| 1. |
- Adebahr, B., et al.
(författare)
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Apercal - The Apertif calibration pipeline
- 2022
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Ingår i: Astronomy and Computing. - : Elsevier BV. - 2213-1337. ; 38
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Tidskriftsartikel (refereegranskat)abstract
- Apertif (APERture Tile In Focus) is one of the Square Kilometre Array (SKA) pathfinder facilities. The Apertif project is an upgrade to the 50-year-old Westerbork Synthesis Radio Telescope (WSRT) using phased-array feed technology. The new receivers create 40 individual beams on the sky, achieving an instantaneous sky coverage of 6.5 square degrees. The primary goal of the Apertif Imaging Survey is to perform a wide survey of 3500 square degrees (AWES) and a medium deep survey of 350 square degrees (AMES) of neutral atomic hydrogen (up to a redshift of 0.26), radio continuum emission and polarisation. Each survey pointing yields 4.6 TB of correlated data. The goal of Apercal is to process this data and fully automatically generate science ready data products for the astronomical community while keeping up with the survey observations. We make use of common astronomical software packages in combination with Python based routines and parallelisation. We use an object oriented module-based approach to ensure easy adaptation of the pipeline. A Jupyter notebook based framework allows user interaction and execution of individual modules as well as a full automatic processing of a complete survey observation. If nothing interrupts processing, we are able to reduce a single pointing survey observation on our five node cluster with 24 physical cores and 256 GB of memory each within 24 h keeping up with the speed of the surveys. The quality of the generated images is sufficient for scientific usage for 44% of the recorded data products with single images reaching dynamic ranges of several thousands. Future improvements will increase this percentage to over 80%. Our design allowed development of the pipeline in parallel to the commissioning of the Apertif system.
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| 2. |
- Carozzi, Tobia, 1966
(författare)
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Simple estimation of all-sky, direction-dependent Jones matrix of primary beams of radio interferometers
- 2016
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Ingår i: Astronomy and Computing. - : Elsevier BV. - 2213-1337. ; 16, s. 185-188
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Tidskriftsartikel (refereegranskat)abstract
- The dual-polarized primary beams of imaging radio telescopes are generally not perfectly orthogonal nor have the same gain, the resulting polarimetric images are distorted, in other words, they exhibit instrumental polarization. This is often modeled in radio astronomy using a Jones matrix formalism, and the standard practice is to calibrate (i.e. determine the Jones matrices) using known point source, polarized calibrators. Using point source calibrators on the other hand can be difficult and is ineffective for wide fields-of-view (FoV). Often however, a large portion of the FoV of imaging radio telescopes consists of unpolarized background. In this paper I estimate Jones matrices over the FoV by assuming that most of the background image is unpolarized and then taking the square-root of the brightness matrices. Results from LOFAR LBA data are shown and are consistent with expectation. The usefulness of this particular method, compared to using polarized point source calibrators, is its simplicity and the fact that it can cover most of the FoV.
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| 3. |
- Creaner, O., et al.
(författare)
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beamModelTester: Software framework for testing radio telescope beams
- 2019
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Ingår i: Astronomy and Computing. - : Elsevier BV. - 2213-1337. ; 28
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Tidskriftsartikel (refereegranskat)abstract
- The flux, polarimetric and spectral response of phased array radio telescopes with no moving parts such as LOFAR is known to vary considerably with orientation of the source to the receivers. Calibration models exist for this dependency such as those that are used in the LOFAR pipeline. Presented here is a system for comparing the predicted outputs from any given model with the results of an observation. In this paper, a sample observation of a bright source, Cassiopeia A, is used to demonstrate the software in operation, by providing an observation and a model of that observation which can be compared with one another. The package presented here is flexible to allow it to be used with other models and sources. The system operates by first calculating the predictions of the model and the results of an observation of linear fluxes and Stokes parameters separately. The model and observed values are then joined using the variables common to both, time and frequency. Normalisation and RFI excision are carried out and the differences between the prediction and the observation are calculated. A wide selection of 2-, 3- and 4-dimensional plots is generated to illustrate the dependence of the model and the observation as well as the difference between them on independent parameters time, frequency, altitude and azimuth. Thus, beamModelTester provides a framework by which it is possible to calibrate and propose refinements to models and to compare models with one another.
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| 4. |
- de Souza, R. S., et al.
(författare)
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A graph-based spectral classification of Type II supernovae
- 2023
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Ingår i: Astronomy and computing. - 2213-1337. ; 44
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Tidskriftsartikel (refereegranskat)abstract
- Given the ever-increasing number of time-domain astronomical surveys, employing robust, interpretative, and automated data-driven classification schemes is pivotal. Based on graph theory, we present new data-driven classification heuristics for spectral data. A spectral classification scheme of Type II supernovae (SNe II) is proposed based on the phase relative to the maximum light in the V band and the end of the plateau phase. We utilize a compiled optical data set that comprises 145 SNe and 1595 optical spectra in 4000-9000 angstrom. Our classification method naturally identifies outliers and arranges the different SNe in terms of their major spectral features. We compare our approach to the off-the-shelf UMAP manifold learning and show that both strategies are consistent with a continuous variation of spectral types rather than discrete families. The automated classification naturally reflects the fast evolution of Type II SNe around the maximum light while showcasing their homogeneity close to the end of the plateau phase. The scheme we develop could be more widely applicable to unsupervised time series classification or characterization of other functional data.
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| 5. |
- Moskovitz, N. A., et al.
(författare)
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The astorb database at Lowell Observatory
- 2022
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Ingår i: Astronomy and Computing. - : Elsevier. - 2213-1337. ; 41
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Tidskriftsartikel (refereegranskat)abstract
- The astorb database at Lowell Observatory is an actively curated catalog of all known asteroids in the Solar System. astorb has heritage dating back to the 1970s and has been publicly accessible since the 1990s. Work began in 2015 to modernize the underlying database infrastructure, operational software, and associated web applications. That effort involved the expansion of astorb to incorporate new data such as physical properties (e.g. albedo, colors, spectral types) from a variety of sources. The data in astorb are used to support a number of research tools hosted at https://asteroid.lowell.edu. Here we present a full description of the software tools, computational foundation, and data products upon which the astorb ecosystem has been built.
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