1,492 research outputs found
Gas and dust properties in the afterglow spectra of GRB 050730
We present early WHT ISIS optical spectroscopy of the afterglow of gamma-ray
burst GRB 050730. The spectrum shows a DLA system with the highest measured
hydrogen column to date: N(HI) = 22.1 +/- 0.1 at the third-highest GRB redshift
z = 3.968. Our analysis of the Swift XRT X-ray observations of the early
afterglow show X-ray flares accompanied by decreasing X-ray absorption. From
both the optical and the X-ray spectra we constrain the dust and gas properties
of the host galaxy. We find the host to be a low metallicity galaxy, with low
dust content. Much of the X-ray absorbing gas is situated close to the GRB,
whilst the HI absorption causing the DLA is most likely located further out.Comment: 5 pages, 2 figures. Accepted for A&A Letter
Perturbations of nuclear C*-algebras
Kadison and Kastler introduced a natural metric on the collection of all
C*-subalgebras of the bounded operators on a separable Hilbert space. They
conjectured that sufficiently close algebras are unitarily conjugate. We
establish this conjecture when one algebra is separable and nuclear. We also
consider one-sided versions of these notions, and we obtain embeddings from
certain near inclusions involving separable nuclear C*-algebras. At the end of
the paper we demonstrate how our methods lead to improved characterisations of
some of the types of algebras that are of current interest in the
classification programme.Comment: 45 page
Modeling Eridani and asteroseismic tests of element diffusion
Taking into account the helium and metal diffusion, we explore the possible
evolutionary status and perform seismic analysis of MOST target: the star
Eridani. We adopt the different input parameters to construct the
models by fitting the available observational constraints: e.g., ,
, , . From computation, we obtain the average large spacings of
Eridani about Hz. The age of the diffused models has
been found to be about 1 Gyr, which is younger than one determined previously
by models without diffusion. We found that the effect of pure helium diffusion
on the internal structure of the young low-mass star is slight, but the metal
diffusion influence is obvious. The metal diffusion leads the models to have
much higher temperature in the radiation interior, correspondingly the higher
sound speed in the interior of the model, thereby the larger frequency and
spacings.Comment: 16 pages, 4 figures, accepted for publication in ChjA
An Introduction to Data Analysis in Asteroseismology
A practical guide is presented to some of the main data analysis concepts and
techniques employed contemporarily in the asteroseismic study of stars
exhibiting solar-like oscillations. The subjects of digital signal processing
and spectral analysis are introduced first. These concern the acquisition of
continuous physical signals to be subsequently digitally analyzed. A number of
specific concepts and techniques relevant to asteroseismology are then
presented as we follow the typical workflow of the data analysis process,
namely, the extraction of global asteroseismic parameters and individual mode
parameters (also known as peak-bagging) from the oscillation spectrum.Comment: Lecture presented at the IVth Azores International Advanced School in
Space Sciences on "Asteroseismology and Exoplanets: Listening to the Stars
and Searching for New Worlds" (arXiv:1709.00645), which took place in Horta,
Azores Islands, Portugal in July 201
Combating COVID-19-The role of robotics in managing public health and infectious diseases.
COVID-19 may drive sustained research in robotics to address risks of infectious diseases
Distribution of carrier multiplication rates in CdSe and InAs nanocrystals
The distribution of rates of carrier multiplication (CM) following photon
absorption is calculated for semiconductor nanocrystals (NCs). The NC
electronic structure is described using a screened pseudopotential method known
to give reliable description of NC excitons. The rates of biexciton generation
are calculated using the Fermi golden rule with all relevant Coulomb matrix
elements, taking into account proper selection rules. In CdSe and InAs NCs we
find a broad distribution biexciton generation rates depending strongly on the
exciton energy and size of the NC. The process becomes inefficient for NC
exceeding 3 nm in diameter in the photon energy range of 2-3 times the band
gap.Comment: 4 pages 3 fi
Planck intermediate results. XXIX. All-sky dust modelling with Planck, IRAS, and WISE observations
We present all-sky modelling of the high resolution Planck, IRAS, and WISE
infrared (IR) observations using the physical dust model presented by Draine
and Li in 2007 (DL). We study the performance and results of this model, and
discuss implications for future dust modelling. The present work extends the DL
dust modelling carried out on nearby galaxies using Herschel and Spitzer data
to Galactic dust emission. We employ the DL dust model to generate maps of the
dust mass surface density, the optical extinction Av, and the starlight
intensity parametrized by Umin. The DL model reproduces the observed spectral
energy distribution (SED) satisfactorily over most of the sky, with small
deviations in the inner Galactic disk and in low ecliptic latitude areas. We
compare the DL optical extinction Av for the diffuse interstellar medium with
optical estimates for 2 10^5 quasi-stellar objects (QSOs) observed in the Sloan
digital sky survey. The DL Av estimates are larger than those determined
towards QSOs by a factor of about 2, which depends on Umin. The DL fitting
parameter Umin, effectively determined by the wavelength where the SED peaks,
appears to trace variations in the far-IR opacity of the dust grains per unit
Av, and not only in the starlight intensity. To circumvent the model
deficiency, we propose an empirical renormalization of the DL Av estimate,
dependent of Umin, which compensates for the systematic differences found with
QSO observations. This renormalization also brings into agreement the DL Av
estimates with those derived for molecular clouds from the near-IR colours of
stars in the 2 micron all sky survey. The DL model and the QSOs data are used
to compress the spectral information in the Planck and IRAS observations for
the diffuse ISM to a family of 20 SEDs normalized per Av, parameterized by
Umin, which may be used to test and empirically calibrate dust models.Comment: Final version that has appeared in A&
Planck 2015 results. XXIII. The thermal Sunyaev-Zeldovich effect--cosmic infrared background correlation
We use Planck data to detect the cross-correlation between the thermal
Sunyaev-Zeldovich (tSZ) effect and the infrared emission from the galaxies that
make up the the cosmic infrared background (CIB). We first perform a stacking
analysis towards Planck-confirmed galaxy clusters. We detect infrared emission
produced by dusty galaxies inside these clusters and demonstrate that the
infrared emission is about 50% more extended than the tSZ effect. Modelling the
emission with a Navarro--Frenk--White profile, we find that the radial profile
concentration parameter is . This indicates
that infrared galaxies in the outskirts of clusters have higher infrared flux
than cluster-core galaxies. We also study the cross-correlation between tSZ and
CIB anisotropies, following three alternative approaches based on power
spectrum analyses: (i) using a catalogue of confirmed clusters detected in
Planck data; (ii) using an all-sky tSZ map built from Planck frequency maps;
and (iii) using cross-spectra between Planck frequency maps. With the three
different methods, we detect the tSZ-CIB cross-power spectrum at significance
levels of (i) 6 , (ii) 3 , and (iii) 4 . We model the
tSZ-CIB cross-correlation signature and compare predictions with the
measurements. The amplitude of the cross-correlation relative to the fiducial
model is . This result is consistent with
predictions for the tSZ-CIB cross-correlation assuming the best-fit
cosmological model from Planck 2015 results along with the tSZ and CIB scaling
relations.Comment: 18 pages, 16 figure
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