129 research outputs found
The BMW Detection Algorithm applied to the Chandra Deep Field south: deeper and deeper
Chandra deep fields represent the deepest look at the X-ray sky. We analyzed
the Chandra Deep Field South (CDFS) with the aid of a dedicated wavelet-based
algorithm. Here we present a detailed description of the procedures used to
analyze this field, tested and verified by means of extensive simulations. We
show that we can safely reconstruct the LogN-Log S source distribution of the
CDFS down to limiting fluxes of 2.4x10^-17 and 2.1x10^-16 erg s^-1 cm^-2 in the
soft (0.5-2 keV) and hard (2-10 keV) bands, respectively, fainter by a factor ~
2 than current estimates. At these levels we can account for ~ 90% of the 1-2
keV and 2-10 keV X-ray background.Comment: 27 pages 16 figures, accepted for publication in the Astrophysical
Journa
The Brera Multi-scale Wavelet Chandra Survey. I. Serendipitous source catalogue
We present the BMW-Chandra source catalogue drawn from essentially all
Chandra ACIS-I pointed observations with an exposure time in excess of 10ks
public as of March 2003 (136 observations). Using the wavelet detection
algorithm developed by Lazzati et al. (1999) and Campana et al. (1999), which
can characterise both point-like and extended sources, we identified 21325
sources. Among them, 16758 are serendipitous, i.e. not associated with the
targets of the pointings, and do not require a non-automated analysis. This
makes our catalogue the largest compilation of Chandra sources to date. The
0.5--10 keV absorption corrected fluxes of these sources range from ~3E-16 to
9E-12 erg cm^-2 s^-1 with a median of 7E-15 erg cm^-2 s^-1. The catalogue
consists of count rates and relative errors in three energy bands (total,
0.5-7keV; soft, 0.5-2keV; and hard, 2-7keV), and source positions relative to
the highest signal-to-noise detection among the three bands. The wavelet
algorithm also provides an estimate of the extension of the source. We include
information drawn from the headers of the original files, as well, and
extracted source counts in four additional energy bands, SB1 (0.5-1keV), SB2
(1-2keV), HB1 (2-4keV), and HB2 (4-7keV). We computed the sky coverage for the
full catalogue and for a subset at high Galactic latitude (|b|> 20deg). The
complete catalogue provides a sky coverage in the soft band (0.5-2keV, S/N =3)
of ~8 deg^2 at a limiting flux of 1E-13 erg cm^-2 s^-1, and ~2 deg^2 at a
limiting flux of ~1E-15 erg cm^-2 s^-1.Comment: Accepted by A&A, Higher res. Figs 4 and 5 at
http://www.ifc.inaf.it/~romano/BMC/Docs/aapaper/9601f4.eps
http://www.ifc.inaf.it/~romano/BMC/Docs/aapaper/9601f5.eps, Catalog Web
pages: http://www.brera.inaf.it/BMC/bmc_home.html
http://www.ifc.inaf.it/~romano/BMC/bmc_home.html (Mirror
Spectral evolution and polarization of variable structures in the pulsar wind nebula of PSR B0540-69.3
We present high spatial resolution optical imaging and polarization
observations of the PSR B0540-69.3 and its highly dynamical pulsar wind nebula
(PWN) performed with HST, and compare them with X-ray data obtained with the
Chandra X-ray Observatory. We have studied the bright region southwest of the
pulsar where a bright "blob" is seen in 1999. We show that it may be a result
of local energy deposition around 1999, and that the emission from this then
faded away. Polarization data from 2007 show that the polarization properties
show dramatic spatial variations at the 1999 blob position arguing for a local
process. Several other positions along the pulsar-"blob" orientation show
similar changes in polarization, indicating previous recent local energy
depositions. In X-rays, the spectrum steepens away from the "blob" position,
faster orthogonal to the pulsar-"blob" direction than along this axis of
orientation. This could indicate that the pulsar-"blob" orientation is an axis
along where energy in the PWN is mainly injected, and that this is then
mediated to the filaments in the PWN by shocks. We highlight this by
constructing an [S II]-to-[O III]-ratio map. We argue, through modeling, that
the high [S II]/[O III] ratio is not due to time-dependent photoionization
caused by possible rapid Xray emission variations in the "blob" region. We have
also created a multiwavelength energy spectrum for the "blob" position showing
that one can, to within 2sigma, connect the optical and X-ray emission by a
single power law. We obtain best power-law fits for the X-ray spectrum if we
include "extra" oxygen, in addition to the oxygen column density in the
interstellar gas of the Large Magellanic Cloud and the Milky Way. This oxygen
is most naturally explained by the oxygen-rich ejecta of the supernova remnant.
The oxygen needed likely places the progenitor mass in the 20 - 25 Msun range.Comment: Accepted by MNRAS on December 6th 2010, 18 pages, 15 figures. The
article with full resolution figures is available here
ftp://ftp.astro.su.se/pub/peter/papers/pwn0540_2010_corrected.pd
ESO Imaging Survey: Optical follow-up of 12 selected XMM-Newton fields
(Abridged) This paper presents the data recently released for the
XMM-Newton/WFI survey carried out as part of the ESO Imaging Survey (EIS)
project. The aim of this survey is to provide optical imaging follow-up data in
BVRI for identification of serendipitously detected X-ray sources in selected
XMM-Newton fields. In this paper, fully calibrated individual and stacked
images of 12 fields as well as science-grade catalogs for the 8 fields located
at high-galactic latitude are presented. The data covers an area of \sim 3
square degrees for each of the four passbands. The median limiting magnitudes
(AB system, 2" aperture, 5\sigma detection limit) are 25.20, 24.92, 24.66, and
24.39 mag for B-, V-, R-, and I-band, respectively. These survey products,
together with their logs, are available to the community for science
exploitation in conjunction with their X-ray counterparts. Preliminary results
from the X-ray/optical cross-correlation analysis show that about 61% of the
detected X-ray point sources in deep XMM-Newton exposures have at least one
optical counterpart within 2" radius down to R \simeq 25 mag, 50% of which are
so faint as to require VLT observations thereby meeting one of the top
requirements of the survey, namely to produce large samples for spectroscopic
follow-up with the VLT, whereas only 15% of the objects have counterparts down
to the DSS limiting magnitude.Comment: 24 pages, 10 figures, accepted for publication in Astronomy and
Astrophysics. Accompanying data releases available at
http://archive.eso.org/archive/public_datasets.html (WFI images),
http://www.eso.org/science/eis/surveys/release_65000025_XMM.html (optical
catalogs), http://www.aip.de/groups/xray/XMM_EIS/ (X-ray data). Full
resolution version available at
http://www.astro.uni-bonn.de/~dietrich/publications/3785.ps.g
A spectroscopic survey of thick disc stars outside the solar neighbourhood
We performed a spectroscopic survey of nearly 700 stars probing the galactic
thick disc far from the solar neighbourhood towards the galactic coordinates
(l~277, b~47). The derived effective temperatures, surface gravities and
overall metallicities were then combined with stellar evolution isochrones,
radial velocities and proper motions to derive the distances, kinematics and
orbital parameters of the sample stars. The targets belonging to each galactic
component (thin disc, thick disc, halo) were selected either on their
kinematics or according to their position above the galactic plane, and the
vertical gradients were also estimated. We present here atmospheric parameters,
distances and kinematics for this sample, and a comparison of our kinematic and
metallicity distributions with the Besancon model of the Milky Way. The thick
disc far from the solar neighbourhood is found to differ only slightly from the
thick disc properties as derived in the solar vicinity. For regions where the
thick disc dominates, we measured vertical velocity and metallicity trends of
d(V_phi)/dZ = 19 +/- 8 km/s/kpc and d[M/H]/dZ = -0.14 +/- 0.05 dex/kpc,
respectively. These trends can be explained as a smooth transition between the
different galactic components, although intrinsic gradients could not be
excluded. In addition, a correlation d(V_phi)/d[M/H] = -45 +/- 12 km/s/dex
between the orbital velocity and the metallicity of the thick disc is detected.
This gradient is inconsistent with the SDSS photometric survey analysis, which
did not detect any such trend, and challenges radial migration models of thick
disc formation. Estimations of the scale heights and scale lengths for
different metallicity bins of the thick disc result in consistent values, with
hR~3.4 \pm 0.7 kpc, and hZ~694 \pm 45 pc, showing no evidence of relics of
destroyed massive satellites.Comment: 19 pages, 15 figures, accepted for publication in A&
Spectroscopic survey of the Galaxy with Gaia I. Design and performance of the Radial Velocity Spectrometer
The definition and optimisation studies for the Gaia satellite spectrograph,
the Radial Velocity Spectrometer (RVS), converged in late 2002 with the
adoption of the instrument baseline. This paper reviews the characteristics of
the selected configuration and presents its expected performance. The RVS is a
2.0 by 1.6 degree integral field spectrograph, dispersing the light of all
sources entering its field of view with a resolving power R=11 500 over the
wavelength range [848, 874] nm. The RVS will continuously and repeatedly scan
the sky during the 5 years of the Gaia mission. On average, each source will be
observed 102 times over this period. The RVS will collect the spectra of about
100-150 million stars up to magnitude V~17-18. At the end of the mission, the
RVS will provide radial velocities with precisions of ~2 km/s at V=15 and
\~15-20 km/s at V=17, for a solar metallicity G5 dwarf. The RVS will also
provide rotational velocities, with precisions (at the end of the mission) for
late type stars of sigma_vsini ~5 km/s at V~15 as well as atmospheric
parameters up to V~14-15. The individual abundances of elements such as Silicon
and Magnesium, vital for the understanding of Galactic evolution, will be
obtained up to V~12-13. Finally, the presence of the 862.0 nm Diffuse
Interstellar Band (DIB) in the RVS wavelength range will make it possible to
derive the three dimensional structure of the interstellar reddening.Comment: 17 pages, 9 figures, accepted for publication in MNRAS. Fig. 1,2,4,5,
6 in degraded resolution; available in full resolution at
http://blackwell-synergy.com/links/doi/10.1111/j.1365-2966.2004.08282.x/pd
Deep Near-Infrared Survey of the Pipe Nebula II: Data, Methods, and Dust Extinction Maps
We present a new set of high resolution dust extinction maps of the nearby
and essentially starless Pipe Nebula molecular cloud. The maps were constructed
from a concerted deep near-infrared imaging survey with the ESO-VLT, ESO-NTT,
CAHA 3.5m telescopes, and 2MASS data. The new maps have a resolution three
times higher than the previous extinction map of this cloud by Lombardi et al.
(2006) and are able to resolve structure down to 2600 AU. We detect 244
significant extinction peaks across the cloud. These peaks have masses between
0.1 and 18.4 M_sun, diameters between 1.2 and 5.7e4 AU (0.06 and 0.28 pc), and
mean densities of about 1e4 cm, all in good agreement with previous
results. From the analysis of the Mean Surface Density of Companions we find a
well defined scale near 1.4e4 AU below which we detect a significant decrease
in structure of the cloud. This scale is smaller than the Jeans Length
calculated from the mean density of the peaks. The surface density of peaks is
not uniform but instead it displays clustering. Extinction peaks in the Pipe
Nebula appear to have a spatial distribution similar to the stars in Taurus,
suggesting that the spatial distribution of stars evolves directly from the
primordial spatial distribution of high density material.Comment: Accepted for Publication in The Astrophysical Journal, 10/10. 49
pages, 16 figure
Automatic stellar spectra parameterisation in the IR CaII triplet region
(Abridged) Galactic archaeology aims to determine the evolution of the Galaxy
from the chemical and kinematical properties of its stars. The analysis of
current large spectroscopic surveys (thousands of stars) and future ones
(millions of stars) require automated analysis techniques to obtain robust
estimates of the stellar parameters. Several on-going and planned spectroscopic
surveys have selected their wavelength region to contain the IR CaII triplet
and this paper focuses on the automatic analysis of such spectra.
We investigated two algorithms, MATISSE and DEGAS, both of which compare the
observed spectrum to a grid of synthetic spectra, but each uses a different
mathematical approach for finding the optimum match and hence the best stellar
parameters.
We identified degeneracies in different regions of the HR diagram: hot dwarfs
and giants share the same spectral signatures. Furthermore, the surface gravity
of cooler dwarfs is difficult to determine accurately. These effects are
intensified when the information decreases (e.g. metal-poor stars or low SNR
spectra). Our results show that the local projection method MATISSE is
preferred for high SNR spectra, whereas the decision-tree method DEGAS is
preferred for noisier spectra. We therefore propose a hybrid approach of both
methods and show that sufficiently accurate results for the purposes of
galactic archaeology are retrieved down to SNR~20 for typical thin or thick
disc stars, and down to SNR~50 for the more metal-poor halo giants.
If unappreciated, degeneracies in stellar parameters can introduce biases in
derived quantities for target stars such as distances and full space motions.
These biases can be minimised using the knowledge gained by thorough testing of
the proposed algorithm, which in turn lead to robust automated methods for the
coming extensive stellar spectroscopic surveys in the Local Group.Comment: 17 pages, 11 figures, accepted for publication in A&
Wavelet Analysis for Wind Fields Estimation
Wind field analysis from synthetic aperture radar images allows the estimation of wind direction and speed based on image descriptors. In this paper, we propose a framework to automate wind direction retrieval based on wavelet decomposition associated with spectral processing. We extend existing undecimated wavelet transform approaches, by including à trous with B3 spline scaling function, in addition to other wavelet bases as Gabor and Mexican-hat. The purpose is to extract more reliable directional information, when wind speed values range from 5 to 10 ms−1. Using C-band empirical models, associated with the estimated directional information, we calculate local wind speed values and compare our results with QuikSCAT scatterometer data. The proposed approach has potential application in the evaluation of oil spills and wind farms
<i>Gaia</i> Data Release 1. Summary of the astrometric, photometric, and survey properties
Context. At about 1000 days after the launch of Gaia we present the first Gaia data release, Gaia DR1, consisting of astrometry and photometry for over 1 billion sources brighter than magnitude 20.7.
Aims. A summary of Gaia DR1 is presented along with illustrations of the scientific quality of the data, followed by a discussion of the limitations due to the preliminary nature of this release.
Methods. The raw data collected by Gaia during the first 14 months of the mission have been processed by the Gaia Data Processing and Analysis Consortium (DPAC) and turned into an astrometric and photometric catalogue.
Results. Gaia DR1 consists of three components: a primary astrometric data set which contains the positions, parallaxes, and mean proper motions for about 2 million of the brightest stars in common with the HIPPARCOS and Tycho-2 catalogues – a realisation of the Tycho-Gaia Astrometric Solution (TGAS) – and a secondary astrometric data set containing the positions for an additional 1.1 billion sources. The second component is the photometric data set, consisting of mean G-band magnitudes for all sources. The G-band light curves and the characteristics of ∼3000 Cepheid and RR-Lyrae stars, observed at high cadence around the south ecliptic pole, form the third component. For the primary astrometric data set the typical uncertainty is about 0.3 mas for the positions and parallaxes, and about 1 mas yr−1 for the proper motions. A systematic component of ∼0.3 mas should be added to the parallax uncertainties. For the subset of ∼94 000 HIPPARCOS stars in the primary data set, the proper motions are much more precise at about 0.06 mas yr−1. For the secondary astrometric data set, the typical uncertainty of the positions is ∼10 mas. The median uncertainties on the mean G-band magnitudes range from the mmag level to ∼0.03 mag over the magnitude range 5 to 20.7.
Conclusions. Gaia DR1 is an important milestone ahead of the next Gaia data release, which will feature five-parameter astrometry for all sources. Extensive validation shows that Gaia DR1 represents a major advance in the mapping of the heavens and the availability of basic stellar data that underpin observational astrophysics. Nevertheless, the very preliminary nature of this first Gaia data release does lead to a number of important limitations to the data quality which should be carefully considered before drawing conclusions from the data
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