30 research outputs found
The Brera Multi-scale Wavelet (BMW) ROSAT HRI source catalog. II: application to the HRI and first results
The wavelet detection algorithm (WDA) described in the accompanying paper by
Lazzati et al. is made suited for a fast and efficient analysis of images taken
with the High Resolution Imager (HRI) instrument on board the ROSAT satellite.
An extensive testing is carried out on the detection pipeline: HRI fields with
different exposure times are simulated and analysed in the same fashion as the
real data. Positions are recovered with few arcsecond errors, whereas fluxes
are within a factor of two from their input values in more than 90% of the
cases in the deepest images. At variance with the ``sliding-box'' detection
algorithms, the WDA provides also a reliable description of the source
extension, allowing for a complete search of e.g. supernova remnant or cluster
of galaxies in the HRI fields. A completeness analysis on simulated fields
shows that for the deepest exposures considered (~120 ks) a limiting flux of
\~3x10^{-15} erg/cm2/s can be reached over the entire field of view. We test
the algorithm on real HRI fields selected for their crowding and/or presence of
extended or bright sources (e.g. cluster of galaxies and of stars, supernova
remnants). We show that our algorithm compares favorably with other X-ray
detection algorithms such as XIMAGE and EXSAS. A complete catalog will result
from our analysis: it will consist of the Brera Multi-scale Wavelet Bright
Source Catalog (BMW-BSC) with sources detected with a significance >4.5 sigma
and of the Faint Source Catalog (BMW-FSC) with sources at >3.5 sigma. A
conservative estimate based on the extragalactic log(N)-log(S) indicates that
at least 16000 sources will be revealed in the complete analysis of the whole
HRI dataset.Comment: 6 pages, 11 PostScript figures, 1 gif figure, ApJ in pres
AGAPE, an experiment to detect MACHO's in the direction of the Andromeda galaxy
The status of the Agape experiment to detect Machos in the direction of the
andromeda galaxy is presented.Comment: 4 pages, 1 figure in a separate compressed, tarred, uuencoded uufile.
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A Wavelet-Based Algorithm for the Spatial Analysis of Poisson Data
Wavelets are scaleable, oscillatory functions that deviate from zero only
within a limited spatial regime and have average value zero. In addition to
their use as source characterizers, wavelet functions are rapidly gaining
currency within the source detection field. Wavelet-based source detection
involves the correlation of scaled wavelet functions with binned,
two-dimensional image data. If the chosen wavelet function exhibits the
property of vanishing moments, significantly non-zero correlation coefficients
will be observed only where there are high-order variations in the data; e.g.,
they will be observed in the vicinity of sources.
In this paper, we describe the mission-independent, wavelet-based source
detection algorithm WAVDETECT, part of the CIAO software package. Aspects of
our algorithm include: (1) the computation of local, exposure-corrected
normalized (i.e. flat-fielded) background maps; (2) the correction for exposure
variations within the field-of-view; (3) its applicability within the
low-counts regime, as it does not require a minimum number of background counts
per pixel for the accurate computation of source detection thresholds; (4) the
generation of a source list in a manner that does not depend upon a detailed
knowledge of the point spread function (PSF) shape; and (5) error analysis.
These features make our algorithm considerably more general than previous
methods developed for the analysis of X-ray image data, especially in the low
count regime. We demonstrate the algorithm's robustness by applying it to
various images.Comment: Accepted for publication in Ap. J. Supp. (v. 138 Jan. 2002). 61
pages, 23 figures, expands to 3.8 Mb. Abstract abridged for astro-ph
submissio
AgapeZ1: a Large Amplification Microlensing Event or an Odd Variable Star Towards the Inner Bulge of M31
AgapeZ1 is the brightest and the shortest duration microlensing candidate
event found in the Agape data. It occured only 42" from the center of M31. Our
photometry shows that the half intensity duration of the event6 is 4.8 days and
at maximum brightness we measure a stellar magnitude of R=18.0 with B-R=0.80
mag color. A search on HST archives produced a single resolved star within the
projected event position error box. Its magnitude is R=22.Comment: 4 pages with 5 figure
AGAPE: a microlensing search in the direction of M31
A status report of the microlensing search by the pixel method in the direction of M31, on the 2 meter telescope at Pic du Midi is given. Pixels are stable to a level better than 0.5%. Pixel variations as small as 0.02 magnitude can clearly be detected
Variable stars towards the bulge of M31: the AGAPE catalogue
We present the AGAPE astrometric and photometric catalogue of 1579 variable
stars in a 14'x10' field centred on M31. This work is the first survey devoted
to variable stars in the bulge of M31. The R magnitudes of the objects and the
B-R colours suggest that our sample is dominated by red long-period variable
stars (LPV), with a possible overlap with Cepheid-like type II stars. Twelve
nova candidates are identified. Correlations with other catalogues suggest that
2 novae could be recurrent novae and provide possible optical counterparts for
2 supersoft X-ray sources candidates observed with Chandra.Comment: 11 pages, Latex, accepted for publication in A&
AA manuscript no.
AgapeZ1 is the brightest and the shortest duration microlensing candidate event found to date in the Agape experiment. It occurred only 42 from the centre of M31 at RA = 0 h 42 m 41:47 s and Dec = 41 16 39:1 (J2000). Our photometry shows that the half intensity duration of the event is 5.3 days and at maximum brightness its magnitude is R = 17:9 (MR 6) with B R = 0:80 mag colour. A search on HST archives produced a single resolved star within the projected event position error box. Its magnitude is R = 22, and its colour is compatible with that of the event at the 2 level