68 research outputs found
The X-ray spectral properties of X-ray selected AGN : ROSAT spectra of EMSS AGN
Using a sample of 63 AGNs extracted from the Extended Medium
Sensitivity Survey (EMSS), we study the X-ray spectral properties of X-ray
selected AGN in the 0.12.4 keV ROSAT band. These objects are all the EMSS
AGN detected with more than 300 net counts in ROSAT PSPC images available from
the public archive (as of May 31, 1995). A Maximum-Likelihood analysis is used
to find the mean power-law spectral index and the intrinsic
dispersion $\sigma_p$. We find =1.42 with =0.44. This
value is significantly steeper (0.4) than the mean
/IPC spectral index obtained applying the ML analysis on the whole
sample of EMSS AGN. This result shows that the soft excess already noted in
optically selected AGN is present also in X-ray selected AGN. The relatively
high value obtained for the intrinsic dispersion confirms that in the soft band
AGN are characterized by a variety of spectral indices and the increase with
respect to results obtained from the analysis of Einstein data (0.16) suggests a further broadening of the spectral index
distribution as one moves to softer energies. A comparison between the mean
spectral index of Radio-quiet and Radio-loud subsamples shows that the mean
index of the RL sample is flatter than that of RQ, both in the IPC (0.3) and in the PSPC (0.4) data. This suggests
that the additional X-ray component in RL AGN dominates the X-ray emission of
RL AGN over almost two decades of energy (0.110 keV).Comment: 8 pages LaTex file; mn.sty macro (enclosed), 5 LaTex Tables, 12
Postscript figures; accepted for publication in MNRA
A method for space-variant deblurring with application to adaptive optics imaging in astronomy
Images from adaptive optics systems are generally affected by significant
distortions of the point spread function (PSF) across the field of view,
depending on the position of natural and artificial guide stars. Image
reduction techniques circumventing or mitigating these effects are important
tools to take full advantage of the scientific information encoded in AO
images. The aim of this paper is to propose a method for the deblurring of the
astronomical image, given a set of samples of the space-variant PSF. The method
is based on a partitioning of the image domain into regions of isoplanatism and
on applying suitable deconvolution methods with boundary effects correction to
each region. The effectiveness of the boundary effects correction is proved.
Moreover, the criterion for extending the disjoint sections to partially
overlapping sections is validated. The method is applied to simulated images of
a stellar system characterized by a spatially variable PSF. We obtain good
photometric quality, and therefore good science quality, by performing aperture
photometry on the deblurred images. The proposed method is implemented in IDL
in the Software Package "Patch", which is available on
http://www.airyproject.eu.Comment: 11 pages, 9 figures, 7 tables, accepted by A&
End to end numerical simulations of the MAORY multiconjugate adaptive optics system
MAORY is the adaptive optics module of the E-ELT that will feed the MICADO
imaging camera through a gravity invariant exit port. MAORY has been foreseen
to implement MCAO correction through three high order deformable mirrors driven
by the reference signals of six Laser Guide Stars (LGSs) feeding as many
Shack-Hartmann Wavefront Sensors. A three Natural Guide Stars (NGSs) system
will provide the low order correction. We develop a code for the end-to-end
simulation of the MAORY adaptive optics (AO) system in order to obtain
high-delity modeling of the system performance. It is based on the IDL language
and makes extensively uses of the GPUs. Here we present the architecture of the
simulation tool and its achieved and expected performance.Comment: 8 pages, 4 figures, presented at SPIE Astronomical Telescopes +
Instrumentation 2014 in Montr\'eal, Quebec, Canada, with number 9148-25
Stellar photometry with Multi Conjugate Adaptive Optics
We overview the current status of photometric analyses of images collected
with Multi Conjugate Adaptive Optics (MCAO) at 8-10m class telescopes that
operated, or are operating, on sky. Particular attention will be payed to
resolved stellar population studies. Stars in crowded stellar systems, such as
globular clusters or in nearby galaxies, are ideal test particles to test AO
performance. We will focus the discussion on photometric precision and accuracy
reached nowadays. We briefly describe our project on stellar photometry and
astrometry of Galactic globular clusters using images taken with GeMS at the
Gemini South telescope. We also present the photometry performed with DAOPHOT
suite of programs into the crowded regions of these globulars reaching very
faint limiting magnitudes Ks ~21.5 mag on moderately large fields of view (~1.5
arcmin squared). We highlight the need for new algorithms to improve the
modeling of the complex variation of the Point Spread Function across the field
of view. Finally, we outline the role that large samples of stellar standards
plays in providing a detailed description of the MCAO performance and in
precise and accurate colour{magnitude diagrams.Comment: 17 pages, 12 figures, SPIE 201
The VLA-COSMOS Survey: V. 324 MHz continuum observations
We present 90 cm VLA imaging of the COSMOS field, comprising a circular area
of 3.14 square degrees at 8.0"x6.0" angular resolution with an average rms of
0.5 mJy/beam. The extracted catalog contains 182 sources (down to 5.5sigma), 30
of which are multi-component sources. Using Monte Carlo artificial source
simulations we derive the completeness of the catalog, and we show that our 90
cm source counts agree very well with those from previous studies. Using X-ray,
NUV-NIR and radio COSMOS data to investigate the population mix of our 90 cm
radio sample, we find that our sample is dominated by active galactic nuclei
(AGN). The average 90-20 cm spectral index (S_nu~nu**alpha, where S_nu is the
flux density at frequency nu, and alpha the spectral index) of our 90 cm
selected sources is -0.70, with an interquartile range of -0.90 to -0.53. Only
a few ultra-steep-spectrum sources are present in our sample, consistent with
results in the literature for similar fields. Our data do not show clear
steepening of the spectral index with redshift. Nevertheless, our sample
suggests that sources with spectral indices steeper than -1 all lie at z>1, in
agreement with the idea that ultra-steep-spectrum radio sources may trace
intermediate-redshift galaxies (z>1).Comment: 10 pages, 12 figures, accepted for publication in MNRA
The numerical simulation tool for the MAORY multiconjugate adaptive optics system
The Multiconjugate Adaptive Optics RelaY (MAORY) is and Adaptive Optics
module to be mounted on the ESO European-Extremely Large Telescope (E-ELT). It
is a hybrid Natural and Laser Guide System that will perform the correction of
the atmospheric turbulence volume above the telescope feeding the Multi-AO
Imaging Camera for Deep Observations Near Infrared spectro-imager (MICADO). We
developed an end-to-end Monte- Carlo adaptive optics simulation tool to
investigate the performance of a the MAORY and the calibration, acquisition,
operation strategies. MAORY will implement Multiconjugate Adaptive Optics
combining Laser Guide Stars (LGS) and Natural Guide Stars (NGS) measurements.
The simulation tool implements the various aspect of the MAORY in an end to end
fashion. The code has been developed using IDL and uses libraries in C++ and
CUDA for efficiency improvements. Here we recall the code architecture, we
describe the modeled instrument components and the control strategies
implemented in the code.Comment: 6 pages, 1 figure, Proceeding 9909 310 of the conference SPIE
Astronomical Telescopes + Instrumentation 2016, 26 June 1 July 2016
Edinburgh, Scotland, U
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