Context. The majority of stars form in clusters. Therefore a comprehensive view of star formation requires understanding the initial conditions for cluster formation. Aims. The goal of our study is ...to shed light on the physical properties of infrared dark clouds (IRDCs) and the role they play in the formation of stellar clusters. This article, the first of a series dedicated to the study of IRDCs, describes techniques developed to establish a complete catalogue of Spitzer IRDCs in the Galaxy. Methods. We have analysed Spitzer GLIMPSE and MIPSGAL data to identify a complete sample of IRDCs in the region of Galactic longitude and latitude 10° < |l|< 65° and |b| < 1°. From the 8 μm observations we have constructed opacity maps and used a newly developed extraction algorithm to identify structures above a column density of $N_{\rm{H_2}}$ $\ga$ 1 $\times$ 1022 cm-2. The 24 μm data are then used to characterize the star formation activity of each extracted cloud. Results. A total of 11 303 clouds have been extracted. A comparison with the existing MSX based catalogue of IRDCs shows that 80% of these Spitzer dark clouds were previously unknown. The algorithm also extracts ~20 000 to 50 000 fragments within these clouds, depending on detection threshold used. A first look at the MIPSGAL data indicates that between 20% and 68% of these IRDCs show 24 μm point-like association. This new database provides an important resource for future studies aiming to understand the initial conditions of star formation in the Galaxy.
Full text
Available for:
FMFMET, NUK, UL, UM, UPUK
Gaia Data Release 2 Riello, M.; De Angeli, F.; Evans, D. W. ...
Astronomy and astrophysics (Berlin),
08/2018, Volume:
616
Journal Article
Peer reviewed
Open access
Context.
The second
Gaia
data release is based on 22 months of mission data with an average of 0.9 billion individual CCD observations per day. A data volume of this size and granularity requires a ...robust and reliable but still flexible system to achieve the demanding accuracy and precision constraints that
Gaia
is capable of delivering.
Aims.
We aim to describe the input data, the treatment of blue photometer/red photometer (BP/RP) low-resolution spectra required to produce the integrated
G
BP
and
G
RP
fluxes, the process used to establish the internal
Gaia
photometric system, and finally, the generation of the mean source photometry from the calibrated epoch data for
Gaia
DR2.
Methods.
The internal
Gaia
photometric system was initialised using an iterative process that is solely based on
Gaia
data. A set of calibrations was derived for the entire
Gaia
DR2 baseline and then used to produce the final mean source photometry. The photometric catalogue contains 2.5 billion sources comprised of three different grades depending on the availability of colour information and the procedure used to calibrate them: 1.5 billion gold, 144 million silver, and 0.9 billion bronze. These figures reflect the results of the photometric processing; the content of the data release will be different due to the validation and data quality filters applied during the catalogue preparation. The photometric processing pipeline, PhotPipe, implements all the processing and calibration workflows in terms of Map/Reduce jobs based on the Hadoop platform. This is the first example of a processing system for a large astrophysical survey project to make use of these technologies.
Results.
The improvements in the generation of the integrated
G
–band fluxes, in the attitude modelling, in the cross-matching, and and in the identification of spurious detections led to a much cleaner input stream for the photometric processing. This, combined with the improvements in the definition of the internal photometric system and calibration flow, produced high-quality photometry. Hadoop proved to be an excellent platform choice for the implementation of PhotPipe in terms of overall performance, scalability, downtime, and manpower required for operations and maintenance.
Full text
Available for:
FMFMET, NUK, UL, UM, UPUK
Aims. We present the Second Palermo Swift-BAT hard X-ray catalogue obtained by analysing data acquired in the first 54 months of the Swift mission. Methods. Using our software dedicated to the ...analysis of data from coded mask telescopes, we analysed the BAT survey data in three energy bands (15–30 keV, 15–70 keV, 15–150 keV), obtaining a list of 1256 detections above a significance threshold of 4.8 standard deviations. The identification of the source counterparts is pursued using two strategies: the analysis of field observations of soft X-ray instruments and cross-correlation of our catalogue with source databases. Results. The survey covers 50% of the sky to a 15–150 keV flux limit of 1.0 × 10-11 erg cm-2 s-1 and 9.2 × 10-12 erg cm-2 s-1 for |b| < 10° and |b| > 10°, respectively. The Second Palermo Swift-BAT hard X-ray catalogue includes 1079 (~86%) hard X-ray sources with an associated counterpart (26 with a double association and 2 with a triple association) and 177 BAT excesses (~14%) that still lack a counterpart. The distribution of the BAT sources among the different object classes consists of ~19% Galactic sources, ~57% extragalactic sources, and ~10% sources with a counterpart at softer energies whose nature has not yet been determined. About half of the BAT associated sources lack a counterpart in the ROSAT catalogues. This suggests that either moderate or strong absorption may be preventing their detection in the ROSAT energy band. The comparison of our BAT catalogue with the Fermi Large Area Telescope First Source Catalogue identifies 59 BAT/Fermi correspondences: 48 blazars, 3 Seyfert galaxies, 1 interacting galaxy, 3 high mass X-ray binaries, and 4 pulsars/supernova remnants. This small number of correspondences indicates that different populations make the sky shine in these two different energy bands.
Full text
Available for:
FMFMET, NUK, UL, UM, UPUK
Context. A catalogue of the features for the complete Spitzer Survey of Stellar Structure in Galaxies (S4G), including 2352 nearby galaxies, is presented. The measurements are made using 3.6 μm ...images, largely tracing the old stellar population; at this wavelength the effects of dust are also minimal. The measured features are the sizes, ellipticities, and orientations of bars, rings, ringlenses, and lenses. Measured in a similar manner are also barlenses (lens-like structures embedded in the bars), which are not lenses in the usual sense, being rather the more face-on counterparts of the boxy/peanut structures in the edge-on view. In addition, pitch angles of spiral arm segments are measured for those galaxies where they can be reliably traced. More than one pitch angle may appear for a single galaxy. All measurements are made in a human-supervised manner so that attention is paid to each galaxy. Aims. We create a catalogue of morphological features in the complete S4G. Methods. We used isophotal analysis, unsharp masking, and fitting ellipses to measured structures. Results. We find that the sizes of the inner rings and lenses normalized to barlength correlate with the galaxy mass: the normalized sizes increase toward the less massive galaxies; it has been suggested that this is related to the larger dark matter content in the bar region in these systems. Bars in the low mass galaxies are also less concentrated, likely to be connected to the mass cut-off in the appearance of the nuclear rings and lenses. We also show observational evidence that barlenses indeed form part of the bar, and that a large fraction of the inner lenses in the non-barred galaxies could be former barlenses in which the thin outer bar component has dissolved.
Full text
Available for:
FMFMET, NUK, UL, UM, UPUK
We present an independent confirmation of the zero-point offset of Gaia Data Release 2 parallaxes using asteroseismic data of evolved stars in the Kepler field. Using well-characterized red giant ...branch stars from the APOKASC-2 catalog, we identify a Gaia astrometric pseudocolor ( eff )- and Gaia G-band magnitude-dependent zero-point offset of ϖ seis − ϖ Gaia = 52.8 2.4 (rand.) 8.6 (syst.) − (150.7 22.7)( eff − 1.5) − (4.21 0.77)(G − 12.2) as, in the sense that Gaia parallaxes are too small. The offset is found in high- and low-extinction samples, as well as among both shell H-burning red giant stars and core He-burning red clump stars. We show that errors in the asteroseismic radius and temperature scales may be distinguished from errors in the Gaia parallax scale. We estimate systematic effects on the inferred global Gaia parallax offset, c, due to radius and temperature systematics, as well as choices in bolometric correction and the adopted form for Gaia parallax spatial correlations. Because of possible spatially correlated parallax errors, as discussed by the Gaia team, our Gaia parallax offset model is specific to the Kepler field, but broadly compatible with the magnitude- and color-dependent offset inferred by the Gaia team and several subsequent investigations using independent methods.
Expanding on ideas explored by the artworks in the exhibition SAM Contemporaries: Residues & Remixes, this book contextualises the exhibition’s curatorial approach and the featured artistic ...practices through documentation, field-notes, scholarly essays, speculations and conversations of various forms (formalities) between artists and curators, making for a dynamic and engaging reading experience.
While the book focuses on the SAM Contemporaries exhibition, the ideas, themes and artistic practices it discusses are of global relevance, making it a valuable resource for or art enthusiasts, students, and researchers alike.
This book shows you how to harness the power of linked data and integrated discovery systems to manage and link widely varied content across your library collection.
In diesem Beitrag werden zwei Methoden zur Schätzung der Energieverluste beim Einsatz von Kataloglagern auf globaler Ebene vorgestellt. Diese Methoden, die auf aktuellen Normen basieren, liefern eine ...Näherung für die Bestimmung der Energiebilanz von Lagern. Die Vor- und Nachteile der vorgeschlagenen Methoden werden diskutiert.
PDF
