ABSTRACT
fink is a broker designed to enable science with large time-domain alert streams such as the one from the upcoming Vera C. Rubin Observatory Legacy Survey of Space and Time (LSST). It ...exhibits traditional astronomy broker features such as automatized ingestion, annotation, selection, and redistribution of promising alerts for transient science. It is also designed to go beyond traditional broker features by providing real-time transient classification that is continuously improved by using state-of-the-art deep learning and adaptive learning techniques. These evolving added values will enable more accurate scientific output from LSST photometric data for diverse science cases while also leading to a higher incidence of new discoveries which shall accompany the evolution of the survey. In this paper, we introduce fink, its science motivation, architecture, and current status including first science verification cases using the Zwicky Transient Facility alert stream.
The XMM-Newton serendipitous survey Rosen, S. R.; Webb, N. A.; Watson, M. G. ...
Astronomy and astrophysics (Berlin),
2016, Letnik:
590
Journal Article
Recenzirano
Context. Thanks to the large collecting area (3 ×~1500 cm2 at 1.5 keV) and wide field of view (30′ across in full field mode) of the X-ray cameras on board the European Space Agency X-ray observatory ...XMM-Newton, each individual pointing can result in the detection of up to several hundred X-ray sources, most of which are newly discovered objects. Since XMM-Newton has now been in orbit for more than 15 yr, hundreds of thousands of sources have been detected. Aims. Recently, many improvements in the XMM-Newton data reduction algorithms have been made. These include enhanced source characterisation and reduced spurious source detections, refined astrometric precision of sources, greater net sensitivity for source detection, and the extraction of spectra and time series for fainter sources, both with better signal-to-noise. Thanks to these enhancements, the quality of the catalogue products has been much improved over earlier catalogues. Furthermore, almost 50% more observations are in the public domain compared to 2XMMi-DR3, allowing the XMM-Newton Survey Science Centre to produce a much larger and better quality X-ray source catalogue. Methods. The XMM-Newton Survey Science Centre has developed a pipeline to reduce the XMM-Newton data automatically. Using the latest version of this pipeline, along with better calibration, a new version of the catalogue has been produced, using XMM-Newton X-ray observations made public on or before 2013 December 31. Manual screening of all of the X-ray detections ensures the highest data quality. This catalogue is known as 3XMM. Results. In the latest release of the 3XMM catalogue, 3XMM-DR5, there are 565 962 X-ray detections comprising 396 910 unique X-ray sources. Spectra and lightcurves are provided for the 133 000 brightest sources. For all detections, the positions on the sky, a measure of the quality of the detection, and an evaluation of the X-ray variability is provided, along with the fluxes and count rates in 7 X-ray energy bands, the total 0.2–12 keV band counts, and four hardness ratios. With the aim of identifying the detections, a cross correlation with 228 catalogues of sources detected in all wavebands is also provided for each X-ray detection. Conclusions. 3XMM-DR5 is the largest X-ray source catalogue ever produced. Thanks to the large array of data products associated with each detection and each source, it is an excellent resource for finding new and extreme objects.
Post common envelope binaries from the SDSS Schwope, A. D.; Nebot Gomez-Moran, A.; Schreiber, M. R. ...
Astronomy and astrophysics (Berlin),
06/2009, Letnik:
500, Številka:
2
Journal Article
Recenzirano
Odprti dostop
We report the discovery of the ninth pre-polar consisting of a late-type ZAMS secondary and a magnetic white dwarf. The white dwarf accretes at an extreme low rate, $\dot{M} \sim 10^{-14}$ $M_\odot$ ...yr-1, from the wind of the companion donor star. The source was found in our systematic search for WD/MS binaries within SDSS/SEGUE. Based on seven Sloan spectra we estimate a binary period of ~200, 230, or 270 min. The UV to IR spectral energy distribution was decomposed into a dM3-dM4 ZAMS secondary and a cool white dwarf, ~9000 K, which consistently imply a distance between 360 and 420 pc. The optical spectrum displays one pronounced cyclotron hump, likely originating from a low-temperature plasma, ~1 keV, in a field of 108 MG. We comment on the evolutionary link between polars and pre-polars.
We lay the foundations of a statistical framework for multi-catalogue cross-correlation and cross-identification based on explicit simplified catalogue models. A proper identification process should ...rely on both astrometric and photometric data. Under some conditions, the astrometric part and the photometric part can be processed separately and merged a posteriori to provide a single global probability of identification. The present paper addresses almost exclusively the astrometrical part and specifies the proper probabilities to be merged with photometric likelihoods. To select matching candidates in n catalogues, we used the Chi (or, indifferently, the Chi-square) test with 2(n-1) degrees of freedom. We thus call this cross-match a chi-match. In order to use Bayes' formula, we considered exhaustive sets of hypotheses based on combinatorial analysis. The volume of the Chi-test domain of acceptance -- a 2(n-1)-dimensional acceptance ellipsoid -- is used to estimate the expected numbers of spurious associations. We derived priors for those numbers using a frequentist approach relying on simple geometrical considerations. Likelihoods are based on standard Rayleigh, Chi and Poisson distributions that we normalized over the Chi-test acceptance domain. We validated our theoretical results by generating and cross-matching synthetic catalogues. The results we obtain do not depend on the order used to cross-correlate the catalogues. We applied the formalism described in the present paper to build the multi-wavelength catalogues used for the science cases of the ARCHES (Astronomical Resource Cross-matching for High Energy Studies) project. Our cross-matching engine is publicly available through a multi-purpose web interface. In a longer term, we plan to integrate this tool into the CDS XMatch Service.
The ARCHES project Motch, C; Carrera, F; Genova, F ...
arXiv.org,
09/2016
Paper, Journal Article
Odprti dostop
ARCHES (Astronomical Resource Cross-matching for High Energy Studies) is a FP7-Space funded project whose aim is to provide the international astronomical community with well-characterised ...multi-wavelength data in the form of spectral energy distributions (SEDs) for large samples of objects extracted from the 3XMM DR5 X-ray catalogue of serendipitous sources. The project has developed new tools implementing fully probabilistic simultaneous cross-correlation of several catalogues for unresolved sources and a multi-wavelength finder for clusters of galaxies for extended sources. These enhanced resources have been tested in the framework of several science cases.
The nature of the low- to intermediate-luminosity (Lx\(\,\sim 10^{32-34}\) erg s\(^{-1}\)) source population revealed in hard band (2-10 keV) X-ray surveys of the Galactic Plane is poorly understood. ...To overcome such problem we cross-correlated the XMM-Newton 3XMM-DR4 survey with the infrared 2MASS and GLIMPSE catalogues. We identified reliable X-ray-infrared associations for 690 sources. We selected 173 sources having hard X-ray spectra, typical of hard X-ray high-mass stars (kT\(\,>\,5\,\)keV), and 517 sources having soft X-ray spectra, typical of active coronae. About \(18\,\%\) of the soft sources are classified in the literature: \(\sim\,91\%\) as stars, with a minor fraction of WR stars. Roughly \(15\,\%\) of the hard sources are classified in the literature: \(\sim\,68\%\) as high-mass X-ray stars single or in binary systems (WR, Be and HMXBs), with a small fraction of G and B stars. We carried out infrared spectroscopic pilot observations at the William Herschel Telescope for five hard X-ray sources. Three of them are high-mass stars with spectral types WN7-8h, Ofpe/WN9 and Be, and Lx\(\sim\,10^{32}-10^{33}\)erg s\(^{-1}\). One source is a colliding-wind binary, while another source is a colliding-wind binary or a supergiant fast X-ray transient in quiescence. The Be star is a likely \(\gamma\)-Cas system. The nature of the other two X-ray sources is uncertain. The distribution of hard X-ray sources in the parameter space made of X-ray hardness ratio, infrared colours and X-ray-to-infrared flux ratio suggests that many of the unidentified sources are new \(\gamma\)-Cas analogues, WRs and low Lx HMXBs. However, the nature of the X-ray population with Ks \(\geq\) 11 and average X-ray-to-infrared flux ratio remains unconstrained.
Context. Detached white dwarf + main sequence (WD+MS) systems represent the simplest population of post-common envelope binaries (PCEBs). Since the ensemble properties of this population carries ...important information about the characteristics of the common-envelope (CE) phase, it deserves close scrutiny. However, most population synthesis studies do not fully consider the effects of the observational selection biases of the samples used to compare with the theoretical simulations.; Aims. Here we present the results of a set of detailed Monte Carlo simulations of the population of WD+MS binaries in the Sloan Digital Sky Survey (SDSS) Data Release 7.; Methods. We used up-to-date stellar evolutionary models, a complete treatment of the Roche lobe overflow episode, and a full implementation of the orbital evolution of the binary systems. Moreover, in our treatment we took the selection criteria and all the known observational biases into account.; Results. Our population synthesis study allowed us to make a meaningful comparison with the available observational data. In particular, we examined the CE efficiency, the possible contribution of internal energy, and the initial mass ratio distribution (IMRD) of the binary systems. We find that our simulations correctly reproduce the properties of the observed distribution of WD+MS PCEBs. In particular, we find that once the observational biases are carefully considered, the distribution of orbital periods and of masses of the WD and MS stars can be correctly reproduced for several choices of the free parameters and different IMRDs, although models in which a moderate fraction (<= 10%) of the internal energy is used to eject the CE and in which a low value of CE efficiency is used (<= 0.3) seem to fit the observational data better. We also find that systems with He-core WDs are over-represented in the observed sample, because of selection effects.; Conclusions. Although our study represents an important step forward in modeling the population of WD+MS PCEBs, the still scarce observational data preclude deriving a precise value of the several free parameters used to compute the CE phase without ambiguity or ascertaining which the correct IMRD might be.
Peer Reviewed
The X-ray emission of O-type stars was first discovered in the early days of the Einstein satellite. Since then many different surveys have confirmed that the ratio of X-ray to bolometric luminosity ...in O-type stars is roughly constant, but there is a paucity of studies that account for detailed information on spectral and wind properties of O-stars. Recently a significant sample of O stars within our Galaxy was spectroscopically identified and presented in the Galactic O-Star Spectroscopic Survey (GOSS). At the same time, a large high-fidelity catalog of X-ray sources detected by the XMM-Newton X-ray telescope was released. Here we present the X-ray catalog of O stars with known spectral types and investigate the dependence of their X-ray properties on spectral type as well as stellar and wind parameters. We find that, among the GOSS sample, 127 O-stars have a unique XMM-Newton source counterpart and a Gaia data release 2 (DR2) association. Terminal velocities are known for a subsample of 35 of these stars. We confirm that the X-ray luminosities of dwarf and giant O stars correlate with their bolometric luminosity. For the subsample of O stars with measure terminal velocities we find that the X-ray luminosities of dwarf and giant O stars also correlate with wind parameters. However, we find that these correlations break down for supergiant stars. Moreover, we show that supergiant stars are systematically harder in X-rays compared to giant and dwarf O-type stars. We find that the X-ray luminosity depends on spectral type, but seems to be independent of whether the stars are single or in a binary system. Finally, we show that the distribution of log(Lx/Lbol) in our sample stars is non-Gaussian, with the peak of the distribution at log(Lx/Lbol) around -6.6.
Detached white dwarf + main sequence (WD+MS) systems represent the simplest population of post-common envelope binaries (PCEBs). Since the ensemble properties of this population carries important ...information about the characteristics of the common-envelope (CE) phase, it deserves close scrutiny. However, most population synthesis studies do not fully take into account the effects of the observational selection biases of the samples used to compare with the theoretical simulations. Here we present the results of a set of detailed Monte Carlo simulations of the population of WD+MS binaries in the Sloan Digital Sky Survey (SDSS) Data Release 7. We used up-to-date stellar evolutionary models, a complete treatment of the Roche lobe overflow episode, and a full implementation of the orbital evolution of the binary systems. Moreover, in our treatment we took into account the selection criteria and all the known observational biases. Our population synthesis study allowed us to make a meaningful comparison with the available observational data. In particular, we examined the CE efficiency, the possible contribution of internal energy, and the initial mass ratio distribution (IMRD) of the binary systems. We found that our simulations correctly reproduce the properties of the observed distribution of WD+MS PCEBs. In particular, we found that once the observational biases are carefully taken into account, the distribution of orbital periods and of masses of the WD and MS stars can be correctly reproduced for several choices of the free parameters and different IMRDs, although models in which a moderate fraction (<=10%) of the internal energy is used to eject the CE and in which a low value of CE efficiency is used (<=0.3) seem to fit better the observational data. We also found that systems with He-core WDs are over-represented in the observed sample, due to selection effects.
Post common envelope binaries from SDSS Schreiber, M. R.; Gänsicke, B. T.; Rebassa-Mansergas, A. ...
Astronomy and astrophysics (Berlin),
04/2010, Letnik:
513
Journal Article
Recenzirano
Odprti dostop
Context. The standard prescription of angular momentum loss in compact binaries assumes magnetic braking to be very efficient as long as the secondary star has a radiative core, but to be negligible ...if the secondary star is fully convective. This prescription has been developed to explain the orbital period gap observed in the orbital period distribution of cataclysmic variables but has so far not been independently tested. Because the evolutionary time-scale of post common envelope binaries (PCEBs) crucially depends on the rate of angular momentum loss, a fundamental prediction of the disrupted magnetic braking theory is that the relative number of PCEBs should dramatically decrease for companion-star masses exceeding the mass that corresponds to the fully-convective boundary. Aims. We present the results of a large survey of PCEBs among white dwarf/main sequence (WDMS) binaries that allows us to determine the fraction of PCEBs as a function of secondary star mass and therewith to ultimately test the disrupted magnetic braking hypothesis. Methods. We obtained multiple spectroscopic observations spread over at least two nights for 670 WDMS binaries. Systems showing at least 3σ radial velocity variations are considered to be strong PCEB candidates. Taking into account observational selection effects we compare our results with the predictions of binary population simulations. Results. Among the 670 WDMS binaries we find 205 strong PCEB candidates. The fraction of PCEBs among WDMS binaries peaks around Msec ~ 0.25 $M_{\odot}$ and steeply drops towards higher mass secondary stars in the range of Msec = 0.25–0.4 $M_{\odot}$. Conclusions. The decrease of the number of PCEBs at the fully convective boundary strongly suggests that the evolutionary time scales of PCEBs containing fully convective secondaries are significantly longer than those of PCEBs with secondaries containing a radiative core. This is consistent with significantly reduced magnetic wind braking of fully convective stars as predicted by the disrupted magnetic braking scenario.
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