a quantum well, under centre-of-mass
quantization, is computed by a variational self-consistent microscopic theory.
The Wannier exciton envelope functions basis set is given by the simple
analytical model of ref. [1], based on pure states of the centre-of-mass wave
vector, free from fitting parameters and "ad hoc" (the so called additional
boundary conditions-ABCs) assumptions. In the present paper, the former
analytical model is implemented in order to reproduce the centre-of-mass
quantization in a large range of quantum well thicknesses (5a_B < L < inf.).
The role of the dynamical transition layer at the well/barrier interfaces is
discussed at variance of the classical Pekar's dead-layer and ABCs. The Wannier
exciton eigenstates are computed, and compared with various theoretical models
with different degrees of accuracy. Exciton-polariton transmission spectra in
large quantum wells (L>> a_B) are computed and compared with experimental
results of Schneider et al.\cite{Schneider} in high quality GaAs samples. The
sound agreement between theory and experiment allows to unambiguously assign
the exciton-polariton dips of the transmission spectrum to the pure states of
the Wannier exciton center-of-mass quantization.Comment: 15 pages, 15 figures; will appear in Phys.Rev.
SN 2008inâBridging the Gap between Normal and Faint Supernovae of Type IIP
We present optical photometric and low-resolution spectroscopic observations of the Type II plateau supernova (SN) 2008in, which occurred in the outskirts of the nearly face-on spiral galaxy M61. Photometric data in the X-ray, ultraviolet, and near-infrared bands have been used to characterize this event. The SN field was imaged with the ROTSE-IIIb optical telescope about seven days before the explosion. This allowed us to constrain the epoch of the shock breakout to JD = 2454825.6. The duration of the plateau phase, as derived from the photometric monitoring, was ~98 days. The spectra of SN 2008in show a striking resemblance to those of the archetypal low-luminosity IIP SNe 1997D and 1999br. A comparison of ejecta kinematics of SN 2008in with the hydrodynamical simulations of Type IIP SNe by Dessart et al. indicates that it is a less energetic event (~5 Ă 10^(50) erg). However, the light curve indicates that the production of radioactive ^(56)Ni is significantly higher than that in the low-luminosity SNe. Adopting an interstellar absorption along the SN direction of AV ~ 0.3 mag and a distance of 13.2 Mpc, we estimated a synthesized ^(56)Ni mass of ~0.015 M_â. Employing semi-analytical formulae derived by Litvinova and Nadezhin, we derived a pre-SN radius of ~126 R_â, an explosion energy of ~5.4 Ă 10^(50) erg, and a total ejected mass of ~16.7 M_â. The latter indicates that the zero-age main-sequence mass of the progenitor did not exceed 20 M_â. Considering the above properties of SN 2008in and its occurrence in a region of sub-solar metallicity ([O/H] ~ 8.44 dex), it is unlikely that fall-back of the ejecta onto a newly formed black hole occurred in SN 2008in. We therefore favor a low-energy explosion scenario of a relatively compact, moderate-mass progenitor star that generates a neutron star
A two-component model for fitting light-curves of core-collapse supernovae
We present an improved version of a light curve model, which is able to
estimate the physical properties of different types of core-collapse supernovae
having double-peaked light curves, in a quick and efficient way. The model is
based on a two-component configuration consisting of a dense, inner region and
an extended, low-mass envelope. Using this configuration, we estimate the
initial parameters of the progenitor via fitting the shape of the
quasi-bolometric light curves of 10 SNe, including Type IIP and IIb events,
with model light curves. In each case we compare the fitting results with
available hydrodynamic calculations, and also match the derived expansion
velocities with the observed ones. Furthermore, we also compare our
calculations with hydrodynamic models derived by the SNEC code, and examine the
uncertainties of the estimated physical parameters caused by the assumption of
constant opacity and the inaccurate knowledge of the moment of explosion
SARCS strong lensing galaxy groups: I - optical, weak lensing, and scaling laws
We present the weak lensing and optical analysis of the SL2S-ARCS (SARCS)
sample of strong lens candidates. The sample is based on the Strong Lensing
Legacy Survey (SL2S), a systematic search of strong lensing systems in the
photometric Canada-France-Hawaii Telescope Legacy Survey (CFHTLS). The SARCS
sample focuses on arc-like features and is designed to contain mostly galaxy
groups. We briefly present the weak lensing methodology that we use to estimate
the mass of the SARCS objects. Among 126 candidates, we obtain a weak lensing
detection for 89 objects with velocity dispersions of the Singular Isothermal
Sphere mass model ranging from 350 to 1000 km/s with an average value of
600km/s, corresponding to a rich galaxy group (or poor cluster). From the
galaxies belonging to the bright end of the group's red sequence (M_i<-21), we
derive the optical properties of the SARCS candidates. We obtain typical
richnesses of N=5-15 galaxies and optical luminosities of L=0.5-1.5e+12 Lsol
(within a radius of 0.5 Mpc). We use these galaxies to compute luminosity
density maps, from which a morphological classification reveals that a large
fraction of the sample are groups with a complex light distribution, either
elliptical or multimodal, suggesting that these objects are dynamically young
structures. We finally combine the lensing and optical analyses to draw a
sample of 80 most secure group candidates, i.e. weak lensing detection and
over-density at the lens position in the luminosity map, to remove false
detections and galaxy-scale systems from the initial sample. We use this
reduced sample to probe the optical scaling relations in combination with a
sample of massive galaxy clusters. We detect the expected correlations over the
probed range in mass with a typical scatter of 25% in the SIS velocity
dispersion at a given richness or luminosity, making these scaling laws
interesting mass proxie
Aeronautical engineering: A special bibliography with indexes, supplement 82, April 1977
This bibliography lists 311 reports, articles, and other documents introduced into the NASA scientific and technical information system in March 1977
SN 2015ba: A type IIP supernova with a long plateau
We present optical photometry and spectroscopy from about a week after
explosion to 272 d of an atypical Type IIP supernova, SN 2015ba, which
exploded in the edge-on galaxy IC 1029. SN 2015ba is a luminous event with an
absolute V-band magnitude of -17.10.2 mag at 50 d since explosion and has
a long plateau lasting for 123 d. The distance to the SN is estimated to
be 34.80.7 Mpc using the expanding photosphere and standard candle
methods. High-velocity H-Balmer components constant with time are observed in
the late-plateau phase spectra of SN 2015ba, which suggests a possible role of
circumstellar interaction at these phases. Both hydrodynamical and analytical
modelling suggest a massive progenitor of SN 2015ba with a pre-explosion mass
of 24-26 M. However, the nebular spectra of SN 2015ba exhibit
insignificant levels of oxygen, which is otherwise expected from a massive
progenitor. This might be suggestive of the non-monotonical link between O-core
masses and the zero-age main-sequence mass of pre-supernova stars and/or
uncertainties in the mixing scenario in the ejecta of supernovae.Comment: 42 pages, 7 pages Appendix, 20 figures, 10 tables, Accepted for
publication in MNRAS, 14-June-201
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